Underground Mine Communications, Control and Monitoring

Home , Loopback, Pager, Speaking tube

Bureau of Mines Information Circular/l984

By Staff, Bureau of Mines

UNITED STATES DEPARTMENT OF THE INTERIOR

- -- Information Circular 8955

Underground Mine Communications, Control and Monitoring

By Staff, Bureau of Mines

UNITED STATES DEPARTMENT OF THE INTERIOR James G. Watt, Secretary

BUREAU OF MINES Robert C. Horton. Director Library of Congress Cataloging in Publication Data : .

Underground mine communications, control and monitoring.

(Information circular / United States Department of the Interior, Bu- reau of Mines ; 8955) Includes bibliographical references. Supt. of Docs. no.: I 28.27:8955. 1. Mine communication systems. I. United States. Bureau of Mines. 11. Series: Information circular (United States. Bureau of Mines) ; 8955.

TN295,U4 [Till3441 622s [622',2] 83-600288

& PREFACE

Since 1969, the Bureau of Mines, U.S. Department of Interior, has sponsored numerous programs aimed at improving methods of underground communication. As a result of these research and development programs, a wealth of information has been made available to the mining industry. Unfortunately, some of this material is highly analytical, and most is written in terms best understood by communication specialists. Because of the volume of data (over 100 studies have been performed) and its highly technical nature, most of the information is not readily available for practical application by mine operators. This manual brings together relevant data from all previous reports, studies, and other sources, and presents these data in such a way that they may be applied by the mining industry to improve communications in underground mines.

This report is intended as a guideline and not as a comprehensive documentary of mine equipment. Installation of equipment in a mine should be done only by people thoroughly qualified to do such work. Installations should follow procedures recommended by the equipment manufacturer and should comply with good safety practices. All installations should also comply with applicable codes and regulations. CONTENTS Page

Preface ...... Chapter 1.--Introduction ...... 1.1 History of Underground Comrmnications ...... mm...... 1.2 Productivity and Safety ...... 1.3 Constraints on Equipment ...... m...... m...... 1.4 Comrmnication Requirements ...... m.m.m.mm...... 1.4.1 The Working Section Crew ...... 1.4.2 The Maintenance Crew ...... 1.4.3 Motormen ...... 1.4.4 Inspectors and Management Personnel ...... mm... 1.4.5 The Dispatcher ...... 1.4.6 Hoist Communications ...... m...... m 1.5 Present Communication System ...... m...m...... mm... 1.6 Sumry...... m.m...... mm.m...... m Bibliography ...... m..mmmm.. Chapter 2.--Communication System ...... 2.1 Introduction ...... 2.2 Wired Phone System ...... 2.2.1 General Telephone Theory ...... a . Magneto-Type Telephones ...... b . Sound-Powered Telephones ...... c . Paging Telephones ...... d . Dial-and-Page Telephones ...... Distribution System ...... w~...... m..m.m....~..... a . Single Pair...... b . Figure-8 Multipair Cable ...... c . Coaxial Cable ...... d . Multiplex System ...... i . Frequency Division Multiplexing...... ii . Time Division Multiplexing...... Telephone Exchanges ...... a . Manual Switchboard ...... b . Private Automatic Branch Exchange ...... c . Computer-Controlled Switches ...... Radio System ...... General Radio System Theory ...... a . Amplitude Modulation ...... b . Frequency Modulation ...... m.m...... Distribution System ...... a . Antenna Theory ...... i . Half-Wave Dipole Antenna ...... ii . Quarter-Wave Antenna ...... iii . Long-Wire Antenna ...... iv. Loop Antenna ...... b . Leaky Feeder System ...... c . Waveguide Propagation ...... d . Repeaters ...... i . F1-F1 Repeater ...... ii. F1-F2 Repeater ...... Through-the-Earth Radio ...... Radio Pagers ...... CONTENTS.. Continued Page

Carrier Current Systems ...... eeeeeeeeeeeeeeeeeeeeeeeeee.eeeeee

Trolley Carrier Phone ...... eeeeeeeeeeeeeeeeeeeee.eeeeeeeeeeee Hoist Kope Kadio ...... Medium-Frequency Kadio ...... Hybrid Systems ...... ~...e...... e.e.eeeeee.eeeeeeee.eeee......

Improvements in System Versatility ...... eeeeeeeeeeeeee.e...e..eee.. Dial Phone-Pager Phone system^...... ^^^^^..^^....^...^..^^.... Other Systems ...... Seismic Systems ...... eeee.eee.e.eee.e.eee....e...... e..e..e. Stench System ...... e...eeeee.eeeeee.eeee...... Hoist Bell Signaling...... Visual Pagers ...... e...... e..ee.eeeeeeee...... Summary ...... Bibliography ...... Chapter 3... Solutions to the Communication Kequirements ...... 3.1 Introduction ...... 3.2 The Mine Entrance ...... eeeeee....eeeee.eeeeeee..e...... e....e...... 3.2.1 Bell Signaling Systems ...... 3.2.2 Trailing Cable Systems...... e....ee.eee.ee..e..ee.e...e..... 3.2.3 Radio system^...... ^^^^^.^^^^^^.^^..^^^...... e.e..eeeeee.e.eee. 3.2.4 Hoist Rope Carrier Current System ...... eeeee...... e.eeeeeeee.e

3.2.5 Hoist Signaling Summary ...... ee.e...... ee.eee.eeeee..~...... 3.3 Permanent and Semipermanent In-Mine location^...... ^^^^^ ...... 3.3.1 Single-Pair Pager Phones ...... e....e...eeeeee.eee.e..e...... 3.3.2 Multipair Systems ...... 3.3.3 Multiplexed Systems ...... 3.4 Mining Area ...... e...... eee.e.e...... e..e..ee..e......

3.4.1 Radio Systems ...... eee....e...... eee...... 3.4.2 Longwall Mining ...... eeeeeee...eee.e.ee.eeee...e...... 3.5 Haulageways ...... eee...... 3.5.1 Trolley Haulage ...... e.eee.e...... e...... e...... a . Dedicated Wire ...... ee...e.eeeeee.eeeee....~~.eeeee b . Summary ...... e.ee.e...... eeee.ee....e...... 3.5.2 Nontrolley Haulage ...... eeeee...... e...... a. Leaky-Coax Systems ...... e...... e...... e...... b . UHF Keflective Techniques in Underground Mines...... c. Dedicated-Wire Radio Systems...... d . Wireless Radio System ...... e.e.e...... ee...... i . Interference...... e....ee...... ii. Signal Attenuation in the Haulageway ...... iii . Signal Attenuation Around Corners ...... 3.5.3 Belt Haulage ...... 3.6 Special Requirements ...... ee.e..e.e....ee...... ee...... e...... 3.6.1 The Roving or Isolated Miner ...... a. One-Way-Voice (Pocket) pager^,...,...... ^^..^.^.^^.^^^^^.^ 3.6.2 Motorman-to-Snapper...... a. Telephone and Trolley-Carrier Phone System ...... be Walkie-Talkie System ...... e.eeee.eee..eeeeeee.eee 3.7 Emergency Communications ...... e...... ee.....e...e. 3.7.1 Detecting and Locating the Trapped Miner ...... eee..eee.e..... CONTENTS.. Continued Page

Refuge Shelter...... 72 Rescue Team Communications ...... 73 Medium-Frequency Rescue Systems ...... 73 a . Specific Application of MF Communications to Rescue Teams ... 74 b . System Concepts ...... 75 c . Location and Communications Systems for the Rescue of Trapped Miners ...... 76 d . Performance Data ...... 79 Emergency Warning Systems ...... 79 Bibliography ...... 82 Chapter 4...Computerized Mine Monitoring ...... 85 4.1 Introduction ...... 85 4.2 Uses of a Mine Monitoring System ...... 85 4.3 Petitions for Modification ...... 87 4.4 Technical Factors ...... 88 4.4.1 Sensors ...... 88 4.4.2 Telemetry ...... 89 4.4.3 Reliability ...... 89 4.5 Commercially Available Mine Monitoring Equipment ...... 90 4.5.1 Introduction...... 90 4.5.2 Telemetry-Analysis and Display Systems ...... 91 a . Systems Suppliers ...... 93 b . Summary ...... 98 Sensors ...... 99 a . Air Velocity Sensors ...... 100 b . Methane Sensors ...... 101 c . Carbon Monoxide Sensors ...... 103 d . Dust sensors ...... 104 4.6 Existing Mine Monitoring Systems ...... 104 4.6.1 U.S. Underground Coal Mines ...... 105 4.6.2 U.S. Underground Metal-Nonmetal Mines ...... 115 4.6.3 Foreign Mines ...... 115 References ...... 119 Chapter 5...Communication System Design and Improvement ...... 121 5.1 Introduction...... 121 5.2 New Phone System Design ...... 121 5.2.1 Wired Phone Systems ...... 122 a . Single-Pair Systems ...... 122 b . Multipair Systems ...... 124 c . Multiplexed Phone Systems ...... 126 5.2.2 Cable Selection...... 127 5.2.3 Sum~ry...... 130 5.3 Improving Existing (In-Place) Phone Systems ...... 131 5.3.1 Trolley Carrier Phone Systems ...... 131 a . Isolating Loads at the Carrier Frequency ...... 132 i . bctifiers...... 133 ii . Heaters ...... 136 iii . Vehicle Lights ...... 137 iv. Other Loads ...... 137 b . Using a Dedicated Wire ...... 138 CONTENTS.. Continued .Page c . Using a Remote Transceiver...... d . Summry ...... 5.3.2 Improving Telephone Systems ...... a . Loopback Methods ...... b . Sectionalizing the Underground Network ...... 5.3.3 Summary ...... Bibliography ...... Chapter 6...Installation Techniques ...... 6.1 The Basic Philosophy ...... 6.2 Pager Phone Installation...... 6.2.1 Mounting ...... 6.2.2 Connections ...... 6.2.3 Batteries ...... 6.2.4 Fuses ...... 6.2.5 Amplifier Loudness ...... 6.3 Phone Lines and Transmission Cables ...... 6.3.1 Phone Lines ...... 6.3.2 Leaky Feeder Cable...... 6.4 Carrier Phone Installation...... 6.4.1 The Dispatcher Location...... 6.4.2 Vehicle Installations ...... 6.5 Carrier Current Hoist Phone ...... 6.5.1 Cage ...... 6.5.2 Hoistroom and Headframe ...... e...... 6.6 Summary ...... Bibliography ...... Chapter 7.--Maintenance ...... 7.1 General ...... 7.2 Preventive Maintenance and Inspections ...... 7.2.1 Cables ...... 7.2.2 Pager Phones ...... a . Listen Circuit ...... b . Page Circuit and Talk Circuit ...... c. General Comments ...... d . Battery Condition...... e . Battery Testing...... Carrier Phones ...... a . Microphone ...... b . Batteries ...... c . Wet Cell Maintenance ...... d . Gelled Electrolyte Battery ...... e . Troubleshooting on the Vehicle ...... f . Mapping Signal Levels...... Summry ...... Bjbliography ......

Appendix A*.. Communication System example^...... ^...^^^.^..^...... ^... Appendix B.--Federal Regulations ...... e...... eeee.e.e...... Appendix C.--Equipment Suppliers...... ee...e.e....e...... Appendix D.-. Glossary of Terms ...... e.e...... e...... CHAPTER 1.--INTRODUCTION

1.1 History of Underground Both of these telephone sets Communications required "pipe" or conduit, not a very practical item for a 100-squaremile coal Although the technology involved in mine. A common thread prevalent in the removing material from below the earth's first 40 years of design and development surface has a long history, communication is that the primary effort was placed on systems in underground workings are rela- the telephone set. tively new to the industry. Communica- tion equipment did not begin appearing in In the early 19701s, as work began underground mines until the early 1900's. on the design of modern communication Figure 1-1 shows a miner using a Western systems for use in underground mine Electric standard telephone set for environments, the following requirements underground mines in 1913. These early were established: phones were essentially the same as those used aboveground, except that they were 1. Must meet intrinsic safety enclosed in cast-iron boxes as protection standards .--This applies not only to against moisture, acid fumes, and gases. coal mines, but to other explosive environments. In the 1950's, the Chesapeake and Potomac Telephone Co. of West Virginia 2. Must be compatible with the introduced a telephone set for use in environment.--The system must with- explosive atmospheres that was designed stand dust, moisture, and corrosive around the philosophy of explosion conditions. containment. To contain an explosion within the telephone set required a 3. Must be rugged in structure.-- 39-pound casing, which greatly limited The system must withstand maintenance by portability. 10-inch pliers and 4-pound hammers, as well as impact from a falling piece of roof.

4. Must be size-flexible.--Whatever is built must be sized for the small operator as well as the large companies.

5. Must be a total system in design.--The system must be intrinsically safe, including cable, power supply, and station set.

6. Must work with present telephone system.--The system should be compatible with aboveground communications already in place; it should not be the single cause of change in aboveground communications.

7. Value-added pricing.--The system should be reasonably priced so that sav- FIGURE 1-1. - Coal miner talking on on under- ings created by its introduction will ground telephone in 1913. more than offset the installation cost. 8. Full-service full-support con- 1.2 Productivity and Safety cept.--The service offering the system must provide for maintenance, training Underground mining operations, like (initial and continuing), route design, other industrial enterprises, are tied and transmission engineering. together by communications. Adequate communication within a mine and between In recent history, the most common the surface and the underground work sta- method of underground mine communications tions is a vital part of the proper consisted of loudspeaking- or paging- operation of any underground facility. type telephones, or alternatively, mag- This communication capability is not only neto ringing telephones. In most cases an important factor in the concept of these phones were connected on a common safety, but also is an aid to the day- party line with one telephone for each to-day operations and the task of working section and additional phones at extracting and moving the product to the other key locations, such as maintenance surface. If a rapid, accurate flow of shops, both underground and on the sur- data is automatically and continuously face. As mining operations became more presented to management, then decisions mechanized, underground rail haulage sys- can be made sooner and more accurately. tems were developed. Eventually, these Some people consider the operation of a were driven by electrically powered loco- mine to be a relatively static operation motives, and trolley carrier current com- planned many months, even years, in munication systems were developed. While advance. However, the productive time a few mines have begun to use dial-type per shift and productivity trends indi- telephones underground, their use to date cate that a large amount of waste time has been very limited. It is expected, accumulates due to unpredictable daily however, that more and more mines will events. If management were aware of install dial-and-page telephones and breakdowns within minutes, attention radio-type communication systems in the could be more quickly focused on solving future. Today's rail transportation sys- the problems, thereby increasing long- tems are typically equipped with carrier term production. current phones to provide communications between vehicles and between vehicles and Safety can certainly be enhanced by a central dispatcher. accurate fast communication channels. Quicker medical assistance, faster evalu- Early shaft communications consisted ation of the situation underground, and of bells or whistle signaling systems. accurate location of problems will be Today these systems have been replaced direct benefits. In addition to these with radio and carrier current systems obvious advantages, remote monitoring and that allow two-way voice communication to control of equipment and conditions and from personnel in the cage. underground will allow management personnel to prevent accidents and other It is recognized that presently causes of production losses. available mine communication systems need improvement. Kesearch and development A study of 9,300 injury-causing ,r programs are continually being conducted accidents that occurred in underground by the Bureau of Mines, the mining indus- bituminous coal mines during 1974 found try , and equipment manufacturers to that the financial cost totaled almost improve communication technology and $57 million, or an average of $6,100 per techniques. The primary objective of all accident. This figure did not include of these programs is to increase the pro- the intangible cost of reduced efficiency ductivity of the mining industry and in fellow workers resulting from the increase the safety of miners. accident. The study detected a marked tendency of mine crews in or near the limits, an alarm may be initiated. At area where the accident occurred to slow the same time, the electric typewriter down their pace of operations for a connected to the computer types out period of time, especially after a seri- either a warning or a danger message to ous accident; consequently, production specify what is wrong and at which sensor would drop. Such a drop was in addition the trouble is being detected. to the accident itself, and to the time required to clean up after the accident. In the United Kingdom, a commercial About 41%, or an estimated $23.6 million, mine monitoring and control system, MINOS of the total (current and future) cost of (Mine Operating System), is being devel- underground coal mine accidents in 1974 oped. The heart of the system is a digi- was borne by mining companies in the form tal computer (fig. 1-2) located within of compensation payments to accident vic- the system control center. This computer tims and survivors, lost coal production, is programed to obtain various data from and the expense of investigating the remote sensors and monitor the satis- accidents. Any devices or techniques, factory operation of the mine, giving including good communication systems, audible and visual alarms as well as that will reduce accidents will quickly initiating automatic shutdown of equip- pay for themselves. ment when necessary. Control of the conveyor system including startup, shutdown, The evolution of mining technology, and feed rate is also possible. Print- including underground commnications, is outs and daily summaries of specified inevitable as coal assumes a more sig- information are outputted automatically nificant role in the national energy or are available on demand by key- plan. Another factor that will aid this board commands entered at the system development is the application of modern center. Remote control and monitoring remote control and monitoring methods to of surface facilities and preparation increase production. Advances in remote plants as well as underground equipment monitoring and control of equipment and such as pumps and fans can also be conditions underground will involve accomplished with the computer-controlled increased use of computers. Mine moni- systems. toring systems using a computer have already been installed in some mines. Any remote monitor and control sys- Basically, these systems consist of tem is relatively sophisticated, and an sensors placed at strategic locations, data relay stations, and a digital com- puterin the mine office. The computer VISUAL DISPLAY SCREENS is programed to process the data, deter- INDICATOR LAMPS mine when and where abnormal conditions / exist, and alert mine personnel.

Six types of sensors in common use detect methane, carbon monoxide, temperature, relative humidity, airflow, or dif - ferential air pressure. Systems can include an electronic display of the mine layout, electric typewriters, and video display screens connected to the computer. The computer receives data from the remote stations in the form of electrical signals, which are translated into numerical measurements and checked against a set of standards to see if all factors are within normal limits. If any factors at a remote station exceed normal FIGURE 1-2. - MlNOS system center. economic analysis of the tradeof f s Much of the comnunication equipment involved in the mechanization is in coal mines today is located in venti- required. However, minewide remote moni- lated areas where there is less likeli- toring and control, coupled with an hood of an explosion. However, if a ven- effective commnication system, is one of tilation system is required to control the tools that can be used to increase the gas or dust hazard and basic comnuni- safety and productivity in underground cations must be maintained in the event mines. of a ventilation failure, then this communication equipment must not be capable 1.3 Constraints on Equipment of generating an ignition spark. Thus, much of today's mine commnication equip- The environmental constraints on ment carries a "Permissibility" label equipment expected to operate in any granted by the Mine Safety and Health underground mine are severe. Equipment Administration. To achieve the permissi- designed for surface operation, even if bility rating without explosion-proof it would work underground, could not be packaging, all sources of sparks must be expected to last for any length of time controlled by limiting voltages, cur- in the harsh mine environment. rents, and the amounts of stored energy-- such as in batteries, capacitors, and Equipment must be protected from, or inductors--to safe levels. Such a device immne to, high-moisture atmospheres (0 is defined as "intrinsically safe. " to 100%humidity levels) and remain operable over wide temperature ranges. Dust The amount of spark current in a can be expected to clog airflow passages, resistive circuit required to ignite plug relay contacts, and cause switches a methane-air mixture varies with the to stick. Dust accumulation onelec- open-circuit voltage. Guidelines to tronic components can also cause heat safe operating limits, such as shown buildup and even "short circuits. " Some in figure 1-3, indicate a hazard at mine atmospheres are highly corrosive, and equipment in these mines must be constructed from materials that are resistant to the corrosion, or else protected from it. The very dry atmosphere in some mines causes gaskets and seals to quickly dry out and start leaking. Static elec- tricity in these mines can also pose a problem for certain types of solid state electrical circuits. HAZARDOUS

In addition to the environmental constraints, physical considerations must be taken into account. Space is often at a premium in underground mines, especially in low coal seams. Commnica- tions, control, and monitoring equipment must be small in size and should be light in weight. Because it rmst exist in close proximity with heavy mining machinery, commnication equipment must also be ruggedly designed and shock protected. Reliability and ease of maintenance are other reasons why most equipment designed MINIMUM IGNITION CURRENT (AMPERES) for surface operation cannot be utilized in underground mines. FlGUKE 1-3. - Typical ignition hazard curve. 2 amperes in a 20-volt resistive circuit. Working section crew However, no greater hazard exists with 10 amperes in a 12-volt resistive cir- Maintenance crew cuit. When reactive circuits (circuits with inductors or capacitors) or energy Mot ormen storage elements (batteries) are considered, limits on safe circuit design Inspectors and management personnel are even tighter. These safety considerations have directed the design of all The position of dispatcher is con- the "permissible" communication devices sidered separately because he or she gen- on themarket today. Oneof themost erally coordinates the communications as recent pager-type phones does not contain well as the haulage traffic. any inductive components other than the speaker and handset and uses only a In small mines and belt-haulage-type single 12-volt battery. mines the communication center may be the responsibility of the hoist engineer, the In gassy mines, only permissible or supply man, or the maintenance foreman. intrinsically safe communication equip- Because hoist communication requirements ment should be acceptable for use in all are unique, they also can be treated locations under all conditions. separately.

The permissible rating requirement 1.4.1 The Working Section Crew rules out use of most systems designed for surface applications. For instance, Under normal operating conditions a permissible rating cannot be given to the section forman communicates by fixed a standard telephone connected to a phone to the shift foreman to request telephone switchboard because of high supplies and maintenance services and to voltages (48 volts dc while on hook and file periodic productivity reports. as much as 120 volts ac while ringing) Under emergency conditions he must be and use of many highly inductive devices able to request medical aid for personnel in the circuit. While placing the tele- and report hazardous conditions in his phone in an explosion-proof housing could area. be considered as a means of making it "permissible," the cost would be The high acoustic noise level cre- unreasonable. ated by the mining machinery greatly reduces the effective communications Other restrictions on communication between the foreman and his crew. This equipment used underground are specified noise also interferes with the foreman in the U.S. Code of Federal Regulations receiving calls. Often a motorman must (See appendix B of this manual.) deliver a call-in message to the foreman when he is transferring hauling cars in 1.4 Communication Requirements his section. Some belt haulage mines must even resort to turning off the con- In an ideal communication system an veyor system, thereby causing all the individual should be able to initiate and section foremen to call in. Communica- receive calls regardless of his or her tion requirements of the section crew can position in the mine. To accomplish be satisfied by loudspeaking pager phones this, more than one communication system that can easily be moved to keep them may be required. Communication require- within hearing range, or by some form of ments are more readily defined by sep- radio link (two-way radio, pocket pager, arating the underground personnel in or "'beeper"). present-day mine operations into four functional groups: 1.4.2 The Maintenance Crew (Newer phones have backup batteries installed in each phone so this may not Unlike a working section crew, the be a problem.) maintenance crew is spread throughout the mine. The maintenance foreman must be In spite of these drawbacks, carrier able to receive repair requests and dis- phone systems usually meet the require- patch his crews for both emergency and ments of the motormen, except for an scheduled repair work. He should also be emergency that severs the trolley wire or able to maintain communications with the otherwise removes power from the wire. individual crew members while they are in transit or after they have arrived at the In mines without tracked-trolley repair site. The dispatcher may provide haulage systems, a radio link must be assistance by routing messages for equip- established to allow motormen to remain ment repair and parts to the foreman from in contact with one another. the maintenance crew. 1.4.4 Inspectors and Management Wireless mobile communication equip- Personnel ment, linking the maintenance foreman and his crew together, would be ideal for the These people are underground pri- above tasks. However, any portable radio marily to observe mine conditions and equipment used must be small and light- personnel. They should be able to stay weight because crew members already have in continuous contact with the communica- much to carry. tion center for the following reasons:

1.4.3 Motormen To be informed of any emergencies that might arise. The motormen are responsible for coal or ore haulage and the delivery of To keep the center informed of their men and supplies to the working sections. location. Kights-of-way and the disposition of haulage cars must be known to all motor- To receive calls from other parts of men to avoid accidents. In mines using the mine. tracked-trolley haulage, activities can be coordinated by a trolley wire (car- These requirements could be satis- rier) phone system. These are known as fied by an effective, extensive wireless "carrier" systems because the communica- mobile communication system. A vehicle- tion is "carried" on a wire not intended mounted system may be sufficient in some for communication, in this case the cases, such as the trolley carrier phones trolley line; the term "carrier," how- in track haulage mines. ever, refers to the technique, not the wire itself. This single-channel network 1.4.5 The Dispatcher keeps the dispatcher and all motormen in continuous contact with one another. The dispatcher's location in some This phone system also allows the dis- mines has developed into a communication patcher to notify all motormen of any center for all underground operations. mine emergency. The two drawbacks to He is in direct contact with all motormen this system are via the trolley wire phone system, and directs all vehicle traffic in the mine. 1. Dead zones, which are sections In some mines, he also controls the fixed of track where the phone is inoperative phone circuits via a small switchboard. owing to excess electrical noise or He locates personnel by the paging phones excess attenuation of signal strength. or by relaying messages through the motormen to the sections. He serves as 2. Trolley wire power failures, the human coupler between the different which cause the phones to go dead. phone systems, and he is in the best position to quickly notify all under- is impossible. This deficiency is espe- ground personnel of any emergency cially crucial during shaft inspection or condition. repair, where movement of the cage must be controlled precisely. Today, however, If this evolution continues, the equipment is available that allows two- dispatcher's job will expand to the point way voice communication between persons where he may become overworked. For in the hoist cage and the hoistman or safety and productivity reasons the voice other locations at the shaft top or traffic control and the monitoring func- bottom. tion of the dispatcher's job cannot interfere with his prime responsibility Reliable hoist-shaft communication of vehicle traffic control. Therefore, should be considered as a vital part of it may be desirable to transfer these the overall communication system, espe- responsibilities to other personnel or to cially during or following an accident or automatic dialing and alarm equipment. disaster situation. Experience has For this reason some mines have estab- taught that the hoist often becomes a lished a separate communication system bottleneck during rescue or evacuation "operator" position. This person has operations, and good communication to and responsibility for voice traffic control, from the cage is essential. and also for monitoring environmental conditions in the mine. The operating 1.5 Present Communication Systems conditions of the haulage and mining equipment could also be monitored from Communication systems currently used the communication center. in many mines generally consist of two systems, the trolley wire carrier phones 1.4.6 Hoist Communications and the fixed pager phones. The trolley wire channel must be a party line to keep A hoist-shaft communication system all motormen informed of one another's should satisfy the requirements for com- location. The pager phone system is munication throughout the full travel often divided into multiparty circuits of the cage, providing two-way voice com- which are controlled by the dispatcher. munication between the cage and the For example, one mine studied used eight hoistman. The system should also party line phone circuits terminated at a allow for shaf t-inspection communication simple switchboard in the dispatcher's between the inspector and the "hoistman." office. A logical partitioning of the For the modern, automated shaft, signals pager phone network into a multichannel are also required for a slack-rope indi- private line system would be to give each cation, to permit selection of level, working section a separate line, or at enable interface with interlocks, and jog the most two sections per line, and have for exact position at any level or shaft one common line for all haulageway station. Cage equipment must be small phones. Individual section phone lines and capable of being located so that it wou1.d eliminate peak traffic demand dur- cannot be damaged by any of the various ing production reporting time and provide uses of the cage such as transporting the section foreman with a private line supplies and machinery into the mine. during an emergency situation. Other phone lines could be used for monitoring Additional microphone-speaker sta- the environment and equipment. Based on tions should be located on each cage data and survey results to date, it level when multilevel "man trip" cages appears that about two to eight phone are used. Until recently, bell signaling lines, depending on activity of the mine, was the only form of hoist-shaf t communi- would be sufficient to provide efficient cation. A disadvantage of the bell sig- service for the working sections and also naling system is that communication provide a common private line for the with the cage when it is between levels haulageways. 1.6 Summary addition to the obvious advantages of reliable and effective communications, The need for effective communication there are intangible benefits that may between locations underground and between not be recognized: underground and surface locations has been recognized for some time. Unfor- 1. The general attitude of the tunately, the equipment to totally sat- underground workforce will be improved if isfy these requirements in underground they know that they are not "cut off" mines has only recently become available. communicationwise from the surface. Part of the reason for lack of equipment can be blamed on the uniquely 2. Mines with good commnication harsh environment present in underground systems should be able to more effec- mines. tively compete in the labor market. High turnover rates, which are costly owing to Despite past deficiencies, equipment training requirements, will be reduced. is now available to meet most of the requirements for effective underground 3. Mines with effective comnunica- commnication systems. The operational tion systems and good safety records are requirement of the ultimate system may be usually subjected to inspections less simply stated as follows: Each indi- frequently, and since studies have shown vidual should be able to initiate and that production rates decrease when it is receive commnications regardless of his known that inspection personnel are on location within the mine. In practice, the property, the effect on production this ultimate requirement will normally should be good. be modified. The size and age of a mine, operating conditions, and economic con- Adequate communications within a siderations will affect the degree to mine and to the surface is a vital part which a system fully meets this ultimate of the proper operation of an under- requirement. ground facility. This commnication capability is not only an important Vehicles operating on rails within a factor in the concept of safety precau- mine should have a communication unit tions, but also an aid to the day-to-day mounted in every powered vehicle operations and the task of moving the (required in some States). Operational mined product to the surface. The mining safety is increased when there is industry exists to bring the product out an intervehicular commnication system. and to bring it out safely and econom- Operators can report to each other or to ically. Adequate communication is one of a central dispatcher, thereby reducing the tools available to assist in this the chances of a collision. Carried to task. the ultimate, the central dispatcher can control the movement of all vehicles at In a like manner, a judicious choice all times. of remote monitoring and control of parameters in the underground environment Often there is a need to call a man and on selected machinery will yield a who is not near any vehicle or phone. As cost savings in production and augment a minimum, some form of paging capability safety. Many man-hours and dollars can should be included in the overall mine be saved by knowing conditions before phone system that can be used to tell a they become a problem. Situations that called party to go to the nearest phone could be disastrous can be predicted and and return the call. The ability to com- proper solutions implemented before the municate with men underground, no matter disaster occurs. Proper environmental what their location, is essential to the and machine monitoring is another key efficiency of any mine. Safety and pro- to safer, more productive underground ductivity are directly related, and both mining. depend upon good communications. In B IBL IOGRAPHY

1. Betsh, K. W., G. Trace, and P. B. Paper in Underground Mine Communications. Day. A Permissive ~ial/~ageTelephone 1. Mine Telephone Systems. BuMines for Coal Mine Communications. Proc. 2d IC 8742, 1977, pp. 27-41. WVU Conf. on Coal Mine Electrotechnology, Morgantown, W. Va., June 12-14, 1974, 4. Lagace, Re L., W. G. Bender, J. D. pp. 8-1--8-13. Foulkes, and P. F. OIBrien. Techni- cal Services for Mine Communications 2. Collins Kadio Co. (Cedar Rapids, Research. Applicability of Available Iowa). Kesearch and Development Contract Multiplex Carrier Equipment for Mine Tel- for Coal Mine Communication System, Vol- ephone Systems. BuMines OFR 20( 1)-76, ume I, Summary and Kesults of System July 1975, 95 pp.; NTIS PB 249 829. Study. BuMines OFK 69(1)-75, Novem- ber 1974, 46 pp.; available from NTIS 5. Parkinson, H. E. Mine Communica- PB 244 169. tions. . Proc. 2d WVU Conf . on Coal Mine Electrotechnology, Morgantown, W. Va. 3. Drake, J. L. and J. M. Sticklen. June 12-14, 1974, pp. 5-1--5-5. An Industrial Communications Sys tem, CHAPTER 2.--COMMUNICATION SYSTEMS

2.1 Introduction panel shows a simple single pair party line system. In this system each phone Any commnication system requires at is connected to a common pair of wires, least three elements in order to func- and a person speaking into one phone will tion: a transmitting device, a receiving be heard at all the other phones on the device, and a transmission line or propa- line. The bottom panel shows a multipair gation medium. Even the device children private line phone system. In this type use, tin cans connected with string, con- of system, each phone is connected by its sists or these three elements. One own individual pair of wires to a central speaks into one can (transmitter), which switch or telephone exchange. To estab- vibrates at the same frequencies as the lish a call between two phones in this voice. The string (transmission path) system, the lines between the two phones picks up the vibrations of the can and must be connected (switched together) carries them along its entire length. within the telephone exchange. The other can (receiver) detects the vibration and reproduces the original In early exchanges, the connections sounds to a lesser extent depending on were made manually by an operator. These distance, tightness of string, type of exchanges are called Private Branch string, etc. All communication systems Exchanges (PBX's ) . Today, equipment depend on these three elements: trans- within the exchange can automatically mitter, transmission path, and receiver. connect each phone to any other phone in the system. These exchanges are called Communication systems can be divided Private Automatic Branch Exchanges into three fundamental categories: wired (PABX's). There are many different types phone systems, radio systems, and carrier of automatic exchanges. Some utilize current systems. Sections 2.2, 2.3, and switches to physically make each connec- 2.4, respectively, describe these systems tion according to the number dialed. and explain the basic principles of how Other, more advanced exchanges are com- each works. pletely solid state and may even be computer controlled. Hybrid systems are those systems that use various combinat ions of the three basic commnication meth- PHONES ods. Hybrid systems are described in section 2.5.

DISTRIBUTION There are some other methods of sig- SYSTEM naling (stench warning, bell signaling, a). SINGLE PAIR (PARTY LINE) SYSTEM etc.) that can be used in underground mines to transmit or convey information. These systems, although they cannot be considered true commnication systems since they do not provide voice or even PHONES two-way communication, are briefly n) described in section 2.6.

2.2 Wired Phone Systems DISTRIBUTION SYSTEM L Wired phone systems are all those TELEPHONE EXCHANGE that depend on a wire connection between (PBX OR '------PABX) phones with the wire carrying the voice I b). MULTlPAlR (PRIVATE-: LINE) SYSTEM --j signals. Figure 2-1 is a diagram of two typical wired phone systems. The top FIGURE 2-1. - Wired phone systems. Telephone exchanges are described in furnished by the speaker's voice. These ection 2.2.3. The various types of phones have highly efficient transmitters hones in use today and a description of and receivers for converting voice into how they operate is given in sec- electrical signals. tion 2.2.1. Distribution systems are described in section 2.2.2. The sound-powered handset is comparable in size and appearance to the famil- 2.2.1 General Telephone Theory iar battery-powered handset. Two of these phones were usually connected There are many different types of by a single line to constitute an phones in use today, including intercom circuit. Such a circuit will reproduce speech with reasonable good Magneto type quality for short distances in quiet surroundings. Sound-powe red For special commnication applica- Paging tions requiring exceptionally rugged and durable sets for private commnication purposes, and particularly when the line loops are short, sound-powered sets are well adapted. These phones and the basic princi- Sound-powered sets find their prin- ples of how they operate are described cipal application in mines, as indepen- in the following paragraphs. dent intercom systems. The simplicity and convenience of operating without 2.2.la Magneto-Type Telephones batteries and the service reliability and ruggedness of the sound-powered telephone One of the earliest types of under- when used in adverse surroundings are ground communication instruments was the points in their favor. magneto phone, also known as the crank ringer phone. These phones consisted of 2.2.1~ Paging Telephones a transmitter, receiver, hookswitch, ringer, battery, and hand generator (mag- The most common type of comnica- neto). As the spindle handle was turned, tion system used in underground mines is 80 to 100 volts at 15 to 18 cycles per a paging telephone system. These phones second was produced by the magneto. This are sometimes referred to as squawk current caused the other phones to ring. phones or squawk boxes because of the Once the called phone was answered, harsh sound of the speaker. Each phone talking power was supplied by battery in the system is usually connected to a voltage. twisted pair cable in party line fashion. Each pager phone has internal batteries Magneto phones were connected in that power audio amplifiers to boost sig- party line fashion with a code of short nal level for normal comrmnication. A and long rings to identify the called paging amplifier allows each phone to station. Some mines still use this type broadcast a page call on a loudspeaker of system. However, as mines expanded in that is also housed within each phone size, the system proved to lack adequate (fig. 2-2). signal strength to power a large number of phones. The paging telephone has gained widespread use for two reasons. First, 2.2.lb Sound-Powered Telephones it permits persons and station areas to be paged by name and thus does not A sound-powered set is one that pro- require the miners to learn ringing codes vides a means of voice comrmnications or telephone numbers. Second, the use of with the use of no energy except that page amplifiers in each phone makes the paging amplifier at each station is turned on. The person making the call then squeezes the press-to-talk button on his handset and makes an announcement. The handset signal is amplified and then transmitted over the two-wire network to all other phones. After completing the page, the caller releases the "Page" switch. The individual paged can respond by squeezing the press-to-talk button and talking into the handset. Because the two-wire line is common to all phones, any conversation on the party line may be heard at all stations.

Most of the pager phones that are available are directly interchangeable within a system or can easily be modified to be interchangeable. Two major areas FIGURE 2-2. - Generalized two-wire payer phone. of difference among available equipment are the battery voltage used for the system less affected by poor line splices page-call function, and the character- and induced noise. The loudspeaker also istics of the internal relay that yields a higher sound level at the responds to the dc page signal. The two receiver, which is important in the choices of battery voltage are presently vicinity of noisy machinery. The primary 12 volts and 24 volts. The 24-volt sys- disadvantage of paging telephone systems tem was the standard for several years. is that the telephone line must be used Most installations also used electro- in a party line arrangement. This pre- mechanical relays to "switch in" the pag- vents simultaneous conversations in the ing amplifiers. system and reduces its usefulness for discussing maintenance problems or other In recent years, new designs using uses which can tie up the system for long solid state switching circuits that oper- periods of time. ate at 12 volts have become popular. Besides being more reliable, solid state In a large mine there may be 30 to systems have a high impedance and thus 40 phones on a single twisted pair cable. present a minimum load to the paging However, as the mine develops and the circuit. In a large complex multiphone miles of twisted wire pair increase, a system, with several miles of intercon- limit is reached. The limiting factor is necting cable, the minimum loading caused the power,available to signal the paging by these phones means that more phones amplifier in other phones to turn on. can be installed. The application of an electronic switch, in place of the low-voltage "page relay," Options included by the manufac- has extended the operating range of newer turers of some paging phones include a paging phones. battery-test button, an improve-hearing button, and a flashing light to help A schematic of a generalized two- attract attention in noisy areas. The wire pager phone is shown in figure 2-2. battery-test button, when pressed, lights When the ("Page") switch on the page a lamp on the front panel to indicate phone is pressed, a dc voltage from the that the battery is in good condition. battery is placed on the line. All tele- When the improve-hearing button is phones connected to the line are ener- pressed, the gain of the receiver ampli- gized through their "page relay," and the f ier in the handset is increased. To assist the loudspeaker in attracting a miner's attention, the flashing light is turned on when the page is initiated.

2.2.ld Dial-and-Page Telephones SPEECH INPUT SWITCH

The use of normal surface-type tele- PAGINL phones in underground mines has two SPFAKER disadvantages: The potential hazard, in a methane atmosphere, from the 120-volt 20-hertz bell-ringing voltage; and the inability to locate a person who is not in his immediate work area. Surface-type telephones also have two advantages, how- DIALER ever: The selective call feature and the IWORK I multiple private lines. I

L I I I A unique system combines the dial I I telephone with the page phone. A surface interface is provided to isolate the & OUTPUT potentially hazardous voltages from the TERMINALS TO SURFACF underground line, and a converter changes INTERFACE ring voltage into the low-voltage direct current required to turn on the paging FIGURE 2-3. - Mine dial phone. speaker in the dial-selected pager phone. The handset switch eliminates the need both inside and outside telephone ser- for a hook switch. Pressing the handset vice. Dial systems provide for many switch accomplishes all functions nor- simultaneous conversations, but do need mally accomplished by lifting the handset to use some form of signal multiplexing of a conventional phone from the cradle. or multiconductor cables. These problems When a call is dialed, the interface mod- can be minimized by using multiconductor ifies signaling to interface another cables only in the main haulageway where underground phone or a conventional tele- few roof falls or line breaks are likely phone on the surface. to occur and by taking conventional two- wire cable up to each section. However, Figure 2-3 is a diagram of a dial- this means all telephones in one area and-page phone. The telephone consists must be on a party line. of a handset, containing a transmitter in the mouthpiece and a receiver in the ear- 2.2.2 Distribution Systems piece, and a main housing. The main housing contains a speech dialer network, The distribution system for wired which isolates the outgoing and incoming phones is the equivalent of the string signals, a pulsing switch that is actu- between the two tin cans described in the ated by the rotary dial to signal a num- introduction. This is the propagation ber to the surface interface, and the medium that carries the voice signal. paging speaker. The speech network fil- For wired phones, the distribution system ters noise and processes the talker's may be single pair, multipair, or a mul- voice. A common-page button permits tiplex system. paging all phones, as is required when searching for a roving miner or for mak- All wired systems used in mines are ing a general announcement. inherently unreliable. That is, if a telephone line is broken or shorted by a Automatic dial systems are used at roof fall, for example, all telephones several mines that operate their own Pri- beyond that point are severed from com- vate Automatic Branch Exchange (PABX) for munication to the outside. If the line is shorted, communications in the entire STEEL MESSENGER system may be severely affected or lost R completely. s

2.2.2a Single Pair I OUTER A single pair of wires is the mini- JACKET mum requirement for wired commnications. A single twisted pair is used for magneto FIGURE 2-4. - Figure-8 multipair cable. phones, paging phones, and intercom phones, connected in party line fash- 2.2.2b Figure-8 Multipair Cable ion. Single-pair wires are generally 14 AWG (0.06408-inch diameter). This Figure-8 aerial distribution wire is relatively heavy gage wire is used in shown in figure 2-4. In cross section, order to minimize signal loss over long the wire looks like a figure-8 with a distance. steel support wire, called the messenger, in the top half and a core of twisted The signal loss per mile, or attenu- pairs in the lower half. The outer ation as it is called, is dependent upon jacket covering the messenger cable and the frequency of the signal and the size twisted pair bundle is highly resistant of wire gage as shown in table 2-1. This to abrasion, moisture, and environmental table shows that as wire size increases stress cracking. Each wire is solid, and gage decreases, the signal loss commercially pure, annealed copper. One (attenuation) decreases. conductor of each pair is usually color coded by a solid body color with a con- Each attenuation of 3 dB means that trasting spiraling color strip. The the signal power has decreased by one- other conductor has the complementary half. For example, if the output of a color combination. Figure-8 cable is commnication device was 4 mW, the -3 dB recommended for mine applications be- attenuated value of this signal is one- cause the messenger cable adds consider- half the output, or 2 mW. A 6-dB attenu- able strength to the cable and the in- ation of a 4-mW signal results in a l-mW stallation is similar to that of trolley (4 x 1/2 x 1/2) signal level. wire.

TABLE 2-1. - Cable attenuations

Wire size Frequency 13 gage 16 gage 19 gage (kHz ) Decibels Percentof Decibels Percentof Decibels Percentof per mile signal power per mile signal power per mile signal power remaining remaining remaining - 10 0.80 83 1.32 74 2.43 57 20 1.04 79 1.55 70 2.77 53 30 1.27 75 1.78 66 3.02 50 50 1.75 67 2.24 60 3.53 44 100 2.72 54 3.31 47 4.80 33 150 3.60 44 4.27 37 6.00 25 2.2.2~ Coaxial Cable (in this case a single pair of wires), can be employed in underground communica- Coaxial cable consists of an inner tion systems. conductor and an outer conductor, as shown in figure 2-5. This type of cable Figure 2-6 illustrates the FDM con- has two main advantages over twisted pair cept. At the transmitting terminal, each for transmission. First, the coax usu- of the voice channels (CH 1 through CH n) ally has lower attenuation. Second, the is applied to a modulator. Each modu- shield over the central conductor keeps lator shifts that voice signal to an the electrostatic and electromagnetic assigned frequency (f, through f,) and fields contained within the coax, thereby transmits the resulting signal over the minimizing crosstalk and interference common line to the receiving terminal. problems. At the receiving terminal, a bank of 2.2.2d Multiplex Systems filters separates the signals according to frequency. Individual demodulators The term "multiplex" is applied to recover the original voice signal. Note any system in which a single wire or wire that the multiplexing system shown in pair is used for the transmission of more figure 2-6 operates in only one direc- than one simultaneous signal. In this tion. Most communication systems require type of system, a means must be provided two-way voice transmission. This is for inserting the individual signals onto accomplished by a complete duplication of the common transmission line and then separating these individual signals at INSULATION CENTER CONDUCTOR the output of the line. There are two principal methods of multiplexing sig- OUTER JACKET-. nals. One is based on frequency transla- OUTER CONDUCTOR tions and is called frequency-division multiplexing, or FDM. The other is based FIGURE 2-5. Coaxial6 cable, cross-sectional view, on time-sharing the transmission line and - is called time-division multiplexing, or TDM . TRANSMITTING TERMINAL RECEIVING TERMINAL 2.2.2d.i Frequency Division Multiplexing Frequency division multiplexing is a process by which two or more signals are sent over the same line by transmitting each signal at a different frequency. The FDM concept can be illustrated by considering how the commercial radio broadcasting systems operate. Each radio station transmits at a specific frequency that has been assigned by the Federal Communications Commission (FCC). The CHn CHn signal from each radio station is trans- FlGlJRE 2-6. - Frequency division multiplex (FDM), mitted by a common path (the atmosphere), with many stations being on the air at the same time. To receive a particular - - - - SINGLE WIRE PAIR OR COAX T T T ---- station, a person merely tunes his radio ---A (receiver) to the frequency of the desired radio station. MODEM

This same principle, transmitting more than one voice signal, each at a different frequency, over a common path FIGURE 2-7, - Multiplex phone system, multiplexing facilities, with the compon- is connected to the TDM line. During ents in reverse order and with the signal time slot 2, signal B is removed and sig- waves traveling from right to left. Each nal A is placed on the TEM line. This terminal has a transmitting modulator and process is repeated with each signal a receiving filter and demodulator com- alternately occupying a time slot on the bined to form a "modem." TDM line. The bottom waveform in figure 2-8 shows the resulting time divi- A block diagram of the multiplexing sion multiplexed signal. The TDM signal principle is shown in figure 2-7. Each consists of signal A during the even- phone is connected to a subscriber termi- numbered time slots and signal B during nal unit or modem. The transmission line the odd-numbered time slots. To separate is a twisted pair or coaxial cable whose the signals, when they are received at gage depends on the system size. Repeat- the other end of the TDPI line, a demulti- ers can be inserted in the line to com- plexer must be used. The demultiplexer pensate for attenuation. is similar to a multiplexer except that the input and output are reversed. The 2.2.2d.ii Time Division Multiplexing demultiplexer reconstructs the original signals (A and B) from the multiplexed Time division multiplexing is a signal . process by which two or more signals are transmitted over the same line by allo- In order to illustrate the TDM con- cating a different time interval for the cept, the preceding discussion considered transmission of each signal. The time multiplexing only two signals together. available is divided up into small slots, This concept can be extended to multiplex and each of these is occupied by a piece many signals together onto a single TDM of one of the signals to be sent. The line. For instance, if eight different multiplexing equipment scans the input signals are to be multiplexed, then each signals in a sequential round-robin signal would be placed onto the TDM line fashion so that only one signal occupies each eighth time slot. Figures 2-9 and the TDM line at any one time. 2-10 show eight switches at one location and eight lamps at another which must be The basic concept, showing two sig- controlled by those switches. nals (A and B) being time division multiplexed together, is illustrated in The system shown in figure 2-9 is figure 2-8. During time slot 1, signal B simple and easy to understand; however, eight separate wires must be strung between the switches and the lamps. This TDM LINE SIGNAL6 (A MULTIPLEXED WlTH BI can be quite costly and impractical when the switches and lamps are separated by large distances. Figure 2-10 shows how each lamp can still be controlled by its SIGNAL A associated switch using a single wire (TDM line) between the switches and lamps. With the wiper on each of the TlME multipole switches synchronized, this system would sample the status of the first input switch (Sl) at the transmitting end and communicate that informa- SIGNAL B TlME tion to the receiving end. At the next interval of time, both multipole switches would step to position 2. Control of the second lamp would be accomplished by sam- A MULTIPLEXED WlTH B TlME pling the status of the S2 input switch

TIMESLOT 123456789 ---- at the transmitting end. At the next time interval, both scanner switches FIGURE 2-8. - Time multiplexing two signals. would step to position 3 and a similar INDICATOR located within a private branch exchange SWITCHES LAMPS (PBX). As the number of phones in use increased, the size and complexity of manual switchboards also increased. This led to the development of an automatic switching system called a private automatic branch exchange (PABX). Since telephone lines are currently used as data links for computers, teletypwriters, and various other data equipment, faster, more reliable exchanges were needed. To fill this need, the computer is presently used to control large solid state exchanges and perform many other central office (CO) functions.

2.2.3a Manual Switchboard

POWER ISWLY /J, The earliest switchboards allowed the operator to manually patch two cir- FIGURE 2-9, - No multiplexing (eight wires required), cuits together. When the central office received ringing current, the operator inserted the answering plug into the jack INDICATOR LAMPS SINGLE of the caller. After verbally receiving TDM LINE the called number, the operator inserted I the calling plug of the same circuit into the called party's jack and applied ringing voltage on the ringer of the called party. After the conversation has been concluded, both parties would ring off, informing the operator that the plugs could be disconnected.

2.2.3b Private Automatic Branch Exchange

POWER SCANNER Gb SWITCHES The private automatic branch exchange performs the same end function FIGURE 2-10, - Time division multiplexing (one wire), as the operator at the old manual switchboard. It makes a connection between the control action would result for the third phone line of a caller to the line of the lamp. After all eight positions had been phone being called. Connections through scanned, the scanner switch would return PABX's can be made using electro- to position 1 and start the sequence over mechanical devices (rotary switches, again. If the scanning were fast enough relays, etc.) or solid state electronic the lights would appear to glow steady circuits. and not blink. In a like manner, if this were a voice system, it would not sound In rotary dial phone system, the chopped. phone loop, which includes the two speech wires and the telephone set, is momentar- 2.2.3 Telephone Exchanges ily interrupted by the dial switch as the dial runs down. The number of loop The function of any telephone interruption electrical pulses thus gen- exchange is to connect a calling phone to erated corresponds to the number dialed. a called phone. The earliest method of In pushbutton-type phone systems, the connection was the manual switchboard numerical information (each digit dialed) is transmitted to the switching equipment Two-way voice utilizes a device called a in the form of coded frequency or voltage transceiver (combined form of transmitter s ignals . In either case, the PABX and receiver). switching equipment must receive and decode the "number dialed" signals from 2.3.1 General Radio System Theory the calling phone to determine what phone is being called. Voice frequency (VF ) signals could be transmitted directly from one antenna 2.2.3~ Computer-Controlled Switches to another; however, because of the low frequencies (and therefore long wave- Modern solid state exchanges under lengths) involved, the antennas required computer control can efficiently handle would be very large. For this reason, VF thousands of phone lines. In addition to signals are combined with higher fre- being faster and more reliable, computer- quency RF (radio frequency) carrier sig- controlled equipment occupies only a nals which can be effectively transmitted fraction of the space required by systems and received by antennas of reasonable using mechanical relays or rotary size. The two primary methods of com- switches. bining VF signals and RF carriers are amplitude modulation (AM) and frequency Alterations to these systems no modulation (FM). longer require a lot of time and hardware since the switching is under control of a 2.3.la Amplitude Modulation computer program. Changes such as adding phones, deleting phones, changing a phone In amplitude modulation the height, number, etc., can be made by simply or amplitude, of the RF carrier is made changing the program. The computer also to vary with the VF signal. This prin- can keep track of billing functions and ciple is illustrated in figure 2-11. The special events. Special features, such top waveform shown in figure 2-11 is a as conference calls, automatic call for- typical VF signal. The middle waveform warding, and abbreviated dialing, can be of figure 2-11 represents an RF carrier incorporated into computer-controlled that will easily propagate between an- exchanges by making changes to the com- tennas of convenient size. The bottom puter program. waveform shows the result of "amplitude modulating" the RF carrier with the VF System maintenance can also be han- signal. This signal retains the basic dled by computer program. Instead of shape of the original VF signal but will many labor hours spent in attempting to also easily propagate between antennas locate and correct a fault, the computer because it is being transmitted at the RF can cycle through all parts of the system carrier frequency. The original voice and locate a trouble spot within a matter signal is regenerated by demodulation of minutes. Because computer operations circuits in the receiver. are very fast, they can be performing maintenance functions even while handling 2.3. lb Frequency Modulation the switching function for thousands of calls. A voice signal may also be superimposed on a carrier frequency through 2.3 Radio Systems the use of frequency modulation techniques. In FM, the frequency of the RF Radio systems do not depend on a carrier is made to vary at the VF signal wire connection between transmitter and rate. As the amplitude of the VF signal receiver. There are many types of sys- changes, the frequency of the RF carrier tems in this category: one-way voice, (instead of the amplitude) changes. one-way signal, and two-way voice. In one-way operations, the transmitter sends Figure 2-12 shows the principles of a code or voice signal to the receiver. frequency modulation. The voice signal TIME

RF CARRIER

AMPLITUDE

TIME

FIGURE 2-12. - Frequency modulation (FM).

FM receivers are less susceptible to '\V/' noise when receiving a signal of only moderate strength or when the background FIGURE 2-1 1. - Amplitude modulation (AM). electromagnetic (EM) noise is almost as "loud" as the signal. This advantage of is shown by the top waveform and the RF FM over AM can become an important con- carrier by the middle waveform. The bot- sideration in underground mining opera- tom wavgform shows the resultant tions where electrical equipment is being f requency-modulated RF carrier. As the operated and the amount of EM noise being voice signal increases to its maximum generated is large. value, the carrier frequency increases (the waves bunch up). As the voice sig- 2.3.2 Distribution Systems nal decreases to its minimum value, the carrier frequency decreases (the wave For the most part, the distribution spreads out). The amount of carrier fre- system or propagating medium for radio quency change is referred to as frequency transmission is not hardwired but takes deviation or carrier deviation. The the form of electromagnetic (radio) waves unmodulated carrier frequency is referred in the air. (Radio waves at certain to as the center frequency. The amount frequencies will also propagate directly of carrier deviation is proportional to through the earth.) Electromagnetic the amplitude of the voice signal, with energy (radio waves) in empty space maximum carrier deviation occurring at travel at the speed of light. Because the peaks of the voice signal. the speed of any traveling wave is its wavelength times its frequency, we have a Usually an antenna is a straight formula of propagation (f X = speed of section of conductor, either a wire or light) where X is the wavelength and f is hollow metal tubing, which is suspended the frequency . X and f are thus in space. When a radio transmitter is inversely proportional (as f increases, X connected to the antenna, rapidly varying decreases), as shown in figure 2-13. electrical currents are set up in the Commonly used units are X in meters and f antenna. These currents cause electro- in hertz (Hz) (cycles per second). If magnetic waves to radiate from the the wave is traveling through anything antenna and travel through the atmosphere other than empty space, its speed is or other surrounding medium. When these reduced depending upon the electrical waves strike another antenna they induce properties of the medium through which it electrical currents in it similar to the is passing. Radio waves are slowed down current flowing in the transmitting only slightly by the earth's atmosphere. antenna. These currents, although they In solid insulating materials the speed may be very small if the antennas are far is generally much slower; for example, in apart or if they are transmitting through distilled water (which is a good insu- the earth, can be amplified by electronic lator) the waves travel only one-ninth as circuits (receivers) to reproduce the fast as they do in free space. In good original signal. The range of radio dis- conductors such as metals the speed is so tribution systems can be extended by low that opposing fields induced in the leaky feeder cable (special coaxial cable conductor by the wave almost cancel the designed to allow radio waves to "leak" wave itself. This is the reason why thin from the cable to the surrounding atmos- metal enclosures make good shields for phere and/or radio repeater stations. electrical fields at radio frequencies. 2.3.2a.i Half-Wave Dipole Antenna 2.3.2a Antenna Theory The strength of the electromagnetic In normal electronic circuits the field radiated from an antenna is propor- physical size of a circuit is small com- tional to the amount of current flowing pared with the wavelength of the fre- in the antenna. It is, therefore, desir- quencies being used. When this is the able to make the current as large as pos- case, most of the electromagnetic energy sible. This can be accomplished by stays in the circuit itself or is con- adjusting the length of the antenna so verted into heat. However, when the that it resonates at the operating physical dimensions of wiring or compon- frequency . ents approach the size of the wavelength being used, some of the energy escapes by If a straight wire, or antenna ele- radiation in the form of electromagnetic, ment, were to be suspended in space, the or radio, waves. Antennas can be con- lowest freqdency at which it would sidered as special circuits intentionally resonate has a wavelength of twice the designed so that a large part of the length of the wire. When used to trans- energy input to the antenna will be mit or receive RF energy that has a wave- radiated as electromagnetic energy. length of twice the length of the wire,

FREOUENCY IN HERTZ

3x10~ 3x10~ 3x10~ 3x10~ 3 ~XIO-~ 3xC4 3~10-~ 3X 10-a ~XIO-'~

WAVELENGTH IN METRES FIGURE 2-13. - Electromagnetic energy spectrum, -

CURRE

FIGURE 2-14. - Half-wave antenna, voltage and GROUND current distribution.

DIPOLE ANTENNA

TRANSMISSION /- TRANSMITTER/ LINE RECEIVER

1 A FIGURE 2-15. Dipole antenna, FIGURE 2-1 6. - Quarter-wave antenna, voltage and current distribution. the wire is known as a halfwave antenna. The current and voltage distributions 2.3.2a.iii Long-Wire Antenna along such a wire are shown in figure 2- 14. Such an antenna, when connected to a A long-wire antenna is one that is receiver as shown in figure 2-15, is long with respect to the wavelength of called a dipole. the incoming and outgoing signals. The length should be an integral number of 2.3.2a.ii Quarter-Wave Antenna half -wavelengths (ZX, 2-1/2X, 3X, 3-1/2X, etc.) to radiate effectively. A 1/2X An antenna may also be a quarter (dipole antenna) is said to operate wave in length. This is possible because on the fundamental frequency, X oper- of its connection to ground, which elec- ates on the second harmonic, 1-1/2X trically acts as the other quarter- operates on the third harmonic, 2X oper- wavelength. Refer to figure 2-16. The ates on the fourth harmonic, and so ground plane reflects the quarter-wave on. antenna so it has electrical characteristics similar to those of a half-wave 2.3.2a.i~ Loop Antenna antenna. Loop antennas can be utilized for An antenna of this sort may be through-the-earth radio transmissions or any odd multiple of a quarter-wavelength: as receiving antennas in direction- 1/4A, 3/4X, 5/4X, 7/4X, etc. These finding systems. These antennas can be antennas are commonly used for low- and composed of one or more turns of wire on medium-f requency applications. If a a round or square form, or the loop can quarter-wave whip antenna is installed on be established by simply laying the wire a vehicle, the vehicle becomes the ground in a loop on the ground or floor of a plane. A modified quarter-wave antenna mine tunnel. is commonly used for citizens' band (CB) radios on vehicles. 2.3.2b Leaky Feeder Systems COAXIAL CABLE 1

CENTER Figure 2-17 shows a cross-section CON DUCTOR 4-SH IE LD view of a standard coaxial cable and the lateral variation of its associated I INTERNAL FIELD STRENGTH fields, Insuchcables,thebulkofthe radio frequency electromagnetic energy is COUPLING LOSS transported down the cable between the THROUGH THE SHIELD center conductor and the shield, How- STRENGTH OF ever, the shields of most coaxial cables ! do not provide perfect containment of the internal electromagnetic fields or isolation from external fields, As shown in figure 2-17, a small fraction of the cable's internal field is leaked to the external space, External fields also 7 leak into the cable in a similar manner. DISTANCE FROM CABLE FIGURE 2-17. - Coaxial cable, field strength. The leaky feeder system is based on the use of semiflexible cable with spe- 2,3,2c, Waveguide Propagation cially designed shielding that has a greater coupling to the external space, A waveguide is a hollow conductor, Therefore, this cable easily leaks radi- through which electromagnetic waves ated signals and saturates the area (radio waves) may propagate. Such a around the cable with these signals, One waveguide may be made of copper (the type of leaky feeder cable is shown in ideal), or other materials, such as coal figure 2-18, The cable has a solid cop- or shale (nonideal), Hence, a mine entry per shield in which holes have been ma- is a waveguide, In order for a wave to chined to increase the amount of leakage efficiently propagate in a rectangular to and from external space, In large waveguide (mine entry or haulageway), the mines, repeaters may also be used to wavelength must be equal to or less than amplify and retransmit incoming and out- two times the greater dimension (a or b going signals to roving miners carrying of figure 2-19), Table 2-2 shows the portable radios. The spacing of these frequency spectrum designations with repeaters along the cable is governed their wavelength ranges, The dimension primarily by the receiver sensitivity, of "a" that would be common in under- the longitudinal attenuation rate of the ground communications is 3 meters, This cable, the coupling loss from the cable limits the lowest frequency range of to the portable units, and the trans- signals that will effectively propagate mitter power, Since the portable unit's within mine tunnels to the upper VHF and transmitter power is generally lower than the UHF range. A communication device that available for fixed repeater or base such as a CB radio has no application stations, the portable units set the cov- since it operates at approximately erage limits for two-way communications. 27 MHz, a frequency which is too low,

OUTER COVER HOLES IN SHIELD 7 LH,ELD7 CONDUCTOR

LINsuLATIoN

FIGURE 2-18. - Cutaway view of leaky feeder cable. TABLE 2-2. - Frequency spectrum designation

Abreviation Description Frequency Wavelength range VF...... Voice frequencies...... 300-3,000 Hz...... lo6-lo5 m VLF...... Very low frequencies...... 3-30 kHz...... lo5-lo4 m LF...... Low frequencies...... 30-300 kHz...... lo4-lo3 m MI?...... Medium frequencies...... 300-3,000 kHz...... lo3-lo2 m HF...... High frequencies...... 3,000-30,000 kHz...... 100 -10 m VHF...... Very high frequencies...... 30-300 MHz...... 10-lm UHF...... Ultra high frequencies...... 300-3,000 MHz...... 1 - 0.1 m SHF...... Super high frequencies...... 3,000-30,000 MHz...... 10 - 1 cm EHF...... Extremely high frequencies.. 30-300 GHz...... 1 - 0.1 cm

Other factors that influence wave- repeaters and frequency translation guide propagation are wall texture (the (Fl-F2) repeaters. In its simplest form smoother the wall, the better the propa- a repeater consists of two basic ele- gation) and tunnel straightness, and ments, a receiver unit and a transmitter electrical properties of the roof, walls, unit, as shown in figure 2-20. and floor. 2.3.2d.i F1-F1 Repeater 2.3.2d. Repeaters Single-frequency repeaters are used Two general types of repeaters will in most wired systems such as coaxial be considered for application in the mine systems where the transmission energy is environment : Single-f requency (Fl-F1 ) confined within the coax. These repeaters function as signal amplifiers. The attenuated input signal is detected, amplified, and retransmitted. Since the signals are confined to a separate coax, isolation between transmitter and receiver is maintained.

Single-frequency repeaters are also used in some wireless repeater systems, but extreme caution must be used to prevent feedback between repeater transmitter and receiver. Isolation must be maintained between the transmitter output and receiver input to prevent the transmitted signal from being received and amplified by the same unit. This

RECEIVE TRANSMIT ANTENNA ANTENNA OR COAX OR COAX

RECEIVER TRANS - MITTER

COPPER WALLS (IDEAL) FIGURE 2-19. - Waveguides. FIGURE 2-20. - Basic repeater block diagram. feedback can cause an oscillation or One possible system configuration squealing problem very similar to that which includes both a telephone link and caused by placing a microphone in front talk-through capability is shown in of its own speaker. Directional antennas figure 2-21. This configuration allows can be used to minimize this feedback for two modes of communications: F1-F2 problem; however, the use of high-gain would be used for a local mode, that is, directional antennas is not considered miner to miner within the working section practical in the mine environment owing through the repeater; and the second mode to installation problems and their sus- could support communications between a ceptibility to mechanical damage. miner located in a working section with a second miner located somewhere else in Another method of overcoming these the mine. The audio link (fig. 2-21) problems is to use special repeaters that between the receiver and transmitter of a do not depend on directional antennas. repeater can be used to customize repeat- In general terms, these units function ers to fit a variety of applications. An by separating the transmit and receive audio wireline can also be used to link signals with time division multiplex- a number of repeaters together to pro- ing. The repeaters transmit pulses vide complete radio coverage of the mine of RF energy and receive between these on a party line basis as shown in pulses. In this type of system all re- figure 2-22. peaters must be phase-locked with each other to synchronize the time division 2.3.3 Through-the-Earth Radio process. VF (0.3- to 3-kHz) radio waves will 2.3.2d.ii F1-F2 Repeater penatrate, to some extent, directly through the earth. Although signal F1-F2 repeaters receive signals from strength is greatly attenuated, experi- a portable unit on one frequency (Fl) and ments have shown that up to 1,000 feet retransmit these signals on another frequency (F2) to another portable unit. The mobile radios transmit on F1 and receive on F2. In this mode, all information goes to the repeaters, then back to the portable units. Some portable units are also capable of transmitting on F2 and, therefore, are able to talk to one another without the repeaters on a local simplex basis. With these systems, ------REPEATER the receive and transmit antennas at the r I repeater are often covering the same 1 general frequency bands and they can be I RECEIVER TRANS- - combined so that only one antenna is I AUDIO LINK e~'TT~R I - - 4 ' required. I I I I Thus far, repeaters have been dis- I 1 cussed only as a means to permit communication over greater distances than would be possible using direct transmission between portable radios. However, the audio link between the transmitter and INTERFACE receiver in the repeaters allows radio access to and from other types of audio circuits, such as specialized paging con- soles or the telephone system. FIGURE 2-21. - Repeater linked to telephone system. 2.3.4 Radio Pagers

Radio pagers are usually small FM radio receivers. The simplest type of radio pager is a one-way signal detector REPEATER REPEATER or "beeper." These devices emit an audi- 9 ble tone and/or blink a small light on and off. The miner must then go to the + nearest phone to receive the message. Another type of radio pager is a one-way voice pager. These devices are similar to the simple beeper-type pagers except that the caller can deliver a short verbal message to the person being paged. A common type of one-way voice pager sounds a tone to alert the miner that a message will follow, and then REPEATER broadcasts the verbal message. A disadvantage of these pagers is that, although LT-' it is possible to transmit instructions, FIGURE 2-22, - Minewide repeater system linked by such as "turn off the power to number 4 audio pair, left," it is not possible for the caller to know for sure that the instruction was (305 meters) of overburden may be even received, let alone carried out. penetrated. For this reason, one-way voice pagers should not be used to instruct personnel The transmitter may be a simple gen- to perform specific tasks that may affect erator with a loop or grounded wire safety. antenna. The receiver may be a loop antenna connected to a power amplifier with Some one-way voice, and even beeper, a set of earphones or a meter. When the pager systems allow the caller to selec- transmitter is activated, it sets up a tively page a specific section or an magnetic field directly through the earth individual miner. The heart of these (the overburden). systems is an encoder, which translates the number of each pocket pager to a spe- These characteristics of through- cific frequency or code that activates the-earth radio can be utilized in emer- only the designated pager. gency situations to detect, locate, and even communicate with miners trapped 2.4 Carrier Current Systems underground. Once the position of an underground transmitting antenna has been Any underground wire or cable, when determined using direction-finding tech- fed an RF signal, tends to distribute niques, a loop antenna can be positioned that signal throughout its length. Car- on the surface directly above the under- rier current systems utilize this fact to ground position. The trapped miner has a establish communication paths using method of pulsing his transmitter off and existing mine wiring. The wire used may on, such that a coded message may be sent be ac or dc power lines, neutral lines to the surface. A high-power transmitter such as the hoist rope, existing phone attached to the surface loop may also be lines, or other wiring. utilized to establish down-link voice communications with the underground Carrier current devices are basic- location. ally FM radio transceivers that transmit and receive over existing mine wiring instead of using an antenna system. The LF (low-f requency) and MF (medium- frequency) KP ranges propagate best in carrier current systems. A common exam- MICROPHONE WITH ple of a carrier current system is the PUSH-TO-TALK trolley carrier phone systems presently SWITCH used in many mines using trolley or rail haulage. Another example is the shaft communication systems that utilize the hoist rope itself to establish communications to and from the cage. The most modern system, based on MF, promises to FIGURE 2-23. - Trolley carrier phone, block be the most effective of all. diagram.

2.4.1 Trolley Carrier Phone

A simplified block diagram of a &?) PCI* f? TLc* CW.>T SWITCH typical trolley carrier phone is shown in figure 2-23. As mentioned earlier, the basic elements of any carrier current phone are the FM receiver and transmitter.

In a trolley carrier current phone system, the receiver and transmitter are connected to the trolley wire through a coupler capacitor, The coupler capacitor acts as a short circuit at the frequency of the FM voice signals, but as an open TRANSCEIVEA circuit to the trolley wire dc power I SPEAKER n voltage. The high voltage levels on the - trolley wire are thus blocked from enter- MICROPHONE- . -. .-. ing the receiver and transmitter sections PUSHTO swmcH-,--l'RILL '.-\ -q1 of the carrier phone, while the FM voice signals pass freely through the coupler capacitor. BATTERY

COUPLER C&BLI <.,UPLEPl The FM transceiver shown in figure 2-23 contains a power supply that FIGURE 2-24. - Hoist radio hardware. converts trolley wire high voltage down to low voltage levels to provide power to of the push-to-talk, release-to-listen the carrier phone circuits. The power design. During transmission, the sending supply may also contain a battery for unit feeds its coupler with a frequency- backup power in case power on the trolley modulated (FM) carrier. The coupler wire is lost. Such a system operates induces a signal in the hoist rope, which in the push-to-talk, release-to-listen is then picked up by the coupler of the mode. second unit. Both couplers are electrically identical, and each operates 2.4.2 Hoist Rope Radio both as a transmitting and as a receiving element. Operation of the hoist radio is Figure 2-24 shows a block diagram of the same as for a trolley carrier phone, a hoist rope carrier current system. The except that the hoist radio signal is system consists of two signal couplers inductively coupled to the propagation and two transceivers. Each unit is medium (hoist rope). Some hoist phones are simply modified trolley carrier Mine radio systems based upon this phones. Other hoist phone systems have effect are available commercially. These been specifically designed for operation are UHF systems operating around 450 MHz in a vertical shaft and usually provide which provide useful but limited cover- better coverage. age. In high coal (6.5 feet), line- of-sight ranges of 1,000 feet are often The transceivers of the hoist room possible. Range is reduced severely in and cage are identical, except for the non-line-of -sight, such as when going battery required in the cage. The hoist around a coal pillar. In lower coal, or room power supply provides the power for when obstacles exist in the propagation the surface equipment. Surface equipment path, range is reduced even more. For also may include a boom-type microphone this reason, conventional UHF radio sys- and a f oot-actuated push-to-talk switch tems require an extensive network of to facilitate hands-free operation. leaky feeder transmission cables and repeaters to become useful. Even so, 2.4.3 Medium Frequency (MF) Radio range from the cable is not usually in excess of 30 to 50 feet, and equipment Although radio transmission on cost is very high. Clearly another the surface of the earth is well under- approach is desirable. stood, transmission in an underground environment generally is not. Complex An important contribution to under- interactions occur between the radio wave ground radio communications was made by and the environment. Characteristics of the Chamber of Mines of South Africa. As the geology (stratified layering, bound- early as 1948, programs were in place to ary effects, conductivity, etc.) and the develop radio systems for deep mines, mine complex (entry dimension, conduc- primarily gold mines. The result was tors, electromagnetic interferences, that by 1973, an advanced 1-watt single etc.) had to be measured and understood sideband (SSB) portable radio system had before a practical mine radio system been developed that apparently worked could be built. To this end, consider- well. The Bureau of Mines procured sev- able research has been directed. eral of these units for evaluation. Per- f ormance in U.S. coal mines was not sat- In a confined area such as a mine, isfactory. There were several reasons radio waves can propagate useful dis- for this. First, U.S. mines are highly tances only if the environment has the electrified, producing considerable elec- necessary electrical and physical proper- tromagnetic interference (EMI) not nor- ties. The "environment" takes into mally found in the South African mines, account the natural geology and manmade which completely desensitized SSB radios. perturbations such as the mine complex Second, 1 watt was not enough power. itself. As an example, if the wavelength U.S. mines are mostly room and pillar, (A) of a radio wave is small compared which means that any radio system would with the entry dimensions, a waveguide have to have reasonable range from local mode of propagation is possible. Attenu- conductors. Third, geological electrical ation depends primarily upon the physical parameters were less favorable in the properties of the entry such as cross- United States. For these reasons, the sectional area, wall roughness, entry South African system was not acceptable. tilts, and obstacles in the propagation path. Secondary effects such as the The Bureau's approach was to first dielectric constants and earth conduc- determine the actual propagation charac- tivity also influence attenuation. teristics of MF in U.S. mines, and then to relate the propagation to the underground environment such as the geology, entry size, existing conductors, and EMI. Several exhaustive in-mine measurement Coal and analysis programs were conducted. or These programs formed the foundation for entry the first true understanding of how MF propagates in a stratified medium of various electrical parameters, which are transmitting often interlaced by manmade conducting antenna I structures (rails and power lines) and artificial voids (entryways).

Figure 2-25 is a simplified geometry FIGURE 2-25. - The coal seam mode. of an in-mine site that illustrates one of the most important findings of the measurement program, the "coal seam mode." For this mode to exist, the coal seam conductivity (a,) must be several Local mine wiring orders of magnitude less than that of the + rock a. A loop antenna that is at *---- least partially vertically oriented pro- L,-,, station duces a vertical electric field (E,) and a horizontal magnetic field (H9). In the T/fl or fe T/f, or f, rock, the fields diminish exponentially Vehicular in the Z-direction. In the coal seam, transceiver transceiver the fields diminish exponentially at a rate determined by the attenuation con- FIGURE 2-26. - Global repeater concept. stant (a), which in turn depends upon the electrical properties of the coal. An existing conductors. The frequency inverse square-root factor also exists effects are quite broad. Anything from because of spreading. The effect is that 400 kHz to 800 kHz will usually be the wave propagates between the highly adequate. conducting rock layers bounding the lower conductivity coal seam. The fact that The MF system described here is the coal may have entries and crosscuts based upon vehicular and personnel is of minor consequence. transceiver units, base stations, and repeaters. It applies prior fundamental In the presence of conductors, the research in the area of MF and utilizes picture changes considerably. In this the existing mine wiring network (power case, the effects of these conductors can cables, trolley line, etc.) to achieve totally dominate the effects of the ge- whole-mine coverage. The basic system ology. In general, the presence of con- configuration is shown in figures 2-26 ductors (rails, trolley lines, water and 2-27. pipes, air lines, phone lines) is always of advantage. Figure 2-26 illustrates a minewide repeater-base station concept known as MF can couple into, and reradiate the global maintenance net. In this con- from, continuous conductors in such a way figuration, mobile units (persons using that these conductors become not only the transceiver vests and/or vehicular trans- transmission lines, but also the antenna ceivers) can maintain local communica- system, for the signals. The most favor- tions by operating at frequency fl. The able frequency depends to some extent on range of communications in this case is the relationship between the geology and solely dependent on point-to-point radio propagation, aided by parasitic coupling. Paaer ohone line (existina) A transmission on fp causes repeater action to occur, permitting the two mobile units to be separated very large bU qhBTransmitter bU distances. To achieve this repeater Cellular Receiver action, it is only necessary for the reDeater transmitting unit to reach the repeater, either directly or by parasitic effects T/fl or f, T/fl or f, to the repeater line coupler. Comnica- tions with a base station are also Vehicular possible. transceiver transceiver Figure 2-27 illustrates a local FIGURE 2-27. - Cellular repeater concept. repeater concept constituting a local cellular net. This local repeater is known as a "cellular repeater" because it illuminates a "cell" or area of the mine, such as a working section, only. The antenna for the cellular repeater is a dual wire loop attached to timbers or the rib. An interface to the mine telephone system permits communications "off section. " The system design is distributed in the sense that each net can be operated independently of the other. In practice, a net can be easily installed by coupling a base station (at the portal) to electrical conductors in the wire plant (phone lines, power lines, etc.). Mobile transceivers operating on the assigned net frequency communicate with each other and the base. Other nets use different frequencies and are installed in the same way. Two types of mobile transceivers have been developed for the system. These transceivers consist of vest units for individuals and vehicular units for rolling stock. Functionally the two are equivalent, differing only in power levels and physical configuration. These transceivers are shown in figures 2-28 and 2-29. An important human factor problem was solved by the vest design. By placing the radio circuit modules in pockets on the vest, the weight and bulk of the transceiver have been evenly distributed. The loop antenna is sewn into the back of the vest. The pockets are located where medical records show less frequency of injury. Sound is directed toward the FIGURE 2-28. - Vest transceiver. FIGURE 2-29. - Vehicular transceiver, ears from epaulet speakers. A hinged and base stations. (See figures 2-26 and control head is conveniently located on 2-27.) For proper system operation it the front. The design allows the miners is necessary that these fixed trans- to maneuver in tight quarters and perform ceivers have very efficient antennas so normal mining tasks without catching the that the local wire plant can be prop- radio on obstructions. erly illuminated and signals on the wire plant are properly received. This The vehicular unit can be conveni- efficiency is paramount for whole-mine ently placed on any mine vehicle. It is coverage. used in conjunction with a special loop antenna of advanced design that produces The cellular repeaters use dual-loop high magnetic moment. Mechanically, the antennas (for transmit and receiver) antenna is enclosed in high strength attached to the rib or posts in such a lexan and is attached to the vehicle via way that there is little danger of damage special brackets. The lexan will not in normal mine activities. The trans- break even if severely flexed by impact. mit antenna produces a large magnetic moment that provides the signal for local Besides the mobile transceivers dis- cellular coverage, which is usually aided cussed above, the system also consists by parasitic coupling and reradiation of fixed transceivers such as repeaters effects. The receive antenna is similar. The global repeater and base station use a newly designed KF line coupler (see fig. 2-30) that permits very efficient coupling to the mine wire plant. Like a current probe, the coupler can be easily clamped around local conductors. MI? signal current flowing through the wire plant conductors produces a coupler vo output signal (Vo), which is applied ZT'T to the input of the base station or repeater. EQUIVALENT NETWORK ACTUAL NETWORK The base station is intended to be FIGURE 2-30. RF line coupler for base sta- placed where mine management finds it - most advantageous, usually in the surface t ions and repeaters. office complex or with the dispatcher. If desired, the base station can be subaudible tone is used in the vest controlled remotely via signal lines that transceiver to cause the cellular allow the control console to be placed in repeater to switch the message (page) to a surface building for convenience, while the pager telephone network. The re- the actual base transceiver is placed in peater includes both a noise-operated the mine where it can more efficiently squelch and a subaudible tone squelch for couple into the local wiring. Both the use in telephone switching. Subaudible global repeater and the base station uti- tone signaling is useful in identifying lize the RF line coupler for maxi- "stuck on" transmitters that can block mum efficiency. The cellular repeater the communications net. In-band signal- is generally located in a working sec- ing is useful in emergency situations. tion. It enables the vest to operate as a mobile pager telephone by switching 2.5 Hybrid Systems voice signals between the local pager telephone network and the vest. Vehic- Each of the communications systems ular radios can also operate in this already discussed has some individual mode. shortcomings. However, one system may complement another system to alleviate The system was developed around an certain problem areas. A hybrid is an interchangeable set of plug-in radio cir- interconnection of two or more sub- cuit modules. The same receiver, synthe- systems, taking advantage of the benefits sizer, and transmitter modules are used of each. in the vehicular transceiver, base sta- t ion, and repeaters. Servicing the 2.5.1 Improvements in System Versatility equipment only requires troubleshooting to the board level. Since the equipment As mines have grown and mining tech- uses the same radio circuit modules, the nology has improved, needs have arisen performance specifications of all trans- for new and improved communication capa- ceivers are similar. The signaling used bilities that cannot adequately be pro- depends upon the specific network re- vided by the traditional mine pager-type quirements. All receivers are designed phones or trolley wire carrier phones. with an adaptive noise-operated squelch These needs include the following: network that allows every transceiver on the net to hear the same message (party 1. Ability to communicate when the line). phone line or the trolley wire breaks.

The transmitters are designed with 2. Ability to communicate with both subaudible (100 Hz) and in- personnel not in the vicinity of a band (1,000 Hz) tone oscillators. A telephone. 3. Ability to communicate over pri- interconnected with the public phone vate channels. system on a selective or temporary basis. The intent of these systems is to provide 4. Ability to deliver important greater emergency communication capabil- messages during periods of heavy communi- ity during off-hours. These systems cations traffic during emergencies. enable a person at a mine pager phone to gain access to the public phone 5. Ability to communicate with sur- system, or permit access to the mine face public phones. page or phone system from any public phone. The following techniques are capable of satisfying the foregoing needs using Figure 2-31 shows one system in hybrid systems : which the interconnect between public phone and mine phone is made automat- 1. Underground phones with manual ically. In this type of system small trunking or automatic switching can pro- hand-held tone-generators are required to vide privacy and an interconnection to activate the automatic interconnect at the public telephone system on the sur- the mine office. f ace. Also, a larger number of simul- t aneous communications can take place If aperson inthe mine wantsto with multipair or multiplexed phone reach a prearranged public telephone from systems. his mine phone, he sends a tone via the tone generator and mine phone to a tele- 2. Low-f requency radio offers a phone interconnect unit of the surface. means of paging and communicating At this surface interconnect, the tone is directly using the mine structure within detected and activates a relay which, in a working section, and through the mine turn, automatically dials the preset tel- overburden in times of emergency. ephone number.

3. Medium-frequency radio can be used with power cables, trolley wires, and roof bolts to provide haulageway and ,?FTq) GENERATOR 11 11 EXCHANGE m section paging throughout the mine to key !,=, mining personnel carrying pocket pagers. I TELEPHONE OFFICE I L------J 4. Very-high-frequency radio can be used with leaky feeder cable or coaxial ------A - - - - 1 cable and antennas, as a technique for I guiding radio waves throughout the mine I AUTOMATIC haulageways and entries. This technique I INTERCONNECT can be used to provide whole-mine com- I I I AOTO ANSWER I 'I munications with hand-held radios carried MAIN OFFICE by key mining personnel. MINE PHONE LINE ------5. Ult ra-high-f requency radio can 7 provide wireless communication between key roving miners carrying radios within a working section, without the aid of GENERATOR additional wiring.

2.5.2 Dial Phone-Pager Phone Systems

Interconnect devices are avilable FIGURE 2-31. - Dial hone to pager hone that permit mine paging telephones to be hybrid. When a person calls the "auto answer" telephone number from a public WHEN ESCAPE IS CUT OFF phone, the interconnect unit automat- ( 1 ically answers the phone, and upon recep- I. BARRICADE fB@== tion of the audio tone from the outside 2. LISTEN for 1-1-33-!-11111 party, connects the incoming call 3 shots. then.. . directly to the mine pager phone line, 3. SIGNAL by thereby enabling the calling person to pounding hard 10 times page and talk to the desired person in the mine. 4. REST 15 minutes, then REPEAT signal unt~l... Systems also exist where the inter- 5. YOU HEAR 5 shots, which means you are located connection between the mine phone system and help is on the way. and the public telephone system is made I I manually, such as by a person on the surf ace. FIGURE 2-32. - MSHAsignaling sticker. 2.6 Other Systems air and the compressed air as priority. Wherever miners may be in the mine, 2.6.1 Seismic Systems driven air is required and eventually the driven air and stench will arrive at A seismic system can be used for their location. Stench may be any trapped miner location. If a miner clearly distinguishable odor. strikes a roof bolt, floor, or rib of the mine with a heavy object, the vibrations The delay time in a stench warning travel through the earth to the surface system is one of its most important and can be converted into electric drawbacks. Another very important signals by seismic transducers called negative point is that stench warning geophones. These signals can be ampli- cannot inform the miner what has hap- fied, filtered, and recorded. Because pened, where it has happened, or what he the shock waves reach individual geo- should do. Many times this type of in- phones at different times, the seismic formation can be worse than no informa- recordings can be analyzed and the location at all. tion of the miner can be determined. Analysis of seismic signals is a highly 2.6.3 Hoist Bell Signaling specialized field and beyond the scope of this manual. This method requires the Much of the communication between assistance of an individual trained in the various levels of a mine and the seismic methods. However, the seismic hoist room consists of hoist bell signal- system is the only trapped-miner system ing. This is a one-way communication presently in operation and accepted by system by which miners can request a cage MSHA. Every miner should have a sticker and/or desired level. (fig. 2-32) affixed to the inside of his helmet that he can refer to if entrapment In the hoist room, there is a power should ever occur. source for the system and a buzzer. Each shaft station has a buzzer and a pull 2.6.2 Stench System bottle. The bottle, when pulled, closes a switch that sounds the buzzer in Stench is used primarily as an evac- the hoist room and at all other levels uation warning. It should be introduced (fig. 2-33). The number of times the into the underground system at as many bottle is pulled corresponds to a command locations as possible, with the intake code. phone systems include common dial HOISTROOM BUZZER telephones, pager phones, dial-type pager phones, magneto phones, intercoms, and sound-powered phones. These may be connected in party line fashion using a two- wire pair, or in selective calling fashion using mltipair or multiplex techniques. Wired phone systems may have no switchboard (party line) for small TWISTED systems, a manual switchboard, an auto- SURFACE matic exchange, or a more sophisticated computer-controlled switch. A major disadvantage of any wired phone system is SWITCHED LINE that a roof fall could disrupt communications between miners and the surface.

Radio systems include all wireless communication systems. Coverage is limited in radio systems because of poor propagation of radio waves underground. TO OTHER LE VE LS Voice frequency ranges can be used for through-the-earth radio. Ultra-high- FIGURE 2-33. - Hoist bell operation. frequency radio can be used when it is combined with leaky feeder cables, anten- 2.6.4 Visual Pagers nas, and repeaters to extend coverage. Personal radio pagers can be used to sum- One of the most common type of mine mon an individual to a wired phone. communication devices is the pager phone. However, with these systems, many calls Carrier current systems utilize are lost because the phone is too far existing mine wiring to propagate RF sig- from a working face or the page is nals. An RF signal from a carrier phone not heard owing to high ambient noise. is induced onto a cable and transmitted Visual pager systems are being developed throughout the length of that cable. A that may eventually alleviate this transceiver, inductive or capacitive problem. coupled to the carrier cable, receives the RF signal, strips off the carrier, The most common type of visual pager and lets the electromagnetic voice signal system consists of strobe lights located activate a speaker or earphone. at strategic locations in the mine. These lights are controlled by a dis- Modern MF radio systems are being patcher who can set or reset them as developed that combine the best features required. They are usually used in con- of radio systems and carrier current sys- junction with pager phones. Some modern tems. In these systems, no physical con- multichannel phones have a light on the tact to existing mine wiring is required. face of the phone that provides the visual paging function. Since one system cannot usually satisfy all the communication requirements 2.7 Summary in a mine, interfaces have been developed to make hybrid systems. Hybrids (two or There are three basic types of com- more systems interconnected) take advan- munication systems used in underground -tage of the beneficial qualities of one mines: wired phone systems, radio sys- system to alleviate the deficiencies of tem, and carrier current systems. Wired another system. BIBL IOGKAPHY

1. Aldridge, M. D. Analysis of Com- Mine Communications (in Four Parts). munication Systems in Coal 14ines. Bu- 1. Mine Telephone Systems. BuMines Mines OFK 72-73, May 1, 1973, 127 pp.; IC 8742, 1977, pp. 42-57. available from NTIS PB 225 862. 10. . MCM-101 Call-Alert Pag- 2. Alton, J. E. A Uial-and-Page Tel- ing. Paper in Underground Mine Communi- ephone System. Paper in Underground Mine cations (in Four Parts). 2. Paging Sys- Communications (in Four Parts). 1. Mine tems. BuMines IC 8743, 1977, pp. 3-6. Telepl~one Systems. BuMines IC 8742, 1977, pp. 18-26. 11. . Kadio Paging. Paper in Underground Mine Communications (in Four 3. Anderson, D. W. Stout, and H. E. Parts). 2. Paging Systems. BuMines Parkinson. Interconnecting New Communi- IC 8743, 1977, pp. 29-33. cations to Existing Systems. Paper in Mine Communications, Proceedings: Bureau 12. Dobroski, H., Jr., S. J. Lipoff, of Mines Technology Transfer Seminar, and J. E. Trombly. Call-Alert Paging for Bruceton, Pa., March 21-22, 1973. Bu- Pager-Phone Sys tems . Paper in Under- Mines IC 8635, 1974, pp. 73-86. ground Mine Communications (in Four Parts). 2. Paging Systems. BuMines 4. Bradburn, R. A., and J. D. IC 8743, 1977, pp. 24-28. Foulkes . Lone~allMining Communications. Paper in Underground Communications 13. Dobroski, H., Jr., and J. E. (in Four parts). 4. Section-to-Place Trombly. Visual Paging System. Paper in Com~nunications. Bui4ines IC 8745, 1977, Underground Mine Communications (in Four pp. 44-62. Parts). 2. Paging Systems. BuMines IC 8743, 1977, pp. 16-23. 5. Bradburn, K. A., and K. L. Lagace. UHF Section-to-Place Kadio. Paper in 14. Ginty, J. J., K. L. Lagace, and Underground Nine Communications (in Four P. G. Martin. Applicability of State- Parts). 4. Section-to-Place Communica- of-the-Art Repeaters for Wireless Mine tions. BuMines IC 8745, 1977, pp. 3-30. Communications. Arthur D. Little, Inc., Cambridge, Idass., July 1975. 6. Bradburn, R. A., and H. E. Parkin- son. Two-Way Communications With Face 15. Lagace, R. L. Report Highlights Machine Operators. Paper in Mine Com- of the Working Group on Electromagnetic munications, March 21-22, 1973. BuMines Through-the-Earth Mine Communication IC 8635, 1974, pp. 36-45. Link-s. Proc. 2d WVU Conf. on Coal Mine Electrotechnology, Morgantown, W. Va., 7. Chufo, K. L., K. L. Lagace, and June 12-14, 1974, pp. 12-1--12-18. L. R. Wilson. Medium-Frequency Mine Wireless Kadio. Paper in Underground 16. Lagace, K. L., W. G. Bender, Mine Communications (in Four Parts). J. D. Foulkes, and P. F. O'Brien. Appli- 4. Section-to-Place Communications. Bu- cability of Available Piultiplex Carrier Mines IC 8745, 1977, pp. 65-72. Equipment for Mine Telephone Sys tems . Arthur D. Little, Inc., Cambridge, Mass., 8. Chufo, R. L., and R. G. Long. June 1975. Pager-Phone Guidelines and Test Equip- ment. Paper in Underground Mine Communi- 17. Lagace, K. L., and H. E. Parkin- cations (in Four Parts). 2. Paging Sys- son. Two-$Jay Communications With Roving tems. BuMines IC 8743, 1977, pp. 7-15. Miners. Paper in Mine Communications, March 21-22, 1973. BuMines IC 8635, 9. Dobroski, H., Jr. A Coaxial-Cable 1974, pp. 46-72. Telephone System. Paper in Underground 18. Long, K. G. Technical Guidelines Telephone Sys tems . BuMines IC 8742, for Installation, Maintenance and Inspec- 1977, pp. 3-17. tion of Underground Telephone Systems. Arthur D. Little, Inc., Cambridge, Mass., 22. Powell, J. A., and K. A. Watson. June 1975. Seismic Detection of Trapped Miners Using In-Mine Geophones. BuMines RI 8158, 19. Murphy, J. N., and H. E. Parkin- 1976, 8 pp. son. Underground Mine Communications. Proc. IEEE, v. 66, No. 1, January 1978, 23. Sacks, H. K. Trapped-Miner Loca- p. 26. tion and Communication Sys tems . Paper in Underground Mine Communications 20. Parkinson, H. E. EmergencyINon- (in Four Parts). 4. Section-to-Place Emergency Mine Communications. Paper in Communications. BuMines IC 8745, 1977, Mine Communications, March 21-22, 1973. pp. 31-43. BuMine IC 8635, 1974, pp. 3-16. 24. Spencer, R. H., and H. E. Parkin- 21. Parkinson, H. E., and J. D. son. Roving Miner Paging. Paper in Mine Foulkes. Conventional Telephone Equip- Communications, March 21-22, 1973. Bu- ment. Paper in Underground Mine Com- Mines IC 8635, 1974, pp. 17-35. munications (in Four Parts). 1. Mine CHAPTER 3.--SOLUTIONS TO THE COMMUNICATION REQUIREMENTS

3.1 Introduction wired phone system by using a remote portable radio. Three types of communication systems have become popular in solving communica- 3. Remote monitors that alert per- tion requirements underground: Loud- sonnel when there is a toxic or explosive speaking pager phones, carrier current gas buildup. phones, and magneto ringing phones. Basically, all three are simply single- 4. Control interfaces that allow channel party line systems. Although remote control of fans, pumps, or other these systems are quite reliable, the devices. single channel creates a variety of problems. For example-- 5. Transmitters and receivers that can serve as emergency links. 1. Since no call is confidential, messages are sometimes purposely made 6. Loopback that allows an alter- vague, especially if accidents or safety nate path of communications if the main topics are being discussed. path is cut.

2. A potential user must literally This chapter focuses on equipment "wait in line" until the channel becomes and methods to meet the special communi- clear for his use; thus, when foremen cation needs of individuals in various have to wait to call in reports or supply places of the underground mine. The com- requests, this single chan-nel creates a munication requirements can be broken serious productivity bottleneck. down into four categories:

3. In many large mines, there are 1. The mine entrance (shaft independent branch lines that must be communication). tied together by a dispatcher, adding further delays to the system. 2. Permanent and semipermanent locations (shop areas, lunchroom, crusher To solve these problems, some mines stations, etc. ). have installed other phone systems-- mostly commercial dial phones in indus- 3. Mining areas (the room-and- trial enclosures that offer extra channel pillar sections, longwall faces, block capacity and private line features . caving areas, etc. ) . Others have installed a system that combines both dial- and page-phone features 4. Haulageways (tracked trolley in a single unit. haulage, diesel, belt haulage).

Although these do represent improve- Methods of implementing systems to ments, they do not truly solve the over- meet the communication needs of these all problems that face modern mines. areas are described in sections 3.2 Besides extra channels, a communica- through 3.5. tion system should have the following features to enhance productivity and Section 3.6 discusses methods of safety: satisfying special communication requirements that exist. Major topics in this 1. A means of paging a roving miner category include communications with rov- to alert him that he is wanted on the ing personnel, the isolated miner, and phone. mo torman-to-snapper communications.

2. Wireless-to-wired system inter- Emergency communication systern are connects by which a miner can talk on the described in section 3.7. Detecting and locating the trapped miner, rescue team One of the biggest reasons for this communications, and emergency warning deficiency in communications to and from systems are discussed. the cage has been that reliable equipment simply was not available for establishing Although the methods of establishing this vital two-way voice communication communications throughout a mine are link. This reason is no longer valid. broken down and described in separate Today, equipment is commercially availa- sections, as outlined above, it is impor- ble to implement effective two-way voice tant to realize that these systems should communication, even while the cage is be tied together or interconnected in moving, down to depths in excess of some way. The overall design plan must 10,000 feet. include provision for integrating the various communication subsystems together A useful hoist-shaft communication into a minewide system. Such a system, system must satisfy the requirements for designed with the total mine operating communication throughout the full travel plan in mind, will be the most effective. of the cage, providing voice communica- In a like manner, a judicious choice of tion between the cage and the hoistman, monitored parameters in the underground as well as to underground shaft stations. environment and selected machinery will An effective system should also provide yield a cost savings in production and for shaft-inspection communication be- augment safety. Many man-hours and dol- tween the inspector and the hoistman, and lars can be saved by knowing conditions should have a slack-rope indication. For before they become a problem. Situations the modern, automated shaft, signals are that could become disastrous can be pre- also required to permit selection of dicted and proper solutions implemented level, enable interface with interlocks, before the disaster occurs. Because and permit jogging for exact position at proper environmental and machine monitor- any level. ing and control is another key to safer and more productive underground mining, The limited space within the cage these factors should also be considered places an operational restraint on equip- in the overall plan of any communication ment. Equipment must be small and should system. be located so that it cannot be damaged by any of the various uses of the cage 3.2 The Mine Entrance such as transporting supplies and machinery. An additional microphone-speaker The entrances to underground mines station may also be desired for multi- are either vertical shafts, slope en- level cages or when several cages are trances, or horizontal drifts. Slope and joined together. horizontal drift entrances can be considered as a continuation of a haulageway A reliable hoist-shaft communication and are treated in section 3.5. This system should be considered as a vital section is devoted primarily to shaft part of any overall communication system. communications. Shaft communication is especially important during or following an accident or In the past, operators of single- disaster situation. Experience has level mines with overburdens less than taught that the hoist often becomes a 1,200 feet have felt that communications bottleneck during rescue or evacuation between the top of the shaft, the bot- operations, and good communication to and tom, the hoistroom, and possibly a com- from the cage is essential. munications center were adequate. Many mines in this category (which includes Traditionally, bell signals have most underground coal mining operations) been used between those requesting the did not have the capability of two-way cage and the hoistman, and until re- voice communication with personnel in the cently, bell signaling was usually the cage. only form of hoist-shaft communication. Today, however, equipment is available (level A, level B, and level C). To sig- that allows two-way voice communication nal the hoist operator, a miner at any between persons in the hoist cage and the level pulls the pull bottle, causing the hoistman or other locations at the shaft associated switch to close. This applies top or bottom. voltage to the buzzer at that level, and also to the hoistroom buzzer and all oth- Presently available methods of im- er buzzers, through the switched line of plementing two-way voice communication the twisted pair. with the hoist cage include trailing cable systems, radio systems, and hoist Bell signaling systems, although rope carrier current systems. proven to be reliable, do have some severe shortcomings. First, there is no 3.2.1 Bell Signaling Systems way to convey special messages to the hoistman. Special equipment or assist- There was a time when bell signaling ance or unusual cage movements cannot be was the only form of communication requested unless a signaling code has between those requesting a cage and the been defined for that specific request. hoist operator. Because of this, bell A second disadvantage, especially for signaling systems have gained widespread mines with many shaft stations, is that acceptance and are used on many hoists. the bell codes required can become quite long. Long or complicated bell codes are Figure 3-1 shows a simplified sche- obviously more difficult to remember and matic diagram of a typical shaft buzzer can become a source of confusion, espe- signaling system. In the system de- cially during an emergency or disaster picted, a single twisted pair wire is run situation. During these critical periods down the mine shaft and "tapped off" at of high emotional stress, mistakes are those shaft stations where signaling is easy to make even when signaling codes required. Figure 3-1 sh->ws a system with are posted. Some mines with many levels the twisted pair tapped at three levels and/or shaft stations have partially overcome this disadvantage by assigning an employee to the hoist cage. Because HOISTROOM BUZZER this miner, called a cager, is permanently assigned to act as the hoist cage POWER SOURCE operator, the bell signaling code has SURFACE become "second nature" to him. // /// / / // //////// UNDERGROUND ,-TWISTED PAIR Another disadvantage of the bell signaling system is that communication

LEVEL A with the cage is impossible when it is BUZZER between levels. This deficiency is

PULL BOTTLE especially crucial during shaft inspection or repair. Some mines have partially overcome this problem by running a pull cord down the shaft. This cord is kept in a position next to the shaft tim- LEVEL B BUZZER bers by staples and can be used for emer- PULL BOTTLE gency stops and signaling between shaft stations. This system does provide some degree of emergency communication from the cage while it is between shaft sta- LEVEL C tions; however, operation of the system BUZZER can be extremely dangerous since it itrequires the operator to reach out of the U PULL BOTTLE cage and grab a cord, which may be moving F IGURE 3-1. - Bell signaling system. relative to the cage. 3.2.2 Trailing Cable Systems tied into the existing wired communication system in the mine, or it can be One method of establishing two-way implemented as an independent, shaft- voice communication with the hoist cage only, communication system. is by using a trailing cable. In this type of system. A communications cable In addition to the disadvantages is physically attached to the bottom of associated with any wired communication the cage and allowed to hang down the system (normal cable maintenance and line shaft below the cage. breaks), the trailing cable system has limitations in terms of depth because of Figure 3-2 shows a typical trailing the amount of cable that can be trailed cable system. In the figure, three from the cage. phones (one in the hoistroom and one at each of the two shaft stations) are con- 3.2.3 Radio Systems nected by a phone line that has been strung down the shaft to a junction box Another approach to satisfy the located about halfway down the shaft. voice communication requirements with Connections are made within the junction personnel in the cage is by using two-way box to the trailing cable which provides radio systems. Some recently installed the link to the phone mounted in the radio systems are meeting the hoist com- cage. The trailing cable system can be munication requirements. One radio system currently being used at an iron ore mine is illustrated in figure 3-3. In this system, portable police-type 150-MHz FM radios were used in 19-foot-diameter shafts. The surface antenna is a dipole mounted on plywood bolted to the steel collar at the top of the shaft. A coax runs from the dipole to the hoist room, a distance of about 500 feet. In the cage, the radio and 12-volt battery are mounted in a plywood box.

Results of studies indicate that the attenuation of radio signals increases

TRAILING

ANTENNA 4; 1 , 1 RADIO IN CAGECONNECTED TO ANTENNA ON TOP OF CAGE

FIGURE 3-2. - Trailing cable system. FIGURE 3-3. - Hoist cage radio. sharply as shaft size is decreased. For SHEAVE straight, unobstructed shafts with a diameter in the neighborhood of 12 feet, radios opefating in the frequency range of 500 to 1,000 MHz should provide commu- HOIST nication to a depth of approximately SHEAVE 1,500 feet. For smaller diameter shafts, COUPLER radio communications will only be possible over shorter distances.

3.2.4 Hoist Rope Carrier Current System

A carrier current system using the hoist rope as the carrier has been developed that provides reliable two-way voice communication between the cage (even while in motion) and the hoistman to cage depths in excess of 10,000 feet. The principle of operation of the hoist rope carrier current system is similar to that of the carrier current commonly used in trolley carrier phone systems. Both systems transmit and receive RF energy over a transmission line. In a trolley CAGE system, the transmission line is the trolley wire. In the hoist system, the carrier signal is transmitted on the hoist rope. Both systems utilize transmitters and receivers (transceivers) that FIGURE 3-4. - Hoist rope carrier current system. communicate with each other by RF currents superimposed on a cable. rope and is picked up by the coupler at the other transceiver. Each coupler The principal difference between the operates as both a transmitting and trolley carrier system and the hoist rope receiving element. The cage coupler is carrier system is the way in which RF clamped to the hoist rope at a point just energy is transferred to, and received above the cage. The coupler for the sur- from, the transmission line. Because the face transceiver should be permanently hoistman's transceiver at the headf rame mounted below the sheave wheel and about cannot be physically attached to (or even 6 inches from the rope. Coaxial cable touch) the hoist rope, a different method should be used to connect each coupler to of superimposing RF energy onto the rope its transceiver. must be used. 3.2.5 Hoist Signaling Summary The solution is to inductively couple the hoistman's transceiver to the The pull-bottle shaft bell has been hoist rope. Figure 3-4 shows a block the universally accepted means of cage diagram of a hoist rope carrier current signaling. More than 60% of the hoists, system. The system consists of two sig- notably those in bedded deposit mines, nal couplers and two transceivers. Each have only one underground level; hence transceiver is of the push-to-talk, this type of signaling system is simple release-to-listen design. During trans- and effective. In multilevel mines, sig- mission, the sending transceiver feeds naling codes become complex to the point its coupler with an FM carrier. The where a full-time cageman may be required coupler induces a signal into the hoist to control the cage during all man and rope, which travels up and down the hoist equipment lifts. Depending on the size and nature of the shaft, commercial radio maintenance, and management personnel. equipment operating at 150 or 450 MHz can Communications equipment associated with provide a voice link down to 2,000 or advancing or frequently moved face areas 3,000 feet. is treated in section 3.4.

For a very deep (2,500 feet or The single-pair wired phone system greater) or narrow shaft (less than is the communication system commonly 10 feet in diameter), communication sys- employed to satisfy the requirements of t ems are available that inductively permanent locations. Magneto phones were couple RF signals to the hoist cable. first used, but although many are still These carrier current systems provide in use, they have been largely replaced two-way communication with the cage in by loudspeaking pager phones. even the smallest shafts down to depths in excess of 10,000 feet. In a few mines the conventional telephone with a rotary dial and ringer 3.3 Permanent and Semipermanent In-Mine (mounted in an explosion-proof housing) Locat ions has been used. Systems using these dial phones are usually an extension of an Looking only at the permanence of a aboveground private automatic branch ex- telephone installation, phone locations change (PABX) or a single-party indepen- can be divided into the following three dent system with a small switchboard. categories: Recently multipair cable and even multiplex systems have been used to intercon- Permanent (life of the mine). nect phones and to connect individual phones to an aboveground PABX. Semipermanent (more than a year between moves). 3.3.1 Single-Pair Pager Phones

Frequently moved (weekly to Pager phones were specifically monthly). designed to meet the requirements of permanent and semipermanent locations for Permanent locations include surface underground mining operations. They dif- sites, the dispatcher's station, under- fer from a conventional telephone in that ground offices and shop areas, lunch- instead of a ringer, a loudspeaker is rooms, rail or belt heads, storage areas, used in each phone to alert the person the crusher operator, and along main being called, and each phone has its own haulageways. batteries for power instead of being centrally powered. In a single-pair instal- Semipermanent phones would be found lation, the pager phones are inter- mostly in the submains of a mine. After connected by a single twisted pair of panels have been fully developed, most of wires and all phones are on a single the phones in the submain would be re- party line. A 14- to 18-gage copper pair located to more active sections. One or with a neoprene jacket is most often two phones would remain for use by roving used. personnel. If a submain became part of the haulage system, in all likelihood Figure 3-5 shows a hypothetical, more phones would remain in use to meet moderate-sized room-and-pillar coal mine the operating practices of the mine. with an average working section size of 300 feet by 400 feet, and an average Frequently moved phones are pri- panel size of 800 feet by 1,200 feet. marily located near the working faces of the mine, typically in working sections The upper half of figure 3-5 shows off submains. These phones are moved the main haulageway, the operational sub- with the section in order to maintain mains, and the working sections and close coamunication with the dispatcher, illustrates how a single-pair pager phone ROOM AND PILLAR PANELS 1. Telephones in the dispatcher's 1800 X l2W PANELS) office, shop area, and main haulageway, SPLICE CASE and opposite each submain, would rarely, FREOUENTLYMDVEDPHONE SEMIPERMANENT PHONE if ever, be moved (permanent). PERMANENT PHONE 2. Telephones opposite each butt entry would remain in place for one year or so until more panels in the submain have been developed (semipermanent).

3. Mine safety regulations require that a communication link must be established within 500 feet of the working face; hence, telephones at the working sections are required to be moved frequently (perhaps once a week). FREOUENTLYMOVED PHONE IS KEPT NEAR THEWORKING 3.3.2 Multipair Systems

For a multipair access installation (fig. 3-6), planning for future mine growth becomes important. The figure shows an example of how a multipair system may have grown in our hypothetical FlGU RE 3-5. - Single-pair pager phone instal lation. mine, which has four working sections (A, B, C, and D). In this example, when the system would be wired. The solid black system was installed, working section A line represents the single pair. The did not exist, so three-pair cable was black squares represent splf.cingpoints, used to give sections B, C, and D private and the circles represent the telephones. lines. (The telephone at the working Telephones can be seen at the dis- face is an extension of the butt entry patcher's office, in the underground shop phone, which may not be reasonable in low area, and along the main haulageways; coal.) When section A came into opera- there is one at each butt entry and one tion, either more cable had to be in- near each working section, and a twisted stalled or more telephones had to be con- pair is shown running to the pager phone verted into extensions without private at each working section. When a panel is lines. Figure 3-6 shows that six-pair worked out, the phone at that butt entry cable was run along the main haulageway, may be removed and installed at another so that at this stage of development, location. Usually, as shown in fig- several telephones were forced to share a ure 3-5, a few phones are left behind pair. along the submains in worked-out sections. These phones may be used peri- Several telephones are extensions, odically by roving maintenance personnel and as long as that is a satisfactory or inspectors. condition, six-pair cable in the main haulageway is sufficient. However, if A mine is not static; its architec- the objective is to provide every tele- ture or layout changes, but fortunately phone with its own pair (which really is these c11;inges are usually known well in the point of a multipair dial access sys- advance so that cable selection and the tem), additional cables have to be run phone line layout in the mine can be down the main haulageway. The lesson, of planned to accommodate future growth. As course, is to keep future needs in mind far as changes are concerned, the phones when planning cable layouts, particularly shown in the example of figure 3-5 fall in areas like main haulageways and main- into the three basic categories as tenance areas where telephone locations follows : are unlikely to change for many years. LEVEL - 1A 2 A 3A

SPLICE CASE

- SlNGLE -PAIR CABLE --- THREE PAIR CABLE

@ FREaUENT,. -2 WIRE PAlR MOVE0 PWII I

CARRIER TERMINALS 1 I A FIGURE 3-6. - Multipair installation.

-2 WlRE PAIR Figure 3-7 shows details of the multipair system; once again, the three categories of telephones--permanent, semipermanent, and frequently moved telephones--can be seen.

7 B 3.3.3 Multiplexed Systems

Various types of multiplexed systems can also be implemented to satisfy commu- FIGURE 3-8. Multiplex system with PABX, nication requirements of permanent and - semipermanent locations underground. drift to the underground headframe of One system using multiplex equipment shaft B, and then down shaft B to the and a small PABX has been installed in a 5,600-foot level. An air-conditioned deep, multilevel, metal mine in the West- room was available in the shaft B area at ern United States. This system utilized the 3,700-foot level that met all envi- an existing twisted pair already strung ronmental requirements of commercially through the mine to establish two seven- available PABX systems. Additionally, channel private communication links. A this location was approximately centered simplified diagram of the system is shown with respect to the physical locations of in figure 3-8. the desired phones. The single twisted pair was opened at this point, thereby The single twisted pair utilized by forming two independent wire pairs (one the systems extended from the surface, running back to the surface, the other down shaft A to the 3,700-foot level, running down shaft B). A carrier system horizontally through a 5,000-foot-long was then installed on each pair, and these two independent carrier systems THREE P&IR CeBLE I were then connected to the PABX line cir-

I.NGLt I cuits. This provided 14 private channels CABLE (1A through 7A and 1B through 7B) for communication within the mine. This system (described in more detail in appendix SEMIPERMANENT TELEPHONE A), not being intrinsically safe, is not FREOUENTLY MOYEDTELEPHONES SPLlCE CASE suitable for use in coal mines. PERMANENT TELEPHONES

SIX PAIR CABLE Presently, there is no intrinsically safe multiplexed telephone system de- FIGURE 3-7. - Detail of multipair. signed for mine use that is commercially available. However, the Bureau of Mines communication with other parts of the is developing such a system. This system mine. provides eight full duplex channels, some of which can be dedicated to monitor and Most existing mine communication control functions. The system uses in- systems stop at the last open crosscut of expensive twisted shielded pair and is the section. Present mine communication not under control of any central switch- systems are aimed at satisfying the need ing or control center. Because of this, that the mine section foreman be able to the system will not be made inoperative communicate with the mine shift foreman. because of a\ cable break or a central However, in some mines there may be addi- PABX failure. Other features include a tional communication needs within the message-leaving light on each phone, low- mine section. Needs that are not ade- battery indicators, and compatibility quately met include communications be- with standard loudspeaking pager phone tween the continuous miner operator and systems. the shuttle buggy operators, between the shuttle buggy operators and the "gather- 3.4 Mining Area ing" locomotive operator, and between the general maintenance foreman and the sec- Safety regulations require that a tion maintenance man repairing a machine. communication link must be established By satisfying these needs, both the safe- within 500 feet of the working face. In ty and efficiency of mining operations coal mines a butt entry portable phone can be improved. The existing power meets that requirement at the beginning trailing cables to the face machine proof a panel's development, but a frequent- vide one means to achieve these communi- ly moved section phone must be installed cations capabilities in a reliable and once the face has moved 500 feet from the economic manner. Another method of es- butt entry phone. Weekly movement of the tablishing voice communications between section phone might be necessary to keep miners working at the face is by a radio the section foreman within range. system.

Under normal operating conditions The operational and safety advan- the sectioc foreman communicates by fixed tages of communication capabilities are phone to the shift foreman to request several and diverse. The shuttle buggy supplies and maintenance services, and to operator will be able to alert the con- file his periodic productivity reports. tinuous mining machine operator of an Under emergency conditions he requests impending roof fall. The shuttle buggy medical aid for personnel and reports operators will be better able to coordi- hazardous conditions in his area. His nate their activities as they go in to primary concern is the safety and produc- dump on the belt or into the cars. The tivity of his crew. maintenance mechanic will be able to communicate with the surface while working The high acoustic noise level cre- at a face machine. When maintenance on a ated by the mining machinery greatly face machine is required, the maintenance reduces the effective communications mechanic can be called directly from the between the foreman and his crew. This troubled machine. noise also interferes with the foreman receiving calls. Often a motorman must 3.4.1 Radio Systems deliver a call-in message to the foreman when he is transferring haulage cars in The use of two-way radios can result his section. A standard procedure in in better coordination of section ac- some belt haulage mines is to turn off tivities, especially during the movement the conveyor system, thereby causing all of mobile machines that must work in the section foremen to call in. The concert with each other at the face area. working section crew primarily depends on In many cases the operators cannot see the fixed pager phone system for direct one another, but with a system of communications they can still effectively opening favors better radio wave propaga- work together. Safety will also be tion. Figure 3-9 shows a comparison in improved by better communication with the ability of 450-MHz UHF radio waves to isolated workers; for example, fan-hole propagate in high coal (7 feet) as drill operators in iron ore mines. opposed to low coal (3.5 feet) , assuming a 16-f oot-wide entry. The comparison Improved management can be realized also assumes that 2-watt UHF walkie- by means of effective section communica- talkies are the source of signal. As tion. The foreman can exercise better indicated in figure 3-9, communication is supervisory control, resulting in more possible for ranges up to 1,500 feet, efficient utilization of available per- along a straight entry in high coal, but sonnel. Another benefit is the reduction the range drops to 400 feet in low coal. of unnecessary travel, an extreme burden Of course the same principles apply to when mining low coal or on longwall sec- tunnels in noncoal mines. t ions. Repairmen, mechanics, and util- itymen can be quickly reached and dis- Corners also present obstacles to patched to their place of need at the the propagation of UHF radio waves. For time of need. In spite of these advan- a path that includes one corner, ranges tages, two-way voice communication using are reduced but improve if one of the portable radios is only now becoming radios can be moved closer to the corner. practical for use in underground working However, propagation around a second sections. This has been due to the lim- corner is usually poor. To help off set ited range that could be attained using this corner effect, it is good practice the small handheld units. to transmit from intersections when possible, thus reducing the number of Almost anyone who has ridden in an corners that have to be negotiated. Some automobile is familiar with the radio other obstacles to radio wave propagation fade that occurs when a car enters a tun- at ultrahigh frequencies are equipment nel. One might expect, then, that radio such as shuttle cars and machines that wave propagation would be very poor in reduce the cross-sectional area of the mines, and it is still not feasible to tunnels or entries. Table 3-1 shows that design practical "wireless" portable ra- when shuttle cars are present, the range dios capable of full mine coverage, ex- is typically reduced by 200 feet in high cept possibly for the smallest mines. coal and by 50 feet in low coal. However, both theory and experience show that the propagation characteristics of radio waves in mine tunnels improve as the frequency increases into the UHF band. This is attributable to a waveguide effect that is prominent when the wavelength of the radio wave becomes ..A small compared with the cross-sectional dimensions of the tunnel. In the UHF band from 400 to 1,500 MHz, tunnel propa- At 450 MHz gation is adequate to provide sectionwide radio coverage.

penerrarlon Probably the most important factor that determines the ability of UHF radio waves to propagate in underground mine tunnels is the cross-sectional dimension FIGURE 3-9. - UHF radio wave propagation in of the tunnels. In general, a high, wide high and low coal. TABLE 3-1. - Typical range reduction due to tunnel obstructions at 450 kHz

High coal (7 by 16 ft) Low coal (3-112 by 16 feet) Shuttle car...... ft.. 200...... 50. Bends...... Moderate to severe.... Moderate to severe. Permanent stoppings...... do...... Do. Longwalls...... - ft.. 1,200...... 250.

The range of effective communication repeater and portable radios. Figure 3- can be substantially increased by the 11 shows a sample cable installation for use, and judicious placement, of a reuse with the repeater. In this case, the peater, and in some applications, a radi- signals from radio A are picked up by the ating cable. When this is done, good radiating cable itself, carried to the communication can be established even un- repeater, retransmitted as F2 signals on- der some of the worst conditions encoun- to the cable, carried along by the cable, tered on working sections. Referring to and leaked into tunnels where they are figure 3-10, suppose the two radios la- received by radio B. The reverse occurs beled A and B are out of direct radio for transmission from B to A. range of each other. The repeater can function to bring the radios within range Even though a radio repeater such as in the following manner. When radio A shown in figure 3-10 can extend the oper- transmits on frequency F1, the signal is ating range of radios A and B, this still picked up by the repeater, which ampli- provides only local coverage such as a fies and converts it to a different £re- working section. However, a radiating quency (F2) and retransmits it at a cable-repeater system such as shown in higher power level. Radio B receives the figure 3-11 can extend the operating retransmitted signal. In this way, corn- range for many miles. The limiting fac- munications from radio A to radio B and B tor in this case is the ability of a to A are established. radio to transmit to and receive from the radiating cable. When the tunnels between the portable radios are heavily obstructed by The implementation of a UHF radio machinery or metal roof-support struc- system for a mine working section can be tures, radiating (leaky coax) cable may approached from the standpoint of a basic also be installed in the tunnel to pick up and carry the signals to and from the JJ JJ RADIATING CABLE \

1, TO t2

RADIATING CABLE REPEATER

RADIO REPEATER

1 FIGURE 3-10. - Extending range with radio FIGURE 3-1 1. - Extending range with radiating repeater. cable. "building block" philosophy as shown in For a more comprehensive system, an figure 3-12. The fundamental building interconnect may be installed to inter- block is the UHF walkie-talkie radio face the radio system with other communi- itself. Several of these are sometimes cation systems, such as a pager phone or all that is required for an effective carrier phone system. This would be use- sectionwide communication system. Usu- ful for paging key personnel in the ally, however, certain portable accesso- section who are out of audible range of ries are helpful to some miners; namely, the section pager phone. However, the speaker-microphone headsets, carrying interconnect should operate only on a vests, and remote handheld microphones. selective basis to avoid interference to, or by, the section radios. Hardware for In some situations, it may be neces- implementing this radio interconnect is sary to extend the range of communica- commercially available. tions beyond that achievable when transmitting directly between portable units. UHF section radio has been used suc- This can be accomplished by adding a cessfully on room-and-pillar working sec- radio repeater to the system. A re- tions at several mines. One such mine peater, which can effectively double the had a single conventional room-and-pillar area of coverage, is essentially a signal section as shown in figure 3-13. The booster that receives weak signals from seam height was medium low (42 to 48 distant radios and retransmits them at inches). The section radio system con- full power. Further enhancement is pos- sisted of walkie-talkie radios carried by sible by connecting the repeater to its various miners and a radio repeater lo- antenna by means of a long length of cated at a communications center (known special "radiating" cable that can be run as the communication sled), which was through areas of poor coverage, such as placed near the power sled. The foreman, the area along a longwall chockway. mechanic, shot firer, and a utility Radiating cable, also known as leaky coax cleanup man were equipped with 2-watt ra- or leaky feeder, allows signals to leak dios operating on two channels, 454 and out of or into itself at a controlled 457 MHz. The purpose of the repeater was rate. It effectively behaves as a long twofold: (1) To extend coverage beyond antenna that can guide radio waves around the direct portable-to-portable range, corners and bends.

Face -( 20'b --A 60' k phone system

Interconnect

Antennas

Radiating cable

Radio repeater Communication sled with UHF repeater interfaces

Portable accessories Seam height: 42 -48 ~nches

Portable radios

FIGURE 3-12. - UHF radio system "building FIGURE 3-13. - Section layout of room-and- blocks. It pillar section. and (2) to provide an interconnect mainly because the seam height was 6 to between the radio system and a system of 7 feet. Direct portable-to-portable com- carrier phones, which were mounted on munication was generally good over an mobile machines and interconnected by area encompassing up to three-quarters of means of the trailing cable conductors to the working section, although some dead the machines. It was thus possible to zones were encountered where several communicate between roving miners corners had to be traversed. When the equipped with radios and machine opera- face was at maximum advance from the tors equipped with powerline carrier power center, the repeater located in the phones. Paging into the section radio communication sled near the power center system from a surface point was also pos- was out of reach of some portable radios; sible via a surface-to-section carrier however, this could be rectified by phone link and a special interface in the extending the repeater antenna toward the communication sled. A low-f requency face area by means of a coaxial cable. through-the-earth radio link between the surface and communication sled was also 3.4.2 Longwall Mining provided, as shown in figure 3-14. At this mine the portable radios by them- With investment in a longwall face selves were usable over an area encom- being in the millions of dollars, and passing more than half of the working production delays amounting to hundreds section. With the repeater, sectionwide of dollars a minute, positive control and radio coverage was possible. communication must be obtained. A representative longwall face crew might com- A similar system was used at another prise a foreman, two shearer operators, room-and-pillar mine utilizing continuous three chock advance miners, one or two mining machines. This section radio com- mechanics, a headgate operator, and one munication system also included machine- miner at the tailgate. Voice communica- mounted carrier phones and a surface- tion is frequently required between each to-section interface at a communication of these crew members and between the sled. Conditions at this mine were much headgate and tailgate. Since miners at more favorable for radio communication, the face must work under rather crowded conditions, starting and stopping the SURFACE STATION (PAGE) conveyor and mining machines are particu- CARRIER SIGNAL larly crucial operations. It is essen- I I tial that everyone on the face knows what is happening. During maintenance opera- I I PARTY - LINE tions, frequent interchange of information between miners working at various points along the face is required. Good ,11 I TRAILING CABLES communication will improve the capability I "PARTY LINE". of describing and locating problems and a FOREMAN (PAGE) coordinating maintenance efforts to

SECTION reduce downtime. PORTABLE RADIOS DRILLER CUITER/ BOLTER LOADER Figure 3-15, a longwall installation CARRIER IT' a UTILITY CLEANUP ON MACHINES in low coal, dramatically illustrates the uu SHUTTLE SHUTTLE limited working space in longwall mining. CAR CAR SHOT FIRER The area consists of a long lateral tunnel in which equipment may be easily - WIRED LINKS -----RADIO LINKS damaged. Moreover, it is fatiguing to FIGURE 3-14. - Radio link between surface travel any appreciable distance to get to and cornrnunicat ion sled. a phone placed along the face. Acoustic acceptable on a short face, say 250 feet, but unsatisfactory on faces as long as 400 feet; in contrast, phones are placed 40 to 50 feet apart in West Germany.

3. The conveyor creates a high- noise environment, and shearer noise often makes it impossible for shearer operators to hear a page.

4. Communication is required later- ally along the face, and U.S. pager phones have not been designed with this in mind. FIGURE 3-15. - Typical conditions encountered in longwall mining. Several European systems, however, are available that have been specifically noise is also very high. Therefore, a designed for longwall applications. Fig- communication system designed specifi- ure 3-16 shows one type of phone, which cally for longwall mining applications has already been installed in a few U.S. should meet the following requirements: longwalls and is reportedly well accepted. Figure 3-17 shows the main control 1. Minimum size. unit, which is installed at the headgate. Some of the features of European longwall 2. Rugged. pager phone systems are pull-wire signaling, machinery lockout buttons, prestart 3. Direct acoustic sound along the warning, fault detectors (in some cases) face. which stop the machinery, blast-proof design, and a central power supply at the 4. Rugged cable and connectcr de- headgate with standby batteries in the sign to survive in the harsh environment. individual phone units.

5. Sufficient power to permit oper- For the potential U.S. user, there ation along the maximum length of the are, of course, problems associated with longwall. this equipment. The first is expense. A 10-phone system incorporating all the 6. Certain control and signaling desired features may cost around $25,000. features that can be incorporated into A 10-phone system with voice-only cap&- the phone system. bilities might cost only about $6,000 to $7,000, but this is still at least twice U.S. longwall faces commonly use standard U.S. pager phones as a means of implementing interface communication. However, these systems do not provide an adequate face communication system. Major problems are as follows:

1. The phones and cables are easily damaged owing to the close quarters and severe environment.

2. Miners on the face may have to travel 50 to 100 feet to use phones; sometimes phones can survive only at the headgate or tailgate, which is marginally FIGURE 3-16. - Longwall l hone. RF TOFROM I HEAD ENTRYtr

300 TO 600 FT TYPICAL RADIO REPEATLR LONGWALL FACE

GOB FIGURE 3-18. - Repeater-based UHF radiosys- tern layout for longwalls.

is not feasible at ultrahigh frequencies. Table 3-2 summarizes the important points regarding the design and implementation of a longwall UHF radio system. However, cable-aided UHF radio is feasible and may be another choice for obtaining the linear tunnel coverage required on a longwall section. FIGURE 3-17. - Main control unit. On shorter faces, a radiating cable as much as a U.S. pager phone system. extending along the length of the long- Secondly, there are a limited number of wall and passively terminated at each end suppliers. Thirdly, a mine may have to with a suitable antenna can provide face either carry its own inventory or expect coverage without a repeater. A radio long lead times in getting spare parts. repeater, connected to the cable at one Finally, in-house maintenance skills have end, may be needed on longer faces, or to be developed. However, given the high when coverage to the head entry outby the cost of a longwall system ($1 to $2 mil- headgate is required. A repeater-based lion), a proper understanding of the configuration for a longwall UHF radio value of a good phone system in reducing system is shown in figure 3-18. In this downtime indicates that these systems are system, good radio coverage can be ex- still worth considering. pected along the face area and into the head entry for several hundred feet. If With any system, certain individuals the repeater should fail, direct communi- should be able to communicate from any cation between portable radios is still location along the chockway without the possible at reduced range. This system fatiguing ordeal of crawling to a phone. can be implemented using commercially This requirement cannot be totally met by available battery-operated hardware that any wired phone system, and with some is also MSHA approved (fig. 3-19). exceptions wireless radio for longwalls

TABLE 3-2. - Ranges of completely wireless communication system for longwalls at 450 MHz

Type of roof I Range with no Range with shearer machine, ft support machine, ft High coal Low coal High coal I Low coal Chocks...... 300 1 150 Shield...... I 1,000 150 The reason for this is because the solutions to the communication requirements in these systems are similar. Nontrolley haulage systems include the following:

Rail vehicles with self-contained power sources (battery or diesel powered).

All rubber-tired vehicles.

Communication systems applicable to nontrolley haulage systems are described in section 3.5.2.

FIGURE 3-19, - MSHA-approved UHF repeater 3.5.1 Trolley Haulage and battery unit, with "hardhat" antenna and portable radios. As previously mentioned, carrier phones are usually used to satisfy the 3.5 Haulageways communication requirements in haulageways where rail vehicles that draw power Operators of vehicles in underground from an overhead trolley wire are used. haulageways must be able to communicate One reason carrier phones have become so with one another and with other areas in popular is that they operate over the the mine to improve safety and increase existing trolley wire dc power circuits production. to provide two-way voice communication between the tracked vehicles and with The type of systems that can be fixed stations in the mine. No addi- implemented to meet the communication tional wires or cables must be installed requirements of underground haulageways in the mine. In underground mining, depends upon the method of haulage it- these carrier systems are used exten- self. From the standpoint of communica- sively for traffic control of the tracked tions, haulage systems can be considered haulage equipment and personnel carriers. as either trolley or nontrolley. These phones are FM push-to-talk transmitter-receiver units designed for Trolley haulage, as used in this common talk (party line) operation. manual, means vehicles that are tracked (ride on rails) and are electrically Carrier frequency couplers consist- powered from an overhead trolley wire. ing of bypass capacitors are used to pro- In mines using this type of haulage, a vide continuity of the RF signal path carrier phone system using the trolley between sections of trolley served by wire is almost always used to satisfy the different dc power centers. These car- communication requirements. The trolley rier systems typically operate in the wire and tracks serve as the carrier 60- to 200-kHz range. (See section 2.4 current path. Methods, techniques, and for basic theory of operation of carrier ways of improving carrier phone systems current phone systems.) are given in section 3.5.1. Special control, monitoring, and communications The carrier phone located on each requirements involved when moving off- tracked vehicle is primarily used for track equipment under an energized control of vehicle traffic. All vehi- trolley wire are described in paragraph cles are kept in communication with each 4.4.3d of chapter 4. other and the dispatcher over the single- channel (party line) carrier phone All other forms of haulage systems system. This single-channel network are grouped into the nontrolley category. keeps the dispatcher and all motormen in continuous contact with one another so squelch control. The most significant that right-of-way and the disposition of of these causes is the extreme attenua- haulage cars will be known to all. One tion of the carrier phone signals on the inherent advantage of the trolley carrier trolley wire-rail. The trolley wire- phone system is that it is a party line rail is a poor radio frequency trans- system. In certain applications, this mission line for several reasons, the would be a disadvantage since private most dominant of which is the presence communication channels are not available. of many bridging loads between the trol- For haulageway traffic control, however, ley wire and rail. Branches and the lack it is beneficial if each motorman does of good electrical terminations contrib- hear conversations between other motormen ute to the problem as well. The bridg- and the dispatcher. This phone system ing loads, which both absorb and reflect also allows the dispatcher to notify all power, comprise such items as personnel motormen of any mine emergency. The two heaters, rectifiers, pumps, haulage ve- drawbacks to this system follow: hicles (motors), locomotive and jeep lights, insulators, signal and illumina- Trolley wire power failures, which tion lights, and even the carrier phones cause the carrier communication system to themselves. go dead unless backup batteries are installed. Because of the importance of good communications in the haulageways and Dead zones, which are sections of because a large number of mines use car- track where the phone is inoperative due rier phones to meet these requirements, to excess electrical noise, excess atten- many programs have been sponsored to uation of signal strength, or standing improve trolley carrier phone systems. wave effects. One program was designed to (1) The first drawback, loss of communi- identify poor performance of trolley car- cation due to power outage, can be cor- rier phone systems, (2) assess the causes rected by the use of backup batteries in of poor performance and classify them on each vehicle (required by law if the the basis of equipment, coupling, or carrier current system is the only com- transmission problems, and (3) propose munication system in the mine). The and verify the means to overcome these backup batteries would normally be problems. trickle-charged to full capacity and then maintained at full charge. In the event Figure 3-20 illustrates the signal- of a power failure on the trolley wire, attenuation rate for an "unloaded" the backup batteries would automatically trolley wire-rail transmission line; a power the carrier phones and allow for band of rates is shown because the actual voice communications for many hours. rate depends on the conductivity of the Because the haulage system is vital to surrounding medium. If an attenuation mine operations, extended power outages rate of 1 d~/kmis used, a trolley car- on the trolley line are not tolerated. rier phone line having an allowable Any trolley power failure is immediately transmission loss of 70 dB (from 25 volts recognized and corrected as soon as pos- to 8 millivolts) yields a communication sible. Thus, communication outages due range of 70 km (43 miles). This perform- to power failures are minimal. ance, in the absence of bridging loads, can be compared with that of a sample The second problem associated with trolley wire-rail loaded as illustrated some carrier phone systems is that of in figure 3-21. Here, just three bridg- "dead zones." There are areas where two- ing loads of modest value (typical of way communication between a vehicle and a vehicles and personnel heaters) reduce dispatcher or between vehicles is not the signal 55 dB over a distance of just possible. Dead zones are caused by 4,500 feet. The figure also shows the extreme attenuation of signals, excess signal level that would exist over the noise, standing waves, and/or inadequate same distance on a properly terminated 5on 30 20n SHUNT n LOADS

- - - -

- DATA -55.5 - THEORY 70 0 44 60 DISTANCE ALONG LlNE - FEET

SIMULATED LENGTH = 4460 FEET r::OO OF D CAPACITORS 50n 3011 20n SHUNT LOADS

50 100 200 400 800 (WITH CAPACITORS) FREQUENCY (kHz) C DATA -55.5 FIGURE 3-20, - Signal-attenuation rate for an - THEORY a a unloaded" trolley wire-rail transmission line, -70 1 0 4460 DISTANCE ALONG LlNE - FEET trolley wire-rail without bridging loads. FIGURE 3-21, - Signal level on simulated trolley With such signal reductions, it is easy wirerail, to see why it is difficult to obtain long-range transmission of carrier sig- path as the trolley wire but unloaded by nals using the trolley wire. any bridging loads, would similarly serve as a low-loss line. Such a configuration There is one approach that appears forms a three-wire transmission line. to have merit in overcoming the exceptionally high attenuation rates that can Studies have shown that the primary be expected on the trolley wire-rail--the mode of propagation for such a configura- dedicated wire technique. tion is a low-loss mode supported by the dedicated wire, with the rails serving as 3.5. la Dedicated Wire the return signal path. The signal improvements that can be expected from such The best approach to overcoming the a configuration are illustrated in figure extremely high attenuation rates imposed 3-22, which shows the voltage signal by bridging loads is a single-purpose, or strength versus the distance along a "dedicated," wire. The characteristics heavily loaded trolley wire-rail with a of an unloaded trol1,ey wire-rail are such parallel dedicated wire. that it forms a low-loss transmission line. Therefore, a separate wire strung Four separate conditions of trans- in an entryway, with the same rail return mission and reception are shown in 0 TRANSMIT AND RECEIVE ON high-voltage trolley wire and is not DEDICATED WlRE influenced by its loads. !-I0 '"5 2 -20 Tests indicate that excellent re- w sults can be obtained with a dedicated 2 -30 TRANSMIT ON TROLLEY OR 0 DEDICATED WIRE AND wire. The dedicated-wire concept permits RECEIVEON THEOTHER WlRE installation of a transmission line with -40 controlled branching that can be termi- u2 2 nated to avoid standing-wave patterns. ;-50 TRANSMIT AND RECEIVEON 0 TROLLEY WIRE (WITH A DEDICATED WIRE1 The price paid is that the wire has to be $ -60 installed and maintained in a haulageway.

-70 10 12.5 A recent study (26)' recommends that DISTANCE FROMTRANSMITTER.MlLES the dedicated-wire mesod is usually the

TRANSMITAND RECEIVEONTHE TROLLEY W~RE IWITHOLKA DEDICATED WlRE IN THE TUNNEL1 most effective and practical way of upgrading trolley carrier phone systems. FIGURE 3-22.- Voltage signal strength versus distance along heavily loaded trolley wire-rail .Another research program provided a with a parallel dedicated wire. set of five guidelines for operating personnel to improve their carrier figure 3-22. For example, if the dis- phone systems. These guidelines give patcher transmits on the dedicated wire detailed instructions for installing and the motor operators receive on the trolley carrier phone equipment onboard trolley wire, then the dispatcher's mine vehicles and at the dispatcher's transmission will produce a curve of room, converting a rail haulage trolley trolley signal level versus distance like wire-rail and feeder system into a curve B. At a distance of approximately functional carrier-frequency-transmission 12.5 miles the dispatcher's signal shows line, checking the performance of the only a loss of 50 dB. The remaining sig- trolley carrier phone system, and using nal level is entirely adequate for opera- portable test equipment to aid in system tion of the carrier phones, since the maintenance. A detailed description of allowable transmission loss is about 70 the conclusions and the recommendations dB. set forth in these guidelines are presented in chapter 6 of this manual. The crosshatched area between curves C and D illustrates the improve- Rather than offering detailed com- ment that can be obtained when both the ments on the contents of each of these dispatcher and motor operators still guidelines here, we focus on just one transmit and receive on the trolley wire aspect of the guideline concerned with but when a dedicated wire has been in- converting the trolley wire-rail into an stalled along the haulageway. efficient transmission line. In the preceding discussion on the causes of poor Curve A shows the signal loss be- performance, the extremely poor propaga- tween fixed base stations, both of which tion characteristic of the trolley wire- can transmit and receive over the dedi- rail was cited. Apparently, this poor cated wire. propagation dominates in determining the performance of trolley carrier phone sys- The dedicated wire is installed with tems. Thus, it is appropriate that seri- no direct connection to the trolley wire- ous consideration be given to determining rail; however, a strong electromagnetic the signal and noise levels on each coupling exists between the dedicated trolley wire system. Signal strength and wire-rail and the trolley wire-rail, simply because of their physical proxim- underlined numbers in parentheses ity. Thus, the dedicated wire is not refer to items in the bibliography at the jeopardized by direct coupling to the end of this chapter. electromagnetic noise level measurements means of dispatcher-vehicular communica- should be made at points along the tions. Most problems associated with trolley and noted on a mine map. The these systems are transmission line re- procedure is simple. The dispatcher's lated; a trolley line was never intended transmitter is used as the signal source, to be a good communications line, and it and both the strength of the signal along certainly is not. However, techniques do the haulageway and the corresponding exist for improving overall communica- noise level are measured. This measure- tions. These techniques can be easily ment is conveniently made by equipping a implemented, and the results are often jeepwith a tuned voltmeter. The jeep excellent. moves along the haulageway, stopping at intervals of about 2,000 feet. The opera- 3.5.2 Nontrolley Haulage tor calls the dispatcher and asks for a 10-second keying-on of his transmitter. An increasing number of both newly The received voltage on the tuned volt- developed and older mines have been aban- meter is noted on a mine map, and the doning tracked trolley vehicles and are noise level is also noted. This map then conducting their haulage, maintenance, identifies regions of the mine where ex- and personnel transport operations with cess noise may be the problem, as well as other types of vehicles. Obviously, com- regions where weak signal levels cause munications to and from vehicles operat- problems. The map also aids in identifying independently of a trolley wire can- ing the key bridging loads branches, or not be implemented by the trolley carrier unterminated lines that can cause prob- phones discussed in the previous section. lems. This signal- and noise-mapping process is the key to identifying the ma- Communication systems required for jor causes of poor signal reception in a battery- or diesel-powered rail vehicles particular mine. or rubber-tired vehicles have one common characteristic. Because these vehicles Once the probable source of diffi- are not physically attached or connected culty has been identified, the remaining to any wiring or other conductor in the part of the guidelines can be consulted mine, some form of radio link must be to determine possible ways of treating utilized to establish the final voice the problem. For example, if a rectifier link with the vehicle. If voice communi- is affecting signal propagation, the cation exists from a nontrolley vehicle, guidelines provide three different ways then an antenna-radio link of some form to treat the rectifier to reduce the must be used to replace the direct con- problem. nection provided by the trolley wire.

3.5.lb Summary Several methods exist for providing comnarnication between nontrolley mining Comnications with moving tracked vehicles. Studies have been conducted of vehicles in a rail haulage mine pose a high-frequency systems utilizing the so- difficult problem. These comrrmnications called leaky-coax cable to carry signals take place from dispatcher to vehicles or throughout a mine. Other studies in the from vehicle to vehicle via the trolley wireless radio area have shown that at line, which is a very poor communications medium frequencies, signals follow the line. As a result, dead spots and high- existing mine wiring for great distances. noise areas can occur anywhere along the line; also, signal strength can decrease 3.5.2a Leaky-Coax Systems simply as a function of distance. A leaky coax is a special type of Although trolley carrier phone sys- coaxial cable that allows radio frequency tems leave much to be desired for haul- signals to leak into and out of itself. ageway communications, the fact remains With this type of cable, signals can be that they do represent one practical transmitted to and received from mobile radio units near the cable. Leaky coax an audio return line is required and, is therefore ideally suited for haulage when branches are required, the system applications. In effect, the cable can become complex. guides the radio signals down the tunnel (fig. 3-23). Although signal strength 3. Multiple-frequency repeater does attenuate along a cable run, re- schemes (fig. 3-25) have also been used peaters or in-line amplifiers can be used successfully; the simplest uses one to extend the range of coverage. Several transmitter and one receiver. techniques have been used: Communication benefits of a leaky- 1. Borrowing from conventional coax system are typified by one system mobile radio communications practice, developed for an iron ore mine (block- individual fixed-base stations can be caving operation) using rubber-tired, installed at intervals as necessary to diesel-powered vehicles. The system provide the total range, all stations chosen to satisfy the communication being under a common remote control with requirements at this mine consisted of a the first. Such a system has been in use UHF leaky-coax system. Figure 3-26 is a at a British mine since 1970. simplified diagram of the system.

2. A series of one-way in-line In addition to providing communica- repeaters, such as the daisy-chain system tion to personnel carriers, maintenance shown in figure 3-24, is effective; it and production vehicles, and the does have a slight disadvantage in that ambulance (fig. 3-27), the system provides communications for roving miners, AREA OF RADIO COVERAGE foremen, fan-hole-drill operators, and PA-&';SIGNAL STRENGTH (VOLTAGE OR ELECTRIC FlELOl supervisors. Communication requirements REPEATER were satisfied by using (1) UHF wireless radio, (2) a radiating coaxial cable L!LEAKY -COAX IN HAULAGEWAY or "leaky" transmission line to carry the signal throughout the haulage and L"' subdrifts of the mine, (3) interconnected VHF and UHF repeaters, (4) portable 10 TO 1 110 dB1 REDUCTION IN SIGNAL STRENGTH FOR EVERY 950 FEET OF CABLE transceivers, and (5) vehicle-mounted transceivers. b- b- - 2000 FEET -4 LIMIT OF COMMUNICATIONS IN HAULAGEWAY FIGURE 3-23. - Cable "guidings' radio signal ENCODER FREOUENCY. 420 MHz down a tunnel.

CONTROL CONSOLE

TELEPHONE LINE CARRYING VOICE FREOUENCY REPEATER OR BASE SIGNALS AN0 DC CONTROL SIGNALS STATION WITH SECOND REPEATER SURFACE INTER- OR BASE STATION I CONNECT ANTENNA TERMINATION

J SECTION BRANCH OFF

HAULAGEWAY /

o~~vlNG HANDE TALKIE

FIGURE 3-24. - Blockdiagramof a daisy-chain FlGUR E 3.-25.- Two-frequencyrepeater concept. repeater system. I repeaters transmit on F2 and receive on I F1 as shown in figure 3-28. The VHF re- ROVING FAN HOLE I MINER DRILL peaters use frequencies F3 and F4 to in- OPERATOR terconnect the two UHF zones. Each UHF- VHF repeater station can simultaneously transmit and receive on both UHF and VHF. ZONE I ZONE I The mobile radios transmit on F1 and S~~~l~~' goesreceive to on the F2. repeaters, All information then back therefore to all 1 other units. The portable radios are / / UHF also capable of transmitting on F2 and therefore are able to talk to one another

WIRE PAIR TO UHF without the repeaters on a local simplex THESURFACE basis. Audio control lines are provided from the crusher console to repeater station A and from the surface guardhouse to the shaft bottom station, thus provid- CONTROL $%jiR CONSOLE ing system access from two hardwired &AMBULANCE &MAINTENANCE b VEHICLE locations as well as an important emergency link to the surface. FIGURE 3-26. - RF leaky-coax communication system. As an example, suppose that a mobile radio in zone A wants to talk to a roving miner equipped with a portable radio in zone B. The operator in zone A keys his radio and talks into his microphone to transmit his message on UHF F1. The UHF signal is coupled to the leaky coax and tra-vels to the UHF-VHF repeater in zone A. Repeater A rebroadcasts the message back to zone A on UHF F2 and also sends the message to the repeater in zone B on VHF F4. This signal travels on the coaxial cable to UHF-VHF repeater R where it is picked up by the VHF receiver. The signal is then converted to UHF F2 and routed onto the leaky coax for distribution in zone B. FIGURE 3-27. - UHF mobile radio mounted on underground ambulance.

The mine was divided into two RF regions, with each region (zone) containing &? one UHF-VHF repeater station and associ- I3 ated runs of leaky coax. The system of cables effectively wires the mine for UHF sd signals between portable and mobile units. Each repeater station can receive FI I IF. F3 and transmit signals on the cable at both ' UHF VHF -- VHF UHF UHF and VHF. VHF signals are used on -F4 F1 the cable as a communication link between REPEATER A REPEATER B the stations, while the UHF is used for the communication link to and from the portable and mobile units. The two UHF FIGURE 3-28. - UHF-VHF repeater system. For this type of installation, However, the nature of UHF is such specifications recommended that the cable that propagation around bends and corners be supported every 5 feet. To avoid introduces tremendous signal losses. In installing a large number of anchors in this regard, it is similar to the trans- the rocks, a 3116-inch steel messenger mission of light and, like light, it can wire was attached at 20-foot intervals to be reflected by flat metallic surfaces. roof-bolt-supported T-bars (fig. 3-29). These characteristics of UHF make possi- The cable was then strapped to the mes- ble a whole-mine communication system senger wire with standard cable ties. that does not rely on leaky feeder cables. The Bureau of Mines evaluated such A vehicle-mounted work platform, a system in an underground limestone mine which could be mechanically raised or that had large dimension haulageways. A lowered and which was equipped with a UHF reflective radio sysrem was designed frame for supporting cable reels, facili- to allow communication between super- tated cable installation. The factory visory personnel, maintenance personnel, cut the cable to predetermined lengths, haulage operators, and surface opera- installed connectors, and tagged the tions. Communication was also provided cable with location identifiers. In mine between the hoist operator and slope car areas that were so far removed from the occupants. A closed circuit television main cable that radio transmissions could (CCTV) system allowed continuous, remote not be established, a stub cable was visual monitoring of critical belt trans- installed with one end connected through fer points and underground dust disposal a power divider to the main cable and the operations. other end terminated with an antenna. The Black River Mine was selected as 3.5.2b UHF Reflective Techniques in a typical metal-nonmetal room and pillar Underground Mines. mine. It is nearly 4,000 feet in diameter, 650 feet deep, and has essentially UHF radio (300 mHz to 3 gHz) is the straight crosscuts approximately 30 feet only way of achieving true radio propaga- wide and 24 to 40 feet high with pillars tion in an underground mine. Propagation approximately 35 feet square. Entry is is possible because the mine entries through a 2,200-foot slope by means of a function as waveguides that confine the single drum, hoist-powered flat car and transmitted energy. Several thousand enclosed man carrier. Rubber tired, die- feet of range, line-of-sight, is often sel powered mine vehicles travel along possible without leaky feeder cables if designated haulage and travel roads from the entries are large enough. the active faces on the mine's perimeter to two rock crushers, the shop area, and the base of the slope.

Tests of communication between handheld, 2-watt UHF transceivers in the room and pillar limestone mine were satisfactory for approximately 2,000 feet through straight haulageways but the range of commnication at right angles to haulageways into intersecting crosscuts was quite limited. It was evident that the radiation from the transceivers was not being reflected by the limestone pillars into the intersecting crosscuts.

To improve communication in inter- FIGURE 3-29. - Radiax cable installation on secting haulage roads, 27 passive re- messenger wire. flectors were designed and installed at major intersections. The reflectors were Fifteen 2-watt portable transceivers formed from 4- by 8-foot sheets of No. 16 equipped with automatic identification gage soft aluminum sheet that were sus- and emergency alarm encoders are used by pended from wires attached to roof plates mine department heads, foremen, and per- and bolt anchors. The roof height was sonnel in the mine. sufficient to allow haulage vehicle clearance at each installation. Two dis- Signal margin measurements of the tributed antenna systems were designed base-repeater station signals along to provide either an antenna or reflec- haulage and travel roads were made after tor at the intersection of principal both distributed antenna systems had haulage and travel roads. Each antenna been completed, which demonstrated that system consisted of approximately 1,200 approximately 75% of the mine area re- feet of 718-inch low loss foam dielectric ceived satisfactory signals, but active transmission line which fed, through 2:l mining areas along the perimeter of the power dividers, four 5-dB gain mobile mine were not adequately served. The whip antennas that were suspended at distributed antenna system would have intersections. to be extended to serve additional antennas near the mine faces. However, the A leaky coaxial cable anatenna sys- cable attenuation would drastically re- tem along the principal haulage and duce the power radiated from the antennas travel roads was considered but rejected and the signals received from the mobiles because the range of communication at and portables so that very little im- right angles to the leaky cable into in- provement would be realized. Additional tersecting crosscuts would have been much base-repeater stations were considered; less than the range of communication from however, the added complexity and cost of antennas. The leaky cable system is multiplexing equipment and for extending appropriate for long tunnels but not for the backbone cable control system stim- intersecting roads in a room and pillar ulated the development of a low-cost, geometry. Also, a leaky cable would be two-way multichannel signal booster sys- more expensive. tem. A prototype signal booster was constructed and tested. Six amplifier sig- One central, or "backbone" coaxial nal boosters, 10,000 feet of cable, and cable carried 60 Hz power, radio signals, 16 additional antennas were installed in and CCTV signals for the entire system. the mine. Subsequent signal measurements Redundant routing of the backbone cable showed adequate coverage of all desired insured continued system operation in the areas. event of a cable break. 3.5.2~ Dedicated-Wire Radio Systems Fourteen 11-watt mobile radios equipped with automatic identification It is possible to use trolley car- and emergency alarm encoders were in- rier current techniques and hardware to stalled on vehicles in the mine. The en- communicate with vehicles that do not use coders are used on mine haulage trucks to a trolley line, such as battery-powered automatically send three status signals; railed or rubber-tired vehicles. How- truck bed up (dumping) , truck bed down, ever, in this case, a "dedicated wire" is and hot engine. This information is dis- essential for proper operation. Such a played by number codes along with the system is shown in figure 3-30. truck's identification number on display units in the engineering office above The dedicated wire takes the place ground and the mine foreman's office un- of the trolley line. However, since the derground. A record of all calls, sta- carrier phone on the jeep communicates tus, and alarm messages is automatically with the dedicated wire by a loop printed in the engineering office. antenna, instead of touching it like it DISPATCHER A---- - discussing the advantages and disadvantages of each technique, the subject of radio interference and signal attenuation in underground mines must be considered.

CARRIER 3.5.2d.i Interference PHONE During normal operation, the machinery used underground creates a wide range of many types of intense electromagnetic BATTERY POWERED JEEP interference (EMI), which is a major lim- FIGURE 3-30. - Ded icated-wire radio system. iting factor in the range of a radio communication system. EM1 generated in would a trolley line, this system is rel- mines is generally a random process. atively inefficient. In general, it is Therefore, the most meaningful parameters usually necessary for the loop antenna to for EM1 are statistical ones. In work by be rather close to the dedicated wire for the National Bureau of Standards, time commnications, This problem is caused and amplitude statistics have been used in part by the fact that carrier phones in order to unravel the complexities of were never intended to use antennas, and EM1 noise in mines. Without going into cannot operate at high enough frequencies the details of data collection techniques to make this approach efficient, or advanced statistical analysis, we will summarize the findings and conclusions on However, research has shown that EM1 affecting haulageway radio communica- such a system operates well if medium tions, Figure 3-31 shows interference frequencies are used, These frequencies, levels measured along haulageways in four usually around 500 to 900 kHz (as opposed different mines, to 100 kHz typical of trolley carrier phones) can operate with loop antennas The EM1 noise levels shown for very efficiently, Considerable research mine 1 are based on measurements made in is being done by industry and the Bureau a mine located in southwestern Pennsyl- of Mines to develop whole-mine medium- vania, Room-and-pillar techniques were frequency systems , used with mining accomplished using a continuous miner, shuttle cars, and elec- 3,5,2d Wireless Radio System tric trolley rail haulage,

An obvious advantage of any true radio system is that the system requires no INTERFERANCELOW transmission lines or cables, These sys- AREA tems are immune to communication outages caused by line breaks due to roof falls or damage from machinery. However, the underground mining industry cannot take MINE 1 for granted the utilization of wireless HIGH COAL. RAIL HAULAGE commnications as can their counterparts on the surface, As an example, at CB ra- LOW COAL, BELT HAULAGE dio frequencies, reliable communication in a mine entry is limited to about 100 feet, Two options are available to the HIGH COAL. BELT HAULAGE underground mine operator: (1) To use r- frequencies that are high enough to utilize the entries as waveguides, or (2) to use frequencies that are low enough that propagation through the earth, or by par- FIGURE 3-31. - Interference levels measured asitic coupling, can be insured, Before along haulageways in four mines. The majority of noise measurements was transported by conveyor belt horizon- were made in an area where the overburden tally 825 meters, then lifted to the ranged from 600 to 900 feet. The entire surface by a skip. The other types of mine, including all machinery, is powered haulage equipment used in this mine also by 600 volts dc. All conversion from were diesel powered and rubber tired. alternating to direct current is done on All haulageways were through reliable the surface, with the result that no ac rock or were heavily reinforced with con- power is brought into this mine. crete and steel. The mine used a mixture of incandescent, mercury-arc, and fluo- The EM1 noise levels shown for rescent lighting. mine 2 are based on measurements made in West Virginia. The coal in this mine The noise levels for mine 4 were occurs in a narrow seam, approximately made in a West Virginia mine where room- 3 feet thick, and is called low coal. and-pillar mining techniques were used. The measurements were made in the two The measurements were made primarily in a sections of the mine using the longwall section where overburden was approxi- mining technique where overburden was mately 600 to 900 feet. Mining was between approximately 900 and 1,500 feet. accomplished using a continuous miner, The mine also had seven conventional head-loader, shuttle cars (buggies), con- room-and-pillar sections. This mine used veyor belt, and electric trolley haulage. 250-volt dc trolley haulage to carry coal The electric trolley and the shuttle cars out of the mine, and ac-powered conveyor were powered by 300 volts dc. All other belt haulage from the section to the equipment, including fans and rock dust- trolley. All of the section longwall ing machines, was ac powered. mining equipment was ac powered, with the exception of a dc-powered cable winch The noise measurements taken in which was used occasionally to advance haulageways of these mines tended to show portions of the longwall equipment. The magnetic field strengths typically 60 to face and associated longwall equipment 70 dB pA/m up to a few kilohertz, which were 450 feet long. There were a total then decreases sharply above 8 to 12 of six electric motors in the section kHz. ranging from 15 to 300 hp. The shear and face conveyor were powered by 950 volts, As seen in figure 3-32, the EM noise and the stage loader and hydraulic pumps amplitude decreases with increasing fre- operated from 550 volts. The stepdown quency; however, three propagation mech- transformer supplying these voltages was anisms must be considered: (1) Through kept approximately 150 to 700 feet back the earth, (2) through the entries sup- from the face and was supplied with ported by metallic structures and con- 13,200 volts. ductors, and (3) through the entries where they serve as a "waveguide." For The EM1 noise levels shown for propagation through the entries, it would mine 3 are based on measurements made in appear, from the data presented, that se- a Pennsylvania iron mine. The level lection of frequencies much greater than where measurements were taken was approx- 100 kHz would be desirable. imately 2,300 feet below the surface. The ore body is a large, flat, oval de- For situations in which the propaga- posit about 300 feet thick, mined by un- tion is directly through the earth, at- dercutting and allowing the ore to cave tenuation (signal loss) increases as fre- into drawpoints called entries. Air- quency is increased. Because of lower cooled, V-8 diesel-powered, rubber-tired, attenuation at lower frequencies, better load-haul dump (LHD) vehicles were used signal-to-noise ratios exist at low fre- to haul the ore to the underground crush- quency despite the higher noise levels. er and dump it into the ore crusher; it Figure 3-32 shows that signal attenuation around a corner is considerable. Because GENERAL of the high attenuation of a single cor- LOSS STRAIGHT TUNNEL IN SIGNAL LOSS STRENGTH ner, propagation around multiple corners is even more severely attenuated.

Although it is an advantage to operate at a higher frequency in a straight tunnel, the higher frequencies suffer CORNER the greatest loss in turning a corner. LOSS Therefore, the choice of frequency is often dictated by the type of coverage desired.

r DISTANCE Based on the interference and signal attenuation rates observed, the effective FIGURE 3-32. - EM noise amplitude decrease communication range for UHF radios can be with increasing frequency. predicted. Figure 3-33 shows the predicted range for a 1,000-MHz, 1-watt 3.5.2d.ii Signal Attenuation in the portable transceiver. Haulageway The presence of stoppings for direc- As a radio signal travels down tion of airflow, passages blocked by a haulageway or tunnel, its strength machinery, or blockage caused by a roof decreases. Typical signal attenuation fall seriously limits the communication along a straight tunnel, for three dif- range of a UHF system. Obstructions ferent radio frequencies, is shown in highly attenuate all UHF signal transfer, figure 3-32. Transmission loss may be thus making the same systems impractical combined directly with transmitter power for some mine applications. and antenna gains to determine the received signal for any candidate UHF system. In terms of transmission loss, a pair of 1-watt UHF walkie-talkies has a range of 143 to 146 dB.

Significant propagation characteristics apparent from figure 3-32 are--

Attenuation (in decibels) increases nearly linearly with increasing distance.

Transmission loss decreases significantly at a given distance as the frequency is increased.

3.5.2d.ii.i Signal Attenuation Around Corners

Observed signal attenuation around a corner is also shown in figure 3-32. Corner attenuation is plotted in deci- UOOFT bels relative to the signal level ob- FIGURE 3-33. - Predicted range for 1,000-MHz, served in the center of the main tunnel. I-watt or tab le transceiver. 3.5.3 Belt Haulage The same systems described in section 3.5.2 (nontrolley haulage) can be Mines using conveyor belts to move utilized to meet the communication coal or ore underground usually have a requirements in belt haulageways. secondary transportation system for the movement of men and materials. When the 3.6 Special Requirements man-material transportation system is tracked-trolley, the obvious solution to This section describes ways of meet- haulageway communication requirements is ing those special communication require- the trolley phone system described in ments not directly related to the mine section 3.5.1. If the man-material entrance (section 3.2), permanent and transportation system is nontrolley, then semipermanent locations (section 3.3), some form of radio, leaky feeder, or mining areas (section 3.4), and haulage- wired phone system is required. ways (section 3.5). Major topics included in this area of special require- A common practice in mines using ments include communications with roving belt haulage is to locate telephones at or isolated personnel and motorman- the intersections of all mains and sub- to-snapper communications. mains, and at the head and tail of all working conveyor belts. (Belt fires most 3.6.1 The Roving or Isolated Miner often occur at these points.) In the absence of trolley phones, belt haulage A modern mine is a vast underground mines also usually locate phones approxi- complex of working sections, haulageways, mately every 600 feet along the belts. and repair shops, which extends for sev- These phones are installed for the life eral square miles underground. Key per- of the mine and are seldom moved. sonnel may not work in fixed locations; for instance, a section foreman may be Although a fully developed submain assigned to a single section, but that might have butt entry ports every section could embrace a vast area, or 600 feet along its length, telephones are maintenance personnel or electricians required only at the active or working could be anywhere in the mine at any butt entry ports. This usually limits time. Because such personnel are impor- the maximum number of phones per submain tant to the smooth operation and high to six, owing to the capacity of most productivity of a mine, considerable pro- haulage systems. These phones are moved duction losses can occur if they cannot about every year or so until all panels be located when they are needed. in the submain have been developed. If a feeder belt is used in the submain, addi- Inspectors and other management per- tional phones are recommended at the head sonnel may also be anywhere in the under- and tail of these belts. ground complex. These people need to stay in continuous contact with the com- Phones permanently installed at the munication center so that they can be head and tail, and at other strategic informed of any emergencies that might locations along the belt, usually meet arise and/or make management decisions. the communication requirements during normal day-to-day operations. The draw- The maintenance crew is also spread back to any wired phone system is that a throughout the mine. To receive repair miner must be at a phone to make or requests and dispatch his crews for emer- receive a call. Communication with belt gency or nonscheduled repair work, a maintenance or inspection personnel mov- maintenance foreman must be able to con- ing along the haulageway can only be tact individual crew members dispersed accomplished by some form of radio link. throughout the mine. Communication requirements to and dispatcher who controls the flow of from these key individuals can only be traffic. As explained in section 2.4, completely satisfied by a wireless the trolley line itself is the communi- (radio) paging or walkie-talkie system. cation link between all the vehicles and Several paging systems are presently the dispatcher. available to meet these requirements. The small lightweight pagers that can be However, communication need not be carried by roving personnel are classi- limited to phones connected to the fied as one of three types: trolley line. A special carrier-current tone signal can also be impressed on the Beepers (call alert). trolley line, which will function as a long-line antenna, broadcasting the tone One-way-voice (pocket pagers). signal into the mine where it can be received by special pocket radio pagers Two-way-voice (walkie-talkies). (fig. 3-34). Hardware is now commercially available that allows a dispatcher One shortcoming of the first two to voice-page selected individuals, types of systems (beepers and pocket deliver short messages, or inform them pagers) is that the person initiating the where to go to receive detailed instruc- page has no way of knowing if the page tions. Figure 3-35 is a block diagram of has been received. This can be espe- a general radio paging system based on cially critical in the case of the pocket carrier-current techniques. A carrier pager systems where voice messages can be phone, located at some central loction transmitted to the person being paged. such as a dispatcher's room, is equipped Because the pocket pager is a receive- with a small pushbutton-encoder unit. only device, the person being paged can- This unit causes the carrier phone to not directly notify the dispatcher or transmit short tone bursts whose frequen- person making the page that he has cy depends on which pushbutton was received the message. Therefore, one- pushed. These tone bursts are transmit- way-voice (pocket) pagers should only be ted from the carrier phone in exactly the used for paging messages ("call the dis- same way that a voice signal would be patcher," "report to the maintenance sent out. area," etc.). Instructions such as "shut off the number 2 pump" should not be given using one-way communication devices unless it can be verified that the message was received and acted upon. The advantages gained by any of the three types of paging systems are directly related to the reduced time required to contact key individuals when their location underground is unknown. Even with the simplest beeper systems, the person being paged can, within a few seconds, be headed for a section phone to take a message.

3.6.la One-Way-Voice (Pocket) Pagers

In a mine that uses rail haulage vehicles powered from an overhead trolley wire locomotive or jeep, carrier phones allow the vehicle operators to com- FIGURE 3-34. - Miner equipped with pocket municate with each bther and with a radiopager. CONTROLLED BY EEE; NOT TURN TELEPHONES

TROLLEY LlNE m

AUTOMATIC ENCODER

CARRIER I PHONE TELEPHONES IN MINE I SURFACE BUILDINGS SURFACE

UNDERGROUND I I CARRIER PUSH BUTTON PHONE ENCODED

DISPATCHER'S OFFICE

TROLLEY LlNE FIGURE 3-35. - Block diagram of general radio------I paging system.

The pocket receivers that have been PAGERS developed to respond to these tones are FIGURE 3-36. Block diagram of system with really small EM radio receivers that are - activated by the tones and remain on for remote I accessed encoder. about 15 seconds. Once the tones have been sent, the dispatcher then talks into desired pager, at which time the user can his carrier phone in the usual manner. speak into the mouthpiece to deliver the Only the pocket pager activated by the voice message. tones will receive the message, so that the dispatcher can selectively radio-page Existing pager receivers are any individual. In an emergency, a spe- equipped with a small internal timer that cial tone can activate all pagers at automatically turns the device off after once. The pocket pager is a receiver a preselected time, usually 15 seconds. only and cannot be used to talk back to A continuous "On" mode is usually not de- the dispatcher. Therefore, the system sirable because it wastes battery power. should be used only for paging, not for With the automatic time-out feature, bat- giving instructions. teries last for months. However, there are times when the continuous monitoring The system shown in figure 3-35 is of the radio paging system is important designed so that only the dispatcher can to certain maintenance personnel. initiate a page, because he is the only one who has a carrier phone equipped with A radio paging system can be oper- an encoder. However, other encoders ated on a special channel (frequency), could be used with other carrier phones, or on the regular channel used by the if necessary. Figure 3-36 shows a system locomotives. The only difference is that in which the encoder is remotely accessed if both are included on the same regular by a dial telephone line. Thus, any dial channel, all the carrier phones will telephone associated with the mine hear the paging traffic, but the pagers switchboard (PBX) could be used to initi- will hear only what is sent to them ate a page without ever being near the directly. encoder. Such a system offers an advantage should many people have to page into A radio paging system can incor- the mine from several surface locations. porate both the automatic encoded system To operate the system, a user goes to a (fig. 3-36) and a roof-bolt antenna sys- telephone and dials the number assigned tem (fig. 3-37). The automatic encoder to the pager he or she wishes to call. and carrier phone can be located on the The encoder converts the telephone dial surface; all else is underground. The pulses into tones and transmits them via in-mine roof bolts are separated by about the carrier phone. The tones turn on the 300 feet and connected to the carrier MAIN TRACK MOTORMAN POCKET PAGER LI11] FROM MANUAL OR AUTOMATIC ENCODER SYSTEM TROLLEY LINE 4 ---- (GIVES HAULAGEWAY COVERAGE) \$\ LOOPTRACK /B/ bz.s$y$

(GIVES REMOTE COVERAGE) I POCKET PAGER 1-1 SNAPPER MUST BE CLEAR e WHEN TRAINww IS MOVED / COUPLES AND /////I//////////L DECOUPLES CARS ROOFBELTS Diagram showing need for com- PHONE FIGURE 3-38.- REPEATER I municat ion in haulage loop-around. The design of any practical system to meet the communication needs between motorman and snapper requires that it does POCKET PAGERS not interfere with other communications, FIGURE 3-37. - Block diagram of system using is convenient, has a restricted range so roof-bolt-typeantenna. that similar systems can be used else- where in the mine, and can be built with phone by No. 12 wire. With this system, commercially available hardware. Typi- paging can be accomplished from as far as cally, a range of 1,500 feet or less is 500 feet from a roof bolt antenna. all that is necessary to assure adequate coverage for the maximum separation between the snapper and motorman. Two systems that can presently be implemented Many mines use loading track loops using commmercially available hardware for loading mined coal or ore at the sec- are the telephone and trolley-carrier tions before transporting it to the sur- phone system and the walkie-talkie radio face. This type of operation involves system. the coordinated activities of two individuals: a "snapper" or "swamper" who 3.6.2a Telephone and Trolley-Carrier couples and uncouples the cars; and a lo- Phone System comotive operator, or motorman, who moves the train backward and forward at pre- In the telephone and trolley-carrier scribed times. If the snapper is not in phone system (fig. 3-39) , the snapper the clear when the train is moved, its communicates by means of a belt-carried, sudden motion can injure or kill him. Thus, effective communication between the motorman and snapper is vital. CARRIER PHONE Because of the curvature of the loop track (fig. 3-38) and the location of the locomotive on the main haulage track, the two individuals are not usually within sight or hearing of each other. Without communication or at least some system of signaling, coordination is difficult unless other workers are stationed along- side the track to relay information. However, this wastes time and manpower. It is clear that the safety and efficiency of the loading operation would be vastly improved if there were a reliable communication link between the motorman FIGURE 3-39. - Telephone and trol ley-carrier and snapper, hone system. miniature mine telephone known as a belt phone. A phone line is installed on the rib or roof of the mine along one side of the loading track. The belt phone can be connected to this line by an extension cord that has insulation-piercing clips at one end. Alternatively, receptacles that allow the belt phone to be plugged in at convenient points can be provided on the line.

A pager-phone-to-carrier-phone coupler connects the phone line and the trolley line. Phone line signals are converted to trolley line signals and vice versa by this coupler. The motorman communicates by a trolley phone, which operates on a frequency different from that of the haulage communications.

CAUTION.--Indiscriminate use of this procedure is not recommended. MSHA FIGURE 3-40. Miner wearing belt phone, inspectors should be consulted be- - fore any carrier-phone-to-pager-phone coupling is installed. CARRIER PHONE TROLLEY LINE

I I I

TO PHONELINE OTHER If duplicate systems are used in a LOOPS mine, the range of the trolley line sig- T nals has to be restricted by appropriate- INTERFACE CARRIER PHONE TWISTED PAIR ALONG ly attenuating the transmitter output. LOADING LOOP This system can be implemented using / PORTABLE standard trolley phones and phone-line- HANDSET to-trolley-line couplers. In addition, a WITH JACK belt phone (fig. 3-40) is now commercial- FIGURE 3-41. - Diagram of interface system ly available. Equipped with a hardhat- between phone and trolley lines. mounted speaker and an adjustable-boom- type microphone, it has outgoing paging the phone line using a modified telephone capability and will operate compatibly handset. A twisted-pair phone line, with with available phone-line-to-trolley-line jackboxes connected at 50-foot intervals, couplers. is strung up in the loop-track area and connects to the dedicated phone line. At least one mine has successfully The snapper plugs his handset into a used an interface system between the nearby jackbox to establish communication phone and trolley lines to provide to the motorman. motorman-snapper communication, The system is diagrammed in figure 3-41. A re- 3.6.2b Walkie-Talkie System mote interface, fabricated by technicians at the mine, acts as a coupler between The walkie-talkie radio system uses the trolley line and a dedicated phone UHF portable radio equipment. Both the line, The motorman can communicate via motorman and snapper are equipped with the existing carrier phone system, where- walkie-talkies (fig. 3-42). as the snapper must communicate via uncertainties regarding train movement in the mine. This results in improved efficiency and a reduction in the num-ber of accidents related to the loading opera- t ion. Systems can be custom made from available telephone and carrier phone equipment. Leaky-feeder UHF equipment is similarly available for custom systems.

3.7 Emergency Communications I RADIATING CABLE 1 REPEATER There are two conditions under which a communication system should operate. These are normal operations (regular day- SNAPPER to-day operation) and emergency conditions. The need for reliable underground communications following a disaster is obvious. Two major requirements for any emergency communication system follow:

FIGURE 3-42. - Motorman and snapper walkie-talkie 1. The system must work following system. the disaster. (This implies that the system worked before the disaster and Because of the curvature of the loop that the system is protected from, or tunnel, propagation of radio waves at UHF immune to, fire, explosion, roof fall, is severely restricted. In fact, direct etc. ) radio communication between the two individuals may not be possible in some 2. Miners must be familiar with cases. However, this deficiency can be operation of the system. (Mistakes are overcome with a dual-frequency radio re- easy to make during periods of high emo- peater connected to a radiating cable. tional stress.) The cable carries the radio signals, and the repeater effectively boosts them to It should be recognized that there a higher power level. The coaxial cable are advantages in combining any emergency extends along the loading track and down communication system into the system used the main haulageway far enough to assure for normal day-to-day operations. In communication coverage to the motorman. this way, miners can become familiar Cables several hundred feet shorter can enough with the system to operate it dur- be used if an approprate antenna is con- ing disaster conditions. Daily use of nected at the end. Commercially availa- the system also provides a mechanism of ble portable radio transceivers and re- regular testing, thus insuring that the peaters can be used to implement this system will be operational. system. 3.7.1 Detecting and Locating the Trapped A medium-frequency radio transceiver Miner (520 kHz) with sufficient range has been developed that makes snapper-motorman The history of coal mine disasters communications possible without install- has established a need for a simple, ing additional cables. Transmission is reliable system for locating and communi- aided by the conductors normally present cating with miners trapped underground. in the loop-around. Such a system will not only increase the chances of a successful rescue, but will Effective communication between the also reduce the risks to the rescue team snapper and motorman can provide by keeping them from searching the wrong the coordination needed to eliminate locations. The problems of finding miners After a disaster, miners who manage trapped underground can be illustrated by to escape can direct rescue teams to a disaster that occurred in 1945, in those parts of the mine where others may which 24 men were killed by an explosion. remain trapped. The nature of the mine Figure 3-43 shows the location where nine workings and the circumstances of the men barricaded themselves for 53 hours in disaster can also be used in locating that particular incident. Rescue crews survivors, but all of these techniques tried for 2 days to reach the active area are based on guesswork. Accurate knowl- of the mine in 5 and 6 Lefts while being edge of the location of trapped men is hampered by caved workings, fires, smoke, required to increase their chances for gas, and loose roof. Three days later, survival and to reduce the hazards to the while exploring 9 Right, they found foot- rescue team that might otherwise conduct prints. After investigating, they found an unnecessary, futile search in danger- a chalk-marked board indicating that five ous, incorrect areas. men were in 4 Left entry. In 5 Left, another mark was found directing search- It is obvious that any information ers to second Left off of 5 Left. Seven that could be exchanged between the of the nine men survived the ordeal. All trapped miners and the rescuers during a might have lived if their location had rescue effort would be advantageous. In- been known so they could have been formation such as unusual conditions reached sooner. The time required to known to the miners trapped, or medical rescue barricaded miners is critical. In advice for them to follow until aid the recorded cases of barricading, 75 arrived, are two examples. In other percent of the survivors were rescued words, a system that would provide the within 10 hours. location of trapped miners and permit comrmnication with them would increase the probability of their rescue and also reduce hazards to the rescue and recovery team. Two systems for locating and communicating with trapped miners have been developed: a seismic system and an electromagnetic system. bodies The seismic system relies on detection of small ground vibrations resulting from a miner(s) banging on the roof or ribs with some heavy object. This system is presently operational and is being improved continuously. In this system, the trapped miner signals on the mine floor or roof with any heavy object and seismic detectors (geophones) on the surface are used to detect these signals. Computa- tion of the location of the trapped miner by using the difference in the arrival time of the signals at various geophone positions on the surface has been quite successful. A seismic location system has the advantage that the miners do not require any special equipment and need only to be trained in how and when to signal. The disadvantage is that discontinuities in the overburden can significantly affect rescue signal propa- FIGURE 3-43. - Part of mine showing area to which gation relative to both detection and miners retreated and erected imperfect barricade* computation of location of the signal. Additionally, in a rescue and recovery units also exist. In an emergency, operation, the time required to deploy and when it is decided that all routes of and relocate, if necessary, a massive escape are closed, the antenna wire is geophone array may hamper the progress uncoiled, laid out in as large a loop as desired. However, the seismic system possible, and connected to the trans- does provide the trapped miner with an mitter. The transmitter and loop antenna additional degree of protection when no produce a magnetic field, as shown in other method of communication can be es- figure 3-45. The direction of these tablished. The Mine Safety and Health signal-field lines can be used to pin- Administration maintains a seismic rescue point the location of the underground system as part of its Mine Emergency loop antenna. By measurements taken on Operations group. All miners should ob- the surface, the location of the antenna tain MSHA stickers for their hard hats can be determined within a few feet. (fig. 2-26) in case they should become entrapped. After detecting and locating a trapped miner, the surface search team The electromagnetic system relies on can establish a voice down-link communi- a small voice frequency (VF) transmitter cations path to the men underground. that can be carried by the miner, and This voice link is established by deploy- surface receivers that "listen" for the ing a large loop antenna directly above signals broadcast directly through the the trapped miners and connected it to a earth or through the mine workings by the very powerful amplifier and voice system miner's transmitter. Basic development (fig. 3-46). By speaking into the micro- of VF EM systems is completed, and proto- phone associated with the system, strong type hardware is in the testing phase. electromagnetic signals are generated and transmitted by the loop antenna. These A typical trapped-miner transmitter signals penetrate the earth, and the (fig. 3-44) weighs one-half pound and can trapped miners can hear actual voice from be worn on the belt. Cap lamp battery the surface on their transceiver. The surface can then ask key questions to

FIGURE 3-44. - Underground-miner-carried VF FIGURE 3-45. - Production of a magnetic field equipment for signaling surface rescue crew. by transmitter and loop antenna. ,HEA4l r LOOP ANTFNNAS J

RECEIVER

FIGURE 3-46. - Through-the-earth transmission system. ascertain the conditions underground. As FIGURE 3-47. Surface VF receiver and loop an example, they can ask the trapped - miners to key three pulses of signal for antenna in use at simulated mine disaster. a "yes" answer and two pulses for a "no" answer. This type of down-link voice and signal source, it probably will not work. up-link code signaling system allows the In a large mine, this limitation is a se- surface team to learn anything they wish rious handicap. In mountainous terrain, about the situation underground and also setting up the seismic geophones can pre- allows them to give instructions or sent especially difficult problems. information concerning escape routes and rescue attempts. 3.7.2 Refuge Shelter

One advantage of an electromagnetic When it appears to be impossible to system over a seismic system is that escape, or imprudent to attempt escape, the EM transmitter operates continuously following a mine fire or explosion, once deployed and will function for many miners are trained to isolate themselves hours, or even days, from one cap lamp from toxic gases and smoke by erecting battery. Besides operating continuous- barricades. Although many miners have ly, its electrical signal is a known been rescued from behind barricades, some rhythmic "beep," which is much easier have died behind inadequately constructed to detect than the random thumps of a barricades. As a solution to this prob- miner pounding on the ribs or roof. An- lem, sectional or central refuge chambers other advantage is that the detection re- have been established by some companies. ceiver can be readily carried by one min- If a chamber is constructed, some form of er (fig. 3-47) and can be used to cover a communication to the surface should be reasonably large area. It can also be included to inform rescue crews that the used by underground rescue teams since it chamber is being used and of the condi- is permissible. A version of the surface tion of its occupants. receiver has been adapted for use in hel- icopters. With this unit, large areas Communication to a refuge shelter can be scanned quickly. Once a signal is could be provided by means of a borehole detected, portable surface-carried units equipped with a telephone pair connect- can obtain an exact fix. The surface ing to the surface, by existing wiring gear for a seismic system, on the other within the mine, or by some form of hand, is complex and stationary. Its de- through-the-earth system. The in-mine ployment site must be carefully selected. telephone system would be the least reli- If it is not within 2,000 feet of the able after an explosion unless the cable installation had been specifically hard- The primary advantage of this type ened. Boreholes would be highly reliable of system is that it is simple and yet but would require a new borehole for each usually provides good-quality voice com- refuge chamber or whenever a refuge cham- munication. Also the phone wire trailed ber was moved. behind the rescue team provides a physical link back out of the search area. 3.7.3 Riescue Team Communications This link can become an important factor if the team must retreat under conditions Even though searching a mine after a of poor visibility, or if a second rescue fire or explosion is a slow and often team wishes to "follow" the first team. dangerous job, the rescue team must reach The disadvantages of this type of system any trapped or barricaded miners as soon are (1) the wire spool, which may be as possible. Effective communication heavy, must be transported by the rescue between the rescue team and the surface team, and (2) the wire strung behind the or base camp, as well as communication rescue team is susceptible to damage from between individual members of the team, secondary explosions or roof falls. is an essential element in any successful rescue attempt. 3.7.4 Medium-Frequency Rescue Systems

One method that has proven effective Considerable research has been con- in maintaining communication to and from ducted within the last 8 years in the ar- the rescue team is illustrated in figure ea of underground MF transmissions. This 3-48. In this relatively simple system research showed that MF signals could the rescue team splices into a good phone propagate for great distances in most ge- line and then unrolls line from a spool ologies and offered the hope of a whole- as they advance into the mine. During mine radio system. The Bureau of Mines a recent rescue, this type of system and the South African Chamber of Mines provided good communication even after (SACM) pursued research independently. the rescue team had traveled approximately a mile along a haulageway and then Around 1974, SACM introduced a new descended another 1,200 feet down a shaft single-sideband system and followed up from an underground headframe. later with another designed especially for rescue team use. Performance in South Africa was reported to be good. The evaluation of these units in U.S. mines showed them to be inadequate. The type of modulation used [single sideband (SSB)] made them sensitive to electromagnetic interference (EMI). In addition, power level was far too low and ineffi- ciencies in both circuit and antenna designs produced short-range performance.

PHONE LINE The Bureau's approach to the problem WOUND ON SPOOL was more fundamental. A program was designed and executed to study in-mine MF propagation and learn how it interacted with the complex environment. This environment consists of various geological factors such as stratified layers of dif- FIGURE 3-48. - Effective method for maintain- ferent electrical parameters, entry size, ing communication to and from rescue team. local conductors, EMI, etc. Figure 3-49 is a simplified geometry of an in-mine site that illustrates one of the most important findings of the measurement program--the "coal seam % Coal mode." For this mode to exist, the coal or seam conductivity (a,) must be several entry orders of magnitude less than that of the rock u . A loop antenna that is at least partially vertically oriented, pro- transmitting duces a vertical electric field (EZ) and antenna horizontal magnetic field (H4). In the rock, the fields diminish exponentially in the Z-direction. In the coal seam, the fields diminish exponentially at a FIGURE 3-49. - Coal seam mode. rate determined by the attenuation constant (a) which in turn depends upon the electrical properties of the coal. An inverse square-foot factor also exists because of spreading. The effect is that Local -----mine conductor - the wave, to a large degree, is trapped / signal propgating between the highly conducting rock layers along conductor and propagates long distances within the signal coupling into Signal reradiating lower conducting coal seam. The fact "ocal conductor from conductor that the coal may have entries and crosscuts is of minor consequence. Vest rad~oconcept In the presence of conductors, the picture changes considerably. In this case, the effects of these conductors can r= totally dominate over the effects of the FIGURE 3-50. - MF parasitic coupling and geology. In general, the presence of reradiation. conductors (rails, trolley lines, phone lines) is advantageous. powerlines or belt lines) are present, the range is even greater. This permits MF signals can couple into, and re- a rescue team member to stay in commu- radiate from, continuous conductors in nication with other members, the fresh such a way that these conductors become air base, and outside disaster control not only the transmission medium but centers. also the antenna system for the signals. Figure 3-50 illustrates this concept. To date, MF technology has not been The most favorable frequency depends to specifically applied to rescue team some extent on the relationship between communications. Such application is the the geology and existing conductors. second step in the Bureau's overall MF The frequency effects are quite broad. communications program. However, there . Anything from 400 to 800 kHz is usually is no basic difference between opera- adequate. tional MF systems and postdisaster MF systems. By October 1982, the Bureau's 3.7.4a Specific Application of MF operational MF systems was in place in Commnicat ions to Rescue Teams several cooperating underground mines. By October 1983, performance evaluation The low attenuation of MF signals in of the systems will be completed. As the many stratified geologies, such as coal performance proceeds, emphasis will be mines, can be of great benefit to rescue directed to specific postdisaster-rescue teams. If existing mine wiring (like applications. 3.7.4b System Concepts

The main advantage of MF communication is simplicity. Figure 3-51 shows a rescue team member equipped with a prototype MF vest radio. This vest radio permits rescue team members to maintain local communications (fig. 3-52).

In most cases, rescue teams will utilize a lifeline for rapid retreat in case of smoke when visibility is limited. The lifeline offers interesting possibilities for MF radio communications. Some rescue teams actually use the line already to carry communications via sound- powered telephones. Such a scheme is both archaic and often ineffective.

Since this line is a continuous conductor back to the fresh air base, it provides a convenient parasitic path for MF communication as shown in figure 3-53. To assure even more reliable communications, physical audio links could be made with the lifeline as shown in figure 3- 54. Such an approach provides redundancy via simultaneous audio and radio links.

Figure 3-55 illustrates a total MF base station for rescue team use. At the fresh air base, the briefing officer (as the individual is sometimes called) is equipped with a standard intrinsically safe base station or repeater; the officer could also be equipped with a vest. With such an arrangement, communications FIGURE 3-51. - Rescue team member with are possible not only between rescue team MF vest radio. members, but also with the surface and with other distant rescue teams. In addition, it also provides a possible link to the trapped miners.

Since existing mine wiring is extensive and minewide, it is easily seen that it provides yet another redundant link for the rescue team members. Since other rescue teams are also in the vicinity of mine wiring, interteam communications are possible if desired. This concept of interteam communications is a radical de- parture from existing procedures. It will permit one rescue team, in one part of the mine, to modify the ventilation in FIGURE 3-52. - Basic MF communications such a manner that it does not degrade among rescue team members. Life line------and/or local mine conductors operation is to reach trapped miners in a I timely manner before they succumb to the F' - effects of injury, exposure, or toxic at- radio radio mospheres. To this end, rescue team com- w- - w Advancing Fresh munications is but a part. The key to rescue team alr base successful rescue lies in the rapid loca- FIGURE 3-53. - Lifeline as a parasitic MF path. tion of the trapped miners. Without this, valuable time can be wasted in diverting rescue efforts to the wrong area, often with tragic results.

Bureau research in the area of lo- Plug cation has been addressed by through- the-earth seismic and EM systems. In rad~o the seismic system, trapped miners pound I-\ '. Fresh air on the roof or ribs of the mine to gen- AyEU29 Locol radio base team communications erate seismic vibrations. These vibrations travel through the overburden to FIGURE 3-54. - Lifeline as a redundant commu- the surface where they can be detected nications line for MF and audio communication. by sensitive transducers called geophones. Computer analysis of the arrival times of the seismic signals at the various geophones permits the source to be accurately located. This system Local mine wiring is operational and is kept in readiness by MSHA Mine Emergency Operations. Present / Bureau research in EM means to locate I I and comunicate with trapped miners is / shown in figure 3-56. The system con- / Life line sists of two parts, a transceiver that Microphone is normally carried on the miner's belt Base - and a surface system for detection and stot Ion or communications. brepeoter - FIGURE 3-55. - Total MF base station for rescue teams. Loop antennas the ventilation in the vicinity of another rescue team. Equally important is the fact that trapped miners are also Location signal probably in the vicinity of existing mine o !I voice wiring. Transceiver JI p 3.7.4~ Location and Communications Systems for the Rescue of Battery with Trapped Miners power Loop antenna So far this section has primarily addressed the application of MF com- FIGURE 3-56. - Voice frequency electromag- munication to rescue teams. However, netic system for location and communication the ultimate objective of the rescue with trapped miners, In operation, the trapped miner re- its own disadvantages. The trapped miner moves the transceiver from the belt, de- must be equipped with a special trans- ploys a self-contained loop antenna, and ceiver, and must be able to deploy the attaches the transceiver to a special cap antenna in a sufficiently large area. lamp battery. This antenna consists of Injury or confined quarters may prevent 300 feet of No. 18 wire that must be de- deployment. In addition, under the best ployed in the largest area possible to be of conditions, the system has a range effective. A location signal is trans- limit of about 1,000 feet. Although a mitted directly through the earth. new system is under development that will increase the range to 3,000 feet, this On the surface, sensitive receivers improvement comes about only with com- detect the signal and locate the source. plex, slowly deployed surface equipment. Once detection and location are made, a Therefore, it will be subject to the same large surface transmitter is deployed delays as the seismic system. above the trapped miner. This transmitter is powerful enough to send voice mes- MF communication offers advantages sages by radio, directly down through the over through-the-earth approaches by earth. permitting in-mine communications to the trapped miners. This could be in The trapped miner's transceiver re- addition to, or in place of, through- ceives this voice. The surface personnel the-earth schemes that may fail because then ask the miner "yes-no" questions of excessive overburden or the inability concerning his or her condition and that of the trapped miner to deploy his or her of the mine. The miner responds by sim- end of the system successfully. Fig- ple on-off keying of the transceiver. In ure 3-57 illustrates this concept. this manner a two-way communications link is established, entirely through the In this illustration, the trapped earth, and rescue operations can start in mine,r is equipped with a small MF trans- the most efficient manner. ceiver built into the top of the cap lamp battery or worn on the belt. Note that Details of this EM system can be this is exactly the same packaging con- found in numerous reports. This is known cept used for the VF through-the-earth as a voice frequency (VF) system because syst'em shown in figure 3-56. The intent, all communications take place in the VF however, is not to send a signal through band of 300 to 3,000 Hz. the earth, but rather to induce a signal onto local mine wiring. If this is ac- The seismic system is very effective complished, the in-mine rescue team also in mines up to 2,200 feet deep, and does not require the miner to be equipped with ( A C power line) any special devices. However, it does require the miner to be able to pound. Injury or lack of a sufficiently heavy object with which to pound may render the system ineffective. The most serious drawback is that of time. The surface receiver station (geophones, field truck with computer, etc.) may take too long to set up. Bad weather and terrain can further delay the surface station deployment. transceiver

The EM-VF receiver system is less [~esclue team] rapped miner] affected by adverse conditions on the surface because it is lighter and more FllGURE 3-57. - MF in-mine location and com- easily transportable. However, it has mun~ication system. is likely to be in the vicinity of mine signals of narrow bandwidth that parasit- wiring and can receive the signal. It ically couple onto mine wiring, and are must be pointed out very clearly that widely distributed. This can be received mine wiring does not mean that one con- by the in-mine rescue team. If this oc- tinuous assembly of wiring is involved. curs, they will use their more powerful If the trapped miner is near a power ca- MF equipment (vests or base stations) to ble and not near a trolley line, and the establish a voice link to the trapped rescue team is near a trolley line and miner. By asking the trapped miner yes not near a power cable, this does not or no questions, his or her location can mean that a communications link between be learned. However, direct location via the two cannot exist. An induced MF sig- MF communication is impossible. The par- nal on one type of conductor will para- asitic coupling characteristics of MF sitically couple to all others, even if signals do not permit the through- there is no physical connection. This is the-earth VF type of location; the signal the uniqueness of MF communication. could be on many conductors.

4 In operation, the trapped miner Obviously VF and MF systems could be would deploy an MF loop antenna or cou- combined such that the benefits of both pler, preferably onto available local VF (fig. 3-56) and MF (fig. 3-57) could wiring. The coupler could be a small de- be obtained. Equally important is the vice of small volume similar to a current fact that the MF trapped miner device transformer. The loop could be a coupler could be used in nonemergency situations that was unwound. In either case, the as a page receiver and thereby be a cost antenna is small. If nearby wiring does effective addition to a general mine com- not exist, the loop could be deployed in munication system. Table 3-3 lists MF hope of coupling to distant wiring. When communication system specifications. so deployed, the transmitter sends out MF TABLE 3-3, - MF communication system specifications Emissions, narrowband FM: Occupied bandwidth...... ^^^^^...^^.. 10 Rf frequency ...... mm.m...mma...Id.Iz.. 60-1,000 Peak deviation...... Id.I~.. k2.5 Modulated frequency...... Hz.. 200-2,500 Receiver, superheterodyne:

Sensitivity...... m..mmm.mmmm.mmmmm.mmm.. 1.0 pV (12-db sinad) Selecti~ity...... ~~.~~~~~~..~..~~~...~~~~.~8-pole crystal filter IF 3-dB bandwidth (minimum)...... Id.I~. . 12 IF 70-dB bandwidth maximum)...... ^^. . 22 RF band~idth...... ~~.~.~~.~~..~~~~~.kHz.~ 60-1,000 Squelch...... Noise operated and tone Transmitter, push-pull, class B: Output power, W: Vest...... Vehicu1ar...... Antenna magnetic moment AT^^): vest...... ^^...^^^.^.^..^^^..^.....^ Vehicu1ar...... RF line coupler, transfer impedance (ZT): 1-in coupler, .ohms: 350 ~Hz...... ~.~....~...... ~~.. 520 ~Hz...... ~..~...... ~..... 820 ~Hz...... ~~...... ~...... 4-in coupler, ohms: 520 ~Hz...... ~...... 3.7.4d Performance Data it would demonstrate that if a trapped miner was equipped with a MF transceiver In order to evaluate the potential of similar specifications, he or she of MF signals as a means to locate and could directly communicate with rescue communicate with trapped miners, and to teams in the mine, or search crews on the provide communications for the actual surf ace who were monitoring any conduc- rescue team operation, a test was con- tors egressing the mine. ducted at the York Canyon Mine near Raton, N. Mex., in June 1982. This mine The result of the test showed that is a coal mine located in the York seam communications were possible from almost of the Raton Basin. The terrain is hilly anywhere in the haulage and belt entries such that the mine overburden varies from to either base station. It was even pos- about 200 to 800 feet. sible for the base at the portal, on the telephone line, to communicate with the The mine has four main drift entries base atop the borehole, on the fire moni- that are about 7,000 feet long. Off tor line, even though there was no physi- these entries, submains were driven and cal connection between the two. Whenever longwall mining occurs. A borehole is a vest was within a few feet of mine con- located at about the 7,000-foot mark. ductors, there was an obvious improvement This borehole contains a twisted pair ca- in clarity and signal strength. ble that is associated with the fire monitoring system on the longwall panels. Although this test was preliminary, it clearly highlights the potential of This is an ac mine that transports using MF communications for search and the coal by belt. Rubber-tired vehicles rescue operations. Much more work is provide transportation for personnel and necessary to measure range from mine wir- supplies. The distance from the portal, ing whenever the mine is not operating as down the main entries to the longwall would be the case during search and res- faces, can be nearly 15,000 feet). cue operations. An operational mine produces considerable levels of acoustic and At the mine portal, a MF signal cou- EM noise which reduces MF system range. pler was attached to the mine telephone lines. This coupler was controlled by a 3.7.5 Emergency Warning Systems standard MF base station. A second coupler and base station were placed at the Many types of emergency warning sys- top of the borehole. The coupler was tems are available for alerting under- clamped around the cable that went down ground personnel. One example is the the borehole. stench warning system, which introduces a distinctive odor into the airstream. Two personnel entered the mine and, Visual signals or radio paging could also by vehicle, traveled down the main en- be used to alert underground personnel. tries to the vicinity of the borehole A preferred warning system would operate (7,000 feet). These personnel were over existing wiring, such as the twisted equipped with MF vest transceivers that pair of a pager phone system, and broad- had a magnetic moment of 2.1 AT^^ and a cast an audio warning that can be heard sensitivity of 1 V at 520 kHz. The in- throughout the active areas of the under- tent of the test was to ascertain whether ground complex. Before deciding on an or not these personnel could communicate alarm system, factors that affect the with the base at the portal, or the base range over which an audio alarm can be at the top of the borehole. If so, it heard should be considered. The most im- would demonstrate that MF-equipped rescue portant factors are the noise background teams could communicate with the outside found in mines, the attenuation that the command center without deploying their mine environment imposes on the alarm own communications line, or relying on signal, and the attention-getting quality the integrity of the mine phone line that of different alarms. may, or may not, be intact. In addition, The intensity of a sound is the energy in the sound wave. It is customary to express intensities or pressure levels in decibels. The term "loudness" refers to the response of the human ear to sound. Experiments have established that the loudness of a tone is a function of both frequency and intensity, with the ear most sensitive to frequencies in the region of 1 to 2 kHz. In other words, for tones with the same intensity, tones in the 1,000-to-2,000-Hz region appear louder than those above or below this region.

Figure 3-58 shows the noise level FIGURE 3-59. - Detection thresholds. for a typical continuous miner, with noise samples taken at the operator's po- between 250 and 1,500 Hz require a level sition and with the conveyor running. To in excess of 80 dB to be just detectable. estimate the masking effects of these If we allow an additional 10 dB to insure samples, we must first transform the detectability, alarm tones would have to curves so that they refer to sound levels have a sound level of at least 90 dB at on a per cycle basis. This has been done the operator's position. in figure 3-59. The center curve, labeled "Mask noise source," plots the av- If we move 15 feet away from the op- erage of figure 3-58 in terms of the erator's position (the bottom curve in sound level per cycle of bandwidth. The figure 3-59), these sound levels are re- upper curve, labeled "Detection threshold duced considerably. This curve shows at noise source," shows the estimated that at 800 Hz a level of 60 dB is re- threshold level as a function of tone quired, and thereafter the required level frequency. The curve shows that tones decreases until at 6,000 Hz it is about 40 dB. RANCE MEASURED x' x' As mentioned earlier, the ear is most sensitive in the region of 1,000 to 2,000 Hz and decreases at higher frequencies. Figure 3-59, however, shows that the higher the frequency of a tone (up to 8,000 Hz), the more detectable it is. The spectrum of the masking noise is the cause of this apparent contradiction. The background noise is high at the frequencies where the ear is sensitive and decreases with frequency.

In addition to overcoming background noise, planners must compensate for attenuation of the warning tone. Experi- mental and theoretical investigations are in close agreement on the attenuation of sound in room-and-pillar mines. Figure 3-60 shows a plan of one experi-

FREDUENCIES IN Hz ICPSL ment on attenuation of sound. For this FIGURE 3-58. - Cutting with conveyor on experiment, a 100-dBA source was mounted (operator position). at the position shown in the figure, and DATA GATHERING POSITIONS

FIGURE 3-61. - Attenuation as a function of SOURCE frequency.

considered justified; but to insure reli-

0 50 100 150 200 ability, warning systems must be routinely tested, preferably in an operationally -SCALE (FEET) useful way, such as signaling the end of FIGURE 3-60. - Plan of mine in which experiment a shift. (Fire stations routinely test was conducted. (Coal seam height, 76 inches.) their sirens by sounding off at noon or some other prearranged time.) In addition, any system is subject to false the sound levels at the points labeled 1 alarms and/or pranks. Considering these through 4 were recorded. Figure 3-61 is factors, the presence of a really intense typical of the data obtained. It plots noise source might be regarded as an un- attenuation as a function of frequency at warrantable menace. the four points. Table 3-4 combines the effects of In practice, an audio warning source background noise level and attenuation of must be some distance from the personnel the alarm tone to show the sound level it is intended to alert, and it is desir- required at the source for the warning to able that the warning be detectable above be just detectable by the operator of a the background noise from as far away continuous miner. The significance of as possible. The greater the distance these numbers is best explained by taking the sound must propagate, the louder the a particular example. The entry for source must be; hence, the greater the 1,000 Hz under 210 feet is 100. This hazard that the source will damage the means that at 1,000 Hz the source level hearing of someone who is inadvertently required to just alert the operator of a close to it when it is actuated. In an continuous miner who has "normal hearing" actual emergency, the risk of subject- is 100 dB when the source is 210 feet ing a miner to intense sound may be away from him. TABLE 3-4. - Sound level required at source for warning to be just detectable at operator's position on a continuous miner, dB Frequency (Hz) Distance from source 70 ft 140 ft 210 ft 280 ft 250 93 96 100 10 1 500 95 99 103 105 1,000 94 96 100 103 2,000 9 1 95 99 103 4,000 88 9 1 102 107 There are systems commercially PHONE available that can satisfy the require- LINE ACOUSTICALLY COUPLED ments of audio warning systems using ex- LARM SIGNAL GENERATOR isting mine wiring. These systems use the mine paging telephone network as the emergency alarm system. This approach requires the addition of an alarm signal ALTERNATIVE generator compatible with the pager phone METHODS OF operation. The paging telephone and ex- SOUNDING , OPTIONAL THE ALARM ternal remote speakers act as the alarm sounding units. ' The alarm signal can be transmitted using a standard mine paging J telephone and an acoustically coupled alarm signal generator or by using a ded- M SIGNAL GENERATOR icated on-line alarm signal generator, as shown in figure 3-62. Alarm signals are fed onto the pager phone line in one of two ways.

The first way uses the small portable alarm signal generator shown at the top of figure 3-62. When operated, this unit emits an audio alarm via a small speaker. The speaker is equipped with a suitably sized rubber gasket that enables A ALTERNATIVE ALARMS the sound to be efficiently coupled into FIGURE 3-62. - Use of the existing pager tele- the microphone of any standard pager phone network as an emergency alarm system. phone. Units of this type are commonly used in conventional telephone applications to remotely control such items as The second way of sounding an alarm telephone answering machines and WATS on the system is to use the on-line alarm line access. It can be seen that sound- signal generator shown in ffgure 3-62. ing an alarm in this way is a little When the button on this unit is pressed, awkward since three buttons must be i places the correct dc signals on pushed simultaneously, but this provides the line to actuate the pager phones a safeguard against an accidental alarm. and electronically transmits the alarm In addition, the portable units need only signal. be entrusted to responsible individuals, which is a safeguard against pranksters.

BIBLIOGRAPHY

1. Adams, J. W., W. D. Bensema, and Telecommunictions Division, Cedar Rap- M. Kanda. Electromagnetic Noise in Grace ids, Iowa, February 1978; available Mine. BuMines OFR 37-75, June 1974, for consultation at Bureau of Mines 127 pp.; NTIS COM 741 1687. Pittsburgh Research Center, Pittsburgh, Pa. 2. Bensema, W. D., M. Kanda, and J. W. Adams. Electromagnetic Noise in 4. Bradburn, R. A. Communications Itmann Mine. BuMines OFR 39-75, June for Haulage Loop-Arounds. Paper in 1974, 103 pp.; NTIS COM 741 1718. Underground Mine Communications (in Four Parts). 3. Haulage Systems. BuMines 3. Bergeron, A. A. Grace Iron IC 8744, 1977, pp. 42-48. Ore Mine Effort. Collins Commercial 5. Bradburn, R. A*, and J. D. 14. Dobroski, H., Jr., and R. H. Foulkes. Longwall Mining Communications. Spencer. New Techniques for Trolley Paper in Underground Mine Communications Carrier-Phone Systems. Paper in Under- (in Four Parts). 4. Section-to-Place ground Mine Communications (in Four Communications. BuMines IC 8745, 1977, Parts). 3. Haulage Systems. BuMines pp. 44-62. IC 8744, 1977, pp. 3-11.

6. Bradburn, R. A., and R. L. 15. Dushac, H. M. Portable Remote Lagace. UHF Section-to-Place Radio. Control of Trolley Circuit Breakers. Paper in Underground Mine Communications Proc. 4th WVU Conf. on Coal Mine Electro- (in Four Parts). 4. Section-to-Place technology, Morgantown, W. Va., Aug. 2-4, Communications. BuMines IC 8745, 1977, 1978, 30-1--30-11. pp. 3-30. 16. Foulkes, J. D., R. L. Lagace, and 7. Bradburn, R. A., and H. E. A. W'. Welz. Technical Services for Mine Parkinson. Two-Way Communications With Communications Research. Commercially Face Machine Operators. Paper in Mine Available Equipment for Coal Mine Emer- Communications, March 21-22, 1973. gency Warning Systems. BuMines OFR 137- BuMines IC 8635, 1974, pp. 36-45. 77, December 1976, 77 pp.; NTIS PB 272 459. 8. Chufo, R. L. Leaky-Feeder Ultra-High-Frequency Radio. Paper in 17. Kanda, M., J. W. Adams, and W. D. Underground Mine Communications (in Four Bens'ema. Electromagnetic Noise in Parts). 3. Haulage Systems. BuMines McEl.roy Mine. BuMines OFR 38-75, June IC 8744, 1977, pp. 12-23. 1974., 156 pp.; NTIS COM 741 1717.

9. -- . Trackless-Trolleyless 18. Lagace, R. L., W. G. Bender, Medium-Frequency Radio. Paper in Under- J. D. Foulkes, and P. F. OIBrien. Tech- ground Mine Communications (in Four nicall Services for Mine Communications Parts). 3. Haulage Systems. BuMines Research. Applicability of Available IC 8744, 1977, pp. 49-51. Mu1t:iplex Carrier Equipment for Mine Telephone Systems. BuMines OFR 20(1)-76, 10. Dobroski, H., Jr. A Coaxial July 1975, 95 pp.; NTIS PB 249 829. Cable Telephone System. Paper in Under- ground Mine Communications (in Four 1.9. Laubengayer, W. C., K. Michael Parts). 1. Mine Telephone Systems. Ware, R. D. Gehring, L. R. Wilson, R. P. BuMines IC 8742, 1977, pp. 42-57. Decker, and D. T. Anderson. Research and Development Contract for Coal Mine 11. . Improved Rail Haulage Comnzunication System. Volume 4. En- Communications. Proc. 4th WVU Conf. on vironmental Measurements. BuMines OFR Coal Mine Electrotechnology , Morgantown, 69(4)-75, November 1974, 75 pp.; NTIS PB W. Va., Aug. 2-4, 1978, pp. 29-1--29-14. 244 900. 12. . Radio Paging. Paper in 20. Long, R. G., J. D. Foulkes, P. M. Underground Mine Communications (in Four Kay, and S. J. Lipoff. Systems Study of Parts). 2. Paging Systems, BuMines Metal and Nonmetal Mine Communications. IC 8743, 1977, pp. 29-33. BuMines OFR 32-82, August 1979, 231 pp. 13. . Remote Control of Circuit 21.Murphy, J. N., and H.E. Breakers. Paper in Underground Mine Com- Parkinson. Underground Mine Communica- munications (in Four Parts). 3. Haulage tions. Proc. IEEE, v. 66, No. 1, January Sys tems . BuMines IC 8744, 1977, 1978; p. 26. pp. 24-27. 22. Parkinson, H. E., and J. D. Underground Mine Communications (in Four Foulkes. Conventional Telephone Equip- Parts). 4. Section-to-Place Communica- ment. Paper in Underground Mine Cornmuni- tions. BuMines IC 8745, 1977, pp. 31-43. cations (in Four Parts). 1. Mine Tele- phone Systems. BuMines IC 8742, 1977, 25. Sacks, H. K., and R. L. Chufo. pp. 3-17. Hoist Radio Communications. Paper in Underground Mine Communications (in Four 23. Sacks, H. K. Refuge Shelter Com- Parts). 3. Haulage Systems. BuMines munication System. Paper in Underground IC 8744, 1977, pp. 28-41. Mine Communications (in Four Parts). 4. Section-to-Place Communications. Bu- 26. Spencer, R. H., P. O'Brien, and Mines IC 8745, 1977, pp. 73-76. D. Jeffreys. Guidelines for Trolley Car- rier Phone Systems. BuMines OFR 150-77, 24. . Trapped-Miner Location March 1977, 170 pp.; NTIS PB 273 479. and Communication Sys terns. Paper in CHAPTER 4. --COMPUTERIZED MINE MONITORING~

4.1 Introduction production-related functions and those related to health and safety, was used to Monitoring systems can have numerous develop a questionnaire. It was present- uses in the mine. They can aid in the ed to representatives of the mining com- efficient management of the mine by pro- munity to determine their current moni- viding environmental trend data, pro- toring priorities. duction and maintenance control, and communications. In some cases, they can The responses indicated that the in- provide justification to petition the dust:ryls priorities fall into the follow- Mine Safety and Health Administration ing two categories : (MSHA) foz a variance of one of the mandatory safety standards. They may also increase the gross revenues of the mine by increasing the amount of coal produced Production and haulage or increase profits by reducing the cost of producing that coal. Maintenance

No single system will satisfy the Second priority-- requirement of all mines. Some may require simple hard-wired status-reporting 'Ventilation systems; others, multipurpose computer- based systems that collect, analyze, and Communication store data and perhaps control some mine functions. Even though systems vary in Fire monitoring complexity, they are all composed of three functional components. The first Personnel component is sensors that measure the environmental or production parameters and The survey shows that production- produce an electrical signal that is fed oriented systems were the most appealing into the telemetry. The second is telem- to the questionnaire respondents. Since etry devices that receive the signal from even small improvements in production ef- the sensors and transmit it in either an- ficiency and maintenance can have a large alog or digital format to the third com- financial impact, the desirability of ponent, analysis and display equipment. monitoring systems that focus on these This equipment receives the transmitted areas is understandable. signal and either stores it for later analysis or displays it. The analysis- The results are summarized in table display equipment ranges from simple 4-1, The function that scored 100 was strip chart recorders with preset alarms viewed as the most beneficial monitoring to computers, cathode-ray tubes (CRT1s), func.tion. and line printers that can also provide production reports. From Guidelines for Environmental 4.2 Uses of a Mine Monitoring System Monitoring in Underground Coal Mines. Phase I Report. BuMines OFR 180-82, A list of potential uses for 1982, 177 pp.; NTIS PB 83-147777. mine monitoring systems , including both TABLE 4-1. - Survey results, weighted rank score

Output by section...... Fire: Beltways; a system to detect and warn of incipient Belt monitoring and control.... fires in the beltway due to hot rollers or other problems...... Scheduled routine maintenance.. Beltway for intake air; the use Equipment repair history ...... of improved fire detectors and monitoring system so as to Spare parts inventory...... qualify for a variance and enable use of the beltway for in- Assist in diegnosis of failure. take air......

Power: Fault location...... 23. Communication: Station-to- station...... Face equipment operating time.. 24. Emergency signaling; direct Personnel: Shift organization.. people during any emergency by signaling...... Ground fault detection...... 25. Detect leaky stoppings; venti- Trailing cable failure...... lation monitor to detect open doors, blockages in air course, Power center monitoring...... and leaky stoppings...... Monitor car haulage system..... 59 26. Personnel: Emergency; assist in locating and aiding people Personnel: Locate skills; during an emergency...... assist in locating people with needed or critical skills...... 58 27. Fire: Haulage; detect incipient fires in trolleyways...... Ventilation: Eliminate inspections; eliminate or reduce 28. Ventilation: Control regula- frequency of some periodic tors; monitor ventilation, and inspections...... adjust regulators to improve flow distribution...... Communications: Reliability.. .. 29. Roof fall prediction; automat- Communications: Intelligibility ically plot falls and/or micro- seismic activity to predict Paging...... roof fall...... Plan new ventilation; help in 30. Cage; monitor the operation of planning ventilation, including the cage to predict failures or new ventilation shafts...... 45 minimize delays...... Inspection scheduling; alert 31. Fire: Gob; monitor gob areas foremen or others to scheduled for fire...... or predictable inspection or repair ...... 32. Inventory expendables ...... 11 33. Rock bursts...... Responders were also asked to indi- 75.306 Weekly ventilation cate the relative importance of other examinat ions. cost and technological factors that may affect user acceptance. Results, on a 75.307 Methane examinations. 100-point scale, were 75.310 Methane in virgin territory. 1. Reliablity of monitoring equipment in mine environment...... 100 75.326 Aircourses and belt haulage entries. 2. Maintenance cost...... 90 This review identified a number of 3. Initial cost...... 88 cases where continuous monitoring was used. in a petition for a variance and a 4. Skills required to maintain numbler of others that could have used equipment...... 75 continuous monitoring. Included in the review were petitions that were granted 5. New technology to mining ...... 62 and petitions that were filed, but not acted upon as of the writing of this re- Reliability of the equipment was the port.. General comments on the petitions most frequently cited "very important" f 011.0~. factor. 75.305 Weekly Examinations for Haz- Pet itions for Modification ardous Conditions. - This section requires weekly inspection of at least one Mine monitoring systems can be used entry of each intake and return air- to provide a cheaper and safer alterna- course, in its entirety, for both methane tive to satisfying the mandatory safety and for compliance with the mandatory standards set forth in 30 CFR 75, provid- health and safety standards. Typical ed that the alternate method (in this petitions state that because of poor roof case, the monitoring system) guarantees conditions it is not possible to travel no less than the same measure of pro- the aircourses in their entirety, and tection afforded by the standard (30 CFR offer checkpoint measurements as an al- 44). The extent to which the industry ternative. Continuous methane (75.305) currently takes advantage of these us- measurements could be made with a moni- ages can be determined by reviewing the toring system at these checkpoints. Re- Petitions for Modification of Manda- quired airflow measurements (75.306) tory Safety standards .2 Since ventila- could also be made with the same system. tion regulations appear to be the most likely candidates for modification peti- Only 1 of the 62 petitions that were tions, petitions were reviewed under sub- granted offered continuous monitoring. part D, "Ventilation," in the following An additional 20 petitions were filed, sections: but there was no record of any final decisions. One of these petitions did pro- 75.305 Weekly examinations for pose to install two methane monitors at hazardous conditions. specified points.

2~ourcesinclude the Federal Register , 75.307 Methane Examinations. - This the Bureau of National ~f f airs, Inc., section requires tests for methane at "Mine Safety and Health Reporter, " and each working place immediately prior the McGraw-Hill 1979 "Guide to Modifica- to energizing electrically operated tion of Safety Standards in Coal Mines." equipment. One petition was noted in which 4.4 Technical Factors methane monitoring devices were installed on permissible electric water pumps in The key technical issues are whether the face area to eliminate the meth- the sensors can actually provide the ane examinations by a qualified per- needed input information, the ability of son required prior to energizing the the processing system to interpret cor- pumps. rectly the telemetered information, and, finally, overall system reliability. 75.310 Methane in Virgin Terri- tory. - This section requires that all 4.4.1 Sensors electric power be cut off and men withdrawn when air returning from vir- Sensors are the critical element in gin mining areas contains 2% or more mine monitoring systems since they pro- methane. vide the input data. If the input data are not correct or are not representative Three petitions for modification of the required measurement, the entire were granted under the stipulation that monitoring process is meaningless, i.e., continuous automatic methane monitors "garbage in, garbage out." One problem were used in the return as an alternative with sensors is that their output repre- to measurements made by certified mine sents the response of the sensor to a personnel. number of parameters in addition to the one that is to be measured. Typical ex- 75.326 Aircourses and Belt Haulage amples are the response to changes in Entries. - This section requires that en- temperature and the poisoning of environ- tries used as intake and return air- mental sensors by other gases in the courses be separated from belt haulage mine. entries. The critical problem relates to the Fourteen petitions that were grant- ability of the sensor actually to measure ed and ten that were filed but not act- the parameter of interest. In particu- ed upon were reviewed. Of these, seven lar, ventilation monitoring systems use petitions were granted on the basis point air velocity measurements to repre- of continuous monitoring systems, and sent the total airflow at a cross section seven of the filed petitions proposed in the mine. The total airflow is deter- continuous monitoring of carbon mon- mined either from an empirically derived oxide. A review of MSHA tests that factor and the point measurement or from demonstrate the "equivalency" of car- actual calibration of the cross section. bon monoxide sensors and the customary The problem is further complicated be- point-type heat sensors is presented in cause the only safe location for the reference 15. sensor is on the rib or roof in the low- flow boundary layer. It is possible to In summary, at least 11 continuous have large changes in the overall airflow monitoring systems have been installed in with little or no change in the veloci- U.S. underground coal mines for purposes ties in the boundary layer and conse- of obtaining a variance from the manda- quently in the sensor output. The reader tory health and safety standards. Eight is referred to reference 13 for guide- additional petitions for modification lines for avoidance of these problems in mention such systems. airflow measurement. 4.4.2 Telemetry 4.4.3 Reliability

The telemetry system obtains the The final area of concern is system data from the sensor, converts them to a reliability. The questionnaire identi- standard format, sends them to another fied reliability as the prime concern. unit that receives them, checks their The Bureau is currently sponsoring re- authenticity, and then refers them to the search that provides a methodology for analysis-display device. The principal determining the reliability of systems problem in this area is data security, (12,- -17, 2). This methodology has been i.e., the error rate for information used to evaluate expected failure rates transmission. The problem is not so much of current mine monitoring systems. that an error is transmitted but that an error in transmission goes undetected be- Reliability in monitoring systems cause of the noise on the transmission takes a number of forms. The first is line. The sensitivity to erroneous data mechanical reliability of the components. transmission depends upon factors such as The underground mining environment is no- the cable used, the local noise field, toriously hard on equipment because of length of cable run, and data formatting. water, dust, potential damage due to moving equipment, and rough handling. Techniques for detecting erroneous Therefore, the enclosures for remote sta- data transmissions have been devised tions should be rugged enough to with- principally by computer manufacturers. stand the day-to-day rigors typically Notable among these are IBM's synchronous encountered in underground service. The data link control (SDLC) and Digital enclosures should have tight and durable Equipment Corp.'s digital data communica- seals if the internal components are tions message protocol (DDCMP). sensitive to moisture or dust. All ex- terilor switches and buttons should also Bureau research (4-5)-- ,3 indicates be sealed or be durable enough to with- that the maximum transmission distance stand constant use in the presence of for one undetected random error per year dirt and moisture. Cables should be dur- varies between 1.3 and 6.8 miles in an able enough to withstand occasional rough average noise field, and between 0.1 and treatment. 0.6 mile in an estimated maximum noise field. Since cable runs are frequent- The second aspect of reliability is ly several miles, occasional undetected electrical power reliability. Since pow- transmission errors can be expected. For er outages are all too common in under- typical monitoring applications with fre- ground mining, some type of backup power quent data refresh, this should not be or uninterruptable power supply should be a factor that causes worry; however, in provided for this system. Such a power the case of control systems or the least supply is particularly important for mon- favorable monitoring circumstances, er- itoring systems that provide essential ror rates can be unacceptably high, and health and safety information such as corrective measures such as more secure main fan operation, fire detection, and transmission systems and improved error methane content. Obtaining these data is detection protocols are necessary. important during the common day-to-day, short-term power outages, but it is just as important to have such information 3~nderlinednumbers in parentheses re- during emergency situtions such as roof fer to items in the list of references at falls , fires, or explosions. It is also the end of this chapter. required for system approval. 4.5 Commercially Available Mine the control center that is usually lo- Monitoring Equipment cated aboveground. The output of the sensors can be either a simple status in- 4.5.1 Introduction dication, sometimes called a binary, contact closure, or status output (such as The mine monitoring systems dis- high-low, open-closed) or it can be a cussed in this report are electromechan- continuously variable function of time ical systems that remotely sense various (such as air velocity, methane concentra- environmental and operational parameters tion, etc.). While the continuously var- and transmit the data to a central loca- iable data can provide significantly more tion where the data are analyzed and/or information than the simple status data, displayed. On the basis of this defini- how much more depends on the accuracy of tion, it is reasonable to discuss the the measurement. system in terms of three basic functions: sensing, data transmission (or telemetry) As a practical matter, it is gener- and data analysis and display. In the ally not feasible to run a separate con- case of monitoring and control systems, ductor or conductor pair to each sensor. such as systems that automatically and Theref ore, telemetry systems typically remotely deenergize face equipment when incorporate several remote stations or the methane content at a specified lo- "outstations," each of which accepts and cation reaches a predetermined level, encodes the output of a number of sensors the control operation presents a fourth and transmits the encoded data along a function. common cable to the control center. The two most common encoding techniques are Sensing can be divided into two gen- ( 1) frequency domain multiplexing and (2) eral categories: environmental and oper- time domain multiplexing. Frequency do- ational or production sensing. The first main multiplexing has the advantage that category of sensors is designed to mea- data from all monitoring points are re- sure various aspects of a mine's environ- ceived at all times, although the number ment to assist in maintaining a safe en- of monitoring points is limited by the vironment for underground personnel. The overall bandwidth of the system. Time parameters that are ordinarily of concern multiplexing can be expanded, at least in are gas (i.e., carbon monoxide, methane, principle, to accommodate as many moni- oxygen, etc.) content, air velocity, air toring points as desired. However, each temperature, differential pressure, and point is sampled only intermittently humidity. Typically, the data are used (ie, the receiver obtains data from to detect and locate potential!.^ hazard- only one monitoring point at a time) ous conditions (i.e., fires, gas bursts, since the system interrogates the moni- etc.) so that the appropriate measures toring points sequentially. The cycle can be taken. Production sensors are time, or time between successive Sam- used to monitor the operating status of plings of the same point, is the time the various pieces of underground equipment system requires to interrogate all of the to detect production bottlenecks, equip- monitoring points. ment malfunctions, maintenance requirements, etc. Examples of production pa- Time multiplexed systems, the more rameters that are typically of interest common of the two, often trensmit data in are belt output, face equipment opera- the digital format. That is, a series of tion, belt slippage, blockages, and bear- high-low state indications is transmitted ing temperatures or vibration. to indicate the status of the monitor point. A common technique to accomplish Telemetry is the process of trans- this transmission is to use frequency mitting the data output of the sensors to shift key (FSK) encoding. This encoding process uses two different frequencies and assist the mine during installation, (for example, 3,000 and 2,000 Hz) to rep- testing, and operator training. The resent the high and low states, rather costs for these services, however, may than high and low level signals of the sometimes be broken out separately from same frequency. The FSK encoded data are the hardware costs. For mines that pre- less affected by noise on the transmis- fer to use in-house personnel for these sion line than data transmitted in simple tasks, systems suppliers that restrict high-low digital format. In addition, themselves to providing the hardware current signal detection techniques make alone may be worthwhile. it very easy to detect single frequency signals in the presence of noise. 4.5.2 Telemetry-Analysis and Display Sys tems The third basic function of a monitoring system is the analysis and display Table 4-2 summarizes the major mine of the measured data. These operations monitoring systems currently available in are normally accomplished in an above- the United States. Three of the systems, ground control center. Most of the sys- Davis, Hawker Siddeley, and Transmitton, tems have the ability to trigger audio- were originally based on the MINOS system visual alarms if a sensor detects that developed by the National Coal Board in its predetermined threshold (such as 1% Great Britain. Systems offered for sale methane in a return airway) has been ex- in the United States may, however, differ ceeded. Most of the systems can also from the original MINOS system. Most of provide hard copy documentation of the the systems have the capacity for accept- alarms and display the actual values de- ing input from a wide variety of environ- tected by the sensors, either on meters mentall and production sensors. An indi- or CRT's. The computer-based systems cation of the extensive use of monitoring have the added capability of data storage system abroad can be obtained by compar- for trend analysis, record keeping, and ing t:he U. S. -foreign installat ions for reporting. the two British systems. While these systems are used extensively abroad, they In the following discussion on com- are just beginning to be accepted in the mercially available equipment, a distinc- United States. tion is made between the system suppliers and the sensor suppliers. The distinc- As discussed previously, most of the tion is made since in many cases the systems use an FSK format for data trans- system supplier expects the mine to missi-on. The exceptions are Conspec, select not only the parameters to be Mundi-x, and Transmitton, which use a monitored but also the sensors to be direct binary transmission. used. The system supplier then config- ures a monitoring system using both in- While the range in the number of house hardware and hardware from outside monitoring points and cable length is suppliers to provide the mine with the subst~antial,most systems should provide desired information. Ordinarily, the da- sufficient capacity for typical usage. ta telemetry-analysis and display equipment is the supplier's own brand, while In terms of system costs, one the sensors are obtained from outside manufacturer uses a "rule-of-thumb" of companies. In most cases, the supplier $50,000 for the central station and will assume "full system responsibility." $20,000 per mine section. That is, it will not only provide the telemetry-analysis and display equipment, The final category of table 4-2 in- but will also ensure proper interfaces dicates which suppliers usually assume for any sensors selected by the mine, overall system responsibility. provide software to process the data, TABLE 4-2. - Mine monitoring systems currently available in the United States

I Aquatrol Conspec Davis Giangarlo Hawker Kidde Siddeley Current installations: - -- Coal mining...... 4 1 14 >lo0 4 Metal-nonmetal mining... 12 0 0 NA 0 Other industries...... Several 0 8 NA 100 Specifications: Data transmission...... FSK DB FSK FSK FSK Maximum number of moni- NA 768 15,080 26,400 1,024 toring points. Cable (number of con- 4+S 2+s 2+S 1+S ductors). 4+S Coax. Maximum cable miles.. '0.8 20 20 10 length. Power requirements, V: Ac...... 110 110 110 Dc...... 12 NAP NAP Cost, thousand dollars: Central station...... 25 100 75-100 Outstation...... 0.25 25 3-4 Overall system Yes Yes Yes Yes responsibility. Yes l Mundix Out okompu R.F.L. Sangamo Trans- Wes ton mitton Current installations: Coal mining...... 1 0 1 0 200 Metal-nonmetal mining... 0 1 0 1 0 Other industries...... 0 >loo 100 >loo 0 Specifications: Data transmission...... FSK FSK FSK FSK DB Maximum number of moni- 72,000 Unlimited 4128 8,192 1 7,392 t oring points. I Cable (number of con- 2+S 2+S 2+S 2+S 4+S ductors). 4+S Maximum cable miles. . 8 >6 >10 '2 10 length. I Power requirements, V: Ac...... 110 110 NAP 110 110 D~eeeeeeeeeeeeeeeeem 12 24 12 12 NAP Cost, thousand dollars: Central station...... Outstation...... Overall system 1 Not I yes 1 yes l~ot 1 ~ot I yes responsibility. I normally. 1 I normally.I normally.I DB Direct binary. NA Not available. S Shield. FSK Frequency shift key. NAP Not applicable. l~xtendable. 31ncludes CO monitor. 2~igitalinputs. 4// per station. 4.5.2a Systems Suppliers Telemetry is at 300 baud using RS232C format. The system is typically purchased from a vendor who will supply the A training program about a week long t elemetry-analysis and display equipment. is offered at their plant. They will Since this vendor will usually ask the assume system responsibility and quote a mine operator to specify the sensors used maintenance contract if desired. in the system, sensor operating principles and available sensors are discussed Conspec Controls, Inc. separ'ately . 901 Fuhrmann Blvd. Buffalo, NY 14203 All of the systems suppliers, with (7 16) 854-4769 the exception of R.F.L., provide computer-based systems with printers, CRT's, The Conspec Senturion Series 200 software packages and auxiliary power monitoring system consists of a central in case of main mine power failure. The processor that has a CRT display and key- listing is of necessity incomplete, it board., two printers, one or more "data does not represent endorsement by the concentrators, " which are interface de- Bureau of Mines, nor is responsibility vices', and a capability for up to 768 assumed for any errors that may have sensi.ng (monitoring and/or control) occurred in system performance descrip- p0int.s on any of four trunks, each capa- tions. Much of the material was ab- ble of carrying 128 locations. At the stracted from telephone conversations sensing location, the electronics neces- with and brochures received from the sary to interface a sensor onto the trunk designer-manufacturers. (incl-uding entering its address) are housed on a 4- by 6-inch accessor card, Aquatrol Corp. which in many cases is incorporated into 2258 Terminal Road the sensor package. St. Paul, MN 55113 (612) 636-3950 Transmission is over four-conductor cable; two for power and two for signal. Aquatrol Corp. markets an Intel The power required is up to 30 volts dc, 8085-based monitoring and control system and the maximum end-to-end length is that is sold primarily to water treatment 4,000 ft. If greater distances are re- facilities. It has full system capabil- quired, a trunk extender can be used; ity including color CRT, printer, and powered by 110 volts ac, it permits oper- 262,000 random-access memory (RAM) floppy ation to 40,000 ft. A 600-baud (bit per disk storage. The system will accommo- second) FSK telephone modem is also date up to 98 outstations on the master available. trunk, with up to 18 data channels per outstation. Each channel can be analog, Data transmission is in a noise- resolved to 12 bits, or the 12-bit digi- resistant binary format. There are no talword can be treated as individual remote stations, other than the accessor binary level inputs. at each measurement location. Either binary or analog data can be transmitted. Similarly, each outstation can output up to 6 analog channels or 12 binary Display is in a 20-character alpha- drive levels for each analog channel less numeric format (20 letters or numbers) so than 6. that interpretation is simplified. A compilete software package is offered that The cable is two-conductor voice has the capability to alarm on thresholds grade, operable to 5,000 ft or, with an and set high-low points. Set points can extender, further. Power is 110-volt ac be entered from the keyboard. There is or 12-volt dc for both the central or the central reset of remote points, a pro- remotes. gramed restart or load-shedding feature, time of day or week programing, and se- A variety of system configurations quencing initiated by alarm or keyboard is available. Outstations have been entry . designed primarily for haulage, machinery monitoring, and communication. For Alarm states are printed and dis- example, the type 25200 equipment LC- played separately. Routine information cepts eight thermal probes and two other such as end of shift reports may also be transducers, such as pressure and flow. generated. Thresholds are set locally with a potentiometer. Such a unit would be appropri- Standard accessors available include ate as a compressor, fan, or pump moni- interfaces for thermistors, pressure, tor. There are local and remote stop RTD, power, current (4-20 mA, 0-5 volts, modes. 0-1 mA), potentiometer, alarm states, two- or three-state load control, and Similarly, the FMSl type 25000 ac- electrical demand. commodates six transducer inputs, and has six relay outputs for indication and/or John Davis and Sons (Derby) Ltd. control. It can perform level detection, Alf eton Road temperature detection, and time delay Derby DE2 4AB functions. Applications listed include England haulage, bunker, pump, and refrigeration plant monitoring. It is powered with Service Machine Co., Inc. 110-volt main power. Box 8177 6072 Ohio River Road Other communication, conveyor con- Huntington, WV 25702 trol, and signaling devices are also Attn: Mr. J. H. Nash offered.

Davis of Derby offers a data trans- Giangarlo Scientific Company, Inc. mission system consisting of a surface 2500 Baldwick Road master station with two video displays, a Pittsburgh, PA 15205 control keyboard, and a communications (412) 922-8850 switchboard. Associated with this central station are up to 127 outstations, The Giangarlo system consists of a each capable of monitoring up to 40 central processor with associated outsta- transducers. Interconnection is by ei- tions. The outstations are microcomputer ther two- or four-conductor shielded ca- controlled and are capable of accepting ble. Telemetry is accomplished digitally up to five input boards. Each board may with FSK coding. consist of either 8 analog inputs, 16 digital inputs, or 8 relay inputs, and Outstations can be wired to accommo- each board has light-emitting diode (LED) date prestart warning, belt slip, and status lamps for troubleshooting. There other transducers, including temperature is battery backup power. Telemetry re- and pressure. quires a three-conductor shielded cable with data packaged in an ASCI I1 serial Virtually all Davis of Derby under- FSK digital format, run at 300 to 1,200 ground equipment is housed in flameproof baud. Remote stations can alarm on their housings, and most circuitry is designed own, with visual and audible alarms. to be intrinsically safe. Certification and design are to international stan- At the central computer, software dards, such as Cenelec Standard 50 020 is available that will use redundancy and IS1902 Class I. Circuitry is low- checks of data to identify faulty trans- power CMOS. Standby battery power is mission. It can display data, set remote available with automatic changeover. alarm thresholds, and perform control functions. Central computer alarms are of eight. Power is 110 volt, 50 Hz, or independent of remote alarm status. any standard mine supply.

There is provision for interface The bunker-conveyor monitoring and from the central computer to a teletype, control system can automate haulage from CRT display, disk memory, or another the vicinity of the face to the sur- computer. face, including bunker monitoring and metering. Input parameters that might be measured and transmitted to the central Their mine cage monitor maintains station include carbon monoxide, carbon the cage within speed and distance lim- dioxide, methane, temperature, air veloc- its, comparing cage performance to a de- ity, radon, belt slippage, belt speed, sired operation profile every 0.1 sec and weight, pressure, power, etc. making the appropriate corrections.

Hawker Siddeley Dynamics The environmental monitor can accept Engineering Ltd. eith.er analog or digital inputs from Manor Road sensors such as anemometers, methanom- Hatfield, Hertfordshire ALlO 9LY eters, pressure sensors, and bearing tem- England pera.ture probes. Hatfield (07072) 68234 Kidde Automated Systems United Technologies Bacharach (Formerly S.R. Smith Co., Inc.) 301 Alpha Drive 7256 County Line Road Pittsburgh, PA 15238 Deerfield, IL 60015 Attn: Mr. David M. Nelson (312) 272-8012 (412) 784-2137 The SoRm Smith System uses a remote Hawker Siddeley is one of the quali- "data collection panel" architecture, fied manufacturers of the MINOS system. Each remote station is capable of receiv- It offers systems for environmental moni- ing up to 16 contact closure inputs. The toring, conveyor and bunker control and remote stations also contain relays that monitoring, and mine cage monitoring. are capable of control functions such as The "Dynalink" system for conveyor con- starting-stopping belts. A new system trol and monitoring consists of a surface has a capability for the transmission of control center with provision for local analog levels, control and monitoring or for remote control from the remote station. Out- The central computer facility uses stations are connected to the central Digital Equipment Corp. display and anal- station with six-conductor cable at dis- ysis equipment. A CRT displays informa- tances up to several miles. Sixteen tiorl from any of 1,024 monitor points, outstations can be carried on one cable, conrlected to any of 64 remote stations and seven cables can be accommodated per channel. Telecommunication is over a two--wire pair, or coaxial line, or 3002 The control station has a dual visu- Telco for each channel. al display. Monitored data, or change of state, or even mimic diagram graphics can A complete interactive software be displayed. The central computer is a package is available that displays alarms DEC PDP 11/34 or CAI ALPHA LS1-2/20G. in a prioritized list. Data are also Microprocessors used are Intel 8080 and printed on a high-speed printer, as an 8085. There is dual control with auto- aid to failure diagnosis and as a perma- matic switchover for reliability. nent record. Up to 700 characters of description and instruction are possible Each outstation can accommodate 32 per alarm point. input channels, expandable in increments Intended applications include belt Mundix Control Systems, Inc. monitoring (slip, alignment, power, chute 5495 Marion St. plugging, etc.), power center monitoring Denver, CO 80216 (breaker position, voltage in range, open (303) 296-1790 ground, etc.), environmental monitoring (methane within limits, air velocity Mundix offers a supervisory control within limits, etc.), fire monitoring, and data acquisition system that can ac- and fan monitoring (operating, tempera- commodate up to 128 outstations. Each ture in range, etc.). The system can be outstation can be configured with four used with a card reader to control and electronic interface cards (extensible monitor people underground or in a con- to 16). Each card can accommodate any trolled area. one of the following: four analog inputs (12-bit resolution), eight digital Mine Safety Appliances Co. inputs, eight digital outputs, or four 600 Penn Center Blvd. analog outputs. Pittsburgh, PA 15235 (412) 273-5000 The total system capacity is 4,096 digital inputs or 1024 analog. Telemetry Catalyst Research Corp. to the central station is accomplished 3706 Crandall Lane using a 500-kHz digital phase modula- Owing Mills, MD 21117 tion technique (Manchester coding). As (301) 356-2400 a result, the system uses two-conductor shielded cable. The maximum transmission Catalyst Research Corp. has designed distance is stated to be 128 miles. and tested a computer based supervisory control and data acquisition system The central station is computer- (SCADA) which is also available from MSA. based, and BASIC language programable. The system can accommodate up to 38 field There are printers and color or black and data stations. Each data station is ca- white CRT monitors available. Power to pable of receiving eight analog inputs, the central station is 110-volt ac, while plus any one of the following: 16 digi- remotes can be powered with either 110- tal inputs or 4 digital outputs. volt ac, 24-volt dc, or 120-volt dc.

Remote stations can be up to 18 Outokumpu Engineering miles from the central station. Cabling 4680 Packinghouse Road is by two-conductor No. 19 gage twisted Denver, CO 80216 pair. The central station is computer (303) 371-0540 based. It uses a Digital Equipment Corp. LSI11 microprocessor with 64,000 bytes of There are hundreds of Outokumpu mon- memory. Data transfer from remotes to itoring systems installed in Europe, pri- the central station uses RS232 at up to marily in power control applications. It 2,400 baud. is a computer based system (DEC) with an interactive English control software. Interactive, user friendly software The system has a capability for up to is available. Alarm states are indicated 30,000,000 bytes of storage on a Winches- audibly and automatically printed. Hour- ter disk and printer, CRT options. ly and daily summaries can be generated. The remote outstations are typical- If there is a need to transmit analy configured to accept 4 analog in- log data, the model 64B series converts puts, 16 digital inputs, and 16 digi- input voltages in the 0.4- to 2-volt tal control outputs. There are two types range, or input current 4 to 20 mA, 10 to of outstations, the miniremote described 50 nlA, etc., into a square wave output, above, and larger, higher capacity units. frequency coded in the 5- to 25-Hz range. Outstations can be interconnected in After voltage- or current-to-frequency any series parallel configuration. conversion, these low-frequency codes are Analog data is resolved to a 12-bit transmitted by using the frequency shift precision. transmitter-receiver described.

Telemetry is accomplished using a If large numbers of status-control serial RS232 FSK format at 300 baud (50- signals are to be telemetered, the mod- 600). Outstations can be up to 6 miles el 66A encoder-decoder will accommodate distant. Two-conductor twisted pair ca- 16 input channels. These data are ble is required. then time-division-multiplexed (TDM) with a redundant transmission (normal Power to the central and remote sta- and polarity-inverted, doublescan format) tions is 110-volt ac, 220-volt ac, or 24- to ensure reliable transmission. There volt dc. are two parity check bits, so that parity errors up to the third order can be R.F.L. Industries, Inc. detelcted. Once again the data are Boonton, NJ 07005 telelnetered with one of the frequency- (201) 334-3100 shift, frequency-multiplexed transmitter- receiver pairs. The scan time with the R.F.L. Industries manufactures te- normeal 60-baud system is 1.1 sec with lemetry equipment consisting of build- doublescan and 0.6 sec with single scan. ing blocks that can be combined to Input data can be binary level or switch satisfy progressively more demanding closure inputs. Power is 12 volts dc. system requirements. The simplest system consists of frequency-multiplexed Analog channels can also be accommo- transmitter-receiver pairs that operate dated on the TDM system. Analog inputs with center frequencies between 300 Hz are channeled, one at a time, to an A-D and 30 kHz in spacings of 100 and 120 Hz converter. The analog quantity is digi- or more. These devices are available in tized and this parallel digital signal, two configurations: an AM system, in together with a corresponding digital ad- which the carrier is keyed on or off with dress, is fed to a 66A encoder. Trans- a 12-volt dc input status, or a system mission is now similar to that in the with a switch closure. A more secure foregoing paragraph. At the receiving frequency-shifted version uses the same station, the message is decoded, and the audio band center frequencies, but digital output is channeled to the corre- frequency-shift codes the data in any of sponding D-A converter to produce an ana- four codes including a two-frequency code log output. (mark-space) and a three-frequency code (mark-center-space). Both systems are Sangamo Weston, Inc. powered by 12-volt dc. If standard CCITT Industrial Products channel spacing is used, there are 46 P.O. Box 3041 carrier channels between 300 Hz and 10 Sarasota, FL 33578 kHz, with more at higher frequencies. (813) 371-0811 Sangamo Weston manufactures three The Transmitton control consol consists different monitoring and control systems. of one or two color video displays, a Their RECON I has a capability for up to keyboard, two switch panels, and a com- 127 remote stations, each with 12 analog munications center. The Transmitton sys- inputs, resolved to 12-bit precision, and tem, represented in the United States by 12 output levels. Channels can be ex- Reliability Technology, is designed to tended fourfold as an option. Operation monitor and control the operation of con- is either manual or by computer control. veyors, pumps, electrical switches, shaft Cycle time is 0.5 sec per channel. elevators, ventilation fans, and bunkers, as well as environmental parameters such The RECON 11 has eight channels per as methane, carbon monoxide, air ve- remote and can accommodate eight analog locity, air pressure, temperature, and channels each, resolved to eight-bit smoke. precision (0.4%). It is controlled by an Intel 8080. The output is a printer The system consists of a central terminal. Cycle time is 0.5 sec per control station and up to 168 outsta- channel. tions. Data are transmitted in a digital format, but not frequency coded; i .e. , The RECON I is a computer- high-low states are transmitted. A four- controlled system that uses a Digital conductor cable is used. Equipment Corp. ~~~-11/24programed in RSX11M. Peripherals include a color CRT Conveyor monitoring includes belt and printer. It is capable of 256 remote speed, misalignment, belt weight, torn stations. Reporting is by exception belt, motor voltage current and tempera- (report when exceed limits). Each remote ture, vibration, and alarm states. Sonic is capable of 16 analog inputs and has and visual alarms are available locally 16 output control relays (KU series 20A and can be controlled locally or remote- relays). Resolution of input signal is ly. Belt start sequencing can be done 12 bits (0.024%). The system has a data automatically, so that belts can be shut base and graphics edition and a capabil- down to conserve power. ity to download to remotes over the data line. Remotes can scan subremotes. Pump monitoring might include diagnostics, such as electrical cur- A microprocessor-based system, MIC- rent drain, pressure, flow, etc. Energy RECON, is under development and will be shedding can be accomplished. Power released soon. center monitoring can be used to reset breakers remotely or to locate a prob- Transmitton Ltd. lem. Software for summary analysis is Smisby Road included. Ashby-De-la-Zouch England LE6 5UG The Transmitton systems have been 0530-415941 installed in hundreds of deep coal mining operations, internationally. Reliability Technology 150 Plum Industrial Court 4.5.2b Summary Pittsburgh, PA 15239 (412) 325-3121 A summary of the monitoring systems offered by suppliers currently mar- Transmitton Ltd. is also qualified keting in the United States is given in lomanufacture the British MINOS system. table 4-3. TABLE 4-3. - Mine monitoring system summary Aquatrol Conspec Davis Giangarlo Hawker Kidde Siddeley Trunks...... 1 4 1 1 7 2 Outstations per trunk.. 98 128 127 512 16 64 Total input channels 18 1 analog or 40 5 boards per outstation. 16 digital in; 1 digital out. Inputs per outstation: Analog...... <18 1 (16 bit) 8 Digital...... 218 analog 16 (1 bit) 32 Outputs per outstation: Analog...... <6 NAP . NAp Digital...... 26 analog 1 (1 bit) 4 Transmission distance.. 31 mi 44,000 ft 20 mi Cost, thousand dollars: Central station...... 40-75 25 100 15-23 NA Outstation...... 5-10 0.25 25 53-7 NA MSA Mundix Cbutokompu R.F.L. Sangamo Trans- Weston mitton Trunks...... 3 1 llnlimited 1 32 6 Outstations per trunk.. 38 128 32 1 8 28 Total input channels per outstation...... 6241 716 boards1 20 1 8 boards 1 32 1 28 Inputs per outstation: Analog...... 16 Digital ...... 28 analog Outputs per outstation: Analog...... NAP 14 NAP NAP 16 2 Digital...... 4 '8 16 '16 8 28 Transmission distance.. 8 mi 128 mi >6 mi >10 mi 32 mi 10 mi Cost, thousand dollars: Central station...... 25 80 5-100 1.3-1.5 15-100 50-60 Outstation...... 1 3 3.3 0.7 5-15 4-8 NA Not available. NAp Not applicable. 'per board. 4~ypical,40,000 ft maximunn. 74,096 digital and 1,024 analog, *~imes12. 5~ncludesCO monitor. maximum. j~xtendable. 6575 maximum data points.

4.5.3 Sensors in which the airflow causes the vanes or impellers to rotate at a speed propor- While mine monitoring systems can tional to the airflow. Although they are include both environmental and production most commonly used underground as direct sensors, this report focuses on environ- reading, portable instruments, they can mental sensors. Of particular interest also be adapted to a mine monitoring sys- in environmental monitoring are air ve- tem,. However, despite the advantage of locity, methane and carbon monoxide con- meclnanical simplicity, they are suscepti- centration, and respirable dust. ble to dirt and moisture concentration. Vorttex-shedding anemometers, on the other Air velocity can be measured by us- hand, have no moving parts and use acous- ing either vane anemometers or acoustic tic signals to measure turbulence caused vortex-shedding anemometers. Vane ane- by the airflow. Both anemometers have mometers are basically mechanical devices the disadvantage that they are fixed point measurements normally made in the suitable for remote, fixed point opera- boundary layer near the roof or rib and tion underground and that provide an therefore do not necessarily represent a electrical output that can be interfaced true measure of the average airflow. with standard telemetry equipment will be discussed. Methane and carbon monoxide concentration can be measured by either heat of 4.5.3a Air Velocity Sensors combustion (ie, catalytic combustion) or infrared absorption techniques. For There are two basic types of air carbon monoxide, electrochemical analysis velocity sensors that are applicable to is also commonly used. The heat-of- underground mining: rotating vane ane- combustion sensor is based on the princi- mometers and acoustic vortex-shedding ple that catalytic oxidation (i.e., burn- anemometers. ing) of a combustible gas such as methane will result in a temperature rise in the The rotating vane anemometers are sensor in proportion to the gas concen- mechanical devices with vanes or im- trations. This technique is widely used pellers that are rotated or turned by the in the methane monitors required for face air flowing through the anemometer. The equipment in this country. The infrared better instruments use ball bearings that sensors are based on the fact that dif- reduce the turning friction of the main ferent gases have different infrared en- shaft on which the vanes are mounted to ergy absorption characteristics. These improve the accuracy at low air veloc- sensors have been in use in South African ities. Portable (typically hand held) and German mines for a number of years. vane anemometers have been a standard air Electrochemical analyzers measure the velocity measuring instrument in under- carbon monoxide concentration by chemical ground mines for a number of years. The reaction with electrodes that are im- Davis vane anemometer is probably the mersed in an electrolyte. These sensors most common example of these direct read- have been used recently as part of an ing instruments. Recently there has been early warning belt fire detection system some interest in adopting these in- (that in some cases allowed the use of struments to remote monitoring systems; the beltway for intake air). for example, American Mine Chemical Co. is currently distributing the British Remote monitoring of respirable dust Abbriko anemometer that provides an elec- presents a number of technical difficul- trical pulse count output proportional to ties. Of the various measurement tech- the air velocity. However, while the niques currently in use, the beta- device does have certain advantages be- attenuation and optical devices appear to cause of simplicity of operation, its be the most suitable for integration into susceptibility to excessive dirt and mine monitoring systems. The former uses moisture represents a significant dis- beta radiation to detect dust concentra- advantage. The National Coal Board, ex- tion, i.e., the amount of beta absorption perimenting with such anemometers (such due to the dust deposited on a sample as its BA.1 and BA.2), found that in- plate is proportional to the dust concen- creasing the vane diameter increased the tration. The optical sensors are based torque on the center shaft and thereby on the principle that the dust concentra- reduced the potential of the shaft seiz- tion is proportional to the amount of ing because of dirt accumulation (9). light reflected by the dust-laden air sample. The second category of anemometers, acoustic vortex-shedding, measure air ve- The following sections describe the locity by sensing the frequency at which sensing or measurement techniques for the vortices are shed from a rod placed in four parameters of interest that are most the airstream. The vortices, or eddies applicable to underground mine monitor- in the airstream, are sensed by the ef- ing. That is, only sensors that are fect they have on an acoustic (actually ultrasonic) pulse transmitted through 4.5.3b Methane Sensors them. A typical configuration would consist of a relatively compact package con- There are two primary techniques of taining transmitting and receiving trans- detecting and measuring methane concen- ducers mounted on opposite sides of a tration that are suitable for use in mine small rod and the electronics required to monitoring systems: heat of combustion transmit the data to the appropriate out- and infrared absorption. Of the two, the station or control panel. Since vortex heat of combustion, or catalytic combus- shedding anemometers have no moving tion~, sensors are the most common in this parts, they are particularly well suited country. These sensors detect the pres- for underground mines. However, while ence and concentration of methane by mea- they are less susceptible to contamina- suring the temperature rise of a cata- tion than the vane anemometers, they are lytic element that oxidizes (i.e., burns) also typically more expensive than the the methane at very low temperatures mechanical anemometers. without a flame. The temperature rise in the catalyst is proportional to the meth- It should be pointed out that both ane content of the air surrounding the types of anemometers are fixed point sensor. units and as such have the disadvantage of being able to measure the airflow at There is some difference in the only one point in the airway. This re- technique by which the sensors expose the striction is usually compounded by mount- catalyst to the gas mixture to be mea- ing the unit close to the roof or rib of sured. Some devices rely on diffusion of the airway, i.e., in the boundary layer the gas mixture through a porous metal where changes in the average airflow can- flame arrestor screen. These are often not always be accurately sensed. Al- referred to as "diffusion-head" type sen- though there are empirical methods of sors. Others use mechanical pumps to compensating for this measurement defi- drain air samples across the catalyst. A ciency, they do not always provide the third method, referred to as "sniff and most satisfactory solution. sneeze," alternately draws the sample in and then exhales prior to the next Sam- The two major suppliers of acoustic ple. While the diffusion devices have a anemometry equipment in this country are slower response time they are simpler and J-Tec Associates and Mine Safety Appli- do not rely on mechanical pumps that may ance (MSA). The J-Tec model VA-216B is be affected by dust and moisture. approximately 12 by 7 by 4 inches in size Diffusion-type methane sensors are typi- and can measure air velocity in two cally used in the monitoring and auto- ranges; 50 to 3,000 fpm and 150 to 10,000 matic deenergizing devices required on fpm (22% of full scale). The unit op- face equipment in U.S. coal mines. Al- erates on a 12 to 21 volts dc at a max- though catalytic combustion sensors are imum of 35 mA. While the standard output relatively rugged and simple in opera- is 0 to 5 volts dc, the unit can also tion, they do have (at least in princi- provide 1 to 5 mA or 4 to 20 mA as an ple) a disadvantage in terms of specific- option. Calibration, performed at the ity. That is, the catalyst temperature sensor, is typically recommended at 6- wil.1 rise in the presence of any combus- week intervals. The price of the unit tion gas, not just methane. However, runs between $1,000 and $1,500, including this disadvantage is not always a major output electronics. problem and can be reduced somewhat by operating at a specified temperature or The MSA sonic anemometer can measure selecting a catalyst that favors a air velocities up to 25,000 fpm. The metlhane-oriented chemical reaction. A sensor requires 110 volts ac power (30 w) second, and possibly more important, dis- and produces either 0-1 mA or 4-20 mA advantage is that catalytic sensors are outputs. The list price of the unit is not generally suitable for measuring between $500 and $600. methane concentrations above 5%. The second methane sensing technique proportional to the methane concentra- is based on the absorption, by different tion. Infrared sensors can be used to gases, of different amounts of infrared measure methane concentrations in the en- radiation. In a typical configuration, tire range between 0% and 100%. While infrared energy is passed through a sam- these devices are relatively sensitive ple cell that has windows that do not ab- and specific, they are typically more sorb in the infrared band. Either the complex and expensive than the catalytic sensor is equipped with a reference cell sensors. or the sensor is calibrated by purging the sample cell with nitrogen prior to Table 4-4 summarizes the methane making any measurements. sensors currently available in this country. Although only one infrared sensor An infrared detector, located on is mentioned, it should be noted that the opposite side of the cell, produces several infrared sensors have been de- an electrical signal proportional to veloped in other countries, among them the difference between the reference and the South African SPANAIR and the German the sample. This signal is, in turn, UNOR.

1 TABLE 4-4. - Methane sensors

Company Model Measuring Range, Electrical Power Cost 1 principle % output requirements NA...... 0-99 Digital 110Vac $1,800 Electronics. Catalyst. I 0- 5 1 0-100mV 1 110Vac1 1,100 CEA...... RI550A Infrared. I[ : CSE...... 140 Catalyst. 0- 5 I 1 Dynamat ion...... I 1210EX

...do.... 0- 5

General Monitors... 480

1 ...do .... 1 0- 5 1 0-5 Vdc 1 12-21 V dc I 500-

40008561 Scott Aviation..... 40008015 exa as Analytical... 1930B 1I NA Not available. I~oundedto nearest $100. 4.5.3~ Carbon Monoxide Sensors earlier for methane sensing. That is, the air sample is oxidized in the pres- There are three techniques of car- ence of a catalyst, with the resulting bon monoxide sensing that may be con- temperature rise in the catalyst being sidered suitable for use in mine moni- proportional to the gas concentration. toring systems: electrochemical reac- As mentioned earlier, the basic technique tion, catalytic-combustion, and infrared is nonspecific, and carbon-monoxide-spe- absorption. cif ic catalysts and appropriate filament temperatures are required to reduce the Electrochemical sensors contain a interference of other combustible gases. sensing electrode, a counter electrode, and sometimes a reference electrode in an The infrared technique is also simi- electrolyte (such as sulfuric acid solu- lar t:o that described for methane detection for the Energetic Sciences Ecolyzer tion. The sensor is made selective for 2000). The air to be sampled either is carbon monoxide by modifying the receiver allowed to diffuse into the sensor or is transducer to detect changes in the in- drawn in by a mechanical pump. The car- frared wavelengths that are absorbed by bon monoxide in the air reacts with the carbon monoxide molecules. For a nondis- electrodes, generating an electric signal persive system, the absorption filters proportional to the carbon monoxide con- must be changed, and for the dispersive centration in the air sample. General systems, the refraction grating may have Electric Co. has developed, in conjunc- to be changed. tion with the Bureau of Mines, a fuel cell carbon monoxide sensor that uses a Table 4-5 lists several representa- solid polymer electrolyte. This design, tive carbon monoxide sensor suppliers. of course, has the advantage of not hav- While no infrared carbon monoxide sensors ing a liquid electrolyte that can spill. are listed, at least one is manufactured in South Africa. It is called the The catalytic combustion technique SPANAIR, and it can also be modified for is quite similar to that discussed use as a methane detector.

TABLE 4-5. - Carbon monoxide sensors

Company Model Measuring Range, Electrical Power re- Cost principle PPm output quirements CO-2300 Catalyst...... 0- 300 0-1 mA 117Vac $950 Dynamation...... 110 V ac CO-300 ...do...... 0- 300 mA 925 I 1 12 Vdc]

Energetic Sciencies 4125 Electrochemical 0- 50 0-1 V dc

General Electric... 15ECS6 Fuel cell......

MSA.. 571 Electrochemical ...... 19-60 V dc

Neutronics...... 910 ...do...... NA Not available. 4.5.3d Dust Sensors The second method is piezoelectric sensing. In this type of dust sensor, Although there are many types of particles are drawn through an orifice techniques to measure dust concentrations and deposited on the face of a quartz in mine air, a number of technical diffi- crystal. This crystal is part of an culties limit the availability of dust oscillator whose resonant frequency sensors that would be suitable for use in changes linearly with small changes automatic, remote, mine monitoring sys- in crystal thickness (or mass). As tems. For example, while the Bendix-type particulate mass collects on the crys- personal dust sampler has been used suc- tal face, the frequency decreases. cessfully for a number of years, it is Therefore, the rate of frequency change not amenable to remote monitoring because is proportional to the airborne mass the filters must be manually removed, concentration. weighed, and replaced. Three measurement techniques that might be adopted to re- The third technique is beta attenua- mote monitoring are described below; they tion. In beta attenuation instruments, are optical sensing, piezoelectric sens- the aerosol is drawn through an orifice, ing, and beta attenuation. and particles impact on a suitable sur- f ace. The impact surface is positioned In optical sensors, a beam of light between a beta radiation source and a (from either an incandescent or laser counter. The amount of beta absorption source) is directed into a chamber that recorded by the counter is proportional contains a sample of the dust-laden air. to the dust concentration. The major ex- The intensity or brightness of the light ample of this technique is the GCA high- that is scattered by the dust cloud in concentration dust monitor that GCA de- the chamber is governed by the surface veloped in conjunction with the Bureau of area of the dust particles. The inten- Mines. sity of the reflected light is typically determined by comparison with a portion The major advantage of the GCA dust of the direct light. While the device is monitor over the light-scattering moni- normally manual in operation (the di- tors is that (within certain limits) the rect light is passed through a variable GCA unit measures the mass concentration filter that is adjusted until the inten- independent of the type of dust and par- sity of the direct light equals the re- ticle size distribution. flected light), at least one company manufactures an optical dust monitor with 4.6 Existing Mine Monitoring Systems an electrical output. The Japanese-made Horiba monitor provides an output of 0 to Monitoring systems have been in- 20 mA, but since it requires 110 volts stalled in a limited number of U.S. ac (10 W) , MSHA approval is necessary if coal and metal and nonmetal mines. In it is going to be used in a return air- addition, numerous systems are installed way. Another unit, GCA model RAM-1 dust in foreign countries. In this section, monitor, measures concentrations in the several installations are described; range of 1 to 200 mg/m3, has a 0- to 10- the reasons for their development and volt dc output and runs on 110 volts ac. comments that are relevant to the cen- The cost of this unit is approximately tral issue of monitoring and/or control $6,000. in underground coal mining are given. In cases where the data have been pub- The main disadvantage of this tech- lished and are available, the name of nique is that a direct comparison between the mine is listed. In cases where dust concentrations by this technique and data were obtained from mine person- other methods is possible only when the nel and are not generally available, particle size distribution of the dust in only a letter designation for the mine is the air sample is the same as that used provided. for instrument calibration. 4.6.1 U.S. Undergound Coal Mines off ice computer. Since a communications coordinator is the only one to enter the Mine A data,, it is coded in a uniform fashion.

Coal producer A operates a coal mine In turn, section foremen are able to in support of its steelmaking operations. interrogate the system at any of the A very extensive monitoring and data ac- three underground communication centers quisition system was installed in 1978. (one at base of portal, and one each at The system has production, management, East and West mains). maintenance, and safety components. Spare parts inventory software was In 1978, production was lagging and generated from an existing program used morale was poor. A human relations audit in the mill activity. A detailed, pic- indicated that section foremen and others torial blowup with parts number callout felt isolated and left to fend for them- is available near each section. As a re- selves. Communications were poor. Sup- sult, the inventory status, location, and port to section foremen was perceived as ordering (reorder from vendor, if neces- slow and often ineffectual. sary) can be accomplished quickly underground . Similarly , management can track The system that was installed fo- problems by interrogating the system. cused on improved communication and backup support. It monitors production, pro- Because the bihourly reports are vides maintenance support from a data relatively complete, formal end-of-shift base system, supports underground manage- reports are no longer necessary, and on- ment with improved reporting and communi- going foremen have a current status sheet cation, and enhances safety with tracking on which to base their plans. and followup of unsafe conditions. This mine installed the cable for At present, phone reports are re- the system, purchased modems to enable quired from each section foreman every 2 commi~nication of the data over phone hours (soon to become every hour when a lines, and then leased the remainder of leaky coaxial radio link system becomes the system, including dedicated phone operational). The status reports are re- liners to the computer facility, line ceived by an operator who codes the printers, CRT displays, etc. status, including mechanical problems and repair effort underway, onto a data base Software was developed in-house, al- reporting system. These reports include though some of it already existed, since it .was in use in the associated steel Conditions on section. mill. Software development times were estimated to be When loading of coal started. Production system.... 14 man-months. Mechanical delays. General underground.. 18 man-months. Maintenance...... Existed. Nature of delay. Safety...... 12 man-months.

Start-stop time. Surprisingly, one of the most trou- blesome links in the system has been the Mechanical problems are keyed to ma- leased commercial phone lines (2,400 chine and location. Information is coded baud) used to telemeter data to the cen- by a communications coordinator, then tral computer facility. There have been telemetered over phone lines to a central instances of outages for days. Mine B of worked out panels, eliminating the need for a 4-hour inspection mandated by Coal producer B has a monitoring the State. system that uses equipment built by Larse Corp. of Palo Alto, CA. It is ahard- Extensions of this system might in- wired, time-domain multiplexed system clude ventilation control. In that case, (channels interrogated sequentially in a variable-speed synchronous motor drive time), designed originally for building, on their fan might be used to reduce process control, or energy monitoring. energy demand when the full output is not The producer uses the system for belt needed. At present, 1,600 hp is drawn monitoring and for carbon monoxide and for ventilation. Original plans called temperature monitoring on the slope (the for some airflow and methane monitoring, mine has a propane preheat system). but this step was deferred as "too expen-

s ive with little payback. " The history of the system is that in 1975, local management personnel had de- The monitoring system is maintained cided to upgrade the telephone system to by one man, who also maintains the tele- a dial-phone system. Their chief elec- phone system (which requires much more trical engineer urged simultaneous in- time than maintaining the monitoring stallation of a monitoring capability, system). perhaps integrated with the new phone system. He obtained mine managers' ap- Mine C proval, and invested approximately one- third of his time during the next 3 Operator C has several mines that years selecting, purchasing, installing, have very gassy seams and heavy over- and testing the system. He was assisted burden with difficult roof control prob- underground with cable stringing and lems. As a result, personnel at this other installation tasks about one-sixth mine have received a variance from MSHA of the time. allowing the use of beltways as an inlet aircourse. The Larse system that was purchased is capable of transmitting only binary They have 5 years of experience with data. The sequence time is 3 sec per carbon monoxide monitors, using Energetic station. Transmission is over a spare Sciences sensors. The current Energetic twisted pair of conductors in the mine Sciences monitors that are purchased have phone cable. An independent electronics two level alarms and a built-in battery and manufacturing firm developed and fab- pack for uninterruptable power supply. ricted solid-state interface circuitry designed to convert voltages on control The telemetry system is an S.R. switch terminals to logic levels compati- Smith system that transmits digital in- ble with the Larse system. The converter formation only and necessitates a dual was optically coupled so that belt se- threshold modification to the Ecolyzer. quencer circuitry is uncoupled from the False alarms are generated with the monitor, and the converter has no moving Ecolyzer as the result of power interait- parts, enhancing reliability. A printer tencies, a prime factor in the insistence is used to generate hard copy of alarm or on an uninterruptible battery supply. To status change. A light panel is also enhance reliability, redundant PDP-1114 used to display status. computers have been installed to analyze and display data. Maintenance by DEC has Mine personnel are evaluting the de- sometimes been slow, although the system sirability of installing a J-Tec velocity has been completely down only once in the and methane system. Their most likely last 2 years, thanks primarily to redun- application would be a continuous monitor dant equipment. Plans include staffing up to one two mines are equipped with belt fire full-time engineer per mine for the moni- monitoring equipment and two more are be- toring system. Although the system ini- ing outfitted. The two that are present- t ially gave frequency "nuisance" alarms, ly on-line have been operating for about those problems have largely been solved, 6 months. The system consists of Ecolyz- with the occasional exception of false er carbon monoxide sensors, with up to 40 alarms associated with the monthly cali- monitors per mine, a Giangarlo transmis- bration procedure. They also conduct a sion system, and Niagra Scientific compu- weekly inspection. Where alarms are dis- tational and display equipment. There is played at the surface, the appropriate no maintenance contract. The software site is notified by telephone. was provided by Giangarlo. The system scans stations at a rate of about 1 per Future plans include monitoring of second. The cabling for the system is methane and airflow in returns. They military surplus wire that is four- have a methane drainage research project conductor twisted No. 19 wire with steel for which they have currently purchased armor, which mine personnel purchased in- methane and airflow monitors. During a expensively. It has been found that the 6-week period in the winter of 1981, they digital (frequency shift) signals can be lost 10 shifts of longwall production as transmitted up to about 3 miles with vir- a result of gas outs, shutdowns that are tually no problems. The alarm algorithm sometimes mine wide and are the motiva- at present is simply a level exceedance tion for their ventilation monitoring and alarm. There have been four cable fail- control plans. ures in the last 6 months, two failed open and two failed shorted, owing to ac- Adjustment and deployment of the cidents with large boulders on the belt. monitoring system hardware, including In the case of cables failing open, the sensors, is a nuisance factor. There system continued to operate up to the ca- have also been incidents of either will- ble break, and in the case of cabling ful or careless destruction of equipment, failing shorted, the entire system was particularly sensors. faulted until repaired.

They also monitor bearing tempera- It is estimated that maintenance ture and water gage on their main ven- of th.e system requires about two man- tilation fans, using a FSK audio band shifts per week, including daily, week- telemetry scheme. ly, and monthly inspections. The daily inspe,ction is a physical inspection by The software for the S.R. Smith sys- the fire boss, the weekly inspection in- tem was written by a software specialist. volves electrical tests, and the monthly The costs for software were viewed as inspe.ction involves span calibration. substantial. The maintenance effort was estimated to be alpproximately one-half inspections Mine D and calibrations and one-half repair functions. Coal producer D has made a very substantial commitment to its mine-wide Ac power tends to be unreliable and monitoring, data acquisition, and con- intermittent. As a result, a gel-cell trol. Its mines are deep, with typically power has been installed for each sensor more than 2,000-foot overburden, are very with a 48-hour capacity and continuous gassy, and have difficult roof control trick.le charge. In the event of inadver- problems. As a result, the producer has tent disconnect and resultant battery received permission to use the belt pas- discharge, the Ecolyzer indicates a false sageway for inlet air, provided that alarm. carbon monoxide is monitored. Currently All four systems were expected to be Ventilation monitoring at 11 operating by 1982. Following completion stations. of this carbon monoxide fire monitoring system, the system will be extended to Fan monitoring. monitor belt operation. In the No. 3 mine, there are 25 belts, each typically Trapped Miner-Roof Fall Detection 4,000 feet long. The intent of the belt monitoring is to display remotely infor- The trapped miner system was origi- mation about which belts are down and nally installed several years ago as a possibly, diagnostics as to failure mode. Bureau-funded research project . Six commercial, 40-Hz resonance, moving coil Because the seam being mined is ex- geophones are implanted about 2,000 feet tremely gassy, the required amount of air apart in 50-f t-deep holes backfilled is very high. This demand, combined with with sand. Their seismic output is fed the extreme depth, results in very high to a Texas Instruments 980A computer that water gage and very high ventilation computes the epicenter of any event ob- costs. As a result, variable pitch ven- served by three or more geophones. The tilation fans have been installed, and software package includes graphics that methane and airflow will be monitored in plot the trapped miner-roof fall location the returns and the fan pitch modified with a triangle if three geophones accordingly to reduce ventilation costs. received the signal, a square if four When a 2,000-hp fan was increased to a were activated, and an asterisk if five larger 7,000-hp variable-pitch fan, the or more sensed the disturbance. The co- power costs increased $1,900 per day at ordinates and computed confidence margin that mine. Plans also exist to monitor (error) are printed. Triangulation in the temperature and vibration of fan the southern mine sections where the bearings. equipment is located is to within 50 to 100 feet. A disturbance count is also In addition, the producer is also recorded. The trapped miner equipment is automating its billing, inventory con- all located on the surface. trol, and maintenance functions, such as maintenance history, equipment inventory, Ventilation Monitoring lubrication histories, preventive maintenance, etc., as well as automating some Mine personnel at operation E were mapping and plotter routines. These com- interested in upgrading mine technology putational facilities will use their own and therefore were receptive to a Bureau computers and programs and not piggyback of Mines request for a cooperative devel- on the fire monitoring system. opment. An electrical engineer from research was assigned to design and super- Other monitoring plans include vise the fabrication and installation of production tonnage monitoring, by sec- a ventilation monitoring (methane, carbon tion and shift, as well as power cen- monoxide, air velocity, temperature) sys- ter monitoring, particularly on longwall tem and to assist in the development of a sections. trapped miner location system. The telemetry system he designed is an audio Mine E frequency, FSK serial transmission system. It has a capacity for 16 stations Mine monitoring at operation E has and a capability for up to eight analog the following three distinct functions: inputs at each station (0-5 volts dc). Data are telemetered in an audio band. Trapped miner location-roof fall The system is powered with a converter monitoring. that uses power from the trolley wire, converting -345 volts dc trolley power to converter was that there are massive 13 volts dc. At each station this 13- transients on the trolley wire that the volt power is again converted to +15 and converter could not handle. The solu- 25 for logic and control circuits. Meth- tion was to use a high wattage voltage ane is detected by mounting a Bacharach divider with a zener limit, then dc-to- cell directly on top of the explosion- dc convert the voltage-divided, filtered proof container that houses the elec- dc. tronics. Access to the box is via multi- pin Amphenol environmental connectors. The operation has asked for extension of the ventilation monitoring system Carbon monoxide is detected with an to the north to cover the other half of Ecolyzer 4000 device, from which the 110- the mdne. However, the research staff is volt converter has been removed. Air now committed to other projects. velocity is measured with a J-Tec anemometer, mounted on a 3-ft-long pole near All maintenance and operation is the center of the passageway. Flow cali- perf olrmed in-house. Spare boards are bration is accomplished with a Davis stock.ed for the TI 980 and the computer anemometer. is nlaintained by swapping out defective boardls. Normal maintenance and record The processing display package keeping takes about 45 min per day. The prints hourly summaries of the low read- system costs a little over $100,000. In- ing, high reading, and hourly average at dividual stations cost $2,000 to $2,500. each station. The biggest maintenance cost, by far, is line repair. Manual cross-checks of the system by the fire boss on his round are used to Fan llonitoring verify system accuracy and reliability. Each station is interrogated electroni- The primary ventilation fans are cally every 5 min. The system has a continuously monitored. Local system dc capacity for 16 stations and a maximum power and fan head, in inches of water, cycle rate of 2.5 seconds per station. are reported hourly with a low, average, and high reading. Alarm status is, of Telemetry cables (unshielded twisted course, immediately printed. pairs) are strung adjacent to the trolley wires. The operation is gradually relo- Mine F cating these cables, since the most frequent failure mode for the system is a Operator F has three mines that loss of telemetry because of a cable cut share a power distribution system and by a derailed trolley' pantograph. Be- that have very substantial monitoring in- cause of line losses, the sensors must be strurnentation. Mine personnel have also within 500 feet of the power supply and begun development of a data base acquisi- telemetry system. tion system. The system consists of several layers, developed sequentially. Data are processed at the surface (thresholding , time averaging, high and The initial installation was a sur- low peak) and stored on a Phillips cas- face system for fans and circuit break- sette. The cassettes can be processed ers. Later, haulage monitoring and un- with a print routine to generate hard derground fire detection were added. A COPY large data base supervisory control systlem is now being installed that will A problem encountered during devel- be used to upgrade the fan monitoring opment of the wire power-to-12-volt dc to include vibration and temperature monitoring so as to (1) anticipate failing given to power center control and ure, (2) detect smoldering fires by us- load shedding. At present, overall power ing carbon monoxide monitors, (3) con- drain data are provided to dispatchers, trol utility costs by power shedding when so that they can shed "unnecessary" or desirable, (4) extend haulage monitor- lower priority loads ; however, sheddi.ng ing and control, and/or (5) acquire and rarely happens because of production store maintenance data on machines for pressures and the overwhelming complexity preventive maintenance and failure of the problem. Effective control re- analysis. quires mine-wide information, analysis, and synthesis of the data. Quotations for this system are being solicited from mine monitoring system The operation buys power from the vendors and particularly from process local utility at 69 kV, then distributes control and energy management equipment and transforms the power for the opera- vendors. A brief summary of the equip- tions. Power billing is in proportion ment to date follows. to the highest 30-min average, using sequential time windows (not a floating Surface System window).

The surface system monitors ventila- Methane Monitoring tion fans and the status of circuit breakers. At present, there are 13 fans Methane is continuously monitored in in the complex and 28 monitoring substa- one abandoned area. tions. The system was developed in-house in 1973 and uses a hard-wired FSK tech- Mine G nique, with a 40-channel capac.ity. Operator G has a Motorola Intract Underground Haulage and Fire Detection 2000, UHF high-band transmitter-receiver system that is used at three mines. Per- At present there are about six sec- sonnel at this mine monitor ventilation tions of instrumented haulage. A CRT fan operation, sensing water gage, and display at the dispatcher indicates the measuring bearing temperature and vibra- number of available empty cars at each tion, In each instance, the alarm level station, an estimated time of depletion exceedance is the only data transmitted. of cars (a function of whether the mine In the case of circuit breakers, they is cutting), the number of loaded cars, a have the capability to reset, trip, and count of loaded cars for the shift, and monitor each of these. whether the belt is running. Each mine typically has several fans Heat sensor fire detection outputs and perhaps 20 circuit breakers physical- are also displayed. Data acquisition ly distributed over the countryside, per- is accomplished with a Westinghouse haps up to 4 or 5 miles distant from the neumalogic system. A deluge system is portal. Electrical power is either 7,200 controlled by the output, volts ac three-phase or 300-volt dc trolley power. In the case of circuit break- Power Monitoring ers, the system is used primarily for control and for resetting after interrup- The three mines have a monthly util- tions. They reset as a test, and, if ity bill of several hundred thousand dol- there is a second interruption, they dis- lars. As a result, attention is being patch a man to the site. Since fan monitoring is required by law, the system c. Full cars. saves personnel assignment to monitor the remote fans. d. Empty--full conversions.

At the central station, located in 3. How many cars available at the the maintenance shop, data are displayed dump site? on a console with eight- status lights, designating the presence or absence of The ,goal was to reduce the "no empty" de- threshold exceedance of any one of eight lays at the section. sensed variables at a site. There is also a hard-copy printout on a TI printer The dispatcher has voice communica- of twice-a-day status, plus alarms. One- tion with the locomotive engineer and the third spares are maintained, and Motorola loading supervisor at each section. De- gives a 3-to-8-week turnaround time for velopment of the design began with the repairs. The system has been on-line for following constraints: 15 months, with many initial problems that have evidently been worked out. 1. Commercial sensors to be used, perhaps repackaged. Two fully qualified technicians with FCC licenses are on the staff and 2. Existing phone lines to be used a third is being sought. Testing and (Gaitronics) [but not same wires, i.e., qualification certification is contracted use phone-quality wiring. Cable is fig- out. ure 8, wire-supported, with 40 conductors in pairs.]. Monitoring of this sort dates to 1969 when it began with a FEMCO hardware The sensors tested were system. In 1975, an intermediate radio system was added and, later, the Intract 1. Infrared photocell (car count). 2000. 2. In-track magnetic proximity The parent research organization has (count) . also experimented with the feasibility of monitoring cars, as well as production 3. Sonic level (full-empty). activity, on each section, to improve the efficiency of the dispatch of cars to 4. Current sensor at load center. operating sections. This was a test of instrumentation and technique, using one a. Off section. They measured b. Tramming 1. Is the section operating? c. Cutting a. Continuous miner off. 5. Traffic switch positions. b. Continuous miner tramming. All data were telemetered to the Continuous miner cutting. dispatcher. There are local displays for debugging purposes. Intel microproces- 2. At the section, how many-- sors were used in remote stations.

a. Cars at ramp. A test of the sensing system was conducted by stationing an observer to b. Empty cars waiting. note visually car passage, operating time, empty-full status, and switch posi- coordination will be intensified. " In- tion. The test results were tangibles" (safety, morale, health, labor resistance, sabotage, etc.) are hard to Visual Automatic Error evaluate.

Direction...... 582 599 3% A "smart sensor" standalone is being Empty-full ..... 230 233 1% considered that-- Operating time.....min.. 820 813 1. Obtains power off rail line. Switch position 49 49 0 2. Senses a parameter, converts It was concluded that sensing reliability data to a secure format. was good and quite adequate. 3. Transmits wireless. The most difficult problems were (1) the deployment-redeployment of sensors, Passive (unpowered) sensors are used and (2) cost-complexity of the system. wherever possible, and sensors are minimized (more manual input). It was concluded that this type of rail haulage monitoring is technically Power Monitoring feasible; however, the economic viabil- ity is probabilistic. There is econom- Billing of power used by energy- ic payback only if all sections are intensive industrial users is based on a instrumented, since intersection co- base rate plus a peak load factor. Mine ordination is the goal. The operator G's local utility expects to go to a peak opted for a computer simulation at this factor based on the highest 5-min aver- point to evaluate the economics, using age, perhaps highest floating 5-min aver- a modified version of the Penn State age. Although the potential savings are RailSim program. The results indicated very substantial, an automatic power substantial incremental improvement in management system is clearly required to productivity, but since the operation react within 5-min windows. is market limited, the economics for such a system were not quite attractive; A very ambitious computerized main- i.e., it cannot easily sell more coal per tenance management program has also been year and cannot capitalize on the poten- begun. There seems to be a likelihood tial to run less days per year because that haulage and ventilation monitor- of large capital costs and institutional ing and/or control will eventually be factors. attempted.

A simpler less costly system might Mine H, Federal NO. 2 be viable. For example, a system that reported Sensors for carbon monoxide and methane were placed so as to compare 1. Whether the section is operating methane concentrations entering and leav- (power center). ing each section. Differential pressures i were also measured to highlight ventila- 2. What the car count is at the tion problems owing to partial blockages, dump site. etc. Temperature, humidity, and air velocity were also measured at dozens of 3. Other data manually input by the sensor stations. Computer control was dispatcher. performed at West Virginia University. These early tests served to prove that Since use of longwall sections is the task of underground monitoring was expected soon, problems with haulage technologically feasible (2). More recently, a similar system has One such system has been success- been used to test the concept of ventila- fully employed in the Bethlehem Mines, tion control (1). Ventilation param- Marianna No. 58, located in Marianna, Pa. eters, including methane, carbon monox- This system consists of MSA methane sen- ide, temperature, humidity, airflow, and sors located at 500-foot intervals in the differential pressure, were measured. airway containing the methane drainage Ventilation regulators (louver door de- pipe. The output from these intrinsical- sign) were operated electronically, and ly safe sensors is transmitted to a con- the resultant ventilation redistribution trol panel located in a nearby fresh air was monitored. entry. Also located in the fresh air entry is a small (1-05-cfm) air compres- Mine I sor that supplies air through PVC tubing strapped to the drainage pipe, to the Drainage of methane in advance of pneumatically actuated shutoff valves lo- mining is an effective way of minimiz- cated at each borehole. The valves are ing methane content at the working face. spring loaded and held open by the air Since most coal mining countries have from the compressor. enacted safety regulations that require that face equipment be shut down if the The system can also incorporate methane content in the air reaches a a "receiving" station (located above predetermined level, methane drainage ground) that contains meters that in- has production as well as safety bene- dica.te the methane content measured by fits. Because methane liberation in- the sensors and recorders that provide a creases with rate of coal production, continuous log of the sensor output. methane drainage is more desirable in highly mechanized longwall operations In the event of a power failure, the where production rates are relatively compressor would cease to function, the high. As a result, methane drainage is air pressure in the PVC tubing (normally used extensively in Europe where longwall 55 psig) would drop, and the valves would mining has become very common. In 1975, close. If the methane content in the approximately 7.5 billion cubic feet of airway containing the drainage pipe ex- methane was drained in Polish mines, ceeds 1% (due to a leak in the pipe), the and over 21 billion cubic feet were PVC tubing is vented by solenoids located drained from mines in the Federal Repub- on t:he control panel and the valves again lic of Germany (I). Recently, methane shut down the methane flow. In addition, drainage has also become more important if a roof fall ruptures the drainage as the production rates in U.S. mines pipe, it will also rupture the other PVC have increased. tubing that is strapped to the top of the pipe, automatically dropping the pressure Because of the inherent design that and closing the valves. Finally, if a roof falls, bottom heaving, etc., may sensor fails to operate or a cable is rupture the methane drainage piping, severed, the solenoids will vent the PVC the Bureau of Mines has specified tubing and again close the borehole that drainage systems be equipped with valves. a "fail-safe" monitoring and control system (11). Basically, the system References 10 and 18 discuss this should be able to shut off the flow of system in more detail. methane into the drainage pipe in the event of unsafe conditions such as a A summary of the monitoring systems power failure or break in the drainage reviewed is presented in table 4-6. piping. TABLE 4-6. - Summary of monitoring systems surveyed in U.S. underground coal mines

A B C Function...... Production, maintenance, Belt monitoring...... Belt fire monitor, communication. equipment status. Parameters monitored. Input from section Belt operation, belt CO, fan temperature and foremen. sequencing, motor tem- pressure, degasifica- perature and power, CO. tion pumps, fire sup- pression operation. Size: Remote stations.... Input per station.. lo...... 16 maximum. Telemetry: Cables...... 2- and 4-conductor...... 2-conductor and multiconductor, shielded. Format ...... Voice and digital...... Digital...... Digital. Data display...... Line printer, CRT's above Line printer, light panel. Line printer, CRT. and below ground. Alarm...... NO...... Yes...... 2-leve 1. Year installed...... 1978...... 1978...... 1978. Comments...... Production reports, man- Planned expansion--air Allowed 75.326 power planning. velocity, CH4 monitoring. variance. D E- F Function...... Belt fire monitor...... Environmental, fan opera- Fan operation, haulage, tion, roof falls. fire, environmental. Parameters monitored. CO...... CO, CH4, air velocity, fan Fan operation, haulage, power and pressure, seis- heat-C0, CH4. mic activity, battery voltage. Size: Remote stations.... 13...... ll...... 26. Input per station.. I...... 4...... 16 maximum. Telemetry: I Cables...... 4-conductor, shielded..... 2- and 4-conductor, ~ shielded. Format...... Digital...... Digital...... Digital. Data display...... Line printer...... Line printer, plotter, Line printer, CRT, CRT, light panel. light panel. Alarm...... At station and aboveground Yes...... Yes. Year installed...... 1981...... 1974...... 1978. Comments...... Allowed 75.326 variance, Result of cooperative Planned expansion--fan planned expansion--belt agreement with Bureau of temperature, vibra- monitor, ventilation Mines. tion, maintenance monitor. data. G H I Function...... Fan operation ...... Environmental monitoring.. Methane drainage. Parameters monitored. Fan operation, tempera- CH4, CO, temperature, rel- CH4. ture, pressure, ative humidity, airflow, vibration. differential pressure. Size: Remote stations.... lo...... 12...... >4. Input per station.. 8...... 10 to 20...... 1. Telemetry : Cables...... Radio link...... 2-conductor...... 4-conductor. Format...... FM...... Digital...... Analog. Data display...... Line printer, light panel. Mine maps, CRT, teletype.. Strip chart, meter. Alarm...... Yes...... 2-level...... 2-level. Year installed...... 1979...... 1972...... 1977. Comments...... Had prototype haulage mon- WVU experiment, Bureau of Controls drainage itor, planned expansion-- Mines sponsored. valves, result of maintenance data. Bureau of Mines 1 Research. NA Not available.

NOTE.--Alphabetic designators are those used for mine designations in text. 4.6.2 U.S. Underground Metal-Nonmetal is anticipated. An example with rapid Mines payback is automatic measurement of air quality following a large explosive shot. Mine J At present, a rescue team is dispatched to certify the work areas. The result is Although mine J is not a coal mine, a 3- or 4-hour mine-wide shutdown, which its physical layout and mining technique is, of course, expensive. are very coal-like. It is a very extensive, single-level, room and pillar mine 4.6.3 Foreign Mines that extracts about 5 million tons per year, working about 7 feet of a 9-foot seam that is 1,200 feet deep. The mine is classified gassy because of the pres- As in many countries, mine monitor- ence of oil shale above and below the ing in Canada has become more important seam. However, it is allowed use of the in recent years. The Canadian Mining Re- beltway for fresh air, since metal- search Laboratories (CANMET) has been nonmetal mines are governed by 30 CFR, workwing on carbon monoxide and methane Part 57, which is less restrictive than moni-toring in western Canada since 1976. the sections governing coal. One such monitoring system, which uses an e1ec:trochemical carbon monoxide analyzer, Up to 10 continuous miner sections was installed in a Kaiser Resources mine and a longwall are operated. Underground to detect mine heating. Air samples were equipment is electric, with a combination drawn through 112-inch OD polyethelene of rail and belt haulage. tubing from distances up to 7,000 feet (5). In 1978, this system detected a A very satisfactory 50-station haul- sigrlif icant rise in the carbon monoxide age monitoring system has been installed, levels in one return, indicating the po- and an additional system is on or- tential onset of heating. This early in- der. There is about 20 miles of belt dication of heating was credited with conveyors. allowing the mine to alleviate the situation without interrupting the mining The system, which was built by Aqua- schedule . trol Corp., monitors belt functions such as belt slip, plug up, sequencing, align- CANMET began working on methane mon- ment, etc. itoring in the coal mines in western Can- ada in 1977. This work centered around Mine K the use of remote methane analyzers, again by drawing air samples througfi Operator K operates a multilevel polyethelene tubing. In one mine with a copper mine, and has an ambitious load- history of sudden gas bursts, the system shedding program underway. The haulage suc~zessfullydocumented the sudden meth- is electric-powered track and belt. Face ane liberations (8).- operation is with diesel-powered trackless vehicles. Sump pumps run up to More recently, the Cape Breton De- 5,000 hp. The utility bill is based on a velopment Corp. has installed a computer- 15-min peak load factor, which is hoped based mine monitoring system in its coal to be reduced greatly by load shedding. mine in Nova Scotia (6). The system, The hardware and telemetry will be pur- which monitors methane concentrations, chased from Harris Co. Enlargement to a air velocities, air pressures, fan vibra- mine-wide supervisory control and data tion, machine temperatures, and methane acquisition system, including airflow, pump pressure, was supplied by Transmit - perhaps production monitoring data, etc., ton Ltd. Poland interest in methane monitoring and control is not great. The Swedish mines do As is true for much of Europe, the use diesels, however, and an effort is Polish coal mining regulations consider underway to monitor carbon monoxide, continuous methane monitoring in the nitrogen dioxide, etc. In addition, some return airways with automatic deener- work has been done on the development of gizing as an adequate alternative to automatic air regulation. Because meth- individual monitoring on each piece ane liberation is not a problem in Swed- of face equipment (as is done in the ish mines, mine air regulation, which United States). Furthermore, the methane would be based on the number of diesels threshold values permitted by the regu- operating and on their location, is cur- lations are also increased in mines where rently being studied (19).- continuous monitoring and automatic deenergizing are used (16). As discussed U.S.S.R. earlier, such regulations tend to encourage the use of remote mine monitoring Automatic monitoring and control of systems. mine ventilation systems has been studied in the U.S.S.R. for a number of years. The Polish Research and Development This work has resulted in the development Center for Mining Mechanization, Electro- of an automatic ventilation monitoring technics and Automation Sys tems (EMAG) and control system called ATMOS. This has been working on ventilation monitor- computer-based system is reportedly (14) ing and control systems for Polish coal able to monitor ventilation mines for a number of years. The methane (such as methane concentrat ion, airflow, monitoring systems currently consist of etc.), calculate the required airflows, remote sensors, telemetering equipment, and provide the system operator with in- and a miniprocessor, located in a central formation on the appropriate fan and reg- station that receives and analyzes the ulator settings. Ventilation corrections data. The system has the capability of are made on a weekly basis. automatically switching off electric power if the methane concentrations exceed The system has been operationally the specified level. The system also tested in two mines, and the Ministry of maintains permanent records of warnings Coal Mining is currently in the process and alarms and provides summary reports of commercial development of the ATMOS on methane liberation cycles, etc. system.

For fire monitoring, EMAG has also United Kingdom developed a carbon monoxide monitoring system based on a catalytic sensor and an The development and use of remote ionization fume sensor. The system has mine monitoring systems is probably more been tested, experimentally, in Polish advanced in the United Kingdom than in coal mines. any other country, apparently for two reasons. EMAG has also worked on developing automatically controlled air regulators The first is that British mining for coal mines. The regulator, which regulations tend to encourage the use of has pneumatically or hydraulically actu- such systems. For example, in contrast ated vanes, is intended to become part of with U.S. regulations requiring that an overall mine monitoring and control methane monitoring devices be installed system. on each piece of face equipment that can deenergize the equipment once the estab- Sweden lished methane threshold is exceeded, British regulations permit monitoring of Since most of the mining in Swe- the return airways for methane if the den is metal mining in nongassy mines, data are transmitted to a central control station that can remotely deenergize the samples are drawn through tubes and ana- affected equipment. lyzed by using a gas analyzer located in a surface lab facility. In the latter, The second, and probably the more the output of the transducers is fed to important reason, is that the British outstations that encode and transmit the coal industry is nationalized and is sup- data to the surface via a communications ported by a centralized research organi- cable. In either case, the environmental zation (the National Coal Board's Mining data (methane, oxygen, carbon monoxide Research and Development Establishment-- levels, airflow, differential pressure, MRDE). This arrangement has greatly fa- etc.) are analyzed, stored, and displayed cilitated the development, testing, and on video monitors located on the central implementation of mine monitoring systems control panel. The displays and hard- in the United Kingdom. copy reports can consist of warnings, alarms, actual values, or graphs of long- In the 19701s, the MRDE focused its term trends (9). As of 1980, there were attention on developing a universal moni- approximately~twosuch systems either in toring and control system that could be operation or scheduled for installation used throughout the coal mining industry. The system, called MINOS (for Mine Opera- ting System), is based on a common core Development of a system for moni- of equipment that consists of a control toring face equipment performance began console, central computer(s), and periph- in 1977. One version of the system, erals. The application software is also called FIDO (Face Information Digested the result of MRDE development. The mon- On-line) was installed and tested in four itoring systems are supplied to the mine colllieries by 1980. The National Coal by several independent companies that Board plans to install the system in an are free to market a variety of trans- additional 24 collieries that have ap- ducers, data transmission equipment, and proximately 100 active coal faces (20). accessories. The concept of a universal Although the system originally monitored computer-based operating system has per- only face equipment operations, the NCB mitted the MRDE to achieve certain econo- plans to expand the system to provide mies in the development of the system and data on such parameters as roof height, tends to reduce interface problems. pick force , and equipment orienta- tion, and eventually to permit automatic The applications of the MINOS moni- control of such equipment as longwall toring/control systems can be divided in- sheisrers. to the following six basic categories: Monitoring and control of under- 1. Ventilation monitoring. ground coal conveying systems is relatively advanced in the United Kingdom, 2. Coal face monitoring. with the first system in operation in 1972. The systems provide stop-start 3. Coal clearance monitoring. logic sequencing in addition to sensing of such parameters as bearing tempera- 4. Coal conveying monitoring. tures, blocked chutes, motor operation, etc. As of 1980, there were approximate- 5. Fired plant monitoring. ly 30 such systems in operation in the United Kingdom (20).- 6. Preparation plant monitoring. Monitoring and control of coal Ventilation monitoring in the United preparation plant operations (such as Kingdom is currently being accomplished conveying, reagent mixing, etc. ) is a via tube bundle air sampling as well as relatively new application for the MINOS telemetering of data from electromechan- system. The system began development ical transducers. In the former, air testing in the Lea Hall colliery in 1978. A decision on expanding the use of the matching and (2) the manipulation, pres- system will depend on the results of this entation, and storage of large amounts of inplant demonstration. monitoring data.

It should be pointed out that mine South Africa monitoring systems based on the MINOS concept are currently being manufactured Remote automatic detection of un- in the United States. derground mine fires is a major concern for South African mining companies. This Germany is particularly true for the deep level gold mines because of the large amount In recent years, remote monitoring of timber required for roof support in of methane and carbon monoxide has re- these mines. Instances of spontaneous ceived increased attention in German coal combustion in South African coal mines mines. One reason is that the German have also been reported in recent years. Federal Regulations on mine health and For example, between 1968 and 1973 more safety make such systems desirable and, than 23 mine fires occurred in one South in some cases, necessary. For example, African mining district. Approximately the German regulations permit higher 65% of these were attributed to spontane- methane threshold values if constant mon- ous combustion (11). itoring is carried out by permanently installed recording instruments that can Two basic approaches have been used telemeter the data to a remote control in remote monitoring for underground mine center that can automatically deenergize fires. In coal mines, an infrared gas the electrical face equipment (16). An- analyzer drawing air samples through other example is the German requirement polyethelene tubes has been used to sense for automatic recording of carbon monox- carbon monoxide levels (1-1) , and a corn- ide levels along all belt entries. bination of infrared gas analyzers and ionization chamber detectors has been It has been estimated that as many used in the underground gold mines (23). as 1,400 methane and 1,200 carbon mon- In the latter case, the electrical zg- oxide measuring devices were in use in nals from the transducers were tele- the Ruhr district in 1978. Most of these metered to a control room located above provided remote transmission of the mea- ground. In the control room, data (car- surement data to a central control sta- bon monoxide level for the gas analyzer tion. In addition to the methane and and ionization level for the combustion carbon monoxide sensors, some 500 fixed- and particle detector) are recorded in point air velocity sensors were also es- analog form on continuous logs. In addi- timated to be operating in Ruhr district tion, the system has the capacity to mines as of 1978. initiate alarms if specified levels are exceeded. In addition, investigations have been conducted in Germany into the use of Although some difficulties were en- minicomputers as well as microcomputers countered with the ancillary equipment to receive and process the data from the (such as recorders) in the tube system remote sensors. The primary purposes are and dirt and condensation in the telem- (1) the reduction of false alarms through etry system, both have proven effective trend identification and signature in detecting mine fires. REFERENCES

1. Aldridge, M. D., and R. S. Nutter. 10. Irani,M. C.,F. F. Kapsch, P. W. An Experimental Ventilation Control Sys- Jeran, and S. J. Pepperney. A Fail-Safe tem. Proc. 2d Internat. Mine Ventila- Control System for a Mine Methane Pipe- tion Cong., Nov. 4-8, 1979, Reno, Nev., line. BuMines RI 8424, 1980, 11 pp. pp. 230-238. 1IL. Joubert, F. E., I. F. Buchan, and 2. Aldridge, M. D., N. S. Smith, J. D. R. Beukes. Report on Carbon Monox- R. E. Swartwout, and D. T. Worrell. Con- ide Monitoring System for the Early De- clusions From the WVU Monitoring Experi- tection of Incipient Fires in Mines. J. ments. Pro;. 2d WVU Conf. on Coal Mine Mine Ventilation Soc. South Africa, v. Electrotechnology, June 12-14, 1974, Mor- 29, No. $, April 1976, pp. 74-80. gantown, W. Va., pp. 18-1--18-4. 12. Kacmar, R. M. Reliability of 3. Barham, D. K. Progress in Coal- Computerized Mine-Monitoring Systems. face Monitoring and Control in the BuMines IC 8882, 1982, 12 pp. United Kingdom. Proc. 5th WVU Conf. on Coal Mine Electrotechnology, July 30- 13. Kohler, J. L. An Evaluation of 31--August 1, 1980, Morgantown, W. Va., the rlir Velocity Sensing Unit in the Bu- pp. 16-1--16-18. reau of Mines Remote Monitoring Sys- tem. Ongoing BuMines contract 50308027; 4. Bredeson, J. G, H. Hashemi, and for information contact E. D. Thimons, K. Snedhar. Data Security for In-Mine Pittsburgh Research Center, Pittsburgh, Transmission. Final Report--Part 11. Pa. BuMines contract 50308024; for information contact R. W. Watson, Pittsburgh 14. Kot,V. I.,and E. F. Karpov. Research Center, Pittsburgh, Pa. Coal Mine Ventilation - Monitoring and Cont:rol. Proc. 5th WVU Conf. on 5. Bredeson, J. G., J. L. Kohler, and Coal Mine Electrotechnology, July 30- H. Singh. Data Security for In-Mine 31--,!lug. 1, 1980, Morgantown, W. Va., Transmission. Final Report--Part I. Bu- pp. 15-1--15-14. Mines OFR 76-81, February 1981, 111 pp.; NTIS PB 81-221998. 15. Miller, E. J., P.M. Turcic, and J. L. Banfield. Equivalency Tests for 6. Brezovec, D. Computer Monitors Fire Detection Systems for Underground Mine Conditions. Coal Age, v. 86, No. 8, Coal Mines Using Low Level Carbon Monox- August 1981, pp. 56-60. ide Monitors. Proc. 2d Internat. Mine Ventilation Cong., Nov. 4-8, 1979, Reno, 7. Cervik, J. Experience With Meth- Nev., pp. 236-246. ane Drainage From Horizontal Bore- holes. Proc. 2d Internat. Mine Ventila- 16. North American Mining Consultants tion Cong., Nov. 4-8, 1979, Reno, Nev., Inc. Single Entry Longwall Study. U.S. pp. 257-264. Dept. Energy contract ET-77-C-01-9052, October 1979; available from U.S. Depart- 8. Chakravorty, R. N., and R. L. ment of Energy, Germantown, Md. Woolf. Environmental Monitoring for Safety in Underground Coal Mining. CIM 17. Nutter, R. S. Hazard Evalua- Bull., v. 72, No. 801, January 1979, tion Methodology for Computer Controlled pp. 100-107. Mine Monitoring/Control System. Pres. at Western Electro Technology Conf. , 9. Corbett, A. W. The Use of Compu- Reno, Nev. , September 1981 ; available ters for the Continuous Monitoring of the from R. S. Nutter, West Virginia Univer- Environment at Brodsworth Colliery. Min. sity, Morgantown, W. Va. Eng. (London), v. 138, No. 210, March 1979, pp. 641-650. 18. Prosser, L. J., Jr., G. L. Fin- Instrumentation. BuMines OFR 1-82, June finger, and J. Cervik. Methane Drain- 1981, 137 pp.; NTIS PB 82-146325. age Study Using an Underground Pipeline, Marianna Mine 58. BuMines RI 8577, 1981, 22. Tongue, D. W., D. D. Schuster, R. 21 PP* Neidbala, and D. M. Bondurant. Design and Recommended Specifications for a Safe 19. Rustan, A. Review of Develop- Methane Gas Piping System. BuMines OFR ments in Monitoring and Control of Mine 109-76, July 1976, 97 pp.; NTIS PB 259 Ventilation Systems. Proc. 2d Internat. 340. Mine Ventilation Cong., Nov. 4-8, 1979, Reno, Nev., pp. 223-229. 23. VanderWalt, N. T., B. J. Bout, Q. S. Anderson, and T. J. Newington. 20. Tregelles, P. G. Automation in All-Analogue Fire Detection System for UK Mines: Achievements, Goals & Prob- South African Gold Mines. J. Mine Venti- lems. Coal Min. and Processing, v. 17, lation Soc. South Africa, v. 33, No. 1, No. 9, September 1980, pp. 110-122. January 1980, pp. 2-13.

21. Trelewicz, K. Environmental Test Criteria for the Acceptability of Mine CHAPTER 5.--COMMUNICATION SYSTEM DESIGN AND IMPROVEMENT

5.1 Introduction mine,, stope caving, longwall, room and pillar, etc. ). This chapter analyses the parameters influencing initial design of communica- b. Maximum number of working t ion systems. for new mines and upgrading sections. existing systems. c. Expected mine growth rate and Paragraph 5.2 outlines those varia- eventual maximum size. bles that must be taken into account during the design stages of a new wired d. Haulage methods (tracked trol- phone system. Recommended features, gen- ley, diesel, belt, etc.). eral requirements, and how they can be implemented are treated in this section. em Underground power distribution system (dc, ac, or both). Paragraph 5.3 describes ways of improving or extending the range of trol- f. Features desired (two-way radio ley carrier phone systems and pager phone paging, private line capability for emer- systems already installed in the mine. gency use, etc.).

5.2 New Phone System Design g. Redundant or backup systems for use during outages of the normal The task of designing an adequate systlem. communication, control, and monitoring system for an underground mine must be Although no two mines are alike, the addressed on a system basis. In addition foll~owingitems have been established as to insuring that effective voice communi- the !main characteristics desired for any cation is established, any new system underground communication system: should take into account present and future requirements of remote control and 1. Multiple Communication Paths to monitoring functions. Chapter 4 illus- Outside--the objective here is to give trated the drastic savings in response all telephones a second method of commu- time that can be realized when remote nicating with the surface. control and monitoring are integrated into the overall communication system. 2. Audible Emergency Signaling--the The importance of including control and communication system provides the main monitoring in the overall design plan for means of alerting miners during emergen- any system cannot be overemphasized. cies. The system should include means to broadcast distinct audible signals for Because each mine is unique, and emergency signaling. Initiation of these thus usually has its own special operat- signals should probably be controlled ing characteristics and communication from. a central outside point, such as a requirements, there is no such thing as surface control room. "the one best system" to meet the requirements of all mines. The opthum 3. Emergency Override--provisions communication, control, and monitoring should be included to permit any con- system for a mine must be one that has versation to be overridden with emergency been tailored to meet the special communication. requirements of that particular mine. Factors that must be considered during 4. Selective Area Page--as mines system design include-- grow larger it is apparent that the entire telephone system paging mode need a. Type of mine and mining methods not be activated each time a call is (low- or high-seam coal, deep hardrock initiated. When the general area of a person to be paged is known, only the gage wire is chosen to improve the ten- pagers in that area would be activated. sile strength of the wire, as well as to reduce the overall resistance of the run. 5. Simultaneous Conversation Capa- bility--although the ultimate for this TABLE 5-1. - Single-pair cable characteristic would be a private line for each telephone, this channel capacity Wire Loop resist- may not be necessary in some mines. In Description gage, ance, ohms - general, each working section does not AWG per mile produce much communication activity. Plastic-insulated Haulage and maintenance activities domi- nonj acke ted build- nate telephone use. Since these activi- ing wire...... 18 67 ties tend to originate on the basis of mine "areas," it appears that providing Type SO, neoprene- 18 67 different areas of the mine with a sepa- jacketed portable 16 42 rate communication circuit could meet the cable...... 14 27 simultaneous conversation need and maintain circuit simplicity. Buried distribution wire...... 19 83 6. Manual or Automatic Connection Between Subsystems--provisions must be Plastic drop wire made for connecting telephones within the (copper-clad steel) 18 223 telephone system, and provisions should be made for connecting the telephone sys- An inexpensive wire used for inter- tem into the other communication systems connecting mine phones is vinyl-plastic- used at the mine. coated, 18-gage, two-wire, twisted-pair building wire. Unjacketed wire of this 7. Remote Signaling--the design of type provides little environmental pro- the telephone equipment and circuits tection f or the copper conductors ; there- should be compatible with frequency divi- fore it must be located out of the way of sion multiplexed equipment so frequencies the mining equipment and carefully sus- above 3,000 Hz can be used for control pended to avoid moisture penetration. and monitoring applications. The 14-gage neoprene-j acketed type 5.2.1 Wired Phone Systems (see fig. 5-1) is recommended for most underground applications. The greater The options open to a designer dur- mechanical strength, reduced loop resist- ing planning stages for a hard-wired ance, and superior moisture resistance of phone system include this cable makes it ideal for communication applications. Single-pair phone system The best method of getting a feel Multipair phone system for the design considerations of a single-pair system is to design a system Multiplexed phone system for a representative moderate-sized mine. An example of such a mine is shown in 5.2. la Single-Pair Sys tern figure 5-2. This mine has the following characteristics: Many different types of wire can be used for single-pair (party-line ) communication systems (table 5-1). Smaller gage wire may be satisfactory if the number of telephones in the system is small and the distance between them is short. However, for most applications, a larger FIGURE 5-1. - Single-pair type SO neoprene cable, Health and Safety Act of 1969, in that it provides two-way communication between .SPLICE TAP the surface and each working section. -SINGLE PAIR "MI I(,WVND

---SINGLE PLlR 6O.q LDOISACK ltBOVE GROUND Additional phones were installed at the @ PEaMaMFNTTEI 1-5 IN MAIN HAULAGEWIY intersections of the main haulageway and 0 SEMI PERMANIVr IbLC.HONEQ1T BUTT ENTRIES

@ FaroilPNTLV NbI

Based on the physical characteristics of the mine, the total length of single-pair cable required can be calcu- lated for this stage of development as follows :

Miles

1 main haulageway...... 3.5 3 submains (0.8 mile each)...... 2.4 6 active sections (3,000 feet per section). 3.4 Total...... 9.3

The 3.4 miles of section cable assumes the reuse of the cable as the working sections move from one panel to another. At this stage in the mine's FIGURE 52. - Single-pair installation in typical mine. development, 15 panels have been driven or are being driven which would have Less than 2 years old required 8.5 miles of section cable if reusing it had not been assumed. There- 6 square miles in total area fore, the total cable miles needed are

3.5 miles of main haulageway 9.3 if section cable reused

0.8-mile-long average submain 14.4 if section cable net reused

Average panel size of 800 feet by The least expensive wire for the 2,100 feet above application is plastic-insulated, nonjacketed 18 AWG building wire. How- Average working section size of ever, the high loop resistance (67 ohms 300 feet by 400 feet per mile) of the 18-gage wire will make future expansion impractical; therefore 5 working sections per shift we should consider a larger gage wire.

A maximum of 6 active working A more suitable cable due to its low sections loop resistance is 14 AWG, type SO, neoprene wire. The 14 AWG neoprene cable 17 fixed mine pager phones presently uses annealed copper conductors so that installed it can withstand severe mechanical abuse. (The cable is designed for use as power The fixed-telephone, single-pair supply cable on portable equipment.) If communication system shown in figure 5-2 the 3,000 feet of 14 AWG neoprene wire complies with the Federal Coal Mine used for each active section is mounted on a reel and travels with the working replacing the single-pair cable in the section phone into the panel, then we can main haulageway and the submains with plan on reusing this wire when developing multipair cable. In a new mine, it would future panels. The cost of expanding to mean calculating the maximum channel 6 submains and 60 panels would involve requirements expected during the life of only the additional wire for 3 submains, the mine and specifying the proper multi- assuming we can reuse the section wire. pair distribution system.

The economic importance of reusing The hardware for a multipair system section wire can be elaborated on by the is of proven reliability and has stood following calculations for 54 lengths of the test of time. All of these materials additional section wire needed to reach have been used for aerial distribution the 6-submain development stage if the systems in the telephone industry and section wire is not reused. Each length were refined over the years to survive in is 3,000 feet, or 0.57 mile. any part of the world with a minimum of preventive maintenance. Because it was 54 lengths x 0.57 mile per length designed to be installed and maintained = 30 miles of additional cable by linemen working in all kinds of weather while standing on ladders, on The cost of this additional cable aerial platforms, or in manholes, multi- can be a significant part of the total pair equipment can be handled by elec- cost of the entire single-pair system. tricians in the underground environment. Although material costs are greatly The only new skill that mine personnel reduced if section wire is reused, some may have to learn is the splicing of additional labor costs are involved in small-diameter wires. However, crimp- the removal of cable once a panel has type splice connectors are available to been completed. simplify the splicing of multipair cables. Another alternative that can be employed is to use high-quality 14 AWG Table 5-2 shows the major character- wire for the main and submains, and then istics of multipair cable available from use a less expensive lighter gage wire telecommunication cable manufacturers. for the panels and not reuse this wire. Figure-8 cable is recommended for the A low-cost 18-gage building wire may be mine application because the messenger acceptable as section wire, because its wire adds considerable tensile strength high resistance is not a problem for the to the cable, and the installation is short length involved. similar to that of trolley wire.

5.2.lb Multipair Systems The previous section described a single-pair cable system using a repre- A single-pair cable system restricts sentative moderate-size fictitious mine. the mine communication system to a The same mine will be used to analyze a single-channel multiparty configuration. multipair cable system (fig. 5-3). Introducing multipair cable into the mine communication system allows one to expand Using a cable distribution and load- the number of channels to whatever is ing plan that will allow the servicing of necessary for efficient voice traffic. no more than two sections per twisted In an existing mine, this would mean pair, a minimum of three pairs is

TABLE 5-2. - Range of multipair cables commercially available

Number of pairs...... 3-400 Messenger size (diameter)...... inch.. 0.134-0.250 Conductor size...... AWG.. 26-19 Conductor dc resistance at 68O F...ohms per mile.. 43-220 six-pair cable has been selected for the

SPLICE CASE haulageway. The submains with only two -SINGLE PAIR CABLE ---a PAIR CABLE phones per pair and run lengths of less -0- 6 PAIR CABLE than 1 mile can use 22-gage wire. A -.-LOOP BACK PATHS a PERMANENTTELEPHONES IN MAIN HAULAGEWAY splice case at every third section entry 0 SEMI -PERMANENTTELEPHONESAT BUTT ENTRIES @ FREOUENTLV MOVEOTELEPHONESAT WORKING SECTIONS should be sufficient in this application and will reduce labor costs.

The section cable can be a single pair but must be strong enough to with- BORE HOLE stand the wear caused by the almost constant phone relocating required in the working section. A 3,000-foot reel of wire that travels with the section phone would reach any location in an 800- by 2,100-foot panel. Plastic drop wire has been chosen for the section cable. This wire is made up of two 18 AWG copper- covered steel wires laid in parallel and coated with a black flame-resistant poly-

BORE HOLE vinyl chloride insulation. The high strength of this cable allows for long spans which make for quick temporary installations and also reuse of the cable. A stainless steel drop wire clamp can be hooked to roof bolts or nailed to timbers for support.

In cost comparisons between single- pair and multipair systems (2),l- the wir- FIGURE 53. Multipair installation in typical mine. - ing costs for multipair installations were less expensive because the smaller required to handle the six working sec- gage wire allowed in the multipair cable, tions. The main haulageway phones con- due to fewer phones placed in parallel nected across a single party line require per pairs, kept the per-mile cost of an additional pair for a total of four multipair cable competitive with that of pairs, each of which extends back to a the larger gage single-pair cable. centralized location such as the dispatcher's office. A six-pair cable Two questions worthy of considera- placed in the main haulageway will accom- tion at this point are, How well does a modate the above required pairs while multipair communication system meet the leaving an extra two pairs for future needs of the mine user? and What expansion. Three-pair cable may be ap- improvements can be incorporated into a propriate for the submains because no multipair system that are not possible more than four sections will be active with the present day single-pair mine per submain at any one time. A single- telephone system? pair cable can be used between the panel entry phone, located in the submain, and Advantages the section phone, which must move with the section crew. More Channels.--Using multipair cable, a system can be designed with as Due to the 3.5-mile length of the main haulageway and assuming that a maxi- l~nderlinednumbers in parentheses re- mum of seven phones will be connected fer to items in the bibliography at the in parallel across one pair, a 19-gage end of this chapter. many channels as are deemed necessary trained to use the different splicing for the particular application, the only techniques required and to troubleshoot limits being cost and complexity. this somewhat more complex system.

Private Channels.--Individual pairs 5.2.1~ Multiplexed Phone Systems can be assigned to each working section, thereby producing a private channel Multiplex telephone systems achieve between the section and the mine commu- their private channel capability via nications center. electronic means on a single cable. rr Multiplexing can be via time division Zone Paging.--The communication ten- multiplexing (TDM) or frequency division ter can page over an individual pair multiplexing (FDM). Although TDM systems so that only the section of the mine have been developed and provide certain concerned with the transmission need be advantages, a multitude of disadvantages disturbed. This would eliminate the tend to make this type of multiplexing present situation of requiring miners in unattractive for mine telephone systems. all sections to listen to all pages. FDM systems have been developed and Direct Dialing.--Pairs can be dedi- tested in underground mines with consid- cated to connect underground dial phones erable success. These systems can be directly to the company's private auto- divided into ones that require a central matic branch exchange (PABX) or directly switching station for system control and to a central office through an approved those that do not. In a central switch- interface. This would allow key loca- ing system, most if not all of the system tions in the mine to dial each other, intelligence resides in the central unit place outgoing calls, or receive incoming which assigns frequencies, provides power calls via the local exchange without for the phones, and generates ringing and relaying messages through the communica- busy signals. These systems are gener- tion center. Provisions for preventing ally permitted only in nongassy mines. A abuse of the latter two features could serious disadvantage of such a system is also be included. that a failure in the central unit can render the entire system inoperative. Remote Monitoring.--Extra pairs in the cable may be used for monitoring the A system that does not rely on a mine environment and/or equipment. central switching unit has been developed by the Bureau of Mines. The system is Disadvantages based upon microprocessor control, where intelligence is resident in each tele- Increased Operating Costs.--A multiphone. Eight-channel voice or data com- pair system- -- - incorporating all of the munications is possible. The system uti- above advantages will cost more than a lizes FDM at medium frequencies (340-650 single-pair system, even though the kHz) and is designed for a 10-mile cable multipair cable may cost less than the plant. A failure of any one phone nor- single-pair cable. This is due to the mally affects the multiplex feature of additional cost of a central switching that phone only. Each phone also in- equipment required for multipair systems. cludes a resident pager phone capability For a particular application, the such that even a total failure of the increased efficiency and other benefits microprocessor intelligence will not must be weighed against the added in- normally inhibit a user from making a stallation and maintenance costs in order call. This feature is essential in any to establish its true worth. modern telephone system for underground mines. Supervisory feedback and a vis- Training Costs.--The maintenance per- ual message-leaving capability (as is sonnel assigned to install and main- required in several States) are also tain this equipment will have to be included. 5.2.2 Cable Selection voltages; and to not support combustion in case of fire. Telephone transmission is made over wires which represent a considerable Twisted-pair construction is advised fraction of the cost of any telephone to reduce the effects of induced noise or system. As an example, figure 5-4 shows interference. The 14 AWG solid-conductor three broad categories of equipment in twisted pair, with suitable insulation which telephone companies invest . The dielectric and outer protective jacket is "transmission" category not only repre- very rugged, and will withstand the rough sents wires, but also includes multiplex handiling and stress imposed by abrasion systems, microwave systems, and other agai.nst timbers or falling debris. For wire substitutes. Since transmission the smaller diameter wires, such as equipment accounts for about half of the 19 AWG, a figure-8 cable is recommended. total investment, telephone companies put In this construction, a steel "messenger" considerable effort into planning the or support wire is added to the twisted- layout and the growth of their transmis- pair bundle, so that the overall cross sion facilities. Cable costs account for section resembles a figure 8. The steel even a greater percent of the expense in- messenger cable provides additional volved in an underground communication strength and support so that minimum system. Therefore, mine planners should strain is applied to the signal-carrying also carefully plan the netqork and re- twisted pair. vise the plan on a scheduled basis. Solid conductor is advised, rather The general environment in an under- than the more easily handled multistrand ground mine imposes severe physical re- wire. The multistrand cable is subject quirements on communication cable. Insu- to corrosion buildup on the surface of lation is required to withstand exposure the individual conductor strands, which to moisture, abrasion, and rough han- in time could reduce the conductivity of dling; to afford protection against some a splice or connection and become the level of accidental contact with higher source of added noise and reduced signal level. Conditions within an underground mine dictate the use of press-on or twist-on connectors as common practice to comlplete a splice. Such practices are not compatible with the use of multistrand wire.

The choice of wire size is determined by the configuration of the telephone system and the type of phone in use. Major factors to consider in the choice of wire size are the total length of cable run, the number of phones in the circuit, the average distance between the phones, and the characteristics of the ringing or calling circuit in each phone.

In pager phone systems, the paging relay circuit is one of the more critical parameters to consider in the choice of pager phone wire size. The normal audio signal imposed on the cable is about 1 to 2 M[W; this signal level is sufficient to FIGURE 54, - Telephone company investments, ope.rate a phone receiver at satisfactory volume over several miles of cable as voltage under load approaches 16 volts. small as 19 AWG. The limiting condition There is no specific time at which the is the ability to reliably operate the battery can be identified as not usable. paging relays. In this regard, the cable However, it is generally agreed that the impedance, or resistance per unit length, levels just stated are typical of the end as it affects the available dc voltage at of a battery's useful life and indicate the paging relay, is more influential that it should be replaced. than audio loss. Calculation of the minimum wire size that will insure reliable In many pager phones, the internal operation of all paging relays must take circuit has been designed so that the into account three major parameters: total battery voltage is not available on paging circuit impedance, battery volt- the line for operation of paging relays. age, and wire losses. Circuitry in such phones can add a series dc resistance of from 10 to 100 ohms to Some pager phones use electromechan- limit the short-circuit drain to levels ical relays that have an impedance of of operation that are intrinsically safe. about 2,500 ohms while other systems use A pager phone system can draw significant electronic or semiconductor switching current from the battery in the "paging" circuits that have an impedance of from phone. This causes an internal voltage 8,000 to 50,000 ohms. The minimum dc drop which significantly reduces the voltage required to operate any of these effective voltage presented to the line. relays is about 1.5 to 4 volts. To Estimates of this effect, for a variety insure a safety margin, it is recommended of conditions, are shown in table 5-3. that at least 5 volts dc be available at all telephone paging relays. It is eas- Wire loss per unit length is a func- ier to obtain this minimum voltage with tion of wire diameter and system configu- the higher impedance circuits. ration. These factors include total wire used, telephone spacing, number of Available battery voltage is a func- phones, and input impedance. All of tion of the condition of the battery and these factors must be considered together the load it must operate. In a 12-volt in view of the expected battery voltage system, the battery is at the end of its at end of useful life (8 or 16 volts), useful life when the dc voltage under the relay impedance (2,500 ohms or load condition approaches 8 volts. For a greater than 8,000 ohms), and the inter- 24-volt system, a battery is at the end nal voltage drop because of circuit of its useful life when the available dc losses.

TABLE 5-3. - Effect of paging circuit impedance

(Electromechanical relays, 2,500 ohms)

Battery voltage, Limiting Available battery voltage dc volts resistance, on the line, dc volts ohms 10-phone system 20-phone system 24-volt battery: 10 23.75 23.5 24 (new)...... 100 19 18 10 15.5 15.5 16 (near end of life). 100 13 12 12-volt battery: 10 11.8 11.6 12 (new)...... 100 10 8 10 7.8 7.6 8 (near end of life).. 100 6.5 6 - The simplest calculation is to assume a basic ladder configuration, where all phones are in parallel on the same single two-wire cable, strung the length of the installation (fig. 5-5). This ba- ETC sic installation is the one most normally considered when calculations are made to determine minimum wire size. Tables 5-4 and 5-5 indicate the minimum wire size for both electromechanical and electronic relays, with average phone spacing of 114 Rw and i/2 mile.

In a 12-volt system, with electro- ETC mechanical 2,500-ohm relays, only 12 hones spaced 114 mile apart over 3 miles can be used with 19 AWG wire. However, Rw = LINE IMPEDANCE Rp - PHONE INPUT IMPEDANCE 20 phones can be used over a 5-mile run if 14 AWG wire is used. If electronic FIGURE 5-5. - Basic ladder configuration. 8,000-ohm relays were used, the 24-volt system could support 33 phones over 8 or incorrect branch connections and miles of cable using 19 AWG wire. splices tend to reduce performance--so that using detailed calculations to de- Tables 5-4 and 5-5 do not take into termine marginally usable minimum wire consideration line losses caused by poor size is not a recommended practice. It splices, dampness, or defective phones. makes more sense to determine a minimum However, they do illustrate comparative wire size for safe operating level and conditions as a guide for system design then use that size as a guide to select and component selection. or recommend a wire that meets all the specifications. For multiple-branch con- Consideration of a topography that figurations, the following rules of thumb involves a multiple-branch system may can be used to estimate minimum wire size result in a design that can use a smaller without extensive calculation: diameter wire. Conditions in mines normally degrade even the best of systems-- 1. Determine present telephone moisture causes signal leakage; erratic configuration.

TABLE 5-4. - 114-mile pager phone spacing

System 19 AWG 14 AWG 12-volt, 2,500-ohm relay 3 miles, 12 phones 5 miles, 20 phones 24-volt, 2,500-ohm relay 5 miles, 20 phones 9 miles, 36 phones

12-volt, 8,000-ohm relay 5 miles, 20 phones 9 miles, 36 phones 24-volt, 8,000-ohm relay 8 miles, 33 phones >9 miles, >36 phones

TABLE 5-5. - 112-mile pager phone spacing

System 19 AWG 14 AWG 12-volt, 2,500-ohm relay 4.5 miles, 9 phones 7.5 miles, 15 phones 24-volt, 2,500-ohm relay 7 miles, 14 phones 13 miles, 26 phones

12-volt, 8,000-ohm relay 7.5 miles, 15 phones 13 miles, 26 phones 24-volt, 8,000-ohm relay 13 miles, 26 phones >18 miles, >36 phones to D to J, which includes 10 phones over 2. Estimate probable growth of the about 2.5 miles of cable. If we examine telephone configuration. table 5-2, we find that with 2,500-ohm mechanical relays in a 12-volt system, 3. Sketch the future telephone 19 AWG wire is adequate for the configuration. configuration.

4. Examine the sketch to determine This type of rule-of-thumb estimate the longest combined path that takes into is adequate to identify approximate account a majority of the telephones. requirements for wire size, but it does not replace necessary detailed calcula- 5. From table 5-2 or 5-3 determine tions for a major installation with many the minimum wire size for the longest branches. It must also be emphasized path needs. that calculation of minimum wire size identifies the bottom limit of a marginal 6. The added loads of the other condition and good engineering practice branches will not greatly affect the dictates some margin of reliability. The determination of minimum wire size and general manufacturers1 recommendation of can be ignored for such an estimate. 14 to 16 AWG twisted pair for systems using 2,500-ohm electromechanical relays is The 21 pager phones shown in the top sound, particularly for a 12-volt system. panel of figure 5-6, spaced an average of 114 mile apart, are connected in a For systems using semiconductor pag- branching system, which can be repre- ing circuits (with impedances of 8,000 sented by the impedance diagram shown in ohms or greater), 19 AWG is usually ade- the bottom panel. The longest path is E quate. This is particularly true for 24- volt systems, but also applies to most 12-volt systems that have high-impedance switching circuits.

In summary, the cable wire size depends on a series of factors that include the total number of telephones in an installation, the total length of cable run (distance between the farthest phones), the configuration of branch lines, the available battery voltage, and the type of paging relay used. The preferred cable, regardless of wire size, is a twisted pair of solid conductor wires, WE with individual insulation around each (A) %-MILE PAGER PHONE SPACING wire in the pair and an outer abrasion- resistant covering of waterproof, flame- retardant material.

5.2.3 Summary

The basic system choices that may be selected when choosing an underground wired phone system consist of--

E Single pair.--This is a party line (0) EQUIVALENT CIRCUIT system in which all phones are on the FIGURE 5-6. - Branching ladder network. same channel. Mu1tipair.--A private line system performance of a trolley carrier system, with each phone or group of phones con- and the second treats telephone systems. nected to the system center by its own individual wire pair. 5.3.1 Trolley Carrier Phone Systems

Multiplex.--A private line system WARNING using a single cable, with the audio to and from each phone multiplexed onto the Some of these procedures are un- common cable. de!rtaken with the trolley wire ener- gi.zed; therefore, they are extremely In all of these systems, telephone halzardous. Extreme caution must be transmission is made over wires which exercised to avoid potentially lethal represents a considerable fraction of the shock. The fuses used in the test cost of the entire system, Since trans- leads serve only to protect equipment mission equipment accounts for about half artd do not , in any way reduce the of total investment, companies should put shock hazard to personnel. Only per- considerable effort into planning the sonnel thoroughly familiar with elec- layout and growth of their transmission trical work on trolley wires should facilities . conduct these procedures. The permanent connect ion of components should In planning mine communication be done with power removed. Care systems, the pairs or voice channels should also be taken to insure that that will be needed in the future and components and equipment are suitable the mobility of the telephones involved for use in the desired application. should be kept in mind. In addition, pairs that will be needed for purposes The trolley carrier phones used for other than for telephones (telemetry, dispatch purposes in electrical rail remote monitoring, etc.), which inci- haul-age mines often show problems in pro- dentally may exceed voice communica- viding coverage over the entire haulage tion needs, should also be taken into systern. Direct communication be tween the account. 1 dispatcher and vehicles in certain areas of the mine is often difficult or impos- 5.3 Improving Existing (In-Place) sible. The major reason for these diffi- Phone Systems culties is the effects that loads placed across the trolley wire or rail have on The two types of communication sys- trarlsmission. tems commonly used to date in underground mines are as follows: Both theory and experiment show that the trolley wire-rail by itself is a rel- Carrier current radio system using atively good transmission line for car- the trolley line, rier phone frequencies. In fact, on an unloaded trolley wire-rail transmission Various types of telephone system. line, a distance of 35 miles could be expected for communication range. Communi-- Because these systems have gained cations over a real trolley wire-rail can such widespread usage, methods for up- never achieve this range because the many grading and improving presently installed loads across the trolley wire-rail absorb systems are presented in the following and reflect carrier signal power, The sections. The first deals with improving list of these loads is long and includes rectifiers, personnel heaters, signal l Approved and nonapproved equipment may lights, vehicle motors, vehicle lights, not share the same cables; check with and the carrier phone itself. It is MSHA for details. probable that the net signal attenuation rate for a trolley wire-rail with typical because of poor performance. It is loads placed across it yields a useful recommended that solutions other than range as low as 3.5 miles. The problem Z-boxes be used to improve the perform- of obtaining good signal propagation is ance of trolley carrier phone systems. further aggravated by branches of the trolley wire where the signal splits in a The most straightforward way of totally uncontrollable way. Lack of treating the trolley wire-rail to make it proper signal termination at the ends of into a functional carrier signal trans- the trolley wire-rail further degrades mission line is to physically remove from signal propagation. The vehicles repre- the trolley wire-rail all of the bridging sent moving loads on the transmission loads that impede carrier signal propaga- line and add a further complication to tion. The steps in this process follow: obtaining or predicting good signal propagation. Also, advancing the mine face 1. Identify the bridging loads. means that the transmission network List all the bridging loads across the changes with time, yielding more uncer- trolley wire-rail. Consult figure 5-7 to tainty to the quality of transmission. estimate the seriousness of the impedi- ment to carrier signal propagation that The seriousness of the bridging each load represents. loads can be seen by reference to figure 5-7 where the losses for typical 2. Determine which loads can be loads are tabulated. Using this chart, removed from the trolley wire-rail and be one can make an estimate of the total operated from mine ac power. signal loss by adding the individual losses (in decibels). For practical reasons, physical removal of bridging loads has severe lim- In the past, whenever poor trolley itations. Certain critical loads, in- carrier communications existed, attempts cluding rectifiers, vehicles, lights, were made to remedy the problem using motors, and carrier phones themselves, "Z-boxes," or signal couplers to the cannot be removed from the trolley wire- phone line. Z-boxes are not permissible, rail. In some instances, none of the are usually not the best solution, and loads can be removed from the trolley may actually introduce more problems then wire-rail, and efforts to improve signal they solve. Mines are full of Z-boxes propagation must involve other methods. that- have been disconnected and abandoned Studies conducted have revealed alternative ways of increasing the range HEATERS and quality of existing trolley carrier RECTIFIERS phone systems. These methods include-- 50 Isolated loads at the carrier \ frequency Using a dedicated line

Using a remote transceiver

5.3. la Isolating Loads at the Carrier Frequency

Figure 5-7 shows that as the bridg-

0 I ing resistance is increased, the signal loss decreases. The "isolating loads" BRIDGING LOAD (OHMS1 method involves adding passive circuit FIGURE 5-7. - Signal loss versus bridging load. elements (inductors and capacitors) in series with the particular load to reduce FEED WlRE INDUCTANCE RECTIFIER the effects of the bridging load. The circuit elements do not affect dc equip- ADDEDTUNING CAPACITOR ment (motors, lights, etc.) being powered from the trolley wire, but they do, if properly chosen, add high impedance at the carrier frequency. Rectifiers, heaters, and vehicle lights are the bridging - loads' that most seriously degrade re- A. RESONATING THE FEED WlRE INDUCTANCE ceived signal levels and should be treated first to improve received signal levels.

5.3.1a.i Rectifiers

There are three means of raising the effective carrier frequency impedance of a rectifier. The most practical method depends on where the rectifier is in- -- stalled. If it is located relatively far - from the rail (beyond 40 feet), ,the feed B. RESONATING AN ADDED FIXED INDUCTANCE wires represent sufficient inductance that can be resonated, thereby raising the effective impedance as seen by the TROLLEY WlRE INDUCTANCE RECTIFIER trolley wire-rail (fig. 5-8A ). If the rectifier setback is short (less than 40 feet), two techniques can be used to -

raise the effective impedance: (1) A CAPACITOR CAPACITOR fixed high-current inductor can be added - -

in series with the rectifier and that C. RESONATING THE TROLLEY WIRE/RAIL INDUCTANCE inductor can then be tuned to raise the effective impedance (fig. 5-8B) ; or FIGURE 5-8. - Ways of raising the impedance (2) the inductance of the trolley wire- of a rectifier. rail can be used to resonate short sections of the trolley wire-rail near the as practical, install the temporary test bridging load to raise the effective set shown in figure 5-9. This test set bridging impedance (fig. 5-8C). The ways comprises a decade capacitor, isolating of applying each of these means are de- and protection devices, and a tuned scribed below. voltmeter. Usually two feed wires are run from the rectifier to this point. a. Resonating the Feed Wire Inductance Only one need be treated. The following steps are required to 3. The dispatcher is called from a tune the rectifier feed wires: jeep parked nearby and asked to key on his transmitter for 20 seconds or so. 1. Attach a 1,000-volt (some sys- The decade capacitor box is switched tems may require even higher voltage com- through its range of operation and left ponents), 1- or larger, oil-f illed at the position of maximum signal, as capacitor directly across the plus and indicated by the tuned voltmeter. (The minus terminals inside the rectifier. decade box should have enough range (This capacitor serves to reject to peak the voltmeter.) This value of rectifier-generated interference in the signal should be larger than when the carrier frequency band.) decade capacitor is at its off position. The two values--the voltage when the dec- 2. At the far end of the feeder ade capacitor is off and the maximum wires, as near to the trolley wire-rail TO VOLTMETER TONIP

40 FT OR MORE ------*

TROLLEY

5 AMP FUSE

CAPACITOR 5 vlrt 1000 V

P TUNED - vouMETE+ 5 BURY WIRE - BFYGaTH RECTIFIER 0000 0,r m

CWOYND FIGURE 5-9. - Test configurations for tuning FIGURE 5-10. - Permanent installationof tun- feeder wire, ing elements for feeder wire.

WARNING Some of these procedures are undertaken with the trolley wire energized; therefore, they are extremely hazardous. Extreme caution must be exercised to avoid potentially lethal shock. The fuses used in the test leads serve only to protect equipment and do not in any way reduce the shock hazard to personnel. Only personnel thoroughly familiar with electrical work on trolley wires should conduct these procedures. The permanent connection of components should be done with power removed. Care should also be taken to insure that components and equipment are suitable for use in the desired application. value--should be logged, preferably on a dispatcher. A preliminary test can mine map. There should be an appreciable easily ascertain that this condition has increase in voltage for this condition, been met by sweeping the tuning dial of at least 1 1/2 to 1, and in some in- the tuned voltmeter through the region stances up to 10 to 1. The value of the near the transmitted frequency and leav- capacitance that produces the maximum ing it at the position where maximum voltage should be noted from the value response is indicated. indicated on the decade capacitor, and a suitable capacitor of that value should b. Resonating an Added Fixed Inductance then be installed in a permanent fashion, as shown in figure 5-10. When this in- When the setback is short, an added stallation has been made, a final check, inductor made of a coil of feeder wire using the tuned voltmeter, should be made may be used to provide a series induct- to ascertain that the originally indi- ance that can be tuned. Because feeder cated increased voltage is obtained. wire is expensive, a coil in the so- called Brooks form, which yields the max- For this procedure, it is important imum inductance per length of wire, that the tuned voltmeter be tuned to the should be used. See Appendix A (Mine E) precise transmission frequency of the for an actual installation example. The approximate form is shown in noted, preferably on a mine map. When figure 5-11. A reasonable bending radius the best capacitor value has been found for the typical thousand-circular-mils in this manner, the test set is re- cable used for such feeder wires is 2 moved and a suitable capacitor of the feet; therefore this dimension is approx- value found during the test is perma- imately fixed. Four turns at this diam- nently attached to the coil, as shown in eter yield an inductance of approximately figure 5-13. When completed, a last test 25 )H, which is adequate for tuning most is made to verify that the improved sig- rectifiers. The coil should be installed nal reception is obtained. in the room in which the rectifier is located and should be kept a few feet away c. Resonating the Trolley Wire-Rail from the coal to prevent added losses at Inductance the carrier frequency. The exact value of inductance is unknown, so the coil A method that can be applied if the will have to be tuned in much the same rectifier setback is short, and it would manner as discussed previously for reso- be impractical to install a fixed induc- nating the feeder wires. tor in series with the rectifier feed wires, is to tune the trolley wire-rail Figure 5-12 illustrates the test setup. The dispatcher called and lo00 v is DECADE asked for a 20-second transmission. The CAPACITOR decade capacitor is switched through its positions and left at the position that yields the maximum voltage. (The decade TO RECTIFIER (HOT SIDE) - box should have enough range to peak the voltmeter.) The received voltage with the decade capacitor in the "off" position and the maximum voltage should be

NOTES: MATERIAL. 2x4 LUMBER DIAGONAL BRACKING.OMITTED FOR EASE OF DRAWING. IS REOUIRED

TUNEDVOLTMETER 7rz.pEE.,SSLOTS I I14 WIDE .LEY WIRE 7\ I

\TO RAIL OR GROUND

'3'-0"-

B PIECES A1 THRU Ag 4 PIECESBOJ'O 4PlECESCB3'-11" WARNING 2 PIECES 0 @4' - 2" 4 PIECES E @4'- 5" Somc of tl~csc:~)~oct.dr~~cs itrr 1111dertaLr11 wit11 111e ~rolley wirc er~ergizcd;therclorc, tl~cvare cxtremc.ly I~azartlo~~s. Lxtrelne rautiot~IIIUSI I)c cxrrcisrtl to avoitl ~)ote~~tially Ic~l~alshor k. 'Ih(. fl~svsIISC~ in thv lrsl Icatls servr ortly to ~)roLeclcqlliprnrlll :111(1 do 11o1in allv way rc,duc.c IIIC .shock hazard to 11crson11c.l. 0111) prlson11c.1tl~oro~~ql~ly familiar wit11 clcc~ric:tlwork OII ~roll(,vwircs sl~o~~l(lCOII- d(1cl lhcsc ~Ill)cccillrc.s. 'I'llr pcrnlalIc,l11 cotll~c.(.lio~l 01 ~OI~I~~IICIIIS sl1o111~1l~c do~tr wit11 1)owcr rc~~~ovcd.C.arc sl~o~~ldalso IIe lake11 lo itlxure that c.olllpollrtlts alttl cql~ip- lllr~llarc- s11it:1l)lC for IIS~ ill 111~(lesi~-c(l applicdlio~~.

FIGURE 5-12. - Test setup for tuning fixed FIGURE 5-1 1. - Coil form. inductance. a mine map. Remove the test fixture, and install permanently a suitable capacitor of the indicated value. Request another transmission to verify that the signal improvement observed during the test was maintained after permanent installation.

2. Repeat the same procedure as in step 1, but at a place in the opposite direction along the trolley wire-rail; that is, 80 feet or so on the other side CAPACITOR of the feed point. Keep records as MOUNTED IN FUSE HOLDER IN UTILITY BOX be£ore.

3. Return to the first point and measure and record the signal level for a dispatcher's transmission.

5.3.la.ii Heaters

Personnel heaters with a wide range of wattage ratings are used; however, WARNING 1,000 watts is likely to be the lowest, Some of tl~csc.~)roct.d~~l-es are r~r~dertaker~ will1 tl~rtrolley and each heater of this rating or higher wire cl~rr~ircd;~hrrefore, 111c.y are rxrrc.nirly harartlous. poses a significant signal loss to the t.;r;~rr~r~~cautiori must Ire cxrrcised to avoitl ~)olentially leth;~lslior k. '111~I11sc.s uscd in ~livrrhr Iratls servc or~ly carrier system. Such heaters will range ro protccr cq~~ilr~~~c~ital~ddo ~ior in ally w;iv rrduce 11i(. in resistance from 360 ohms for a 1-kW .shock hazartl ttr pcrsol~rirI. O~ilyprrsonlirl rl~oroiigl~ly fai~iliar!\itl~rlcc~ric;~l work OII troll~vwin.> ~11cr~~l~Iroll- unit on a 600-volt line to 18 ohms for a (111c.rthcsr 1~0ccd11rc:s.'I'l~c. pcr~iid~~r~ircori~~c(.rio~~ ot 5-kW unit on a 300-volt line. Current COI~I\)~II~IIIs slio~~ltl I,(: tlol~rwi 111 :>o\vc.r rt.~iio\c~i.Cnrc will range from 1.5 to 17 amperes for sl~o~~ltialso I)e lakcti [(I irlsl~rrtli;~r (.OIII~)OI~C~IIIS itlid CC~II~[)- nirllt alc sl~iral)lcfor 11sc ill rl~cbtlcsirrtl appliratioll. corresponding conditions. Unlike rectifier currents, these heater currents are sufficiently low that commercial induc- FIGURE 5-13. - Permanent attachment of tun- tors can be used untuned to provide ing capacitor to fixed inductor. isolation of heaters, thereby avoiding the step of individually tuning each isolator. as shown in figure 5-86'. The steps are described below: To raise the impedance level to 300 ohms at 100 kHz using an untuned 1. Locate a position about 80 feet inductance requires an inductor of along the trolley wire-rail from the 500 pH. While it would be convenient to place where the rectifier feed wires find a single inductor usable for all attach to the trolley wire-rail. Install such loads, the wide range of direct the test set as illustrated in figure 5-9 currents that must be handled (1.5 to between the trolley wire and rail. 17 amperes) makes it necessary to select Request the dispatcher to transmit for each inductor on an individual basis. about 20 seconds. Switch the capacitor box through its values to find a maximum The procedure for treating personnel signal level, as indicated on the tuned heaters follows: Locate the heater ele- voltmeter. (The decade box should have ment. Measure the carrier frequency enough range to peak the voltage level.) voltage at this load, using the tuned Note the value with the decade capacitor voltmeter and a dispatcher's transmis- in the "off" position and the value to sion. Note this value on amine map. maximum signal, and list these values on Disconnect the heater and permanently attach a 500-pH inductor in series with 5.3.la.i~ Other Loads the element. Reconnect the heater and measure the voltage produced across the Other loads can also adversely heater and inductor in series, using the affect propagation on the trolley wire- tuned voltmeter and a dispatcher's trans- rail; for example, signal and illumina- mission. An improvement in voltage of up tion lights. As noted earlier, an indi- to 10 to 1 can be expected. Note the new vidual light bulb, or a string of such received voltage on the mine map. Repeat lights, does not impose much insertion this ' procedure for each personnel loss. However, if there are many lights, heater. the total effect could be substantial. A way to estimate whether such lights 5.3.la.iii Vehicle Lights affect propagation significantly is to count the number of lights on the trolley Mine vehicles, including locomo- wire--rail between the dispatcher and the tives, jeeps, and portal buses, all draw farth.est place in the mine, and calculate substantial power from the trolley wire. the total bridging resistance. Approxi- Much of this power is used for motive mate value of loss versus bridging load purposes. Motors represent a relatively can ble estimated from figure 5-7. If the high impedance at trolley carrier fre- toal loss is less than 6 dB, only margin- quencies, particularly for jeeps and por- al im~provementswill result from treating tal buses and to a lesser extent for these lights. If the loss is more than locomotives. However, a part of the 6 dB, consideration should be given to power is used for headlights on the treating the lights. It would be a rath- vehicles. Most conventional vehicles use er unusual situation to find lights that 150-watt, 32-volt, PAR-type lights for really represented a significant impedi- this purpose. The difference between ment to propagation of a trolley wire- 32 volts and the trolley voltage is taken rail. However, when marginal signal lev- up with a ballast resistor. A single els exist, the lights could well make the light circuit of this type presents a difference between marginal and fully resistance of about 50 ohms on a 300-volt usable signal levels. circuit and about 110 ohms on a 600-volt circuit. Because some vehicles use two The most effective way to treat such lights at a time, and some only one, the light,s would be to take them off the line bridging loads represented by the vehicle and operate them from the ac system. lights range from 110 to 25 ohms per This practice is being used in some of vehicle. These values are sufficiently the newer mines. In old mines, where ac low that treatment is desirable. power is not available, little can be done. In some instances, the power rat- The procedure for treating vehicle lights ing of the lights could be reduced, follows : Insert a 10-ampere, 500-pH there!by raising the value of the bridging inductor in series with the light circuit impedlance. Fixed inductors could also be of each vehicle. Make sure that the used but would only have small effects inductor is only in series with the light because the light strings (typically circuit and is not in series with the three 100-watt, 115-volt lights in series motor or trolley phone circuits. Because in a 300-volt system) already have a of the variable conditions faced by the f air1.y high resistance (approximately 300 vehicles, it is not of much utility to ohms for the example above). check the before and after carrier frequency voltages found on vehicles, but Other loads are comprised of such the tuned voltmeter could be used for equipment as pumps and other motor- this purpose if so desired. drivein devices. However, these devices generally have high enough impedances and use a branch, but minimize the number of are placed so infrequently that they re- branches. sult in minimal loading effects. 2. Installation.--Install the wire; 5.3.lb Using a Dedicated Wire No. 10 or No. 12 wire is well suited to the task. Copper-weld construction is As previously mentioned, the trolley recommended for strength and integrity. wire-rail is an inefficient transmission This wire must be insulated and also held path because of the many loads that exist away from the rib or roof for at least - on the line. In the dedicated-wire tech- 3 inches. Installation must be on the nique, an independent wire (called the wide side of the entry, and the wire "dedicated wire") is run down the entry- should be located for least exposure to way with the trolley line on the wide damage. At the far ends of each line, side, but not connected to the trolley the wire is terminated by a 200-ohm, line in any manner. 10-watt resistor to the rail, as illustrated in figure 5-14. If branches are Such a wire, since it is unloaded, used, signal-splitting resistors must be has a very low attenuation rate. There- included (fig. 5-15) to reduce signal fore, if a signal is transmitted on the attenuation. dedicated wire, the signal strength remains high. Since the trolley line and 3. Connection of Transmitter. --Upon dedicated wire are located in the same completion of the installation of the entry, there is a mutual electromagnetic coupling between them. (The effects of loads on the trolley line are transferred to the dedicated wire, and the high signal on the dedicated wire is transferred to the trolley line. ) Fortunately, if INSULATOR the separation between the two is large TIE WRAP enough (9 feet or more), the loading effects of the trolley line are only weakly transferred to the dedicated wire, so that the attenuation rate stays low. But at the same time, the high signal levels on the dedicated wire are strongly coupled to the trolley line. The net result is that commnication is now possible in TO WALL areas where it was not possible before. The procedure for developing a system based on a dedicated wire is divided into the following three steps:

1. Routing.--Ascertain from a mine map the area of coverage desired, considering that the dispatcher position is the key position. Mark out on this map a route for a single line that runs in the same entryway as the trolley wire-rail to which communication is desired. Avoid branches on this route, If necessary, use a second or third such route to cover all regions of the mine. Short side- tracks need not be covered initially. If a branch on the route will cover the desired region with less length of wire, FIGURE 5-14, - Termination of the dedicated wire. ,--UTILITV BOX the mine, although in certain circum- / rFUSE HOLDERS 131 / stances moving it somewhat away from DtDlCATE-D WIRE I 1 DEDICATED WIRE such a center might produce more favorable results. BRANCH

As an example of what might be achieved by this means, consider a dispatcher's position for which the signal

RESISTORS attenuation is 80 dB from his position to 67 OHM 10 WATTS the farthest reach of the mine. This attenuation means that an initial 25-volt rms signal provided by the dispatcher's transmitter would be reduced to 2.5 mV at the farthest reach of the mine. This FIGURE 5-15. - Signal splitter. level of signal is marginal, and thus the dispatcher would have poor communication special-purpose wire, the dispatcher's to those motors on the far side of the transmitter should be directly connected mine. If the dispatcher's transceiver to the end or ends of the wire that con- were moved to the center of such a mine, verge on the dispatcher's station. The the signal attenuation should drop to return wire of the transmitter should go one-half, or 40 dB, from this central po- to earth or to the rail. sition to the extremities of the mine. The 40 dB of attenuation would provide As noted before, the use of branches signal levels of 250 mV at the extremes should be minimized, When the routes are of the mine, 100 times bigger than would short, (considerably less than 10 miles), result if the dispatcher's transmitter resort can be made to branches on a dedi- were located at one edge of the mine. cated wire. When more than one wire is used, they should be run in separate en- Such a substantial improvement in tryways. The reason that branches are signal levels throughout the mine would undesirable is that a branch reduces the change an otherwise marginal operation signal level by 2 to 1 (6 dB). On short into a completely adequate communication runs, such a loss can be tolerated, but system. Insofar as the ispatcher is on runs approaching 10 miles, such a loss concerned, his operation would remain the may be too high. same. He would still have the carrier phone speaker and microphone located at 5.3. 1c Using a Remote Transceiver his dispatching position; however, the control and audio signals would be trans- Frequently the dispatcher is located mitted from his position through a at one edge of the mine complex. If this twisted shielded pair to the remote is the case, the communication range transceiver (fig. 5-16). Thus, it would required must be extensive in order that be necessary to run an audio cable for the dispatcher be able to reach motormen whatever distance was necessary to reach on the opposite side of the mine. In the center of the mine. In mines where some instances, a convenient way of solv- multipair telephone cable is used, a pair ing the dispatcher's problem is to use a may be available for this purpose. If remote transceiver located at the most not, the expense and inconvenience of in- favorable place for reaching all parts of stalling such a cable would be justified a mine complex. The location of such a to assure adequate coverage for the dis- remote transceiver is likely to be near patcher's commnication system. the center of the rail haulage system of NOTE IF THE TROLLEY IS SECTIONALIZED,COUPLlNG CAPACITORS 15 "I, TOWVOLTS~ MUST BE USED 5. Insist that vehicle manufactur- TO PROVIDE A PATH FOR THE CARRIER COMMUNICATIONS. ers indicate the 88- to 100-kHz operating impedance of their vehicles, and select RECTIFIER RECTIFIER aN0.1 TROLLEY WIRE vehicles that show high operating impedance at the carrier frequency. AUDIO AND TO TRANSCEIVER DISPATCHER 6. If possible, use at least a 50- foot setback for rectifiers that are to - RAIL be installed in the mine; this setback will permit tuning of the rectifier leads to raise the impedance of the rectifier.

7. Ask the rectifier manufacturers to supply internal filters in series with the voltage to raise the carrier frequency impedance to a high level.

8. Plan and design isolators for all other appreciable bridging loads across the trolley wire rail.

5.3.2 Improving Telephone Systems

FIGURE 5-16. - Dispatcher's remote transceiver. As mentioned earlier, hardwired phone systems fall into three major categories: single pair (party-line), multi- 5.3.ld Summary pair, and multiplex phone systems. A major disadvantage of single-pair systems A substantial number of the problems is that each telephone must be used in a associated with maintaining good trolley party-line arrangement. This prevents comuunication systems can be avoided by simultaneous conversations in the system advanced planning. For those planning a and reduces its usefulness for discussing comuunication system for a new mine, the maintenance problems or other uses that following suggestions are offered to as- can tie up the system for long periods of sure optimum operation of the trolley time. Multipair and multiplex systems carrier phone system when installed: provide for many simultaneous conversations but until recently did not possess 1. If the trolley wire is section- the paging ability. alized, make sure capacitors (5 pF, 1,000 volts) (some systems may require All three of these systems can usu- even higher voltage components) tie the ally be improved if the basic reasons for sections together. poor performance or high noise levels are understood. For instance: 2. Plan to operate as many auxiliary loads as is practicable on mine ac Heavier gage wire presents less at- power rather than from the trolley wire tenuation to the signal and results in power. better coverage over greater distance.

3. Consider the use of a dedicated Splicing technique has a large ef- wire to aid signal propagation. fect on signal strength.

4. Select carrier phone transceiv- Twisted pair cable can reduce noise ers that show a high value of standby pickup. impedance. Even when proper precautions have loopback switch is left in the open posi- been taken, all hardwired systems are in- tion. If a line break should occur any- herently unreliable. For example, if a where in the underground phone line, the telephone line is broken or shorted by a loopback switch can be closed and each roof fall, all telephones beyond that phone will still be able to communicate point are severed from communication to with other phones. Depending upon the the outside. If the line is shorted, physical layout of the mine, forming an communications in the entire system may underground loop may actually require be severely affected or lost completely. less wire than if a single line is strung These deficiencies can be corrected by with many branches running to the indi- the following methods: vidual phones. It is imperative that the loopback switch be always left open under Adding loopback to the phone line. normal conditions to avoid "masking" line breaks. Sectionalizing the phone system. Another method of establishing loop- 5.3.2a Loopback Methods back is by using an overland radio link. In this type of system the mine telephone A major disadvantage of any wired signals are returned from the end of the phone system is its dependence upon a line to the surface through a ventilation continuous phone line running throughout shaft or borehole. At the surface a two- the mine. If this phone line is broken, way radio base station establishes an communication with all phones inby the overland radio link to a second station break is lost. Alternate communication near the dispatcher or general mine fore- paths, or loopbacks, can be established man's office. Note that provisions must as shown in figure 5-17 to overcome this be made for dc paging. deficiency. If a line break should occur, the loopback switch can be closed, Each of the loopback systems de- allowing each and every phone to still scribed above utilized a loopback switch communicate with all other phones in the that during normal operation (no line system. breaks) is left in the "open" position. This loopback switch serves an important Another way to implement loopback is function in any loopback system. For in- to return the phone line to the main stance, consider what would happen in shaft using a different underground path. a loopbacked system with no loopback No matter which method of loopback is switch, or if the switch is normally left used, the operation of the systems is closed. No communication outages would similar. During normal operation the be experienced when the first line break occurred because each phone would still be connected, through one or the other DISPATCHERS LOCATION legs of the loop, to the system. The - problem is that unless someone under- LOOPBACK PHONE ground noticed the broken phone line, everyone would assume that the system

\ LOOPBACK WITCH was completely intact because no cow muni.cation difficulties were being experienced. The system could operate in this mode for a long period of time. How- LINE BREAK ever:, when a second line break occurred MAIN CABLE comnnxnications to and from all phones be- I I I tween the two breaks would be lost. Note also that each time the dispatcher talks he hears himself on the loopback phone. This feature alone assures that the phone FIGURE 5-17. - Phoneline loopback. line is intact. 5.3.2b Sectionalizing the Underground 5.3.3 Summary Network Advanced planning is essential to The desirability of selective area the successful design and installation paging and simultaneous conversation of any communication system. The design capability along with the maximum possi- plan should take into consideration ble use of two-wire transmission line changes in system requirements to meet makes the use of a zoning or sectional- communication demands throughout the en- ization of the mine telephone system at- tire life of the mine. tractive. In this method, each zone or section in the underground complex is Single-pair, multipair, and multi- served by its own cable pair. plex systems are the basic choices available once it has been determined that To see how the telephone sections a hardwired system will best meet the would be interconnected, consider the communication requirements. A consider- simplified four-section system shown in able percentage of the expense involved figure 5-18. Within each area, the pag- in each of these systems is due to the ing telephones would operate normally. distribution (cable) network, and advance That is, all phones in each area would planning is especially critical in this operate on a party-line basis. When con- area. Wire lines to meet telemetry re- tact with a phone outside the local area quirements for remote control and inon- is desired, connection to the area being itoring of equipment and atmospheric called would be made at an outside cen- conditions should also be recognized. tral exchange. This type of system could Note that MSHA regulations may prohib- also be made more reliable by having two it running two systems in a single different signal paths (loopbacks) avail- cable. able between each area and the central exchange. Methods also exist that allow improvement of systems already installed. The performance of trolley carrier systems can be improved by removing or isolating bridging loads on the trolley wire that cause signal attenuation. Dedicated lines or remote transceivers can also be used to improve the quality of these systems.

General maintenance and splicing technique can have a large effect on the quality of voice service over wire phone systems. These systems can also be made more reliable by providing loopback paths so that each phone will remain connected to the system in case of a line FIGURE 5-18. - Sectionolizotion of a phone system. break. BIBLIOGRAPHY

1. Aldridge, M. D. Analysis of Com- 3. Parkinson, H. E. Mine Pager to munication Systems in Coal Mines. Bu- Public Telephone Interconnect System. Mines OFR 72-73, June 1973, 211 pp.; BuMines RI 7976, 1974, 14 pp. available from NTIS PB 225 862. 4. Spencer, R. H., P. OIBrien, and 2. Lagace, R.L., W. G. Bender, J. D. D. Je.ff reys. Guidelines for Trolley Car- Foulkes, and P. F. OIBrien. Technical rier Phone Systems. BuMines OFR 150-77, Services for Mine Communications Re- March 1977, 170 pp.; available from search. Applicability of Available Mul- NTIS PB 273 479. tiplex Carrier Equipment for Mine Tele- phone Systems. BuMines OFR 20(1)-76, July 1975, 95 pp.; available from NTIS PB 249 829. CHAPTER 6.--INSTALLATION TECHNIQUES

6.1 The Basic Philosophy Each installation should be well planned. After an installation is The investment involved in any com- completed, the technician should ask munication system represents a consider- the question, "What can go wrong with able sum. Even though it is desirable this unit or line?" Remember the adage, that the system work properly each and "Whatever can go wrong, will. " Preven- every time it is called into use, some tive measures taken during installation failures are bound to occur. Most fail- will pay off in the long run. ures, however, and especially those that occur most frequently, are due to poor 6.2 Pager Phone Ins tallation installation techniques. An extra hour spent at an installation site can save The pager phones used in many under- many maintenance trips and many frustrat- ground coal mines are battery-operated , ing hours of system troubleshooting. party-line telephones with provisions for loudspeaker paging. The system is usual- Typical faults likely to cause com- ly two-wire, nonpolarized, and operated munication outrage are by self-contained batteries. Many of the individual units are certified as Pager phone systems permissible.

Poor splices aggravated by corrosion. 6.2.1 Mounting

Strain relief not provided. Pager phones are designed to be mounted on an upright support at the Drip loop not provided. desired location. For convenience, the phone should be mounted 5 feet above the Incorrect branch connections. floor where there is no obstruction to using the handset or removing the cabinet Overloading the circuit. front cover for servicing or battery replacement. In low-coal situations, a Poor battery connections. suitable height for installation should be selected convenient to the normal Improper wire size or type. operator's position at the site selected. About 12 inches of free space on each Lightning strikes. side of the phone should be provided for cabinet access. The phone should be pro- Improper placement of wire runs. tected against direct exposure to dripping water and should not be allowed Carrier phones to rest in a puddle of water. The mounting location should be convenient to Mounting transceiver near load resis- a work location and have a safe, unob- tors or other sources of heat. structed area for a worker to stand and use the phone. The phone must be in a Tracks not electrically bonded. location where the worker will not be in the path of moving vehicles or falling Cable abrasion due to poor mounting debris. Each telephone is normally well location. insulated, but it is still good practice to provide an insulating mat or dry Disconnected battery. planking for the user to stand on.

Poor mechanical installation. 6.2.2 Connections NEDA No. 923 or No. 926 (National Elec- tronic Distributors Association). To in- For handling convenience, the branch stall batteries, it is necessary to open line or connecting cable to each individ- the pager phone cabinet and inspect the ual telephone can be a lighter wire gage battery compartment. Remove the old bat- than the main cable. Each connection to tery by loosening the retaining clamp, the main line should be a good electrical and either unscrew the battery terminals and mechanical joint, protected by a to release the battery wires or remove careful double wrap of plastic electrical the battery plug, depending on the bat- tape. tery type. Remove the battery, and care- fu1l:y wipe out the battery compartment to Special care should be taken to in- remove dirt and moisture. Place a fresh sure that each splice is a good electri- bat tlery in the compartment, and secure cal and mechanical connection. Connec- the retaining clamps tight enough to re- tions that are of poor or marginal strain the battery without crushing or quality, or that are not adequately pro- bending the battery case. Reconnect the tected from moisture, will contribute to battery wires, being careful to observe poor performance. During periods when the polarity markings noted on the case. humidity levels are high, especially dur- If the plug-connector type is used, do ing the summer months, corrosion will not force the connector. Correct polar- form on all exposed splices. As this ity is maintained when the larger connec- corrosion builds, audio levels decrease tor pin fits in the larger hole. The and line noise increases until eventually difference in pin sizes is not great, so the entire system becomes useless. a mismatch can be forced. If the connector does not mate easily, reverse it and Connections at the phone depend on try again without forcing. After replac- each manufacturer's design and on indi- ing the battery, close the cabinet and vidual state or local requirements. A mark the date of battery replacement majority of the phones provide two ex- either on the outside of the cabinet or posed spring-loaded terminals for attach- in a log book. ing the wires. For proper connection, it is necessary to strip the installation CAUTION away from each conductor in the pair, seal off the exposed area of the cable Pager phone circuits are normal- with plastic electrical tape to keep out ly designed to provide sufficient moisture, and then insert one of the ex- current limiting with the specified posed conductors into each of the cabinet battery. If other battery types are terminals. Some states, such as Pennsyl- used, such as the nickel-cadmium re- vania, do not allow the use of exposed chargeable type or one of the alka- terminals at the face area of gassy line, long-life, high-current vari- mines. For these applications, some eties, the circuit may not be able to phones are equipped with twist-lock con- limit the available current to a safe nectors at the end of a short cable. value. REPLACE WITH RECOMMENDED Each connector is mated with a similar ---BA,TTERY ONLY. connector on the drop or branch line to A complete the installation. In either type of installation, there should be a Battery life is not easy to predict, drip loop below the cabinet to prevent beca.use of the many operating variables condensate from running down the cable that affect the average current drain. into the cabinet. In general, the batteries in a telephone system that is used many times a day may 6.2.3 Batteries have to be replaced every 4 to 6 weeks, whi1.e a telephone system that is seldom Pager phones are usually operated by used may keep its batteries at usable one (or two) 12-volt, dry-cell batteries, strength for 4 to 6 months. Each battery change should be re- 6.3 Phone Lines and Transmission Cables corded, either on the telephone cabinet or in a central log. Experience gained 6.3.1 Phone Lines over a period of time will help predict when a battery in a particular phone is The cable used to interconnect un- reaching the end of its useful life. derground pager phones must be rugged Periodic verification of battery status enough to withstand the underground envi- at each phone should be made with a volt- ronment and also have the proper elec- meter and recorded in the log. (Measure trical characteristics for requirements battery voltage while under load; that of the pager system. Generally, the is, during paging.) When the battery cable used for this purpose is a twisted voltage drops to a value that is 75% to pair of solid-conductor wires that has a 80% of the installed level, it should be nonwater-absorbing, flame-retardant insu- replaced. For example, for a 12-volt lation with a rating of 600 volts dc and battery, the replacement level is about an outer abrasion-resistant covering. 8 to 9 volts. The conductor used depends on the installation; recommended sizes are 19 AWG to 6.2.4 Fuses 14 AWG.

Fuses are provided in pager tele- Many telephones used underground, phones as an added precaution against ex- particularly those used at the working cessive current in the external circuit. face, are subject to periodic relocation. Current-limiting circuitry is normally To allow for this, and to reduce the provided in the telephone, but the fuse problems associated with repeated cable is an additional safeguard. No provision splicing, some convenient length of wire is made in most phones to store a spare (say, 500 feet) can be included as part fuse. It is good practice to tape two of the branch line. This extra wire can additional spare fuses to the inside of be kept reeled, or neatly coiled in a the cabinet when the phone is first in- bundle and secured with a few wraps of stalled. Then, the correct fuse will be plastic electrical tape. The extra wire available at the phone if it is needed. should be hung near the telephone in a Make sure the fuses do not and cannot place free of dripping water or water ac- short circuit any circuitry. cumulation, and should be supported by an insulated hanger that is isolated from 6.2.5 Amplifier Loudness power or trolley wires. The practice of coiling the cable is recommended, but Each pager phone has a loudspeaker, with certain restrictions. If the cable powered by its own internal amplifier, is used to transmit monitor signals via that is switched on by the dc paging sig- an RF (radio frequency) carrier imposed nal. The available audio power is about on the two-wire pager phone line, the 5 watts, which is adequate to be heard coiled cable becomes an inductor that above most mine noises. Many telephones will impede the proper transmission of have a volume control for the speaker. the RF signal.' During installation, the speaker should be oriented, and the volume set, to in- Methods and recommended techniques sure adequate coverage in the area. for the permanent installation of phone lines are presented in a Bureau of Mines During setup, someone should page from another location to the phone being l The addition of equipment to a phone installed. The volume control should be system could violate intrinsic safety set to the desired level during the pag- standards; check with MSHA for detailed ing. The telephone cabinet should be application information. positioned to direct maximum sound to the work area. handbook (2), including installat ion, traf f:ic in the mine. The safety and pro- lightning protection, cable selection, ductivity of the mine depend, to a large and splicing methods. Note that 30 CFR measure, on the ability of the dispatcher specifies certain requirements for cable to maintain direct contact with all mo- installation. tormen via the carrier phone system. For this reason, the carrier phone installa- 6.3.2 Leaky Feeder Cable tion should be carefully thought out, and the workmanship should be of the highest Installation of leaky feeder cable caliber. requires some special techniques. A typical installation of leaky feeder cable CAUTION is shown in figure 6-1. For instzllation of the repeaters, refer to the manufac- Installation procedures in this turer's installation guide. Hanging the section are guidelines and not com- leaky feeder cable requires clamps such prehensive technical instructions. as those used for conduits or other power Procedures described in this section cables. In areas where corrosion may be must be performed by people thorough- a problem, stainless steel or plastic ly qualified to do such work. In- clamps should be used. vpical hangers stallations should comply with manu- are shown in figure 6-2. The type of in- f acturer' s recommendations, good sulated hanger shown supports the leaky safety procedures, and all applicable feeder cable from the messenger cable. codes and regulations. Leaky feeder cable should be supported at intervals of 5 feet and is usually termi- 6.4.1 The Dispatcher Location nated with an antenna. The trend in modern coal mining is 6.4 Carrier Phone Installation to locate the dispatcher aboveground in a separate building or a separate room in The primary function of the carrier the rnine office complex. This location phone system is to provide a reliable provides a continuously manned communica- communication network over which the dis- tions center even if the mine must be patcher can direct all tracked vehicle evacuated owing to emergencies or ventilation failures. Since 1974 the mining 2~nderlinednumbers in parentheses re- laws of West Virginia have required that fer to items in the bibliography at the the dispatcher be located on the surface end of this chapter. in all new mines and for existing mines if the dispatcher is relocated (Article 22-2--37, Part T5). / REPEATER 1 1 REPEATER 1 REPEATER

lW0 WAY CI Underground dispatchers1 locations vary greatly, depending on the mine lay- I REPEATER SPACING I out and growth. The two most common lo- I rDOa FEET I cations chosen are at the bottom of the main shaft or near the physical center of FIGURE 6-1. Typical instal lation. - the mine.

The carrier phone equipment is usually installed on a panel which is mounted on a wall adjacent to the dispatchers' desk. l'his panel provides one convenient location for all the subassemblies that make up a carrier phone and INSULATED MESSENGER protects the interconnecting cables METAL HANGER CABLE HANGER from unnecessary flexing- and stretching.- FIGURE 6-2. - Hanger hardware. The panel should be made from at least 118-inch-thick steel plate if the carrier transceiver electronics and to recharge phone uses a power-conditioning unit or the battery. The circuit generally used resistor box that contains series- in this unit contains a large series- dropping resistors. dropping resistor that under normal operating conditions dissipates several CAUTION hundred watts. The high temperature associated with this power dissipation Remove the electronic subassem- would be harmful to the sensitive trans- blies from the mounting plate during ceiver circuitry; therefore, it is a welding operations. Keep all elec- separate unit that can be located where trical cables and other nonmetallic it will not heat up the transceiver. materials away from the welding area. When only the series-dropping resistor is This will prevent the carrier phone contained in this unit, it is called a components from being damaged by heat resistor box. It is also referred to as during welding operations. the battery charger by some manufacturers; in this case, it would contain the The microphone-speaker assembly is dropping resistors and the charging the only part of the carrier phone that circuits. interfaces directly with the dispatcher; therefore, it must be located within easy The main consideration when locating reach. The speaker volume control should this unit is its heat dissipation and its also be within easy reach. relationship to the heat-sensitive transceiver. The heat is dissipated into the Locate the transceiver on the panel ambient air and into the structure on at either side of the speaker assembly, which it is fastened; therefore, it is taking into consideration the location of important to follow the manufacturer's the interconnecting cables. Leave room mounting instructions carefully. for the excess cable to be coiled up and secured to the panel. The power unit should never be mounted below the transceiver (heat Temperature-sensitive electronic rises) or the speaker enclosure. Keep circuits are located inside the trans- the power unit a minimum of 6 inches away ceiver assembly. Therefore, it should be from either side or the top of the trans- protected from the temperature extremes ceiver. If mine personnel can come in produced by load resistor banks and room contact with the hot surfaces of the heaters. For reliable operation, the am- power-conditioning unit, a protective bient operating temperature range that grille should be added. This grille the transceiver is exposed to should be should be open at the top and bottom to restricted to -40' to +140° F. allow for proper air circulation.

Approximately 6 inches of clearance A 12-volt lead-acid automotive-type should be left around all surfaces on storage battery is most often used as an which the connectors and/or fuses are external emergency power source with car- mounted. If possible, the connector- rier phones. When locating this type of mounting surfaces should be protected battery, the prime considerations should from dirt and moisture. Sufficient be the accessibility of the fill caps for clearance should be allowed to remove ac- servicing and proper room ventilation to cess covers and open-hinged panels so handle the outgassing of hydrogen. The that adjustments can be reached and plug- battery should also be kept away from main modules can be changed. terials that are susceptible to corrosion by sulfuric acid. The power-conditioning unit is used to convert the trolley voltage (typical- The ideal temperature range for the ly 300 or 600 volts dc) or the local battery is 60" to 80' F. Low tempera- ac power to 12-volt dc power for the tures reduce capacity but prolong battery life; high temperatures give some addi- ground for the mine. If this is the tional capacity but reduce total battery case,, the RF signal common can be wired life. Temperatures above 125" F can ac- to the shaft structure at the surface or tually damage some of the battery compo- the hoist house structure. A minimum 14 nents and cause early failure. AWG insulated copper wire should be used for this purpose. If the input power is Once the various subassemblies have suppllied by the trolley wire, then the RF been physically mounted to the panel, the signal common and the power common should final installation task is to make the be juimpered together. electrical interconnections. This procedure consists primarily of inserting Connect all chassis and case grounds cablelnounted connectors into the proper from the lugs or studs provided by the receptacles on the subassemblies and con- manufacturer to earth ground. Do not necting the signal and power cords into rely on the mechanical mounting of the the proper mine ectrical systems. case for a ground connection; always run a separate ground wire to the earth A block diagram of a typical carrier grou~nd. Refer to the Code of Federal phone interconnecting cable system is Regulations, Title 30, Part 75, Subpart shown in figure 6-3. The cable connected H, for explicit grounding requirements. to the trolley power and/or building power should be installed last. The other The earth ground connection or cables may be installed in any order that buillding is generally made to a metallic is convenient. water supply pipe or to the structural ironwork of the building. In either CAUTION case, the connection should be made close to where the pipe or structure enters the Clean and inspect all connectors earth to insure a minimum resistance be- before mating. Study the keying ar- tween the connection and the earth. rangement or polarization to prevent j amming and misalinement. The input power to the dispatcher's phone is supplied from either the trolley Before connecting power, verify that wire (typically 300 to 600 volts dc) or the RF signal common and the case and the local 115-volt ac power. If trolley chassis grounds are all connected. The wire input power is to be used with the RF signal common should be an all- dedicated line coupling method, then the metallic connection to the rail system, in-line fuse holder cable is connected to even if the dispatcher is located above- only the hot input power terminal on the ground. Of ten the rails are bonded to phone. The other end of the cable is the steel structural members of the main connected to the trolley wire. Whenever shaft to help establish a good earth trolley wire input power is used, the common power connection and the common sign.al connection are jumpered together and wired to the rails, POWER -! If the carrier phone is not located TRANSCEIVER SPEAKER adjacent to the haulageway, then a wall- mounted fuse box should be used instead of t.he in-line fuse, Terminate the wire on t.he line side of the fuse block, Us- MICROPHONE ing the same type of wire, make a welded

I (IF EXTERNAL TO connection to the rail and run this back I TRANSCEIVER) I L ------1 e to the fuse box. Now, two-wire neoprene- jack-eted-type portable cable may be FIGURE 6-3. - Typical carrier phone intercon- used to supply power to the dispatcher's nect ing cable system. phone. NOTE Direct coupling involves wiring the hot RF signal connecting point directly The manufacturer's detailed in- to the trolley wire with the in-line stallation instructicns should be holder cable provided with the phone. If carefully followed to make certain the dispatcher's office is remotely the carrier phone is compatible with located, then a fuse box adjacent to the the polarity of the mine trolley trolley wire should be used. If the in- power. put power to the phone is t.o be supplied by the trolley wire typically (300 to 603 The 12-volt power fuse and the trol-- vo1t.s dc) , then t.he hot power connecti-on ley power fuse should be removed to per- is jumpered to the hot RF signal connec- mit making the battery connections with- tion with a length of 14 AWG insulated out a load immediately being placed copper wire. Do not install the 3-ampere across the battery. The ground.ed side of in-line power fuse until all ground con- the battery should be connected first. nections are made up. If the mine has a positive trolley system, then the negative side of the bat- A second meth~dof signal coupling tery should be grounded. The battery is to connect the dispatcher's phone to a post is made of lead, as are the internal single conductor dedicated wire. This connections between the post and the bat- wire would originate at the hot RF signal tery plates. If too great a torque is connecting point. applied to the clamping bolt, the internal connections can develop hairline 6.4.2 Vehicle Installations fractures that can cause an intermittent connection. To avoid this condition, a The carrier phone typically consists second wrench should be used to steady of a transceiver assembly, a microphone- the bolthead while tightening the nut. speaker assembly, and power conditioning units; these are sometimes an integral Fuses provide an intentionally weak- part of the transceivers (fig. 6-4). ened part of an electric circuit and Carrier phone equipment is installed on thereby act as a safety valve in the all types of tracked vehicles. Three event of dangerous overloads. This pro- commonly used vehicles found on coal tects both personnel and equipment from haulage systems are locomotives, portal potential fire hazards due to overheating buses, and utility cars. Each of these of the carrier phone. vehicles has a different seating arrangement for the driver (fig. 6-5j.

The microphone-speaker assembly is Fuses do not provide protection the only part of the carrier phone that from dangerous high-voltage shocks. interfaces directly with the vehicle operator. Thus, it must be located sc Fuses come in many sizes, types, and that it can be easily reached. If the electrical ratings. Always use a re- microphone hanger is not conveniently lo- placement fuse that has the same rating cated, it will not be used by the opera- as specified by the carrier phone tor, and the microphone and cord will manufacturers. suffer unnecessary damage from mistreat- ment. The speaker volume control should The last step in installation is to also be within easy reach, and the speak- connect the power wire. Two commonly er should be pointed directly at the used installation methods are direct cou- operator to provide the best reception. pling to the trolley wire, and single dedicated line coupling. For the in- Vehicles without dual controls re- staller's safety, the input power should quire the operator to assume two dif- be connected last. ferent positions in front of the same .T0 BATTERY TROLLEY BOX

TRANSCEIVER FIGURE 6-4. - Typical carrier hones. controls so that he can observe the track are located inside the transceiver assem- ahead of him. This further complicates bly, Therefore, it should be protected the positioning of the microphone-speaker from temperature extremes such as those assembly. It is sometimes helpful to use procluced by load resistor banks and the two microphone hangers for this type of vehicle's drive motors. installation so that the microphone is convenient no matter which way the vehi- It is important that installation of cle is traveling. the transceiver does not reduce the minimum roof clearance of the vehicle. Ap- Entanglement of the microphone cord proximately 6 inches of clearance should with other vehicle controls, causing be lleft between the vehicle and the sur- an unsafe operating condition, should faces on which the connectors and/or also be considered when locating the fuses are mounted. If possible, the con- microphone-speaker assembly. The micro- nectors should be protected from dirt and phone should also be mounted in an area moisture. Sufficient clearance should be that will protect it from falling debris allowed to permit removal of access cov- and/or dripping water. ers and open-hinged panels so that adjustments can be reached and plug-in mod- Once a suitable place for the ules can be changed. microphone-speaker assembly has been determined, the transceiver location can be The main consideration when locating considered. The first restriction on its the power conditioning unit is its heat location is the length of the cables run- dissipation and its relationship to the ning between the different assemblies. heat-sensitive transceiver. The heat is Temperature-sensitive electronic circuits dissipated into the ambient air and into FIGURE 6-5. - Typical mine vehicles. the structure on which it is fastened; CAUTION therefore, it is important to follow the manufacturer's mounting instructions Remove the subassembly from the carefully. The mounting surface should mounting plate during the welding be a massive structural part of the vehi- operation. Keep all electrical ca- cle that can absorb the heat transferred bles and other nonmetallic materials from the unit. away from the welding area. This will1 prevent the carrier phone compo- If it is a horizontal surface, a nents from being damaged by the heat minimum of 3 inches should be allowed on generated from the welding operation. all sides; if possible, nothing should be mounted above the unit. If it is a ver- Procedures for making the electrical ticle surface, a minimum clearance of 3 connections between carrier system compo- inches above and below the unit should be nents are similar to those for the dis- provided for proper air circulation. The patcher's installation (paragraph 6.4.1). power unit should never be mounted below For the installer's safety, the trolley the transceiver; if possible, a minimum shoe should be removed from the trolley separation of 1 foot in all other direc- line., tions should be provided. Proper cable protection will reduce A 12-volt lead-acid automotive-type the downtime of the communication system storage battery is most often used as an and prevent accidents, such as loose ca- external emergency power source with car- bles tripping up mine personnel when en- rier phones. When locating this type of tering or leaving the vehicle. The in- battery, the prime considerations should terconnecting cables should be located, be the accessibility of the fill caps for if possible, away from areas occupied by servicing and proper room ventilation to mine personnel or supplies. This will handle the outgassing of hydrogen. The prevent cutting and crushing of the ca- battery should also be kept away from ma- bles caused by shifting loads. terials that are susceptible to corrosion by sulfuric acid. Heavy-duty plastic ties or cable clamps should be used to lash the cord to The ideal temperature range for the the frame of the vehicle. If possible, battery is 60" to 80" F. Low tempera- the cable should be run under overhanging tures reduce capacity but prolong battery parts of the frame to protect it from life; high temperatures give some addi- falling debris and/or dripping water. tional capacity but reduce total battery Enough slack should be left to form a life. Temperatures above 125" F can ac- drip loop to prevent condensate from run- tually damage some of the battery compo- ning down the cord and into the rear of nents and cause early failure. the connector. All holes in the frame through which the cable runs should be Most carrier phone components are gromnneted. The cable should not be run supplied with mounting plates that can be over sharp edges that might abrade it. tack-welded to the vehicle. This pro- Excess cable should be neatly coiled and vides a permanent mounting surface with secured with plastic electrical tape or tapped holes or threaded studs onto which cable ties and then clamped to the frame. the subassemblies are fastened. This ar- The cable should never be stretched be- rangement also provides an easy means of tween clamps; this will leave it in ten- interchanging subassemblies for mainte- sion, causing an elongation of the insu- nance purposes. lation and the conductor. In addition, the jacket will lose a considerable part 6.5.1 Cage of its resistance to mechanical damage, making it vulnerable to cutting, tearing, The cage equipment consists of the and abrasion. transceiver, which contains a speaker, microphone, and push-to-talk switch, a 6.5 Carrier Current Hoist Phone battery, generally of the lead-acid type, a cage coupler, and the connecting ca- Carrier current hoist phones utilize bles. The transceiver is the only unit existing physical conductors (the hoist that must be mounted within the cage, rope) for a transmission medium. Typical where space is usually at a premium. For hoist radio hardware is shown in figure that reason, it should be recessed in the 6-6. cage wall. The battery must be mounted

MICROPHONE

-TALK FOOT SWITCH

SPEAKER GRILL

COUPLER CABLE

TRANSCEIVER i SPEAKER I GRILL - MICROPHONE\ --- PUSH-TO-TA LK SWITCH --.

CONDUIT

BATTERY

COUPLER CABLE COUPLER

FIGURE 6-6. - Hoist radio hardware. in an upright position either inside the to or suspended from the headframe struc- cage or on top. Mounting the battery on ture. The coupler cable from the head- the top of the cage provides early access frame coupler to the transceiver should for charging or replacement. The cage be run through conduit. coupler is bolted to the hoist rope above the cage with the conical section up to 6.6 Summary act as a rock shield. It is suggested that the battery be placed within a pro- Tables 6-1 through 6-4 are basic tective enclosure to prevent a short cir- checklists for four types of installa- cuit which could be caused by debris. Be tion: Pager phone, carrier phone, hoist sure the cable and unit connectors are phone, and cable. It is evident that not clean before mating them. Conductive all criteria are covered in these basic dust in a connector interface may cause checklists. Additional items that are the equipment to malfunction. Cables be- peculiar to a specific installation may tween the battery, transceiver, and cou- be added. pler should be strategically placed to avoid damage. Cable clamps should be There are some procedures associated used to take up slack; a loose cable is a with any installation. They are hazard to personnel and equipment. It is suggested that cables be run through READ INSTRUCTIONS BEFORE STARTING! heavy-gage conduit. DO IT SAFELY! 6.5.2 Hoistroom and Headframe DO IT CAREFULLY! The hoistroom equipment is shown j-n the upper part of figure 6-6. The hoist- CHECK IT THOROUGHLY ! room will contain the power supply, transceiver, push-to-talk foot switch, SEEK HELP IF NECESSARY! and microphone. The power supply and transceiver may be wall mounted. It is Short cuts in installation will best to leave at least 6 inches between probably lead to equipment malfunction or the power supply and transceiver, and the damage. All communications equipment power supply should not be mounted below should. be tested with transmissions to the transceiver. The microphone should and from another unit after installation. be placed so that it can be within 2 inches of the operator's mouth while the A little extra time spent in the in- operator has both hands on the hoist con- stallation phase of a communication sys- rols. The foot switch should be in easy tem can mean the difference between a reach of the operator's foot while the reliable, well-managed system and an operator is at the controls. undependable system requiring frequent maintenance. The headframe coupler is located at the top of the shaft. It may be clamped TABLE 6-1. - Pager phone installation basic checklist

Item Yes No Comments 1. Has the exposed area of the cable been sealed with electrical tape to keep out moisture? 2. Is the drip loop positioned properly to keep condensate from getting into phone? 3. Is the tension in the spring terminals sufficient for a good connection between the wire and phone? 4. Is the twist-to-lock connector in the locked position? 5. Has the battery been tested? 6. Have spare fuses been provided? 7. Has the phone been called from a distant phone and been found operable? 8. Is the volume satisfactory or has the amplifier been adjusted for proper loudness? 9. Is the phone mounted at a proper height for convenience? 10. Is an insulating mat or dry planking provided on which the user may stand? 11. Is all cabling secured and protected from passing machinery? 12. Are all splices QUALITY splices? 13. Are the cables heavy enough?

TABLE 6-2. - Carrier phone installation basic checklist

Item Yes No Comments 1. Is the microphone-speaker assembly within easy reach? 2. Is the transceiver protected from temperature extremes (away from power conditioning unit)? 3. Is the power conditioning unit mounted so personnel will not come in contact with it? 4. Is the power conditioning unit covered by a protective grille? 5. Has the battery been tested under load? 6. Have mating surfaces of connectors been inspected and cleaned? 7. Have all cable connectors been firmly joined to the units? 8. Are threaded connectors tightened? 9. Have all chassis and case grounds been wired to earth ground? 10. Can the microphone cord become entangled in the vehicle controls? 11. Are cables protected from abrasion? 12. Are all components mounted low enough so that minimum roof clearance has not increased? 13. Has sufficient clearance been given to allow easy removal of access covers, hinged panels, etc. ? 14. Are the bridging capacitors in place on all sectionalized trolley lines? TABLE 6-3. - Hoist phone installation basic checklist

Item Yes No Comments 1. Is the microphone of the transceiver at a proper height (mouth level) for average person? 2. Is the battery accessible for charging or replacement? 3. Is the cage coupler firmly mounted? 4. Have mating surfaces of connectors been inspected and cleaned? 5. Have cable connectors been firmly joined to the units? 6. Are threaded connectors tightened? 7. Are cables protected from damage? 8. Have any slack cables been tied down (clamped)? 9. Is headframe coupler firmly connected to or suspended from headf rame? 10. Are microphone and push-to-talk switch near hoist controls? 11. Is the transceiver frame firmly attached to the cage? 12. Have all completed connections been sprayed with silicone or other moisture-inhibiting spray?

TABLE 6-4. - Telephone cable installation basic checklist

Item Yes No Comments 1. Has proper cable been selected according to system plan (type and gage)? 2. Is the cable supported at the proper interval (approximately 10 feet for twisted pair or figure-8 cable and 5 feet for leaky feeder) ? 3. Do droplines have strain relief on main line and tap line? 4. Are splices mechanically sound and protected from moisture? 5. Is strain relief used at splices? 6. Have lightning arrestors been used according to code? 7. Has extra insullation been provided where the cable crosses the trolley or other high-voltage lines? 8. Is the cable positioned out of the way of machinery and secured in place? 9. Are all splices QUALITY splices? BIBLIOGRAPHY

7.1 General 7.2.2 Pager Phones

Preventive maintenance practices The most readily available test set are listed in the manufacturers' instruc- to determine if a pager telephone is tion books. In general, equipment that operating correctly is the pager phone requires frequent and extensive preven- itse1.f. The following physical check of tive maintenance is generally the most the slystem can be performed at any phone costly. The manpower spent on these fre- stati-on. quent trips to remote areas is such that it is usually better to invest in a more 7.2.2!a Listen Circuit costly system which requires little preventive maintenance. The best preventive Remove the handset from its cradle maintenance for the system is a good and listen to determine if the circuit is installation. f unctlional , as indicated by the presence of noise or conversation on the line. If 7.2 Preventive Maintenance and no noise or voice signals are present at Inspections the handset receiver, take the following corrective action: With any system, periodic inspection is required because of the corrosive at- 1. Operate the handset press-to- mosphere and adverse conditions that ex- talk switch several times. Any corrosion ist in underground mines. These inspec- on the contacts of this switch may cause tions can spot potential trouble in the a receiver to be temporarily inopera- system. Repair or replacement at that tive. Repeated operation may clear the time averts the possibility of losing ef- condition. fectiveness of all or part of the system.

2. ' Open the cabinet and see if the 7.2.1 Cables battery cables are properly connected and are making firm contact. Check the hand- Approximately once per month all ca- set cable and its connections in the cab- bles in the communications system should inet of the pager phone, and see if there be inspected for kinking, chafing, crack- is any evidence of a break in the cable, ing, wear, stretching, or other signs corroded contacts, or poor connections. of physical abuse. Particular attention should be paid to cable glands at the en- 3. Remove the handset receiver ear- try or exit points to the various units piece by unscrewing it counterclockwise in the system, where the cable goes (to the left) , and remove the receiver around sharp corners, in the vicinity of from the socket. Examine the handset holding cleats which may be clamping the cavity; in some units, a patch of cotton cable too tightly causing potential dam- batting or floss is used as a barrier to age, and across the areas where the cable reduce acoustic feedback in the handset. is exposed to physical damage from out- If the cotton patch has absorbed mois- side sources, such as equipment or fall- ture,, remove it and replace with a ing objects. If a cable is damaged, it crumpled ball of soft rubber, stuffed should be replaced as soon as possible. just far enough into the handset so it will not touch the receiver or switch It is mandatory that the ground ted-nals. leads and connections to carrier current phones be thoroughly inspected and main- 7.2.2b Page Circuit and Talk Circuit tained in good condition, since considerable hazard may exist to the operator Push the page switch, squeeze the or equipment if a ground connection is handset press-to-talk switch, and call broken. any other phone. Release the page switch and listen for a reply. If the back- In the environment of underground ground noise is too high, or if the re- mines, switch contacts are particularly ceived signal is either too weak or too susceptible to erratic operation because garbled to be understood, then repairs of corrosion or oxidation of the switch- should be initiated to improve that par- ing contacts. This is particularly true ticular telephone. The phone should be of contacts that are used infrequently. replaced by an operable unit and repaired Repeated operation of each of the by qualified personnel, Ask the answer- switches in the telephone may aid in ing party if the paging signal could be clearing some of the corrosion and ' understood, and also check the quality of restoring the phone to more reliable your received signal, Have the other operating condition. Cleaning individual party page you to verify that your speak- contacts should not be attempted with a er works. Some of the most common prob- phone in service; it should only be done lems with the pager phone system that can by trained or experienced repair person- be remedied by good installation and nel, who have approved burnishing tools maintenance practics are: very low voice specifically designed for use on switch levels and very high noise levels. contacts. Often, the sources of these problems 7,2.2d Battery Condition are-- The battery condition of a pager 1. Poor placement of the phone line phone can be approximately checked by (near rectifiers, motors, etc.). pushing the page button and calling some other phone to determine whether or not 2. Using too light a gage phone the paging signal is sufficiently strong 1ine . to energize all relays within the system, Of particular importance is whether or 3. Using the wrong kind of wire for not the battery has sufficient voltage to the phone line, The line should be of energize the paging relay of the tele- the twisted two-wire type. Nontwisted phone farthest from the phone being line of any gage is not acceptable. It tested. Therefore, one of the most dis- is the twist that provides a great deal tant phones should be called. Batteries of noise immunity. can also be checked with a voltmeter to judge if they are near the end of their 4, Poorly made splices. These life or in a marginal state. There are cause high resistance and leaky joints in several methods of measuring the avail- the line that lower the signal and in- able battery voltage as noted in the fol- crease the noise. (Note that the phone lowing section. systems always are worst in the summer months. This is because the high humid- 7.2.2e Battery Testing ity is affecting the splices.) Most pager phones are powered by one 7.2,Zc General Comments or two 12-volt batteries of the NEDA 923 or 926 drycell type. These are 12-volt, If any of the signals is erratic, metal-cased batteries that measure 2-314 low in signal level, has exceptionally inches wide, 5-114 inches long, and 4-318 high noise levels, or is unintelligible, inches high. The difference between the check whether other phones in the system two types is that the 926 has two screw are having similar problems. If not, re- terminals for lead attachment and the 923 place the defective phone with a good has a two-prong connector system for lead one. If the other phones are not operat- attachment. For those phones using a ing properly, it is possible that the 24-volt system, two batteries are problem is in the line. A cable may be connected in a series. In consideration short-circuited, improperly spliced, or of intrinsic safety, it is common to find running too close to noise-producing some means of current limiting, such as a power or trolley lines. Such conditions 50- to 100-ohm resistor and a fuse in se- should be corrected. ries with the battery system, to limit the maximum current flow. Batteries are log of the voltage readings. This will approaching the end of their useful life assist in maintaining an up-to-date stain a system when the available voltage at tus of the battery condition at individ- the terminals has dropped 25% from the ual phones. This procedure will remain rated value measured under load condi- valid as long as the phone system is tions. In a 12-volt system, this is ap- configured as it was when the original proximately 8 to 9 volts; in a 24-volt listing was made. Substantial change in system, it is 16 to 18 volts. the phone system could require making a new chart . Measurement of the battery voltage can be made by connecting a dc voltmeter 7.2.3 Carrier Phones across the battery terminals, pressing the page switch, and reading the battery CAUTION voltage. Measurement of battery voltage on the line will not give a true measure Some of the procedures discussed of the battery condition, because of in this manual are undertaken with the added voltage drop in the current- the in-mine trolley wire energized limiting resistor. and are therefore very hazardous. Extreme caution must be exercised Remember that it is useless to mea- to avoid accidental electrocution. sure the output of a battery not under Fuses used in test leads protect only load. Under these conditions, even the the equipment and do not provide any poorest battery will still maintain its protection from shock hazard for the rated terminal voltage. operator. Do not attempt any of the electrical tests or installations de- It is not always practical to carry scribed in this manual unless you are a voltmeter into all sections of a mine, qualified for such work and are thor- and checking a battery requires that the oughly familiar with electrical work phone enclosure be opened. The following I on trolley wires. scheme can minimize such difficulties. I Each of the carrier phone units A voltmeter can be permanently in- should be examined for any external phys- stalled at some convenient location ical damage. All fixing screws must be aboveground, such as in a repair or main- tight. All connectors and externally ac- tenance shop. l The meter is connected cessible fuses should be checked for across the line so that it continuously proper seating. indicates any dc voltage on the line. A listing of voltage readings is made from 7.2.3a Microphone each remote phone at this reference station, when the individual phones are pag- The carrier phone microphone is a ing with new batteries installed. A delicate piece of equipment and is most chart is then made of the allowable re- prone to abuse by handling or dropping. duction in voltage for each phone by es- The microphone should be examined for timating a 20% to 25% reduction from the evidence of physical abuse. The action new battery condition. Reference to this of the transmit relay can be observed by chart can give advance warning of the pressing the transmit button and listen- approximate condition of each battery ing for the transmit relay inside the and will provide guidance for planned transmitter (in units where such a relay prelacement. A periodic check can be is used) to produce a sharp click. The made of each phone by requesting a page micicophone quality can then be assessed from each of the phones and maintaining a by transmitting a test count to a remote unit; the operator of the remote unit his could violate MSHA intrinsic will judge the quality of the voice he safety standards; check with MSHA for ap- receives and report back to the unit plication details. being tested so that the receiving quality of the unit being tested may also 7.2.3~ Wet Cell Maintenance be assessed. If a car-type wet cell lead-acid 7.2.3b Batteries battery is used, it should be installed in a well ventilated area easily accessi- Two different types of battery sys- ble for routine maintenance. Each week tems are used in carrier phones. One is the level of the electrolyte in each cell a conventional car battery type or wet should be checked and restored to its lead-acid cell, and the other is a gelled proper level by the addition of distilled electrolyte battery. Both types should water. The electrolyte should read a be tested once a month to insure a proper specific gravity of approximately 1.275 state of charge, and the electrolyte on a battery-testing hydrometer when the should be checked in wet lead-acid bat- battery is fully charged. The voltage teries, if possible. The gelled electro- for each cell should be between 2.2 and lyte battery is also of a lead-acid con- 2.4 volts. Since in normal operation the struction; however, its so-called dry battery is under continuous charge, the electrolyte system cannot be changed specific gravity and voltage of a battery since the cell is sealed to prevent any in good condition should be around the electrolyte loss. Overcharging of either stated values. Values significantly less of the battery types causes considerable are symptoms of problems with either the electrolyte loss, and both types of bat- battery or the battery charger and should tery can be ruined if overcharged for a be investigated. If electrolyte is lost long period of time. from the battery due to spillage, then electrolyte premixed to the same specific CAUTION gravity should be used to refill the battery to its normal level. Electrolyte loss also happens to a lesser extent during a normal Terminal posts on lead-acid batter- charge cycle and results in the emis- ies should be examined and cleaned each sion of hydrogen and oxygen from the month. Petroleum jelly may be used to cells in a ratio which is explosive. coat these posts to prevent corrosion. Slow emission of this hydrogen and Also, any corrosion of the battery box oxygen gas mixture in the enclosures should be scraped clean, and petroleum using a gelled electrolytic battery jelly should be applied to prevent any can create a hazardous mixture of further corrosion. gases inside the units. Some units are vented to prevent a pressure If a vehicle equipped with a carrier buildup inside the enclosure, but phone is to be taken out of service this is insufficient ventilation to for some time, then both battery leads prevent the possible buildup of a should be disconnected to prevent dis- hazardous atmosphere inside the box. charge of the battery while the unit re- Thus, transceivers using a gelled mains in standby mode. Again, petroleum electrolyte battery should only be jelly should be applied to the battery opened in a well-ventilated area posts and the terminals to prevent any where there are no possible sources corrosion, of ignition of the hydrogen and oxygen mixture before it is sufficiently Any battery found to be in a weak diluted by the surrounding air to be- condition should be removed for recharg- come harmless. Wet lead-acid batter- ing and replaced by a fully charged bat- ies should be placed in a well- tery, If a particular vehicle has re- ventilated area in the vehicle to peated battery problems, the batte'ry prevent buildup of pockets of danger- charger in that vehicle should be removed ous hydrogen-oxygen mixture. for checkout. 7.2.3d Gelled Electrolyte Battery discharged and stored in this condition without being recharged, the battery may It is not possible to service the develop a condition where it cannot be electrolyte in a gelled electrolyte bat- recharged and should be replaced. tery since it is sealed at the factory. However, these batteries do vent small 7.2.3e Troubleshooting on the Vehicle amounts of hydrogen and oxygen during the charging process, which will increase to When an operator reports a malfunc- larger amounts if the battery is over- tion carrier phone, initial diagnosis of charged. Normally, the battery should be a problem can be carried out using only charged by a taper-charge process. This the equipment suggested in table 7-1. means that when the battery' is in a dis- The repairman may either take his equip- . charged condition, the battery charger ment to the faulty vehicle, or the faulty can apply a comparatively large amount of vehicle may be returned to the test and current to build the charge up in the maintenance area. battery quickly. However, as the battery charge increases, the charging rate First, the battery voltage should be should decrease. When the battery is al- check.ed to make sure it has not become most fully charged, the charging current disctlarged. If it is found to be good, should fall to zero or maintain a very all external fuses in the unit should be small charge. Each of the two types of check.ed. If a faulty fuse is found, it carrier phones using batteries of this shou1.d only be replaced with a fuse of type have a taper-charge-type battery the proper rating. If the fuse blows charger built in to maintain the cells at again, then the unit is probably faulty. a fully charged state, without the hazard It is possible that replacing the blown of overcharging. fuse with a new one will cause the unit to operate properly since a momentary The important parameter to measure overload could have caused the original for proper gelled electrolyte battery fuse to blow. maintenaxe is the battery voltage. A nominal 12-volt gelled electrolyte bat- Sometimes the phone itself can pro- tery is fully charged when it reads 13.8 vide valuable information on the nature volts across the terminals. This should of a problem. Use of the carrier phone be the voltage reading when the battery will generally isolate the problem into has been fully charged by the operation one of the following three categories. of its battery charger. Any voltage higher than 13.8 is an indication that 1. Cannot transmit to others or re- the battery is being overcharged, thereby ceive from others: suffering a considerable loss of life due to the drying out of the electrolyte. a. Check the main fuse. This also causes generation of dangerous quantities of hydrogen and oxygen gas be Check the ground connection. mixtures as the cell vents. If this is the case, the battery charger should be c. Check all connectors for examined for malfunction. corroded contacts.

Alternatively, if the carrier phone d. Check all cables for breaks. has been left on for an extended time without any battery charging from the e. Check the battery condition. trolley wire, it is possible for the battery to become moderately or deeply dis- f. If cause cannot be readily charged. A moderately discharged battery located, replace with spare unit and can be removed for recharging and gener- take the malfunctioning unit in for ally will not suffer any significant bench maintenance. harm. However, if the battery is deeply TABLE 7-1. - Suggested test equipment

Item Type Use Multimeter...... Various...... Meter can be used for measuring voltages in and around the unit, power consumption, power output, and fuse checking. In order to give useful results for transmitter power output measurements, the meter should be capable of operating with frequencies of at least 100 kHz.

Fuses...... do...... Fuses provide an intentionally weakened part of an electric circuit, and thereby act as a safety valve in the event of dangerous overloads. This protects both personnel and equipment from potential fire hazards due to overheating of the carrier phone.

A blown fuse generally indicates that some part of the circuit of the carrier phone has become defective. Occasionally a temporary external overload condition can cause a fuse to blow; hence it is a useful practice to change a blown fuse one time to see if the unit can be brought back into service. Should the fuse blow again, then a more detailed trouble-shooting process should be attempted.

Substitute units. Same as used in the Each carrier phone consists of a number of mine. different units interconnected by cables. To facilitate troubleshooting on the vehicle, a fully operational spare set of the type used in the mine should be maintained so that initial trouble-shooting can be performed by substitution of the individual units.

Hydrometer...... Battery type...... The hydrometer measures the charge-discharge condition of the battery electrolyte.

Distilled water.. A battery with a low level of electrolyte will require an addition of distilled water.

Petroleum jelly.. Any...... Coating the battery terminals with petroleum jelly aids in preventing corrosion.

Battery charger.. Any applicable (for The battery charger is used to recharge bat- wet battery) or teries that have become discharged. special battery charger for gelled NOTE.--Insure equipment is suitable for electrolyte desired application. battery. 2. Can hear others but cannot ap- 4. Where relevant, change the bat- parently transmit: tery charger box and check for normal operation. a. Check cables and connectors (especially the microphone for cor- When the faulty unit has been iso- roded contacts or breaks). lated and replaced, it should be returned to the repair area for a more detailed b. Replace the microphone. examination, including an overall performance checkout after the fault has c. If neither the above is at been isolated and repaired. fault, the problem is probably in the transmitter; take the malfunc- CAUTION tioning unit in for bench maintenance. The following procedure is undertaken with the trolley wire ener- 3. Cannot hear others but they can gized; therefore, it is extremely hear your transmission: hazardous. Extreme caution must be exercised to avoid potentially lethal a. Check the volume control shock. Only personnel thoroughly setting. familiar with electrical work on trolley wires should conduct the test b. Check the cables and connec- procedures. Equipment used must be tors for breaks and corrosion. appropriate for this application.

-- - c. Replace the speaker assembly On 300-volt systems, a test can be by substitution. made of the transmitter power output onto the trolley line. A simple method of d. Check the squelch setting. measurement in the field makes use of the multi.meter with the range selector switch e. If none of these measures set t.o the 50-volt-ac scale. The black solve the problem, it is probably meter lead should be plugged into the in the receiver; replace the trans- colurnln (-) terminal of the meter and the ceiver with a spare unit and take free end connected to the ground. The the malfunctioning unit in for bench red lead must be plugged into the meter maintenance. output jack and connected to the trolley wire. The trolley pole must be in con- If all these steps fail to make the tact with the wire. A reading of 15- unit operational, then repair by substi- volts or more when the transmitter is tution is usually the quickest way of keyed indicates normal operation provided getting the unit into operation again. the test is made at least 200 feet from Substitution should be in the order of the nearest power rectifier that supplies items considered to be more or less vul- the trolley wire. This test cannot be nerable. Unless it is obvious which unit performed on 600-volt dc systems since is faulty, the process should be carried this voltage will overstress some compo- out in the following order: nents inside the multimeter. In this case, the unit should be returned to the 1. Change the microphone assembly repair shop for a standard bench test. and test for normal operation. It should be noted that the meter will respond to ripple present on the trolley 2. Change the transceiver assembly wire; thus a base reading of up to 10 and check for normal operation. volts will be shown even with the transmitter off. 3. Change the loudspeaker unit and check for normal operation. 7.2.3f Mapping Signal Levels

The maintenance of trolley carrier phone systems requires not only the maintenance of the equipment involved, but the maintenance of the transmission line (trolley wire-rail) used to transmit the signals (refer to paragraph 5.3.1). Evi- dence accumulated over the years indicates that this signal path is subject to many loads that impede the propagation of carrier signals.

One of the most useful ways of determining the state of the overall transmission system is to map the signal and noise strengths at various points throughout the mine. Such mapping requires a tuned signal-measuring device.

The mapping is preferably carried out by measuring the signal produced by the dispatcher's transmitter at vari- FIGURE 7-1. - Example of signal level map. ous points along the rail haulage system where vehicles operate. A satisfactory for many tasks other than the mapping of way of conducting the measurements is trolley carrier signal levels. For this to place a suitable tuned voltmeter reason careful attention must be paid to aboard a mine vehicle (such as a jeep), the tuning of the instrument to the pre- and at appropriate places along the rail cise frequency, attenuator settings, and haulage--f or example, at 2,000- or 3,000- meter indications. Table 7-2 gives spec- foot intervals--measure the received dis- ifications for these tuned voltmeters. patcher's signal and background noise. These values should be noted on a mine The simple straightforward procedure map for future reference as the mine ex- of measuring the dispatcher's signal lev- pands, or as carrier phone problems oc- el from a jeep or vehicle moving about cur. Except under extremely unusual con- the mine can best be accomplished by conditions, the signal-strength map produced necting the trolley wire voltage on board in this manner will also indicate the the vehicle to the input of the tuned level of signal that a vehicle transmit- voltmeter. Because of the hazards asso- ter at the measuring position would pro- ciated with the high voltage of the trol- duce at the dispatcher's place. A por- ley wire, either voltmeter has to be tion of a mine map with signal and noise properly isolated so that personnel oper- readings is shown in figure 7-1. ating the instrument are not subjected to this voltage through error in operation. The equipment for making such a Therefore, it is important that a capaci- signal-strength map must be battery oper- tor and a fuse be connected in the series ated, easily portable, and easy to use with the instrument to insure that the and read. Two such units commercially potentially lethal voltage of the trolley available are shown in figure 7-2. These wire does not inadvertently reach an tuned voltmeters are general-purpose, operator. Figure 7-3 shows a possible battery-operated instruments appropriate way of connecting the instruments. TABLE 7-2. - Key specifications of tuned voltmeters

Specification Sierra 127C Rycom 3115 Frequency range ...... Hz.. 2-350 3-200 Accuracy :

Frequency ...... ~~mmmm~..~~mm Level...... ~~~~..dB.. Selectivity (standard 250 Hz), Hz: 3-dB band~idth...... ~..~~~~~~~~ 35-dB bandwidth...... mmmmmmm 60-dB bandwidth...... ^.^^^^^^ Ranges (full scale)...... ^^^^^

Intermediate frequencies, Mz: 1,305 NAP 2nd...... ~~~~~~~~~~.~~~~. 330 NAP Power requirements...... 6 zinc-carbon or 7 NiCd 2 gel cells rechargeable D-size cells Globe 610 V~ltage...... ~~~~....~~~~~~~... 9 (nominal) 12 Battery life (zinc carbon)....hours.. 100 5 (continuous) Temperature range...... "C.. I - 10-50 1 - 10-55 Dimensions, inches: width...... ^^^^^^^^^.^ Height...... ~mmmmmmmmmmm depth...... ^^^^.^^^^^^^^^^^ weight...... ^^^^^^^ m.mpounds.. I 15 1 6 NAp Not applicable.

WARNING the dispatcher to "key" his transmitter for a 5-second transmission of unmodu- Disconnect the instrument when latled carrier. The response on the indi- the vehicle is moving. Transients cating meter is noted, together with any from the vehicle motor !can cause attlenuator setting, so that an absolute damage. value of voltage (in volts nus) can be noted on the corresponding position on CAUTION the mine map. It may be necessary when starting measurements to switch the range The following procedure is un- knobs of the instruments to make sure dertaken with the trolley wire ener- that the instrument's response is on gized; therefore, it is extremely scale rather than high and off the scale. hazardous. Extreme caution must be In this event, perhaps two transmissions exercised to avoid potentially lethal will be required before on-scale readings shock. The fuses used in the test are obtained. After the transmission leads serve only to protect equipment from the dispatcher is recorded, the sen- and do not in any way reduce the sitivity of the instrument should be in- shock hazard to personnel. Only per- creased and the noise level at the par- sonnel thoroughly familiar with elec- ticular position noted again in volts or trical work on trolley wires should millivolts nus. conduct the test procedures. Equip- ment used must be appropriate for The signal-level map will reveal re- this application. gions of the mine where the dispatcher signals are weak which may cause diff i- To make a measurement, the vehicle culties in carrier communicationm The is moved to the desired location in the mine map will also reveal regions where mine and stopped. The operator then asks excessive noise is the main cause of poor communications. In this event, it is important to locate the source of the of- fending noise and to take measures to alleviate the problem.

The signal-level map will also be extremely useful should carrier communications deteriorate with time, with the installation of new equipment, or with the advancement of the mine. Reference RYCOM 3115 can be made back to the original signal levels to determine if and why communications have been degraded.

7.3 Summary

Good preventive maintenance and periodic inspection practices are the key to successfully maintaining any communication system. Common problems that can affect communications include:

Corrosion or conductive dust on battery terminals.

Cable abrasion and line breaks.

Corrosion on switch contacts or in cable splices.

FIGURE 7-2. - Tuned voltmeters. Weak batteries.

Blown fuses.

7 TROLLEY WIRE Weak or broken springs on spring- loaded connectors.

Poor splicing techniques.

In addition to problems that develop owing to normal system usage and environmental conditions, trolley carrier systems may be affected by characteristics of the trolley wire and rail itself. Poor signal strength may result because of bringing loads across the trolley wire-rail or high signal attenuation rates in the trolley wire. Methods of compensating for the effect of bridging across the wire-rail are given in section FIGURE 7-3. - Instrument connections. 5.3.1. B IBL IOGRAPHY

1. Long, R. G. Guidelines for Instal- Underground Telephone Systems. BuMines lation, Maintenance and Inspection of Handbook, 1978, 44 pp. Mine Telephone Systems. BuMines OFR 116- 78, June 1975, 53 pp.; NTIS PB 287 641. 3. Spencer, R. H., P. OIBrien, and D. Jeffreys. Guidelines for Trolley Car- 2. Long, R. G., R. L. Chufo, and R. A. rier Phone Systems. BuMines OFR 150-77, Watson. Technical Guidelines for In- March 1977, 170 pp.; NTIS PB 273 479. stalling, Maintaining, and Inspecting A.l INTKODUCTION vertical shaft approximately 545 feet deep. Coal is removed from the face area Because no two mines are identical, by shuttle cars and placed in a set of there is no "one best system" that can be six tracked haulage cars. When full, defined to meet the requirements of all the sets of cars are combined into trains mines. The fol.lowing examples of system and brought to the surface through a Installations are presented to indicate slope entry. Average coal production is how some mines have adapted available 4,000 to 5,000 tons per day for 240 work- equipment to meet their particular ing days, setting yearly production at requirements. Selection of examples were approximately 1 million tons. based on the goal of obtaining the widest possible range and cross section of the The mine size is currently 2.4 miles following characteristics: north and south by 3.9 miles east and west with overburden from 545 feet to Type of mine 1,000 feet. All tunnels and haulageways are typically 6.5 feet high by 14 to Age and size of mine 15 feet wide. An average working section is 425 feet by 300 feet long, and 10-foot Electrical power usage roof bolts are used. The mine has only one borehole, which is used to supply the Haulage methods mine with water.

Existing communications Currently the mine has six working sections of whicii five are worked every Usefulness of present communications shift. The shifts run from 8 a.m. to 4 p.m., 4 p.m. to 12 p.m., and 12 p.m. to Examples A through F are of coal 8. a.m. A typical working section cycle mines utilizing various combinations of starts with the continuous miner cutting magneto, pager, and conventional trolley- coal and filling a shuttle car. When the carrier-type phone systems. Example G is shuttle car is full, the driver moves the of a magnetite ore block-caving operation coal load to the tracks and transfers the where a radiating cable and radio system coal to one of the six haulage cars posi- is used. Example H indicates how a dial- tioned on the side track. The shuttle page phone system can be utilized in a car then returns to the continuous miner coal mine. Example I presents a multi- to repeat the cycle. Excluding mechani- channel (multiplexed carrier) system cal trouble, the continuous miner will presently in use in a deep metal mine. cut a block of coal 5 feet high, 15 feet wide, and 16 feet long in 1 hour, and a A .2 MINE A section can mine five blocks this size in an 8-hour shift. The mine typically has Mine Description 100 men underground per shift.

Mine A is part of a connected four- Mine Eaui~mentand Power mine complex. This particular mine is approximately 20 years old, and although The prime power for the mine is there are some new working sections, the 550 volts brought in on a feeder cable. major coal extraction is from retreat In the mine the trolley wire is run par- mining where pillars are being pulled. allel to the feeder cable. At the work- Personnel entry is achieved through a ing section the continuous miner, shuttle cars, and car pull are run off the 550- use of company names is for identifi- volt-dc trolley line fed at nip stat.ions. cation purposes only and does not imply Compressed air is used to run the roof- endorsement by the Bureau of Mines. bolting machine. The equipment at each working sec- answering phone calls, switching phone tion includes one continuous miner, two circuits, personnel calling and location, shuttle cars, one roof -bolting machine, and taking and relaying messages. and one car pull. Other equipment includes 3 bot tom-loading machines, Because the dispatcher is more 2 minor-type cutting machines, and likely to contact a working section 12 pumps. through the motor and an associated carrier phone in that section, the mine The tracked vehicles include 3 dual phone is used relatively little compared locomotives or tandems, 24 Jeeps, and with the carrier phone. 3 portal buses. Based on the observed traffic den- Present Mine Commnications sity and on the number of phones in the system, the probability of a busy signal The present comrmnication consists on the magnetophone system is 5%. of a carrier phone system and a magnetophone system. All vehicles are equipped Trolley Carrier Phone System with FEMCO carrier phones, and all active working sections, along with selected Vehicle-mounted carrier phone usage underground positions, have Western Elec- during a typical shift is shown in figure tric magnetophones. A-1. Telephone Sys tem During a first shift survey, there were 182 dispatching calls, 20 calls The heart of this mine's communica- relating to personnel location, and 58 tion system is a central dispatcher calls relating to placing empty and located at the bottom of the main shaft. loaded cars. Eight party-line magnetophone cir- -Commnications Requirements--Users ' cuits terminate at a simple switchboard --Viewpoint in the dispatcher's office, Each of these 8 circuits has several of the Evidence of this mine's interest in 41 telephones wired in parallel. Calls commnhcations is shown by the expression between circuits must be made through the of one foreman that "their production dispatcher and his or her switchboard, woultd be cut in half if they lost either whereas calls within a circuit need not. telephone or carrier phone commnica- The dispatcher can connect any two phone tions." An important commnications. circuits together and can make two of requirement as defined by the management these connections, generating two inde- of this mine concerned safety. They pendent phone circuits for two-channel strongly felt that a secure channel was operation. needed where only the persons calling and called could hear the conversation. Since this magnetophone system oper- There are two reasons for this: First, ates with a bell ringer rather than a anyone seeking aid for an injured miner loudspeaker, the rings are coded to indi- tends to belittle the seriousness of the cate certain places or individuals. The injury because he knows that friends and dispatcher commnicates through a single relatives of the injured miner, and those headset, and selection of either the mine just: curious, will be listening to the phone or the carrier phone is made using conversation. The problem is not unique a two-position switch. Other switches to this mine. Secondly, the phones of connect and disconnect the various mine these eavesdroppers load the line to the telephone circuits, extent that the emergency communications are impaired. This dispatcher controls all vehicle traffic and serves as a telephone Based on this realistic situation, a operator. Operator duties include basic communications requirement is a w 8-9 9-10 10-11 11 a.m.- Noon- 1-2 a.m. a.m. a.m. noon 1 p.m. p.m. p.m. p.m. FIGURE A-1. - Vehicle-mounted carrier phone use in typical shift.

private line, selective calling channel The fact that the chance of getting over which the person attending an a busy signal is 5% is proof that addi- injured person can privately call, at his tional channel capacity is needed. Add- or her discretion, the mine foreman, the ing additional channels to a wired system dispatcher, the safety foreman, or the appears to be an acceptable solution nearest hospital or ambulance service. since these extra channels will minimize Note that a conventional private dial the telephone duties the dispatcher now system meets this requirement. Mine C performs and will eliminate the communi- (described in section A-4) has a dial cation system blocking problem. Calcula- phone adjacent to each pager phone. This tions indicate that a minimum of five met the need for a secure channel communication channels are needed for for both management and emergency this mine. Furthermore, making one of communications. the five channels a private line will fulfill the requirement for private Communications Requirements--Based communications. on Survey Analysis Also, from observing the mine opera- Although the personnel interviewed tion and talking to various personnel it felt the quality of their communications appears that section foremen, like the was adequate, analysis indicates that foremen in most industrial operations, excessive noise and distortion were pres- are overworked, and yet are the key to ent. Therefore, a requirement that improving productivity. Therefore, wire- applies to this mine as well as to all less communication is needed for at least communication systems is that of reason- the section foremen along with variable signal-to-noise ratio for good ous other supervisors and maintenance intelligibility. personnel. From this brief analysis of the mine loader, and two shuttle cars. With a and its current communications, the fol- full-dimension system, the shuttle cars lowing is a list of minimum communication are replaced by an extendable belt. requirements for Mine A. Coal is brought out of the two mines a. Reasonable communication channel by conveyor belt, and men and supplies signal-to-noise level. are moved by track. The coal is moved by belt from the two mines to a screening b. At least five independent voice house having 1,250 tons of storage capac- channels. ity. To cope with slacks and overflows, coal can be automatically diverted to a c. At least one secure voice chan- 12,000-ton-capacity storage pile. nel, which may be included in the five voice channels. Ac power is brought into the mines at 12,470 volts. Two rectifiers are d. Some form of wireless communica- positioned at every 6,000 feet of track, tion to select individuals on the working each with a capability of 300 kW, to section or roving in haulageways. supply 300-volt-dc power to the trolley wires and their feeders. In addition to A.3 MINE B supplying locomotives with power, the trolley lines supply power, at nip points Mine Descri~tion along the line, for the operation of the 300--volt-dc shuttle cars. Where needed, Mine B consists of adjacent (No. 1 the 12,470 volts ac is transformed to and No. 2) low-coal mines. The No. 1 600 volts to provide ac power for rock Mine employs longwall and continuous min- dusters, conveyor belt drives, miners, ing. The No. 2 Mine employs conventional roof bolters, and belt feeders. and continuous mining and is preparing for its first longwall operation. Both Present Mine Communications mines employ belt coal haulage to closely located drift entrances. Men and sup- The equipment used in each of the plies enter the No. 1 Mine by a 400-foot two mines includes paging-type party line shaft remotely located from the No. 2 telephones, trolley carrier phones, the Mine drift entrance. From the two mines, fire sensor tape recording that would 8,000 tons of coal per day are mined by automatically be patched into the phone about 600 union men under the supervision system should there be a belt fire, and of about 60 officials. the fan sensors that utilize the phone lines. The No. 1 and No. 2 Mines each currently employ one longwall mining unit The No. 1 Mine's communications sys- and conventional working sections of Lee tems are independent of the No. 2 Mine's, Norse continuous miners. For the No. 1 but generally of the same size and equip- Mine's longwall mining, coal is moved by ment types. The No. 2 Mine's chief an armored face conveyor to a stage electrician's office has a No. 1 Mine loader at one end of the longwall, to an phone, as does the No. 2 Mine's foreman's extendable belt, and finally to a con- office. ventional belt. Telephone System In addition to longwall mining, the No. 2 Mine employs a full-dimension unit, Since both mines have similar com- a conventional mining unit, and continu- munication equipment, only the No. 2 Mine ous miners for seven working sections per will be described. The No. 2 Mine has shift. 31 underground loudspeaking telephones. The underground phones are all in a The equipment used in conventional single network. The following seven sur- mining consists of a cutting machine, a face phones are also in this network: Outside mechanics shanty--1 at the inside mechanics shanty, two on utility jeeps, and two on motors. Outside shop--1 One shortcoming of the present car- Audi torium--1 rier system is that there is no way for personnel with carrier phones to commni- Chief electrician--1 cate with working sections. Mine personnel would like some way of patching Cleaning plant--2 the carrier and pager phone systems together. Double breaker switchhouse--1 Longwall Couumnications The paging phones used in these mines use 6 volts for normal phone use Five permissible loudspeaking tele- and 22.5 volts during paging. With these phones are spaced at 125-foot intervals phones, pressing the paging button at any along the 500-foot longwall system. station permits the operator to broadcast These five phones are connected together through the loudspeakers on the remaining to form an independent communications 37 telephones. On releasing the paging system. Near the phones at either end of button the operator can converse with the longwall system are phones of the anyone who picks up the handset on any overall telephone network. Though not other phone. interconnected, the two phone networks are physically close to each other. Tape recordings were taken of both the No. 1 and the No. 2 Mine's party line The five phones are identical to pager phone system and the No. 1 Mine's those of the main telephone system except carrier phone system. Analysis of these that the paging mode is permanently wired recordings revealed that for the No. 2 into all five phones as a safety measure. Mine, based on hour intervals, the most Anything said into any one of the five the system is used is about 50% of the handsets will be broadcast over all five time, between 9 and 10 a.m. But, based loudspeakers, thus alerting all nearby on 15minute intervals, the phones are personnel of activity on the longwall used nearly 90% of the time around 3:30 section. in the afternoon. Belt Maintenance Communications This heavy usage occurs during the last hour of the shift when section fore- Along the belt lines (every men are making their end-of-shift reports 2,000 feet) and at the belt heads are on production status, supplies on hand, located phones of the telephone communi- supply requests, and maintenance work cations system. The belt heads are the requests. The fact that the phone system only spots where belt mechanism fires are is used 90% of the time signifies that likely to occur. other calls that could improve production efficiency must either be delayed or not Belt Fire Alarm System made at all. Although these mines have never had Carrier Phone System a belt fire, their fire alarm system is better than required by law. A tape A second means of voice communica- player is positioned underground and when tions is the carrier phone system that activated will broadcast a warning over uses the dc trolley wire as a carrier of all telephone and carrier phone loud- 88-kHz (No. 2 Mine) and 100-kHz (No. 1 speakers. The recorded message warns Mine) FM. In each 'mine five carrier all personnel of the alarm condition, phones are used: One as a base station specifies the location of the tripped alarms, and advises personnel of safety requirement for personal hands-of f - precautions to be taken. operation radios of insignificant weight and bulk. Coordinating the operation and Fan-Stop Alarm and repair of a 500-foot longwall miner is difficult, especially in low coal. In the event a fan stops, provision is made for utilizing the phone systems Mine personnel felt that having to insure that proper action is taken. nothing would be better than having a At the No. 1 Mine, where there is a phone simpl-e radio pager where a section fore- at the fan site and where personnel are man might have to crawl 700 feet to the within earshot of an audible alarm, the nearest phone to find out that it really person responding to the alzrm can use wasn'lt that important. If the section the normal telephone system in seeking foremen are given anything for mobile help. The fans for the No. 2 Mine are communications, it must be small, light, remote from any mine personnel so the and two-way. In this mine they would alarm is automatically sent over a com- like the section foremen to be able to mercial phone line to No. 2 Mine's easilly contact a general assistant fore- lamphouse. man for supplies and repairs. The need for small portable two-way communications Communications Requirements--User ' s is shown by the case where someone at the Viewpoint mine,, on his own initiative, tried some two-way units he had borrowed from a Through interviews and discussions local hospital. with those who use, plan, and maintain the communications systems, communica- Communication Requirements--Based tions requirements were determined that on Survey Analysis would aid production at these mines. These requirements dealt directly with An analysis of both the NO. 1 and mine operations not using a dispatcher, the NO. 2 Mine survey indicates that the with operations where coal haulage is by communications systems noise levels were belt only, and with operations involving unacceptably high and that communications low-coal and longwall mining. capability is on the verge of becoming unacceptable. Improved communication and The first suggestion made by mine improved mining operation would result personnel was that they needed someone to merel-y by improving the signal-to-noise perform the communications and inf orma- ratio of the present communications tion center tasks often performed by the systems. dispatcher in other mines. Presently they have no way of relaying messages Since the current phone traffic between, or interlinking, the independent makes the chance of getting a busy signal telephone and carrier phone systems. between 350 and 450 times greater than They also would like someone to monitor most industries find acceptable, addi- belt line sensors, from a center, in tional channel capacity is needed to order to coordinate troubleshooting, reduce the chance of blocking to the 1% maintenance, and repair of all belt level-. Although blocking is still lines. Thus, a requirement for a com- 10 times greater than industrial stan- munications center operator (communica- dards, it appears to be a reasonable tions coordinator) would resolve the two selection for mine communications. immediate problems as well as many others. Also, from observing the mine operation and talking to various personnel, it Low coal and longwall mining com- appears that section foremen and select bine in determining a requirement for longwall personnel need some form of fixed communications terminals to be two-way wireless communication of minimum close to all classes of foremen, and a size and weight. All personnel expressed a negative atti tude toward any one-way transferred by shuttle cars to a set of type of communication. 6 haulage cars; 2 of these combinations of 6 cars are attached to make a 12-car Furthermore, the mine personnel felt train, which removes the coal. from the they needed a location where the daily mine . production activity could be monitored. This location can evolve into a communi- The B seam is currently 1.7 miles cation center, since as the mine expands north and south by 3.2 miles east and and more vehicles are equipped with west; the C seam is 0.35 mile north and trolley carrier phones, a combination south by 0.45 mile east and west. The dispatcher, call monitor, and production overburden ranges from 0 at the slope monitor can be financially justified. entry to 2,000 feet. All tunnels are typically 18 feet wide. The average Specifically for these mines, the C seam tunnel is 9 feet high, and the following represents a minimum for future typical B seam height is 15 feet. Since communication requirements: the B seam has coal 22 feet thick in some places, the top level is mined first; a. Reasonable communication channel they return to mine the bottom coal for signal-to-noise ratio. maximum yield. Koof bolt length is typically 6 feet with variations from 4 to b. At least five independent voice 12 feet. These bolts are positioned channels to replace the present one on 5-foot centers in the B seam and on channel . &foot centers in the C seam.

c. Small, lightweight wireless two- The mine has one borehole into the way communicator units for foremen and B seam, which was used at one time for a select personnel. phone line and another time for pumping water out of the mine. A second borehole d. A communication center. in the C seam is used to pump methane out of the mine. A.4 Mine C Currently the mine has two coal- Mine Descri~tion producing sections in the B seam and one coalproducing section in the C seam. Mine C has been operational since Furthermore, the B seam has one large 1903 with production originally estimated cleanup section and two smaller cleanup for 100 years. Coal is being mined in or rehabilitation sections. A typical the B and C seams, and there is 36 to working section is 320 feet square. The 60 feet of vertical displacement between mine has two production shifts and one these seams. The mine employs continuous maintenance shift, and they run from mining techniques, and personnel enter 8 a.m. to 4 p.m., 4 p.m. to 12 p.m., and the mine through a slope entry. Coal 12 p.m. to 8 a.m. The mine has 71 men production is approximately 1 million underground for the first production tons per year and is removed by a com- shift, 55 men underground for the second bination of belt and haulage cars. The production shift, and 45 men underground B seam has two active working sections, for the last or maintenance shift. and each section transfers coal from shuttle cars to a small feeder belt. A Mine personnel typically require longer mother belt then takes the coal 20 minutes to get from the portal to to a main loader head. This loader head their working sections, and they take has the capacity for 18 cars; when 12 30 minutes for lunch some time between cars are filled, these cars are assembled 11 a.m. and 1 p.m. These lunch periods into a 12-car train 240 feet in length are staggered between working sections. for main line haulage. The C seam has On the B seam the work cycle starts with only 1 working section, and coal is the continuous miner cutting coal and filling a shuttle car. When the shuttle paging phones by a trolley coupler. This car is full, the driver transfers the type application should not be used with coal load to one of the 36-inch 550-fpm -intrinsicallv safe hones.- To improve belts run to the section. The belts then communication coverage, auxiliary speak- remove the coal to the south loader head, ers are sometimes used with the loud- where it is loaded into cars that will speaking paging phones. The following make up the main line haulage train. The tabulation shows the number of phones and shuttle car round trip takes approxi- their general location: mately 7 minutes to complete a work cycle - - * -- - - on the B seam. Except for the shuttle Phone type B C Sur- Stor- Vehi- cars dumping directly into haulage cars, -seam -seam - f ace age cle the C seam has the same type of work Dial cycle. Furthermore, the C seam has no telephone... 12 1 16 0 0 belt haulage and uses tracked haulage for Loudspeaking coal removal. pager phone. 5 1 1 1 0 --Carrier phone 1 -0 - 1 0 17 Mine Equi~mentand Power In general, vehicle operators and Three surface substations convert supe.rvisory personnel use the trolley 44,000 volts three-phase to 4,160 volts carrier phones, and mine section foremen, three-phase, the 4,160 volts is carried maintenance personnel, and supervisory underground to various 440-volt-ac and personnel use the dial telephones and 275- to 300~olt-dcpower stations. page,r phones.

At the working sections, the shuttle Dial, Telephone Sys tem cars are powered either by 440 volts ac or 275 to 300 volts dc; the continuous The mine has purchased from the tel- miner is powered by 440 volts ac, and the ephone company dial telephones, telephone roof bolting machines are powered by 275 environmental enclosures, associated to 300 volts dc. The dc voltage can be PABX, and 25-pair telephone cable with obtained by either a trolley nip point or wire size No. 19. All underground tele- an ac-dc load center. phone equipment and wire was installed by mine personnel and has been in service All trolleys are powered by a 275- for the last 10 years. Standard dial to 300~olt-dc trolley line, which is a telephones are mounted in environmental common ring bus fed by 300-kW recti- enclosures. fiers and two 500-kW rectifiers. The quantity and type of trolleys or vehicles The biggest problem the mine has had follow: with the dial telephones was dust and moisture getting into the dial mechanism. This; was understandable since it was found that the majority of the under- Mechanics ' jeeps--2 ground telephone enclosures had been left wide open and were liberally rock dusted. Of the eight underground telephones chec:ked, seven were in good working order and one had rock dust in its dial mechanism contacts. Another problem, not Present Mine Comnunications rela~teddirectly to the telephone equipment:, was that of acoustic noise from This mine utilizes a combination of mine machinery. For example, a telephone loudspeaking paging phones, dial tele- is required near the 3d south loader phones, and 88-kHz vehicle-mounted car- head, and mine personnel find comnunica- rier phones. The carrier phone system is tion difficult when the loader head is tied electrically to the loudspeaking in operation. Mine officials have considered building a telephone enclosure quality, are holding up well, and are that will shield this telephone from apparently being properly used by working external acoustic noise. personnel. However, there is a problem associated with the carrier phones com- Other than leaving the door to the municating from certain dead zones in the environmental enclosures open, the mine mine to the surface. Another problem personnel appeared to operate the tele- with the carrier phones was that the phone system properly. The telephone was battery had to be serviced every 30 days mostly used to call from underground sta- and mine personnel said this was excess- tions to surface stations or call out of ive. Also, the mine officials indicated the mine. Most calls were for supplies, that the ringfed trolley rectifiers added maintenance, and location of personnel. receiver noise and that additional rec- This telephone system was also used as a tifier line filtering helped but did . backup system when commnications were not eliminate the local problem when bad. For example, once personnel were the trolley was near the rectifier contacted using the trolley carrier phone stations. or pager phone and extended conversation was needed, the person would be External audio noise and replacing instructed to go to the nearest dial the internal battery approximately every extension telephone and reestablish con- 90 days were the most annoying problems tact to complete the comrmnication. associated with the loudspeaking paging phones. Over the history of the mine, only one major emergency has occurred, a Although the two systems are elec- destructive fire. This fire destroyed trically tied together, the loudspeaking the telephone cable, and the underground paging phone was primarily used to reach dial telephone system could not be used the working section and the carrier phone for emergency personnel evacuation. This was used for right of way, placing loads points out the basic weakness that tele- and empties, personnel location, and phone systems without loopback paths have requesting supplies. When the trolley- during a real disaster situation, mounted carrier phone was used for self- traffic control, the operator would twice Loudspeaking Paging Phone--Carrier Phone give his location and destination and System then proceed to his final destination. Although this method of traffic control Carrier phones installed at the mine worked for this mine, an improvement include six 10-year-old units and thir- could be seen using a dispatcher. teen 14-month-old units, all with 88-kHz center frequency. The mine personnel Tape recordings for a first 8-hour plan to replace the older carrier models work shift survey show that the most fre- with new models in the near future. The quent call made was concerned with right carrier phone to paging phone coupler (an of way. Also, it was noted that out of application that cannot be used with an the total 296 calls on the trolley and intrinsically safe phone system) is of pager system, only 8 were on the pager. standard manufacture, and auxiliary By listening to tape recordings of both speakers are used with the paging phones the pager and the carrier phone simulta- where the need arises. The loudspeaking neously, it was discovered that 78 calls paging phones communicate through a pair out of the 296 were not heard on the out- of wires from the 25-pair telephone side trolley carrier phone. It was also cable, and the carrier phones use the dc found that the trolley-to-pager hookup trolley wires for their signal paths. failed on 12 occasions. The actual failure of the coupler to function on some With the exception of service prob- signals and the propagation dead zones lems with the older carrier phones, all were major problems associated with this carrier and paging phones are of good system. During the fire previously men- the mine may economically justify a tioned, the carrier phones were the only dispa.tcher. commnication that worked through the evacuation. The telephone wire was Communication Requirements--Based fused, and commnication was not possible --on Su.rvey Analysis using the dial system. However, the carrier phones could and did operate, using This mine is unique in that it has a their internal batteries, through the dial telephone system, a pager system, fire. Although the loudspeaking phones and a carrier phone system. The mine, as were not in widespread service at the configured, has no need for additional time of the fire, their line would have channels, private channels, or the capa- also been fused, making them inoperative bility to interconnect to the public if and when needed. phone since the dial telephone has all these capabilities. Comrmnications Requirements--User's- Viewpoint From the traffic density seen on the pager phone and trolley carrier phone Mine personnel indicated that the system, only two additional channels can most urgent commnication requirement was be justified to get the probability of the elimination of dead zones in their blocking to the 1% level. However, only trolley carrier phone system. 3% of this communications is from the pager phone system, and the vehicle com- Communication between the shuttle munication system must be single-channel cars and from the shuttle cars to the operation for safety reasons. Therefgre, continuous miner was also thought to be there exists no justification for addi- useful. However, there was apparently no tional channels for the pager phone. great need or requirement for this type Using; this analysis and the needs gener- of comrmnication. ated by the mine personnel, the following list was developed to represent commni- Portable two-way wireless commnica- cation requirements for this mine. tion for the maintenance foreman, fire boss, miners on the weekend inspection, a. Reliable two-way vehicle and working section foreman was noted as commnication. a possible requirement. If portable two- way wireless equipment costs were high, b. A dispatcher with commnication the maintenance foreman, roving super- center if the mine increases appreciably visors, and key personnel could use a in size. one-way pager. However, mine personnel did not consider equipping a working sec- c. Portable two-way wireless com- tion with a one-way pager since a working munic.ation for working section foreman, section foreman mostly communicates maintenance foreman, and key personnel. out from his location and is seldom called from other sections or surface d. Portable battery-operated com- locations. munic.ation equipment for mine-to-surf are cmerglency two-way commnication. A requirement existed for battery- operated portable emergency commnica- A.5 Mine D tions that could be moved with the miners as the working section moved. This Mine Description requirement became evident during the fire, when it would have been useful dur- Mine D was opened in 1892. Even ing the emergency and recovery efforts. though the mine is old, they are still Also noted was the fact that if the num- developing in some areas. At present ber of working sections increased, they have eight sections on development and five on retreat. It is estimated is taken to the same cleaning plant as is that there are 15 years of mining left. the coal mined underground. This requires that dispatcher 1 dispatch The mine is entered through one of right-of-way outside as well as two drift mouths. A vertical shaft is underground. available but is seldom used. The mine produces approximately 4,500 tons of coal The mine employs a total of 675 men a day by the conventional, continuous, and works three 8-hour shifts each day, and longwall mining methods in the fol- with the major production done on the lowing percentages: first shift. The start and end of each shift and the total men working follow: First shift: Conventional...... 18 First shift: 6:45a.m. to 3p.m.-- Continuous...... 35 308 men Longwall...... 10 Other shifts...... -37 Second shift: 3:30 p.m. to Total...... 100 11:45 p.m.--216 men

The coal is removed from the mine by Third shift: 12:15 a.m. to track to the cleaning plant about 2 miles 8:30 a.m.--151 men from the mine. The mine has an annual production of about 1,300,000 tons. Mine Equipment and Power

The mine is 7 miles by 5 miles and Power is provided by the power com- has overburden from 300 feet to 800 feet. pany at 138,000 volts ac. This is then All haulage tunnels are at least 6 feet stepped down to 13,800 volts ac and dis- high by 18feet. There is noaverage tributed to eight boreholes, where it is size for a working section; some are as taken underground. At some point under- much as 3,000 feet in length. This ground it is converted to 250 volts dc, requires that coal be removed from the 550 volts dc, or 440 volts ac three- working face to the track by belt. The phase, depending on the equipment being belt is 36 inches in width, and the mine used on the section and location in the has approximately 25,000 feet of belt. mine. One of the reasons for this is If the distance is short (less than that from the outside to dispatcher 2, 500 feet), it is possible to dump coal the mine uses 550 volts dc on the from the shuttle car directly into the trolley. Then branching out from dis- coal car. patcher 2, the mine uses 250 volts dc on the trolley. The 440 volts ac is used in Eight 37-ton locomotives are used to both areas. remove the coal. The mine has 30 miles of track underground at present. Eight The power provided to sections var- boreholes are used to provide access for ies according to the type of equipment 13,800-volt-ac, three-phase, cables to used. There are cases where, on the same the mine. Roof control is obtained by section, 250 volts dc or 550 volts dc the use of roof bolts ranging in length must be provided for the shuttle cars, from 42 inches to 8 or 9 feet. and 440 volts ac provided for the miner. Both longwalls require 440 volts ac, as Owing to the amount of track and do some of the newer continuous miners. layout of the mine, it is necessary to There are also battery-powered scoops on have two dispatchers. This mine is also some sections. They are used for clean- engaged in strip mining at various loca- ing the section and hauling supplies. tions directly above the mine. This coal The mine at present uses the follow- the mine. In the case of an accident the ing equipment: section notifies the dispatcher, who in t:urn calls mine management on the Continuous miners--8 outsi.de.

Loading machines--5 Telephone Sys tem

Longwalls (1 plow, 1 shear)--2 The mine has 77 magneto telephones, 60 of which are underground. These Cutting machines--3 phones are approximately 30 years old. They use simple twisted-pair, No. 14 wire Shuttle cars--29 for the phone circuit.

Present Mine Communications The phones are usually mounted on wood that is connected, in some manner, At present, the mine communication to the roof. They are placed at loca- system consists of a magnetophone system, tions along the main haulage. Phones on carrier phone system, and loudspeaking the section are located at the head and phones. tailpiece of the belt. These phones are not permissible. The loudspeaking phones are used only on the longwalls. Carrier phones The dispatchers are the heart of the are placed on most of the track vehicles. phone system. Dispatcher 1 is respon- At the cleaning plant a 60-watt amplifier sible for the outside phones and for is used as a public address system call- underground phones 1 to 20. Dispatcher 2 ing 14 stations, each of which has a has phones 20 to 60. If a person wished microphone and speaker. to call1 outside from say phone 57, he would. have to ring dispatcher 2. Dis- Each dispatcher is responsible for patchler 2 would then call dispatcher 1, carrier phone and magnetophone control in who would ring outside, then connect the his area of the mine. The two dispatch- lines. ers must consult with each other when routing traffic toward each other. Typi- Since the phones are a ringer type, cally, the telephone network having dis- each station must have a certain ring. patcher 2 as its control point has It sh~ould be kept in mind that the cir- heavier traffic of a more varied nature cuits for the two dispatchers are sepa- than that of dispatcher 1. rated. Therefore, each dispatcher could use the same ring combinations. During the busiest period of the shift, the fourth hour, the busier trunk Recordings and corresponding analy- was used 70% of the time. This three- sis of the traffic on the phone system channel traffic intensity implies that shows that there are periods when the there is a 30% chance of getting a busy system is used 70% of the time and that signal on any given call. This is con- the system is overloaded at times. siderably worse than the one chance in a thousand of commercial telephone stan- Trolley Carrier Phone System dards. A six-channel network would be required to bring the system to commer- The carrier phones are mounted on cial standards. most of the track vehicles. The fact that the mine uses 250 volts dc and There have been no major emergencies 550 volts dc on the trolley requires the at the mine to test the existing system. use of two different carrier phones. It is possible that a roof fall could They have twelve 250-volt, 163-kHz break the phone line and cut off communi- trolley phones and twenty-eight 550- cations to the outside for some areas of volt, 100-kHz phones. Both tube and transistorized versions are used. The individuals on the section. The mine tube type is 20 years old, and the tran- personnel were of the opinion that com- sistorized type is 12 years old. The munications to those two men would be transistorized units are equipped with a desirable. 12-volt battery, so that they will still operate should the power in the mine go The maintenance foreman and master off. mechanic felt that portable two-way communications would decrease the time Pager Phones needed to locate them. Portable communications are also desired for the super- Pager phones are used on the long- visory personnel (superintendent, mine walls and on the outside of the mine. foremen, and maintenance foremen). At The pager phones are mounted on J-hooks the same time a private line was from the roof support jacks. Wires are requested for the phone system for super- hung from the roof supports for the visory personnel. phones. Rocks falling between the jacks have caused the line to break, causing a The safety department personnel sug- potential safety hazard due to inter- gested that remote monitoring of the mine rupted communication. The reason for conditions would help increase safety for this is there is no way of hearing a ring the entire mine. It was suggested that a on the pager system. There are 10 pagers private channel directly to the outside on the plow and 5 on the shear. The for emergency use would decrease the time phones are 10 years old. The mine per- required to get help from the outside. sonnel felt that the phones were mis- This private channel would also insure treated by man and environment, and that that the occurrence of an accident would was the reason for failures. not be heard by men on other sections.

Fan Monitors There should be a secure channel open at all times, from any phone under- The size of the mines requires that ground, to some central communications the fans be located at great distances center aboveground. It is not necessary from the maintenance shop. The fans are that this line be connected to the com- monitored by sending a signal over the mercial phone system. Since the. mine high-voltage lines, which is monitored at management are the first to be notified the outside shop. The five frequencies in case of an emergency, they in turn can used (one for each fan) are 39, 116, 47, call whomever is needed. In a mine this 61, and 33 kHz. size the time saved by placing the call from underground to the commercial system Communication Requirements--User ' s for assistance, then notifying manage- Viewpoint ment, would be of little help.

The phone system performed very Communications Reauirements--Based well considering its age. However, the on Survey Analysis changes in humidity caused some problems. There was also a problem with having to This mine has some communication walk long distances. The phones are not problems that are related only to the permissible; this limits how close to the extreme age of the equipment used. How- working face they can be placed and often ever, problems due to the large size of requires that an individual walk as much the mine may be typical of other large as 500 feet to reach one. mines.

Mine personnel felt that wireless Signal-to-noise ratio (SNR) causes communications of some type would be of problems when talking great distances (5 help on a section. The foreman and the to 10 miles). A new system must start mechanic are the two most sought after by improving SNR on long-distance conve rations, which may be typical of is the "stall machine" used at the tail many large mines. end of the plow longwall to give better roof control. This machine is a limited An analysis of the telephone traffic travel shear that leaves a cleaner end on density indicates that three more chan- the longwall than the plow. About one- nels (total six channels) would make the third of the mining is by longwall, one- system comparable to an estimated mine third is conventional, and the last third standard of 1 in a 100 chances of getting is continuous. The number of working a busy signal. sections for each type of mining follows:

A dial system is recommended for 1st 2d this mine. A multipair or multiplex shift shift system would help to lessen the load of the dispatcher and could also provide the Conventional...... 2 capability for conference calls. These continuous....,,,.^ 2 systems also provide the channel privacy L(ongwal1...... 1 requested by mine management, For safety reasons, the trolley carrier phone system Only a small amount of mining is should remain one channel. done during the maintenance or third shift, The mine is small enough that Using the above analysis and the there is no underground maintenance shop, suggestions of mine management, the fol- Hence, repairs that cannot be made at lowing list of improvements was derived: the site of the failure must be made outside. a. Reliable two-way vehicle system. Coal is moved from the face by b. A total of at least six channels shuttle car except on the longwalls, to meet minimum standards. where it goes directly to belt, Local belt haulage is used between the shuttle c. At least one secure channel. cars and tracked cars on the main line. The longest belt run is 4,500 feet. d. Portable two-way wireless communications for certain key personnel, During the first shift there are no idle sections so there is no need for e. Battery-operated communications maintenance crews when each section crew equipment that will work during an has its own mechanic, Extra mechanics emergency, work along the main line during this shift and help section mechanics when f. A communications center located needed. at dispatcher. During the third shift, when few A.6 Mine E sections are working, there are three maintenance crews whose specific job Mine Description is to work on equipment at the idle sections, Mine E has a drift entry in a 5.5- foot soft coal seam. The working sec- Mine Equipment and Power tions are presently 3.5 miles in from the entrance, with the possibility of eventu- Power is fed to the mainline trolley ally working at twice this distance. wire at 250 volts dc by four rectifiers, Mining at the present rate gives the mine There are deadblocks between the four a life of from 30 to 40 years. The mine sections of trolley wire so that each operates two longwalls about 500 feet rectifier supplies power to only one wide and will travel a range of short length of wire. All face-mining 3,500 feet. New to mining in this area equipment is ac operated so there is no need to have nip points from the trolley consistent pat tern. The people inter- line. viewed could give no suggestions on how the phone system--the one following the Rather thari utilizing power bore- track--could be improved. There are sev- holes, 7,200-volt ac power is brought in eral reasons that could be contributing along the mainline, up to transformers at to their satisfaction: the working sections. There the voltage is stepped down to 440 volts. Thus as a. The phones are relatively new. the sections advance, the transformers must be moved to follow. b. The phone network is not large.

The only power outages have been due c. The time and talent spent on to storms or hunters shooting transform- maintaining the system are great. ers on the power company's distribution system. Outside there are two high lines dm The equipment supplier gave them feeding the mine's single substation. much help in setting up their systems.

Should there be a power interruption em The characteristics of the phone within the mine, the substation attendant lines are good. will check by telephone with the sections before reenergizing the distribution The telephone network is such that system. anyone on a working section is never more than 350 feet from a phone. They feel Present Mine Communications this is adequate and that having a phone any closer would not really be of more Telephone System value. Other phone locations are the boom and tailpiece of every belt, plus Pager phones are used in a network four in the escapeway. No allowance has of 11 phones along the track throughout been made for emergency usage in the the mine, plus a phone in the dis- sense that, should a telephone line be patcher's outside office and one at the broken, there is no loopback to carry the communication repair station in the shop. signal. Tape recordings made during an $-hour shift indicate that there were 160 dis- Carrier Phone System cussions concerning the location and movement of empty and loaded coal cars. The carrier phone is a 72-kHz system For the next most comnon topic, there that uses the trolley power line to carry were nearly 80 discussions concerned with the signals. Even though this is a the production of mined coal. Collec- fairly small mine, they did experience tively the other subjects (reporting, dead zones of unacceptably low signal personnel location, maintenance, etc.) strength in certain areas. add up to about 80, so no one of them is a significant user of channel capacity. The dispatcher has an outside dial Analysis showed that early in the shift, phone as well as a speaker phone, so he and just before the end, the phones are serves as a message relay center and used as much as 50X of the time. This information center as well as a dis- places the probability of a potential patcher. The communications maintenance caller finding a busy line at one chance area of the shop also has a trolley car- in two during these periods. rier phone to aid the maintenance people in servicing the trolley carrier phone The loudspeaker telephones have an system. The carrier phones do not have average age of about 4 years. Rock dust storage battery backup. If there is a does seep in through their cases, but the failure of trolley power, carrier phone users and maintenance men report there communications are lost. are few failures and these fall in no The mine has had a dispatcher for Signal lights are positioned along only the last 2 years. Before that, the longwall miner so the operators can motor operators controlled the track for coordinate their efforts if the phone themselves. At that time the mine tried system fails. The quality of speech tying the telephone system in with the reproduction for the phones was good, and trolley phone system (this type applica- the loudspeaker volume was adequate in tion cannot be used with an intrinsically spite of the high ambient noise of the safe telephone system) but found it only miner. added confusion to have those not near the main line hear all the discussions of The only complaint the personnel had the motormen. was that the push-to-talk button failed often. This button ismounted onthe To get the carrier signal around recessed front face of the unit. The the deadblocks, 2-pF capacitors are used. phones at the ends of the longwall are mount:ed horizontally so the recessed To keep rectifier "hash" out of the panel! acts as a catch basin for the 72-kHz system, L-filters are used at each watered-down coal dust . Evidently the rectifier (paragraph 5.3. la). The filter directional properties of the speaker are consists of a 50-pF capacitor across a such that this mounting is necessary. rectifier's output, with a 10-turn, heavy-cable coil, the coil having an -Comnnllnications Requirements-- approximate diameter of 2 feet. The --User's View manufacturer tuned the filter to reject 72-kHz interference. Except for correction of the minor probl-ems already presented, the mine per- CAUTION sonnel had little to suggest about new comm.nications systems that would make Installation of equipment in a their work safer and more effective. mine should be done only by people This may be due to their present system thoroughly qualified to do such work. being new and seemingly adequate for this Installations should follow proce- size mine, or due to their not having dures recommended by the equipment time to visualize how a higher capability manufacturer and should comply with system might profitably be utilized. good safety practices. All installations should also comply with appli- The one desire expressed at this cable codes and regulations. mine was for a secure channel for seeking aid for an accident victim. As in other Longwall Comrmnication System mines, when an accident is being reported, everyone who knows the phone is The longwall miner has its own com- being used for this purpose will listen munications system consisting of seven if he can. This lowers the productivity loudspeaking telephones, one at each end of th.e eavesdropper; takes his mind off and the other five equally spaced along his work, making him more accident prone; the 500-foot longwall. These loudspeak- and worse, loads the telephone system so ing telephones have no handset and thus that the dispatcher can no longer clearly operate in the pager mode only, with the understand the report. It is not essen- loudspeaker serving as a microphone when tial that the conversation cannot be the push-to-talk button is pressed. The listened to, just that personnel not telephone lines lie in the troughs that become aware that someone in a panic carry the hydraulic lines. At one time is calling the dispatcher. Personnel the wires were hung under the top plate seldom listen in on run-of-the-mill of the jacks, but slate falling between conversations. the jacks kept breaking the wires. Communications Kequirements--Based Coal production is approximately on Survey Analysis 250,000 tons per year. There is one mining section, operating one shift. Coal The exceptional high quality and the is mined via the room and pillar method unusual amount of care given to the tele- with activity rotating through six active phone and carrier phone systems leave rooms. little to suggest as to improving these communications means in mines similar to The mine will ultimately be approxi- this one. mately 1-114 miles square. Mining activity is currently occurring about 314 mile This mine, like some others visited, from the shaft. has a need for a secure channel as an aid in effectively handling injury problems, The overburden at the shaft is and it would be desirable to have a 157 feet, increasing gradually to the secure management channel. working face. Tunnels are typically 12 feet wide and range from 4 to 6 feet Better communications capability high. Four- and 6-foot roof bolts are would increase productivity in the long- installed on 5-foot centers. wall mining sections. Fast, effective hands-free communication is needed by There are no boreholes into the operating personnel during both operation mine. The fresh air entrance serves as and repair of the miner. Because of its the emergency exit and is located about high production rate--and thus the high 500 feet from the main shaft. The main cost of downtime--and because of the shaft serves as the air exhaust. almost impossible working conditions, it seems essential that all longwall workers Mine Management have their own wireless communications network with each having small, light- Since there is only one mining weight equipment, including speakers and section, the mine operates with very bone-conducting microphones mounted in few management personnel, as follows: helmets. The communication center oper- General manager, chief engineer, super- ator should also be able to monitor this intendent, and foreman. network. Management personnel do quite a bit A.7 Mine F of filling in as necessary; however, the chief engineer normally tends to topside Mine Description operations while the superintendent stands by at the bottom of the shaft. Mine F has been operational since The foreman remains at the face. The 1963 with production originally estimated mine has 25 men underground during the for 25 years. Coal is being mined shift. from the Mammoth Seam in the Cherokee Group. Seam thickness is approximately There are five mining operations 60 inches. rotating continuously through the six active rooms at the face. A cycle starts This mine is the only nonunion mine with the cutter undercutting the coal surveyed. As a result, some of the oper- face. This is followed by the coal ations are notably different from those driller drilling holes for the charges. seen at the other mines examined. After the driller moves on, the charges are set and fired by the shot firer. The mine employs conventional mining After a delay for the air to clear, the techniques and employs tracked haulage to loader is moved in to begin loading remove the coal. Personnel entry and shuttle cars, which transfer coal to the coal removal are through a single shaft. haulage cars. When a room has been cleaned of the loose coal, the roof bolt- Ventilation is via a single fan, ers move in to extend the supported sec- blowing into the escape shaft and tion of the roof. exha.usting through the main shaft . Within the mine, water sprays are used to keep dust down. There has never been any Loaded haulage trains are pulled to probllem with excessive water, so the only the shaft where the cars are dumped into wate.r-handling gear is that used to con- a skip, one car to a skipload. The skip trol, dust. is lifted up the shaft and dumped into the crusher. Crushed coal is conveyed Mine Equipment and Power into semitrailer trucks that are used exclusively to haul the mine's output. The following pieces of mining equipment are in use at the mine: The maintenance philosophy of this mine results in a large amount of nonpro- Shuttle cars--3 Roof bolter--1 ductive machine time. There is a com- Loader--1 Coal drill--1 plete operating spare for each type of Cut ter--1 Locomotives--3 machine in the mine. As a result of this philosophy, however, there is virtually In addition to the equipment in use, no downtime for equipment maintenance. A there is one operating spare of each type minor failure is repaired on the spot; in of machine. In case of major breakdown case of a major failure, the spare the spare is placed in operation while machine is placed in service while the the broken unit is repaired. broken one is fixed. Primary power comes into the mine There is no fixed shop location. through the main shaft. A 2,300-volt, The maintenance personnel travel with the three-phase line is run to the two mining crew. The presence of spare transformer-rectifier sets used. One machinery permits repairs and maintenance transformer feeds the trolley for the to be performed thoroughly without slow- haulage system; the other powers all ing production. mach~ineryat the face. All machines in the mine run off 280 to 300 volts dc. Supplies are delivered via the haulage cars. Just before the end of each Pres'ent Mine Communications working day the foreman calls his list of supplies to the hoisting engineer. These The mine currently has a combination are placed at the top of the shaft and of independent voice communication delivered to the face either at the end systems. The loudspeaking phone system of the day or the beginning of the next uses two units, one located at the hoist- one. Repair parts are delivered during ing engineer's position, and the other at the day via a return trip of the haulage the working face. A two-station intercom cars. connlects the top and bottom of the shaft. Anot.her intercom connects the hoisting The mine has a single man-trip car. engineer and the mine office. Two spare This is sufficient to carry the entire 1oud.speaking pagers serve as backup and crew, so only one man-trip is made, morn- permit a third station to be patched in ing and evening. Administration of the if work is being done a long way from the mine operation is quite informal. The face. The hoisting engineer serves as general manager oversees all operations "conununications central," tying the three and assists the topside personnel as syst.ems together. In addition to the necessary. All management personnel internal communication systems, an exten- assist when and where needed. sion of the outside telephone line is located at the chief engineer's desk. multichannel system. The system should The pager at the face is kept mounted have a minimum of seven stations. near the power sled, so the two are moved together. Nothing else is moved. Their locations would be as follows:

All equipment has been holding up Mine office well. Perhaps twice a year, one of the pagers will quit operating. Whenever Hoisting engineer" position this happens, the bad unit is removed and sent to a commercial repair station. Shaft bottom

In normal system use, all calls are Working face made from a remote point to the hoisting engineer "commnicat ion central. " As Bottom of emergency shaft long as calls are being made in this manner, the system functions well. A pos- Midway between bottom and face along sible exception might occur in an emer- inbound haulageway gency situation at the face. The pager at this point is 50 to 100 feet from the Midway between bottom and face along nearest working room, and on the other outbound haulageway. side of air-diverter flaps. It is con- ceivable that an accident could occur in Other stations that might be con- which the phone would not be accessible. sidered include-- The other possibility involving an accident situation would involve the phone Topside storage or shop area cable. There is a single run with no backup or loopback path. This cable is, Chief engineer's desk however, protected in being mounted on vertical timbers and is of armored Crusher construction. Most of the added stations would be When calls are made from the "com- concerned more with safety than with munication central" position to other product ion. As things stand, it is parts of the mine, the system does not possible to be blocked from a phone sta- work so well. A complaint was made that tion or to be a long walk from one. In if the superintendent leaves the bottom addition to the fixed stations, the man- of the hoist it may take a half hour to agement personnel should have radio com- get a message to him. It appears very municators. This would eliminate the unlikely that a call to the pager at the existing situation in which a critical face would find anyone near enough to man can be out of touch when others need hear it. The fastest route to the face a decision or information. appears to involve relaying a message to a motorman at the hdist and having him An expanded system needs no more deliver it to the face when he returns. than two general channels plus a private channel. Radio communicators operate In this mine, commnications ef- best if they can access all three chan- ficiency would be improved by replac- nels, but could operate with access only ing the three independent two-station to one of the general channels. phone systems with a single multistation, The cable into the mine should be a between motormen and/or motormen and a continuous loop of armored wire for maxi- central dispatcher. This description mum reliability and protection. By using illustrates how one mine in this category a multiplex system, all channels plus solved its haulageway communication monitors could be included on a single requirements using a unique system of UHF cable. 1 and VHF repeaters combined with a "leaky coaxial" transmission line. A.8 Mine G This mine was a magnetite ore block Mines that do not employ rail haul- caving operation. Surface access to the age systems powered from a trolley wire Mine (fig. A-2) was by two vertical face unique problems in establishing sat- shafts to the No. 6 production level, isfactory communications between haulage- 2,500 feet, with mining occurring at a way vehicles. Because common trolley depth of 2,500 to 2,800 feet. Diesel- carrier phones cannot be utilized, some powered, rubber-t ired loading equipment other form of radio system must be used was used to transport ore to the crush- to establish the required voice link ers. A conveyor belt ran between the crusher rooms and the ore skip storage l ro roved and nonapproved s ys tems may bins where the ore was automatically not share the same cable; check with MSHA loadled into 20-ton skip cars and hoisted for details. to the surface.

/ No. 2 crusher

B shaft' FIGURE A-2. - Underground map of mine, 6th level. Personnel underground included rov- power. A telltale beep in the system ing miners in production, haulage, and signaled that the system had reverted to shop areas, fan-hole drill operators emergency power. The communication sys- working alone, and maintenance vehicle tem utilized off-the-shelf , readily and ambulance operators. To satisfy the available communications equipment and objective to communicate between these installation hardware. In addition, the personnel and the surface, a guided wire- system was compatible with the installa- less communication system utilizing tion and maintenance capabilities of the equipment available from Motorola, Inc., mine personnel. and Andrew Corp. was selected. Portable HT-220 radios and industrial dispatcher Figure A-3 shows the extent of the mobile transceivers were chosen for radiating cable installation. There was personnel and vehicles, respectively. 11,000 feet of RX5-1R 718-inch Andrew Andrew Kadiax cable, a special type of Radiax in the system. The cable attenua- cable that allows for leakage of signals tion was 1.2 dB1100 ft; thus, two re- out of and into itself, was installed peaters were required to compensate for throughout the major areas of the mine. signal loss as well as provide adequate Because the total cable length exceeded power levels for future system expansion. 2 miles, it was necessary to install two repeaters. Although the system did not The cable specifications state that require a dispatcher or an operator, a it must be supported every 5 feet. To communications center was established at avoid installing 2,000 anchors in the an underground crusher room. Personnel rock, a 3116-inch steel messenger wire could be selectively paged from the con- was attached at 20-foot intervals to sole, and an evacuation alarm could be roof-bolt-supported T-bars. The cable activated from either the console or an was then strapped to the messenger wire alternate monitor station at the shaft with standard cable ties. bottom. The monitor station was wired to the surface where a remote control unit Some areas were so far away from the provided surface access to the system. installed cable that radio transmissions During a power failure, the system would could not be established. This was over- operate for 24 hours on backup battery come by inserting a stub cable with one

LEGEND @--~ower divrder b- Antema 0 Repeater A Fixed station

O- O- .3cQ Scale, ft

Alternate

FIGURE A-3. - Leaky feeder cable layout. end connected through a power divider to mining vehicles. A better radio for this the main cable; the other end terminated app1:lcation was the motorcycle,version of in an antenna located within several hun- the Industrial Dispatcher. All controls dred feet of the desired working area. and the microphone plug were located on the small, rugged loudspeaker enclosure. The repeaters, composed of a unique The loudspeaker can be mounted in a combination of UHF and VHF units, were convenient location, and the larger bolted together and mounted on pallets transceiver unit can be mounted in a more for ease of transport within the mine. protected location. The antennas are The UHF and VHF units were interconnected either 114-wave whips or Sinclair low- by a squelch and audio interface. Vehi- profile blade antennas. The radome cular and personnel comrmnications took version of the blade antenna appears place over the leaky coaxial cable on the to be the most suitable for mining UHF repeater frequencies, while the con- app1:ications. trol between repeaters, located some 2,000 feet apart, used VHF over the same A dispatcher control console at the cable. A 5-MHz UHF transmit and receive No. 2 crusher could be either manned or frequency separation allowed connection unmanned; no operator was necessary for to the common Radiax through a duplexer. system operation. Paging could be initiated from an encoder at the console to The repeaters were prewired, and the send private messages to pager-equipped system was assembled on the surface where radios. Equipping the fan-hole drill it underwent several months of burn-in. operaator with a pager-encoded radio pre- This procedure eliminated the frustra- vents the nuisance of his listening to tions of troubleshooting and testing the general system traffic. He would only system underground. hear messages directed specifically to him. The console also had the provision The fan-hole drill operator, for sending a warning signal to all equipped with a portable radio attached radios in the mine. This wailing siren- either to his belt or to a chest pack as like signal could be used for mine evacu- he preferred, was also equipped with an atioin in an emergency. accessory noise-reducing earmuff and microphone. The receiver audio was routed The alternate control station pro- to small loudspeakers inside his ear pro- videtd an additional access point to the tectors, while the microphone and push- com~nications network. This station to-talk switch were installed in a simi- monitored the activity of the fan-hole lar earmuff which the fan hole drill drill operator. Also, this station was operator placed over his mouth when he connected by wire line to an intercom wished to make a radio transmission. All unit in the surface guardhouse. The portable radios in the mine were equipped guarld could access the system through with the provision to use an external remote control. This feature was espe- speaker microphone accessory so that the cially desirable during maintenance peri- radio need not be detached from the oper- ods when the underground stations are ator's belt and raised to his ear or unmainned or during a mine emergency, mouth. In noisy locations the use of a to coordinate evacuation and rescue noise-reducing speakerlnicrophone is a ~per~ations. necessity. The mine had outfitted an under- Two types of vehicular radios were ground radio shop with the necessary used. The Industrial Dispatcher had all service equipment to maintain the commu- controls, the microphone plug, and nications system. A full-time Federal speaker located on the transceiver pack- Communication Commission second-class age; this necessitated locating the licensed radioman was trained in system transceiver within the vehicle operator's installation, operation, and maintenance. reach, which is nearly impossible on some Reli4ability of the UHF-VHF system was excellent with negligible downtime. This maintenance and adaptation to changes in wireless communications system demon- mine operations. strated that the objectives of personnel and vehicular underground mine communi- The MDP system (fig. A-4) consists cations can be satisfied. Worker and of individual phone stations placed at management acceptance of the system was selected sites within the mine, one or excellent. more interface cabinets located on the surface, a telephone switchboard, and the A.9 Mine H necessary multiconductor interconnecting cable. (One pair of conductors is To meet changing commnication required for each private line.) requirements in many of its mines, one utility company has installed a new mul- Each phone station is contained tichannel mine dial-page phone system at within a bright yellow, molded polyester- its underground operations. The first of fiberglass-reinforced housing. This its type, this fully permissible comrmni- material, coupled with the use of stain- cation system combines the paging capa- less steel hardware, gives a corrosion- bility of current mine page phones with free enclosure. The station includes a the advantages of conventional tele- handset, a telephone dial, a loudspeaker, phones. Manufactured by GAI-Tronics an all-solid-s tate plug-in amplifier, and Corp. , the Mine Dial-Page Phone System a self-contained battery of the standard (MDP) has the following features: 12-volt mine page phone type. 1. Each underground station is on a In addition, since some power for separate circuit ready for instant use system operations is supplied from depending upon the availability of an the surface, the mine phones are designed open channel in the central switch. to have individual power to permit emergency communications in the event of 2. When connected to a telephone a power cutoff. This is accomplished switchboard through a 12- to 48-volt inby a standard 12-volt phone battery, terface circuitry card provided for each while the surface equipment is provided line, any underground station can call with a 12-volt rechargeable battery, re- another underground station directly, or quired only in the event that volt- call any standard telephone at a surface age to the dc power supply should be location. Also, any underground station 10st . can be called from any aboveground standard telephone. Located outside each cable entry into the mine is an interface cabinet. 3. Selective paging capability to The circuitry that converts the telephone any single, specific underground station. switchboard voltages (ac and dc) to permissible levels is contained in this 4. A dial-access, all-station pag- cabinet on a separate plug-in inter- ing capability to call personnel not at face card for each telephone line. their normal location, or to alert all The cabinet also contains the 12-volt underground personnel. rechargeable battery. This battery automatically powers the system if there is a 5. Automatic switching to a push- power failure at the switchboard or in button-operated, all-page-partyline mode the connecting cable between the switch- in the event of a telephone switchboard board and the cabinet. power failure or severance of the cable interconnecting the switchboard and the The switchboard itself is an impor- interface cabinet, one of the key compon- tant link in the MDP operation. ents of the MDP system. This mine's initial installation 6. Plug-in electronic assem- uses a private automatic branch exchange blies, wherever possible, to facilitate provided and installed by the local FIGURE A-4. - Typical mine dial- age hone system. telephone company in the main office a page call will be heard in the handset building at the mining operation. receiver by all parties engaged in calls to, from, and between MDP phones, but it An incoming call triggers the inter- will not interrupt these conditions; the face card circuitry in the cabinet, which conversation can continue at the con- begins with the activation of a timed clusion of the page. The person being holding circuit that completes the dc paged, however, must dial the person loop of the telephone line and halts the initiating the page to carry on a regular incoming ringing signal. The timing cir- conversation. cuit holds the line for approximately 40 seconds and initiates additional cir- The interface cabinet contains a cuitry which produces a distinctive separate fail-safe system to maintain warble ring tone on the appropriate MI)P communications in the event of an acci- phone. The ring tone is applied for a dental disconnection of the cable between 4-second period, and the balance of the the cabinet and the telephone switch- 40 seconds is held for the calling party board, or if there is a failure of the to page a specific person or make an switchboard's power. A second circuit announcement. At the end of this period, network, controlled by a switchboard mon- if the called station has not answered, itor, automatically ties all of the the lines are automatically disconnected. interface cards together in the event of such failure. In this mode, two-way pag- When the station answers before the ing and handset conversation can be end of the 40-second hold period, the carried out in a manner similar to that timing circuitry is returned to its of presentday mine page phones. A push- original standby state and the loud- to-page button is provided for paging in speaker is muted. The party called this mode, with each phone having its own responds by taking the phone handset from battery to provide power for both normal its holder and squeezing a press bar and this alternate-mode operation. located in the center of the handle. Holding of the telephone line is accom- Ability to dial outside calls-- plished by a circuit not associated with including direct-dial long-distance the timing circuit, and the connection is calls--and to receive similar calls is held as long as both parties are pressing limited only by the telephone switch- their respective press bars. board. That is, an kDP phone station can be used to dial any telephone or receive For outgoing calls, the user of the any incoming call that a conventional MDP phone simply removes the handset from telephone connected to the same line the holder and presses the press bar. could handle. When the familiar dial tone is heard, he can dial his call. Release of the Am10 Mine I press bar terminates the connection. A delay circuit is provided to maintain Mine Description the line connection during any brief (2-second maximum) release of the press Mine I is a silver mine centrally bar, such as to change hands. located in the Couer d'Alene mining district in Idaho. The mine was first The aforementioned procedures allow opened in 1884 and presently employs over one party to call another at a specific 500 persons, 400 of whom work under- location. A separate feature is provided ground. Main access to the mine is to page a person when his location is through a 200-foot-long adit to shaft A unknown. By dialing a special number, a at the western edge of the mine. A miner separate amplifier and electronic source proceeds down that shaft to the 3100 and within the interface cabinet activate the 3700 levels and then eastward through loudspeaker at each MDP station to pro- 5,000-foot-long drifts to shaft B, which vide one-way paging communication. Such is collared at the 3,100-foot level. Miners must then go down that shaft to and is equipped with a four-deck man cage the active working levels (fig. A-5). with a total capacity of 48 men. It is used for servicing all levels below Shaft B is bottomed just below the 3700. 6,000-foot level. Ore is being produced on the 4000, 4200, 4400, 4600, 4800, Airflow for the mine is dependent 4000, 5200, and 5400 levels. Level upon pressures developed by fans located development is in progress on the underground (series ventilation). All of 5600 level, and shaft station development the intake air for ventilation of the is in progress on the 5800 level. mine is coursed down shaft A to the 3100 and 3700 levels. The air is split The A and R shafts are each provided between these two levels and travels lat- with electric-powered double-drum hoists erally to shaft B. The air is then and electric-powered single-drum chippy forced down the shaft B to the lower lev- hoists. The double-drum hoists on both els. The return air flows back through shafts are used primarily for hauling ore vent:ilation raises and exhaust airways to and waste materials. The chippy hoist on the surface. shaft A is used for moving men and materials to all levels as far down as The ore deposits occur as long, gen- the 4000 level and for hoisting ore from erally narrow veins containing sulfides the 4000 level to the 3100 level. The of s:ilver, copper, lead, and antimony in shaft B chippy hoist is on the 3700 level a carbonate quartz gangue. The vein dips range from 45' to 90° and are generally to tlne south. Strike lengths on the major ore shoots range up to a known maximum of 2,200 feet and are. normally exceeded twofold or threefold vertically along the dip of the structure. The true vein width varies considerably but generally averages between 2 and 5 feet, The steeply dipping fissure veins are mined by the horizontal cut and sand- fill method by either breasting down or back stoping. Stopes are developed a maximum of 100 feet along the strike of the vein. Level intervals are 200 feet. A raise climber is used to drive the 6- by 6-foot raises between levels. All underground transportation is accomplished using either the hoists or battery-powered locomotives on narrow- gage tracks. The mined ore is transported to a muck pocket on the associated haulage level. This ore, or muck as it is called, is then dumped onto the shaft B hoist skips and transported to the 3100 level. The muck is then trans-

LEGEND ported by locomotive to shaft A and -ESCAPE ROUTES hoisted 3,100 feet to the headframe stor- -BEST MANWAY age bins.

Surface facilities include an office area,, warehouse electric shop, machine FIGURE A-5. - Mine I, mine map. shop, hoist and compressor house, garage, carpenter shop, mine and mill changehouse functions, the system receives central for employees, dispensary, and tailing office signals at one end (such as the ponds. Engineering personnel are also ringing voltage generated by the central located at the mine to provide facility office to ring the telephones) and repro- planning and better control progress of duces them at the other end (it remotely the mining operations. generates ringing voltages to ring the bells as needed). Conversely, the system Present Mine Communications can receive only dial pulses from the telephone end, which it passes to the The telephone permissibility re- central office. When used in this way, quirements are not applicable to metal the system is a transparent substitute and nonmetal mines such as this mine. for copper pairs; that is, users cannot A high-dc voltage on the carrier pair, tell whether the S6A system or copper although a potential safety problem, is pairs are being used. of much less severity in a metal or nonmetal mine. Therefore, an Anaconda S6A The central switching function of system was installed to provide telephone the phone system is handled by a small service underground. private branch exchange. System requirements were carefully examined before The Anaconda S6A is a seven-channel, choosing a location for this PBX. A frequency division multiplex system. The spare single twisted pair was available following items are worth noting in from the shaft A surface to deep within regard to its suitability for mine the mine. Any additional wiring in the applications: shafts was to be avoided. An air- conditioned room was available in the 1. The system provides a suitable shaft B area at the 3,700-foot level that number of channels (seven) on a single met all environmental requirements of the wire pair. PBX. Additionally, this location was approximately centered with respect to 2. The mechanical and environmental the number of telephones desired in the specifications indicate the ability to system. The single twisted pair was operate under the severe conditions found opened at this point, thereby forming two in the mine. independent wire pairs. Carrier terminals were then installed on each pair, 3. The system allows -branches to and these two independent carrier systems individual conventional dial telephones were then connected to the PBX circuits. at any point on the system. This provided up to 14 private channels for communication within the mine. One 4. Remote units (at the telephones) channel in each carrier system was desig- have batteries that are trickle-charged nated for use in a monitor-control sys- over the wire pair. This enables the tem. Of the remaining 12 channels, 5 in system to be freestanding and not con- each carrier system are used to connect nected to 110-volt power underground. phones to the PBX, and the additional channel is reserved as a spare. Addi- 5. Carrier levels require no tional phones for critical locations and adjustment, as the system has automatic functions in the 3700 level shaft B area gain control circuitry. are directly connected to PBX line circuits to provide them with private line The Anaconda S6A system is designed service. This minimizes the possibility to interface a central off ice at one end of getting a busy signal for these and conventional telephones at the other. phones. It was designed as a transparent substitute for copper pairs connecting the Each phone has battery backup that telephone company office to subscriber will allow operation for 24 hours. telephones. To perform its signaling APPENDIX Be--FEDERAL REGULATIONS

The following sections of the U.S. It should be noted that some States Code of Federal Kegulations, Title 30, have enacted laws that further regu- Mineral Resources, Chapter 1--Mine Safety late the use of communications, control, and Health Administration are presented and rnonitoring equipment in underground to assist planners of communication sys- mines. Check State and local reguiations terns in insuring that all requirements before proceeding with the installation are being satisfied. of new or redesigned equipment.

PART 57-SAFETY AND HEALTH 57.11-54 Mandatory. Telephone or other voice communication shall be provided be- STANDARDSMETAL AND NON- tween the surface and refuge chambers and METALLIC UNDERGROUND MINES such systems shall be independent of the mine power supply.

0 57.1 Purpose and scope. The regulations in this part are pro- mulgated pursuant to section 6 of the Federal Metal and Nonmetallic Mine 0 57.18 Safety programs. Safety. Act (30 U.S.C. 725) and pre- scribe health and safety standards for GENERAL-SURFACEAND UNDERGROUND the purpose of the protection of life, the promotion of health and safety, and the prevention of accidents in underground metal and nonmetallic mines which are subject to that Act. Each standard which is preceded by the word "Mandatory" is a mandatory standard. The violation of a mandatory standard will subject an operator 57.18-12 Mandatory. Emergency tele- to an order or notice under section 8 phone numbers shall be posted at appropri- of the Act (30 U.S.C. 727). Those regu- ate telephones. lations in each subpart appearing 57.18-13 Mandatory. A suitable cornmu- under the heading "General-Surface nication system shall be provided at the and Underground" apply both to the mine to obtain assistance in the event of an underground and surface operations of emergency. underground mines; those appearing under the heading "Surface Only" apply only to the surface operations of underground mines: those appearing under the heading "Underground Only" apply only to the underground operations of underground mines.

0 57.19 Man hoisting.

9 57.1 1 Travelways and escapeways.

TRA~WAYS

GEIVERAL-SURFACE AND UNDERGROUND

57.19-55 Mandatory. When a manually operated hoist is used, a qualified hoistman shall remain within hearing of the telephone or signal device at all times while any person is underground. 57.21-1 Mandatory. A mine shall be deemed gassy, and thereafter operated as a gassy mine, if: (a)The State in which the mine is located classifies the mine as gassy; or (b) Flammable gas emanating from the orebody or the strata surrounding the ore- 57.19-90 Mandatory. There shall be at body has been ignited in the mine; or least two effective approved methods of sig- (c) A concentration of 0.25 percent or naling between each of the shaft stations more, by air analysis, of flammable gas ema- and the hoist room, one of which shall be a nating only from the orebody or the strata telephone or speaking tube. surrounding the orebody has been detected 57.19-91 Mandatory. Hoist operators not less than 12 inches from the back, face. shall accept hoisting instructions only by or ribs in any open workings; or the regular signaling system unless it is out (dl The mine is connected to a gassy mine. of order. In such an event, and during other 57.21-2 Mandatory. .Flammable gases de- emergencies, the hoist operator shall accept tected only while unwatering mines or instructions to direct movement of the con- flooded sections of mines or during other veyances only from authorized persons. mine reclamation operations shall not be 57.19-92 Mandatory. A method shall be used to permanently classify a mine gassy. provided to signal the hoist operator from During such periods that any flammable gas cages or other conveyances at any point in is present in the mine, the affected areas of the shaft. the mine shall be operated in accordance 57.19-93 Mandatory. A standard code of with appropriate standards in this Section hoisting signals shall be adopted and used 57.21. at each mine. The movement of a shaft con- veyance on a "one bell" signal is prohibited. 57.19-94 Mandatory. A legible signal code shall be posted prominently in the hoist house within easy view of the hoistmen, and at each place where signals are given or received. 57.19-95 Mandatory. Hoisting signal devices shall be positioned within easy reach of persons on the shaft bottom or constant- VENTILATION ly attended by a person stationed on the lower deck of the sinking platform. 57.21-20 Mandatory. Main fans shall be: 57.19-96 Mandatory. Any person responsible for receiving or giving signals for cages, skips, and mantrips when men or materials are being transported shall be familiar with the posted signaling code.

(f) Provided with an automatic signal device to give warning or alarm should the fan system malfunction. The signal device shall be so located that it can be seen or heard by a responsible person at all times B 57.20 Miscellaneous. when persons are underground.

57.21-29 Mandatory. Booster fans shall 57.20-32 Mandatory. Telephones or other be: two-way communication equipment with (a) Provided with an automatic signal instructions for their use shall be provided device to give warning or alarm should the for communication from underground oper- fan system malfunction. The signal device ations to the surface. shall be so located that it can be seen or 134 F'R 12517, July 31, 1969, as amended at heard by a responsible person at all times 35 FR 3677, Feb. 25, 1970: 42 FR 29424,June when persons are underground. 8, 1977; 42 FR 57044. Oct. 31, 1977; 44 FR (b) Equipped with a device that automati- 31919, 1, 1979; 44 48535, 17, cally deenergizes the power in affected June F'R Aug. active workings should the fan system mal- 19791 function. tc) Provided with air locks, the doors of § 57.21 Gassy mines. which open automatically should the fan Gassy mines shall be operated in accord- stop. ance with all mandatory standards in this (dl Equipped with two sets of controls ca- part. Such mines shall also be operated in pable of starting. stopping, and reversing, accordance with the mandatory standards the fans. One set of controls shall be located in this section. The standards in this section at the fans. A second set of controls shall be apply only to underground operations. at another location remote from the fans. PART 75-MANDATQRY SAFETY § 75.516-2 Communication wires and STANDARDS-UNDERGROUND cables; installation; insulation; support. COAL MINES (a) All communication wires shall be supported on insulated hangers or insulated J-hooks. (b) All communication cables shall be insulated as required by 5 75.517-1, and shall either be supported on insulated or uninsulated hangers or J- hooks, or securely attached to messenger wires, or buried, or otherwise protected against mechanical damage in a manner approved by the Secretary or his authorized representative. (c) All communication wires and § 75.321 Stoppage of fans, plans. cables installed in track entries shall, except when a communication cable is [STATUTORYPROVISIONS] buried in accordance with paragraph Each operator shall adopt a plan on (b) of this section, be installed on the or before May 29, 1970, which shall side of the entry opposite to trolley provide that when any mine fan stops, wires and trolley feeder wires. Addi- immediate action shall be taken by the tional insulation shall be provided for operator or his agent (a) to withdraw communication circuits at points all persons from the working sections, where they pass over or under any (b) to cut off the power in the mine in power conductor. a timely manner, (c) to provide for res- (dl For purposes of this section. com- toration of power and resumption of munication cable means two or more work if ventilation is restored within a insulated conductors covered by an ad- reasonable period as set forth in the ditional abrasion-resistant covering. plan after the working places and C38 FR 4975, Feb. 23, 19731 other active workings where methane is likely to accumulate are reexamined § 75.517 Power wires and cables; insula- by a certified person to determine if tion and protection. methane in amounts of 1.0 volume per centum or more exists therein, and (dl to provide for withdrawal of all persons from the mine if ventilation Power wires and cables, except trol- cannot be restored within such reason- ley wires, trolley feeder wires, and able time. The plan and revisions bare signal wires, shall be insulated thereof approved by the Secretary adequately and fully protected. shall be set out in printed form and a 9 75.517-1 Power wires and cables; insula- copy shall be furnished to the Secre- tion and protection. tary or his authorized representative. Power wires and cables installed on or after March 30. 1970, shall have insulation with a dielectric strength at least equal to the voltage of the circuit.

0 75.521 Lightning arresters; ungrounded 9 75.508-1 Mine tracks. and exposed power conductors and When mine track is used as a con- telephone wires. ductor of a trolley system, the location Each ungrounded, exposed power of such track shall be shown on the conductor and each ungrounded, ex- map required by 8 75.508, with a nota- posed telephone wire that leads under- tion of the number of rails and the ground shall be equipped with suitable size of such track expressed in pounds lightning arresters of approved type per yard. within 100 feet of the point where the circuit enters the mine. Lightning arresters shall be connected to a low resistance grounding medium on the surface which shall be separated from neutral grounds by a distance of not less than 25 feet. C38 FR 4975, Feb. 23, 19731 and such electric power can be supplied only from inby the equipment being moved or transported, power may be supplied from inby such equipment provided a miner with the means to cut off the power, and in direct 9 75.701-4 Grounding wires; capacity of communication with persons actually wires. engaged in the moving or transporting Where grounding wires are used to operation, is stationed outby the ground metallic sheaths, armors, con- equipment being moved. duits, frames, casings, and other me- (2) The settings of automatic circuit tallic enclosures, such grounding wires interrupting devices used to provide will be approved if: short circuit protection for the trolley circuit shall be reduced to not more (a) The cross-sectional area (size) of than one-half of the maximum cur- the grounding wire is at least one-half rent that could flow if the equipment the cross-sectional area (size) of the being moved or transported were to power conductor where the power con- come into contact with the trolley ductor used is No. 6 A.W.G., or larger. wire or trolley feeder wire; (b) Where the power conductor used (3) At all times the unit of equip- is less than No. 6 A.W.G., the cross- ment is being moved or transported, a sectional Erea (size) of the grounding miner shall be stationed at the first wire is equal to the cross-sectional automatic circuit breaker outby the area (size! of the power conductor. equipment being moved and such miner shall be: (i) In direct communication with persons actually engaged in the moving or transporting operation, and (ii) capable of communicating with the responsible person on the surface required to be on duty in accordance with 8 75.1600-1 of this part; 575.1003-1 Other requirements for guard- (4) Where trolley phones are utilized ing of trolley wires and trolley feeder to satisfy the requirements of para- wires. graph (f )(3) of this section, telephones or other equivalent two-way communi- -%:!equate precaution shall be taken cation devices that can readily be con- i;o insure that equipment being moved nected with the mine communication along haulageways will not come in system shall be carried by the miner contact with trolley wires or trolley stationed at the first automatic circuit. feeder wires. breaker outby the equipment being 5 75.1003-2 Requirements for movement moved and by a miner actually en- OF off-track mining equipment in areas gaged in the moving or transporting of active workings where energized operation: and, trolley wires or trolley feeder wires are present; pre-movement requirements; certified and quelified person-..

0 75.1402 Communication between shaft stations and hoist room. (f) A minimum vertical clearance of 12 inches shall be maintained between the farthest projection of the unit of equipment which is being moved and the energized trolley wires or trolley There shall be at least two effective feeder wires at all times during the methods approved by the Secretary of movement or transportation of such signaling between each of the shaft equipment; provided, however, that if stations and the hoist room, one of the height of the coal seam does not which shall be a telephone or speaking permit 12 inches of vertical clearance tube. to be so maintained, the following additional precautions shall be taken: (l)(i) Except as provided in para- 0 75.1402-1 Communication between shaft graph (f)(l)(ii) of this secti~nelectric stations and hoist room. power shall be supplied to the trolley One of the methods used to commu- wires or trolley feeder wires only from nicate between shaft stations and the outby the unit of equipment being hoist room shall give signals which can moved or transported. (ii) Where be heard by the hoisting engineer at direct current electric power is used all times while men are underground. Q 75.1402-2 Tests of signaling systems. (b) The incoming communication Signaling systems used for communi- signal shall activate an audible alarm, cation between shaft stations and the distinguishable from the surrounding hoist room shall be tested daily. noise level, or a visual alarm that can be seen by a miner regularly employed on the working section. tc) Tf a communication system other than ~elephonesis used and its operation ae:~ends entirely upon power from the mine electiic system, means shall be provided to permit continued communication in the event the mine electric power fails or is cut off; pro- Subpart Q-Communications vided, however, that where trolley phones and telephones are both used, Q 75.1600 Communications. an alternate source of power for the trolley phone system is not required. td) Tra4111ey phonzs connected to the Telephone service or equivalent two- trolley wire shall be grounded in ac- way communication facilities, ap- cordance with Subpart H of this part. proved by the Secretary or his author- te) Tel2phones or equivalent two- ized representative, shall be provided way cm-dlmunication facilities shall be between the surface and each landing maintained in good operating condi- of main shafts and slopes and between tion at all times. In the event of any the surface and each working section failure in the systern that results in of any coal mine that is more than 100 loss of communication, repairs shall be feet from a portal. started immediately, and the system restored to operating conditian as soon § 75.1600-1 Communication facilities; as possible. main portals; installation requirements. 138 FR 29999, Oct. 31. 19731 A telephone or equivalent two-way communication facility shall be located on the surface within 500 feet of ali main portals, and shall be installed either in a building or in a box-like structure designed to protect the facilities from damage by inclement weather. At least one of these communica- § 75.1713--2 Emergency co~mmunications; tion facilities shall be at a location requirements. where a responsible person who is ta) Each operator of an underground always on duty when men are under- coal mine shall est~,blishand maintain ground can hear the facility and re- a communication system from the spond immediately in the event of an mine to the nearest point of medical emergency. assistance for use in an emergency. C38 Fa 29999, Oct. 31,19731 t b The emergency cornmunication system required to be maintained § 75.1600-2 Communication facilities; under paragraph (a) of this $75.1713-2 working sections; installation and may be established by telephone or maintenance requirements; audible or radio transmission or by any other visual alarms. means of prompt cornmunication to (a) Telephones or equivalent two- any facility (for example, the local way communication facilities provided sheriff, the State highway patrol, or at each working section shall be locat- local hospitd) which has available the ed not more than 500 feet outby the means of cormunication with the last open crosscut and not more than person or persons providing emergen- 800 feet from the farthest point of cy medical assistance or transporta- penetration of the working places on tion in accordai~cewith the provisions such section. of $ 75.1713-1. APPENDIX C.--EQUIPMENT SUPPLIERS

Pager Phones (And Associated Equipment) Winster Engineering Ltd. Manners Ave. Appalachian Electronics Ilkeston, Derbyshire 801 West Monroe Ave. United Kingdom Ronceverte, WV 24970 Carrier Phones ComTrol Corp. 500 Penna. Ave. American Mine Research, Inc. Irwin, PA 15642 P.O. Box 1628 Bluefield, WV 24701 CSE Mine Service Co. 600 Seco Rd. ComTrol Corp. Monroeville, PA 15146 500 Penna. Ave. Irwin, PA 15642 Fairmont Supply Co. Box 501 CSE Mine Service Co. Washington, PA 15301 600 Seco Rd. Monroeville , PA 15146 FEMCO (See National Mine Service Co.) Fairmont Supply Co. Gai-Tronics Corp. Box 501 P.O. Box 31-T Washington, PA 15301 Reading, PA 19603 FEMCO (See National Mine Service Co. ) Harrison K. Cooper Systems, Inc. AME Box 22014 Harrison R. Cooper Systems, Inc. Salt Lake City, UT 84122 AMF Box 22014 Salt Lake, UT 84122 JABCO (See Schroeder Brothers Corp.) Mine Safety Appliances Co. Mine Safety Appliances Co. 600 Penn Center Blvd. 600 Penn Center Blvd. Pittsburgh, PA 15235 Pittsburgh, PA 15235 National Mine Service Co. National Mine Service Co. 4900/600 Grant St. 4900/600 Grant St. Pittsburgh, PA 15219 Pittsburgh, PA 15219 Hoist Communications ~reiser/Mineco Jones & Oliver Sts. ComTrol Corp. St. Albans, WV 25177 500 Penna. Ave. Irwin, PA 15642 Pyott-Bonne, Inc. P.O. Box 809 Fairmont Supply Co. TazewelL, VA 24651 Box 501 Washington, PA 15301 Schroeder Brothers Corp. Nichol Ave. Box 72 McKees Rocks, PA 15136 FEMCO (See National Mine Service Co.) Wins t:er Engineering Ltd. Manners Ave. Harrison R. Cooper Systems, Inc. Ilkeston, Derbyshire AMF Box 22014 United Kingdom Salt Lake City, UT 84122 Intercoms Mine Safety Appliances Co. 600 Penn Center Blvd. ComTrol Corp. Pittsburgh, PA 15235 500 Penna. Ave. Irwin, PA 15642 National Mine Service Co. 4900/600 Grant St. Executone , Inc. Pittsburgh, PA 15219 Dept. TR-77 Long Island City, NY 11101 Republic Wire and Cable P.O. Box 352 FEMCO (See National Mine Service Co .) . Flushing, NY 11352 Mine Safety Appliances Co. Winster Engineering Ltd. 600 I?enn Center Blvd. Manners Ave. Pittsburgh, PA 15235 Ilkeston, Derbyshire United Kingdom National Mine Service Co. 4900/600 Grant St. PABX and Multiplex Equipment Pittsburgh, PA 15219

Anaconda Telecommunications Wins ter Engineering Ltd. 305 North Muller Manners Ave. Anaheim, CA 92801 Ilkeston, Derbyshire United Kingdom Essex Group 800 East Garfield Ave. Radio Pocket Pagers Decatur, IL 62525 Executone, Inc. Executone, Inc. Dept. TR-77 Dept. TR-77 Long Island City, NY 11101 Long Island City, NY 11101 FEMCO (See National Mine Phelps Dodge Communication Co. Service Co.) 5 Corporate Park Dr. White Plains, NY 10604 General Electric Co., Mobile Radio Dept. P.O. Box 4197 Pulsecom Div. Lynchburg, VA 24502 Harvey Hubbell, Inc. 5714 Columbia Pike National Mine Service Co. Falls Church, VA 22041 4900/600 Grant St. Pittsburgh, PA 15219 Reliable Electric Co. 11333 West Addison Leaky Feeder Equi~ment Franklin Park, IL 60131 Andrew Corp. TI1 Industries, Inc. 10500 West 153d St. 100 North Strong Ave. Orland Park, IL 60462 Lindenhurst, NY 11757 Winster Engineering Ltd. ComTrol Corp. Manners Ave. 500 Penna. Ave. Ilkeston, Derbyshire Irwin, PA 15642 United Kingdom FEMCO (See National Mine Service Co.) Mobile Radio Equipment General Electric Co., Mobile Radio Dept. Fairmont Supply Co. P.O. Box 4197 Box 501 Lynchburg, VA 24502 Washington, PA 15301 General Equipment & Manufacturing General Electric Co., Mobile CO., Inc. Radio Dept. 3300 Fern Valley Rd. P.O. Box 4197 P.O. Box 13226 Lynchburg, VA 24502 Louisville, KY 40213

Motorola Communications & Electronics Mag-Con, Inc. 1301 East Algonquin Rd. 1626 Terrace Dr. Schaumburg, IL 60196 St. Paul, MN 55113

Lee Engineering Mine Safety Appliances Co. 2025 West Wisconsin Ave. 600 Penn Center Blvd. Milwaukee, WI 53201 Pittsburgh, PA 15235

Phelps Dodge Communication Co. National Mine Service Co. 5 Corporate Park Dr. 4900/600 Grant St. White Plains, NY 10604 Pittsburgh, PA 15219

Winster Engineering Ltd. Notifier of Western Penn. Inc. Manners Ave. 3460 Babcock Blvd. Ilkeston, Derbyshire Pittsburgh, PA 15237 United Kingdom Pace Transducer Co. , Div. of Closed Circuit Television C. J. Enterprises P.O. Box 834 Midwest Telecommunications Div., Tarzana, CA 91356 Midwest Corp. 300 T First Ave. Pulsecom Div. Nitro, WV 25143 Harvey Hubbell, Inc. 5714 Columbia Pike Winster Engineering Ltd. Falls Church, VA 22041 Manners Ave. Ilkeston, Derbyshire Pyo t t -Bonne , Inc . United Kingdom P.O. Box 809 Taxewell, VA 24651 Remote Control and Monitor Equipment RFL Industries, Inc. American Mine Research, Inc. Boonton, NJ 07005 P.O. Box 1628 Bluefield, WV 24701 Stevens International Inc. P.O. Box 619 BIF Accutel Inc. Kennett Square, PA 19348 1339 Lawrence Dr. Newbury Park, CA 91320 Winster Engineering Ltd. Ed.mont-Wilson Manners Ave. 1300 Walnut St. Ilkeston, Derbyshire Colshocton, OH 43812 United Kingdom Mine Safety Appliances Co. Environmental Sensors 201 North Braddock Ave. Pittsburgh, PA 15208 Methane : Su.rvivair Div. of U.S. Divers Mine Safety Appliances Co. 3323 West Warner Ave. 201 North Braddock Ave. Sa.nta Ana, CA 91776 Pittsburgh, PA 15208 Te.ledyne Analytical Instruments National Mine Service Co. 333 West Mission 300 Koppers Bldg. San Gabriel, CA 91776 Pittsburgh, PA 15216 Oxidles of nitrogen: Bacharach Instrument Co. 625 Alpha Dr. Energetics Sciences Pittsburgh, PA 15238 85 Executive Blvd. El.msford, NY 10523 CSE Mine Service Co. 2000 Eldo Rd. Air flow sensors: Monroeville, PA 15146 Al.nor Instrument Co. ~reiser/Mineco 7301 North Caldwell Ave. Jones and Oliver Sts. Niles, IL 60648 St. Albans, WV 25177 J-.Tee Associates, Inc. Appalachian Electronics Instruments 31.7 Seventh Ave. SE 810 West Monroe Ave. Cedar Rapids, IA 5240 1 Ronceverte, VA 24970 Taiylor Instrument American Mine Research, Inc. Co~nsumer Products Div. P.O. Box 1628 Arden, NC 28704 Bluefield, WV 24701 Atmospheric pressure : Carbon monoxide: Pace Transducer Co. , Div. of Mine Safety Appliances C. J. Enterprises 201 North Braddock Ave. P.O. Box 834 Pittsburgh, PA 15208 Talrzana, CA 91356

Energetics Sciences Le!eds and Northrup Co. 85 Executive Blvd. Dept. MI337 Elmsford, NY 10523 North Wales, PA 19454

Oxygen :

Beckman Instruments Inc. 3900 River Rd. Schiller Park, IL 60176 Seismic Equipment Pyo t t -Bonne , Inc . P.O. Box 809 Pace Transducer Co. , Div. of Tazewell, VA 24651 C. J. Enterprises Pa 0. Box 834 Corm Resources Tarzana, CA 91356 2857 Mount Vernon SE Cedar Rapids, IA 52403 Consultants U.S. Bureau of Mines Arthur D. Little, Inc. 4800 Forbes Avenue 25 Acorn Park Pittsburgh, PA 15213 Cambridge, MA 02140 Winster Engineering Ltd . Advance Mining Services Manners Avenue 616 Beatty RD. Industrial Court Ilkeston, Derbyshire Monroeville, PA 15146 United Kingdom

ComTrol Corp. Fire Detection Devices 500 Penna. Ave. Irwin, PA 15642 ADT Co. , Inc. 155 Sixth Ave. CSE Mine Service Co. New York, NY 10013 600 Seco Rd. Monroeville, PA 15146 The Ansul Co. One Stanton St. Fairmont Supply Co. Marinette, WI 54143 Box 501 Washington, PA 15301 B. & B. Electric Manufacturing Co. Seward, PA 15954 General Electric Co., Mobile Radio Dept. P.O. Box 4197 Gammaf lex Corp. Lynchburg, VA 24502 821 Michael Faraday Dr. Reston, VA 22070 Midwest Telecommunications Div., Midwest Corp. JABCO 300 T First Ave. Schroeder Brothers Corp. Nitro, WV 25143 P.O. Box 72 Nichol Ave. Mineral Services Inc. McKees Rocks, PA 15136 1276 West Third St. Cleveland, OH 44113 McJunkin Corp. P.0. Boc 2473 National Coal Board 1400 Hansford St. Mining Research and Development Charleston, WV 25311 Establishment Stanhope Bretby Mine Safety Appliances Co. Burton Upon Trent DEISOQD 201 North Braddock Ave. United Kingdom Pittsburgh, PA 15203

National Mine Service Co. National Mine Service Co. 4900/600 Grant St. 3000 Koppers Bldg. Pittsburgh, PA 15219 436 Seventh Ave. Pittsburgh, PA 15219 Notifier of Western Pennsylvania Generisl Cabie Corp. 3283 Babcock Blvd. 600 Reed Rd. Pittsburgh, PA 15237 Broomisll, PA 19008

Prieser Industrial Component Inc. Jones and Oliver Sts. 342 Misdison Ave. St. Albans, WV 25177 Suite 702 New York, NY 10017 Pyott-Boone, Inc. P.O. Box 809 Okonite Co. Tazewell, VA 24651 100 Hilltop Rd. Ramsey, NJ 07446 Southern Engineering and Equipment Co. P.O. Drawer 329 95 Third St., NE Graysville, AL 35073

Figure-8 Communication Cable

Delphi Wire & Cable 700 Carpenters Crossing Folcroft, PA 19032 APPENDIX I). --GLOSSARY QF TERMS

Analog A method of generating or transmitting information that is repl-e-- sented by a continuous (as opposed to digital) voltage or current that is proportional to the information.

Angst rom A unit of length. Usually used to measure the wavelength of light or other radiation. One angstrom is equal to one hundred-millionth of a centimeter.

AM Abbreviation for "amplitude modulation." Nodulation in which the amplitude of the informati.onwaveform modulates the amplitude of a carrier wave.

Attenuation The decrease in signal strength during its transmission from one point to another. Attenuation is usually expressed in decibels.

Balance point In ar: electronic bridge circuit, the point at which the electrical resistances in both branches of the network are the same.

Bandwidth The difference (in cycles per second) between the highest and lowest frequency components required for the adequate transmission of inf ormation.

Baseband The original frequency band (before modulation) of a signal. Usu- ally refers to the baseband of an audio or voice signal, which is approximately 300 to 5,000 Hz.

Binary A digital numbering system with the base 2. In a binary system there are only two possibilities For each digit, selection, choice, or condition. For example, a simple switch is a binary device since it is either open or closed.

Bridge An electrical bridge circuit is a network arranged so that voltage or current in one branch of the circuit may be measured by adjusting components in another branch of the circuit.

CATV Abbreviation for "community antenna television," commonly known as cable television.

Characteristic Pertaining to transmission lines. For a uniform and infinitely long impedance line, it is the ratio of applied voltage to current induced at a given frequency. It is measured in ohms and usually designated as Zo. For maximum signal transfer, the Zo of a line should equal the Zo of a source and load. co Abbreviation for "central office." Refers to the telephone company's central office.

Cross talk Cross-coupling or interference between speech channels or wire pairs. dB Abbreviation of "decibel," a unit that represents the ratio between two amounts of power on a logarithmic scale. A value of +3 dB indicates a doubling of power, while -3 dB is a halving of power. The normal signal level in a pager phone is about 1 milliwatt (1 mW). The designation 0 dBm is used to indicate this l-mW reference level. Thus, +3 dBm is 3 dB above the reference (2 mW) and -3 dBm is 3 dB below the reference (0.5 mW).

Uemodulatf.on A device that receives a carrier wave and recovers or "reconstructs" the original voice or informatio-n stgnal f som the carrier wave.

DTMF Abbreviation for "dual-tone multifrequency." A phone signaling method in which each digit dialeld is converted to a dual-tone signal that will be recognized by the telephone office or PABX switching equipment. These control tones can be heard in the earpiece when dialing on many pushbutton phones.

Electromagnetic Jhving both electric and magnetic properties.

Encoder A unit that produces coded outlput combj.nations depending upon the specific input sel-ected.

FDM Abbreviation for "frequency-division multiplexing. " A process in which two or more signals are sent over a common path by sending each one in a different frequency band.

Feedback In a transmission system, or electrical device, the returning of a fraction of the output signal to the input.

FM Abbreviation for "frequency modulation. " Modulation in which the amplitude of the information waveform modulates the frequency of a carrier signal.

Abbreviation for "f requency-shif t keying. " A form of FM in which a binary code is transmitted by sw~!tching a carrier signal between two dj-ff erent frequencies.

Geophone A device used to detect seismic vibrations or shockwaves in the earth.

Hall effect In a c.onductor located in a magnetic field that is perpendicular to the direction of current, the production of a voltage perpendicular to both the current and the magnetic field.

Handset A receiver-t ransmi tter held by hand.

Headset. A receiver-transmitter that can be attached to the person to allow "hands-f xee" operation.

Hybrid A circuit or commr~nicat~.onssystem that is made up of two or more dissimilar systems,

Hz Abbreviation for Hertz. A unit of frequency equal to 1 cycle per second.

Impedance The total oppositton (reactance plus resistance) that a circuit or transmisa3-on Itne offers to the flow of electrical current. Inductively Method of inducing a signal into one conductor or wire from another coupled conductor even though there may be no mechanical connection between the two conductors. (The magnetic field set up in the space around a conductor carrying alternating current will induce a signal in other nearby conductors.)

Joule heating In an electrical circuit, the heat produced by the flow of current in the circuit.

Leaky feeder A specially designed coaxial cable that allows radio signals to leak into or out of the cable so that they may be picked up by radio transceivers.

LED Abbreviation for "light-emitting diode." A solid state electronic device that emits light when a current flows through it.

Magnetic field The region surrounding a magnet or a conductor through which current is flowing.

Magneto An ac generator for producing ringing signals.

Milliammeter An electric current meter calibrated in milliamperes.

Modem A device that is both a modulator and a demodulator. A modem is a two-way device that both modulates (transmits) and receives (demodu- lates) a signal.

Modulator A device that modulates a voice or information signal and transmits the resulting carrier wave.

Monochromatic A signal or beam of light consisting of a single wavelength or of a very small range of wavelengths.

Multiplexed The simultaneous transmission of two or more signals using a single transmission path or wire.

PABX Abbreviation for "private automatic branch exchange." A private branch exchange in which automatically controlled switches make connections between the phones in the system.

PAM Abbreviation for "pulse amplitude modulation." Modulation in which - the value or amplitude of each sample of the information waveform modulates the amplitude of a pulse carrier.

Parasitic The coupling of radio waves .or electrical signals from one wire or coupling medium to another with the result that the signal strength in the first conductor is decreased.

PBX Abbreviation for "private branch exchange." A private manual telephone exchange requiring an operator at a switchboard to make connections between the phones.

PCM Abbreviation for "pulse coded modulation." Modulation in which the value or amplitude of each sample of the information waveform is quantitized and transmitted as a digital binary code. Abbreviation for "pulse duration modulation." Modulation in which the value or amplitude of each sample of the information waveform modulates the duration, or "width," of a pulse.

Piezoelectric The property of certain crystah or materials that produce a voltage when subjected to mechanical st:ress.

Potentiometer An electromechanical device with a sliding contact on a resistor. Movement of the sliding contact changes the electrical resistance of the circuit and allows the e1ec:tronics to sense the position of the sliding contact.

PPM Abbreviation for "pulse position modulation. " Modulation in which the value or amplitude of each sample of the information waveform modulates the position in time of a pulse.

Propagation The travel of electromagnetic (radio) or sound waves through a medium.

PSK Abbreviation for "phase shift keying." A form of FM in which a binary code is transmitted by shifting the phase of a carrier s ignal.

The "Q" of an ac circuit is th~e ratio of its reactance to its resistance. The voltage developed across the reactance is usable signal, but the voltage developed across the resistance subtracts from the signal. Thus, a high Q indicates an efficient, low-loss ac circuit.

Reactance The opposition to the flow of allternating current (ac). Capacitive reactance (Xc) is the opposition offered by capacitors, and inductive reactance (XL) is the oplposition offered by a coil or other inductance.

Abbreviation for radiofrequency. Any frequency at which electromagnetic radiation of energy (radio waves) is possible.

RFI Radio frequency interference.

Reluctance The resistance of a magnetic path to the flow of magnetic line of force. Aluminum has a high reluctance; iron has a low reluctance.

Repeater A device that detects or receives a signal and rebroadcasts the same s ignal.

Resistance The opposition to the flow of direct current (dc). The unit of resistance .is the ohm.

Resonate To bring to resonance; to tone.

Simplex A communication system, or other device, that operates in only one direction (either transmit or receive) at a time. 2 12

Sine wave The wave form corresponding to a pure, single-frequency oscillation.

Abbreviation for "standing wave ratio." On a transmission line or antenna element the current and voltage set up by waves traveling in the opposite direction are characterized by the presence of a number of stationary maximum and minimum points in the distribution curve. SWR is the ratio of the maximum to minimum current or voltage of these stationary waves.

Synchronize To maintain one operation (or signal) in step with another.

Abbreviation for "time-division multiplexing." A process by which two or more channels of information are transmitted over the same link by allocating a different time interval for the transmission of each channel.

Transducer A device that converts energy from one form to another. A seismic transducer, for instance, converts seismic shock waves into electrical signals.

Transceiver A device that is both a transmitter and a receiver. A two-way CB radio is a transceiver.

Tuned voltmeter A voltmeter that has been tuned to detect voltage levels or signal strengths at specific frequencies.

UHF Ultra high frequency , 300 to 3,000 MHz

Ultrasonic Having a frequency above that of audible sound.

Abbreviation for voice frequency (same as audio frequency). The frequencies corresponding to speech or other audible sound wave.

VHF Very high frequency, 30 to 300 MHz.

Vortex A whirlpool or eddy caused by a fluid or gas movi.ng past an obstruction.

Waveguide A hollow, round or rectangular pipe (or tunnel), used as a transmission line for signaling.