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Continuing Education

Oscilloscopes, Part One

An introduction to the complex educational tool that has varied uses.

by David Herres In this frst of a two-part series, we will confgured so that the location relative to the Y consider the as an educational tool. axis represents voltage, and the location relative It is a wonderful gateway into the world of to the X axis represents time. Crossing the axes electronics, and it seems there is no end to the at right angles to them are lines (known as multiple layers of elementary particle interaction “divisions”) that make it possible to gauge the it can reveal. voltage level of the signal at specifc time When one takes a new oscilloscope out of the intervals. Te trace so constituted may be box, the frst reaction may be, “What was I moving or static, but, either way, it conveys an thinking? How did I ever get myself into this? So immense amount of information about the signal many knobs and buttons, and endless cryptic being investigated. menus!” But don’t worry. Te operating manual, print or online, clarifes a great deal, and History remaining information gaps disappear one by To understand how the oscilloscope works, one as frst elementary and then successively Value: 1 it is instructive to take a look at its history, more complex exercises are performed. particularly in regard to two milestones: contact Te modern digital oscilloscope consists of probes; analog channels (usually two or four); triggering and the digital storage scope. Te hour analog-to-digital conversion; processing and frst involved capturing (0.1 CEU) memory; and, fnally, waveforms by means of measuring voltages at a display (now various points along the circumference of a Approved for predominantly on a spinning rotor. A permanent record in the form Continuing fat screen). Typically, of a graphical image was made by hand drawing Education by Learning Objectives there are two axes, X the image on paper. Needless to say, frequency NAEC for CET® and Y, that intersect response was limited by the speed and and CAT®. After reading this article, you at the center of the endurance of the artist(s). EW Continuing should have learned about: screen. A spot of light Subsequent oscilloscope innovations were Education is moves vertically and ♦ Te history of the oscilloscope incremental. Te frst major breakthrough currently approved horizontally across ♦ Te principal components of involved use of a , which moved a in the following the screen to form the an oscilloscope display pen across a strip of paper wrapped about a states: AL, AR, FL, trace, which is a ♦ Te purpose of the X and Y drum. It rotated at a constant clock-driven rate, GA, IL, IN, KY, MS, graphic axes which provided the time base. Similar MT, OK, PA, VT, VA, ♦ Important innovations in representation of the subsequent methods also involved moving WV and WI. Please oscilloscope development voltage applied at the parts, and because these machines were check for specifc ♦ input of the Disadvantages of TV course verifcation instrument. mechanical (as opposed to electronic), inertia conversion and the computer- of approval at www. based oscilloscope In its most of rest placed a severe limit on frequency elevatorbooks.com. common application, response. the oscilloscope is Continued

May 2016 • ELEVATOR WORLD 55 Breakthroughs triggered-sweep oscilloscope, which An analog-to-digital converter in Hybrid equipment, where refected light facilitated a stable and coherent display of a conjunction with memory chips permit from a trembling mirror created waveform recurrent waveform. Tis expedient contemporary oscilloscopes to record and images on photographic paper, ramped permitted multiple waveform images to store a digital representation of any sort of oscilloscope frequency response as high as coincide on the oscilloscope screen, electrical waveform. Tis development 10 kHz by the 1920s. Later in that century, replacing the meaningless blur of light facilitated the fat-screen display. Together two substantial innovations occurred that resulting from lack of synchronization. An with efective triggering, digitization has made possible the oscilloscopes used unchanging frequency sweep input was not created a work platform that is immensely universally today. required for image stability. useful to engineers, technicians and Te frst of these was triggering, Te other signifcant development students to visualize diverse electronic introduced by Howard Vollum and Jack occurred prior to the 1980s, when Walter phenomena and solve many problems that Murdock, founders of Tektronix. In 1946, LeCroy, founder of LeCroy Corp., arise in research, development and they brought out the Tektronix Model 511 introduced the digital storage oscilloscope. maintenance. Types “Electronic technician” is a broad term and can include the electrical engineer who Replacement DOORS conceives of, designs and may be called upon to debug new innovations. Ten, there MEI Offers Both Entrance & Cab Doors is the “repair professional,” whose job description includes diagnosing and repairing dysfunctional electrical systems • 2-3 Week Lead Time and equipment. Tis task may range from • Competitive Pricing very simple (like resetting a tripped breaker • Entrance Doors are UL Labeled or replacing a worn power cord) to very • 1 or 2 Speed difcult (like troubleshooting an elevator • Side or Center Opening motion controller that cuts out at odd Standard Equipment intervals for no apparent reason). Another • Door Gibs category is the serious independent • Sight Guards inventor or home hobbyist. Tese folks • Astragals range from brilliant innovators who are • Bumpers occasionally at the cutting edge of some altogether new technologies to delusional cranks who break more than they fx. Any of these individuals can beneft greatly by having the use of an advanced oscilloscope. Te sad reality, however, is that a top-of-the-line instrument costs far more than many of us can aford. (Te most Powder Coating or expensive Agilent is priced at approximately Stainless Finish! Quality Crating Keeps US$500,000.) But, the good news is that the Doors Straight! midrange oscilloscopes are much less costly. Many vendors ofer fnancing designed to attract buyers. It is not difcult to imagine that one’s enhanced earning power will What our customers are saying... accompany and justify the expenditure. If Let us make a difference in your next project! “The doors we’ve received from MEI have far exceeded our lead time expectations. MEI has provided a solution to our not, there are other low-cost options, and Contact MEI today for a quote! two largest problems with doors by providing quick lead times we will consider them one at a time, and sturdy packaging. On top of that the doors provided are 1-800-450-3060 straight and provide all the correct drillings needed.” beginning with the cheapest. - James Snider Jr, Quality Elevator - TV Email: [email protected] An old black-and-white portable TV can Website: www.meielevatorsolutions.com “MEI is very impressive with the speed, craftsmanship, and care in which they design, build and ship their be converted into a viable oscilloscope. Te doors! When I see that crate with neatly stacked doors price of materials is about US$1, assuming a arrive from MEI, I am confdent I am getting a product that will impress my customers!” suitable TV can be had at no cost and the - Eric Crowley, Pincus Elevator Co., Inc. - solder and fux, wire, grommets and probes are already available. Continued

56 www.elevatorworld.com • May 2016 Before starting, remember that TVs specialized signal-acquisition board. It low-end market, while others have been harbor hazardous high voltages retained in takes diferent forms, typically an external and are currently investing in R&D, the electrolytic capacitors associated with USB or parallel-port device. Another type seeking to provide top-level quality and their power supplies. (High voltage levels of PCO consists of a card installed in the functionality. Te big players are are needed for the defection circuitry computer. For hardware, there is an Tektronix, LeCroy and Agilent (recently capable of moving the beam of electrons electrical interface providing isolation and spun of into Keysight Technologies but away from the center of the screen.) automatic gain controls, some analog-to- keeping essentially the same product line). Moreover, the cathode-ray tube (CRT) digital converters and bufer memory, or Tese vendors ofer high quality, very itself can store electrical energy. Ten, an internal digital signal processor. Display advanced and durable oscilloscopes that there is also such a thing as distributed and control interfaces are provided by the should be valuable for years to come. capacitance throughout the set. Te chassis computer, and it is for that reason that the must be removed from the cabinet and cost of a PCO is much less than that of a these hazardous voltages discharged to full-scale oscilloscope. ground potential before starting to work As may be expected, there are some on the set. If you are at all uncertain of the signifcant disadvantages in going the PCO procedure, call a professional to help with route, despite the surprising functionality this phase of the project. And, remember of some of the better instruments. Te that if the set is reenergized, the principal drawback is that the computer is discharging process will have to be a source of power supply and repeated. electromagnetic noise. If the PCO is Figure 1: A Tektronix MDO3104 triggered-sweep Two large copper coils surround the endeavoring to examine low-level signals, four-channel digital oscilloscope. cathode-ray tube yoke. Tey make possible obtaining good resolution may be vertical and horizontal defection of the problematic, requiring extensive shielding. electron beam. (In an oscilloscope, they A further difculty is that transfer rates Features and Functionality are defection plates, but the principle is into the computer are certain to be limited A mixed-domain oscilloscope (MDO) is the same.) Trace the wires of one of these by the weakest link in the chain, a capable of displaying electrical signals in coils back to where they terminate at a bottleneck inherent in the cabling media. more than one domain. Te domain circuit board and disconnect them. Return Additionally, the computer will require associated with a function, as calculus the TV to its case and power it up. If there oscilloscope-enabling sofware, which may students are well aware, is the set of inputs is a horizontal line, the wires from the or may not be compatible with the allowed for that function. Te oscilloscope vertical defection coil have been operating system. Of course, compatible display consists of a horizontal line, the X disconnected, and if there is a vertical line, computers usually do not have the great axis, along which the inputs are situated. At the wires from the horizontal coil have life expectancy of high-quality dedicated the center of the display, the Y axis, along been disconnected. If necessary, desolder oscilloscopes. Overall, the PCO is valuable which the outputs are situated, intersects the vertical coil from the circuit board and as an educational tool for hobbyists and the X axis. make the leads long enough to pass students. It is useful for some low- Te most common scenario is to see through a grommeted hole in the TV frequency measurements, but speed and units of time referenced to the X axis, cabinet. Tese wires will attach to the precision are lacking. For serious research where the independent variables are outside power source to be measured. and facility maintenance, the PCO is an represented. Amplitude (voltage) is Ten, disconnect the horizontal coil wires idea that has not yet (and probably never referenced to the Y axis. Various from the circuit board and move them to will) come. amplitudes comprise the dependent the vertical defection-coil terminations. variables. Te relations between points on Used Nothing further is required for a the X axis and points on the Y axis are homemade oscilloscope. Unfortunately, it Another low-cost option is to buy a determined by the function. is very limited compared to instruments used oscilloscope. Te problem here is Sometimes, the domain (X axis) does ofered by vendors. As it can display only that, even if the oscilloscope appears to not represent time. Instead, it can be DC or a low-frequency AC waveform its work, it may be observed later that some of defned in terms of frequency (with Y value is limited to an educational project. the features are not fully functional. If you values still being amplitude). Tis makes a can fnd parts and have the expertise to diferent graphic depiction of the same PC Based repair it, that is fne, but when factory electrical signal. It is possible to translate Another type of oscilloscope is an recalibration is needed, it may not be back and forth between the two domains, instrument that connects to a personal available. Tis option is not recommended. and the procedure for accomplishing this is computer (PC), making use of its data New known as the Fourier Transform, processing and imaging ability to display described in 1822 by Joseph Fourier. Te Finally, if cost is not an obstacle, voltage from an outside power source or protocol at the time was applicable to consider buying new. Tere are numerous circuit under test. Te PC-based nonelectrical phenomena, such as wave oscilloscope (PCO) consists of a manufacturers, some catering to the Continued

58 www.elevatorworld.com • May 2016 action in a body of water and acoustical mechanics. In our time, the main focus is electrical. Te mathematics for accomplishing the Fourier Transform are immensely complex, but in the mid 1960s, an algorithm known as the Fast Fourier Transform (FFT) that greatly accelerates the process surfaced. Tis procedure permits us to accomplish the same back-and-forth translations between the Figure 3: A handheld Tektronix THS3024 two domains with less burdensome oscilloscope calculations. Fortunately, FFT can be invoked in an instant by pressing a simple sequence of buttons on an MDO, and an electrical signal can be seen immediately in either of the domains. Tis functionality is Figure 2: A circuit analyzer will verify correct very useful in gaining insight into the inner polarity and ground continuity. workings of many types of electronic equipment for purposes of maintenance, as from ground, or, if powered by utility- well as R&D. derived AC power, it (like the oscilloscope) must be powered by two Grounding conductors, one of which is at ground Figure 4: A Tektronix TMDP0200 200 MHz high-voltage Before powering up or connecting a potential. If one of these is not the case, it diferential probe bench-type oscilloscope to a signal, we is not safe to connect the oscilloscope to need to go into some detail on the concept the work. protective functions of equipment of grounding both the instrument and the Moreover, the ground reference lead grounding. It sets the stage for disaster circuit under investigation. If this is not that is part of the probe must be connected down the road. thoroughly understood, there is the strong to a point in the circuit under test that is at As mentioned earlier, the hazard under probability that the user will eventually ground potential, leaving the probe tip discussion is not an issue when the work is make an improper hookup and damage or available to contact points within the totally isolated from ground. An obvious destroy the oscilloscope and/or the work circuitry. It is essential that the signal example would be the waveform (a straight being measured. ground of the circuit under test and the horizontal line) of a 9-V battery. Since First and most fundamentally, the oscilloscope equipment ground derived neither side is at ground potential, it is safe oscilloscope (unless it is the handheld, from the AC utility are at very close to the to connect the probe’s ground reference battery-operated type that is isolated from same potential. If these conditions are not lead to either the positive or negative pole. ground) must be correctly grounded met (i.e., equivalence of both grounds and A portable handheld, battery-powered whenever it is powered up. Tis ground correct hookup of the oscilloscope probe oscilloscope (Figure 3) may be connected connection is accomplished by plugging it ground reference lead), there will be a to point-to-point wiring within grounded into a standard three-prong receptacle that heavy fault current that will, at the very electrical equipment. Since both sides of has an equipment ground. Tis least, burn up the probe ground reference the instrument are isolated from ground, presupposes, of course, that the lead and, perhaps, damage the oscilloscope there will not be a hazardous ground fault, equipment-grounding conductor is intact and/or the equipment under test. Tis will regardless of which way the probes are and properly connected at the electrical happen instantly when the ground connected. service and that the overall system has a reference lead contacts a point in the With a bench-type grounded low-impedance connection to the earth. A circuitry that is not at ground potential. In oscilloscope and the need to make a good tool for verifying that the wiring is fact, it will occur even before the probe tip point-to-point measurement on grounded polarized correctly (and, indeed, contacts the equipment. equipment (such as measuring the DC bus grounded) is the circuit analyzer (Figure Tere are some exceptions to the above voltage of a variable-frequency drive), it is 2). grounding protocol. Te oscilloscope may permissible to use a diferential probe Te purpose of the equipment- be isolated from ground by sawing of the (Figure 4). Diferential probes combine the grounding connection is to ensure that the ground plug from the power cord. While functions of two probes in one. Singled- oscilloscope chassis, like that of any tool or this expedient may work to prevent the ended probes measure a voltage with appliance, does not remain energized due problems mentioned above, it is contrary reference to a ground point. In contrast, to a ground fault, resulting in a shock to the National Electrical Code and diferential probes measure the diference hazard. Secondly, the electrical equipment constitutes a depraved indiference to in voltage between two test points. Tere is being tested must be either totally isolated human life, because it disables the not the issue of hazardous arc fash caused Continued 60 www.elevatorworld.com • May 2016 Maintenance, Cabling by connecting the probe ground lead to a oscilloscope, with reference to the Business, Electrical signal voltage that is foating with respect Tektronix MDO3104, will be performed. A Business, Nuts and to the ground plane. Important few simple hookups will demonstrate how characteristics to look for are high Volts, PV Magazine, the oscilloscope can be used to depict Electrical Connection, bandwidth, large dynamic and ofset range, waveforms and illustrate various electronic Solar Connection, Solar and low noise. phenomena that are invisible to the Industry Magazine, Fine Conclusion . Homebuilding Magazine and Tis article has examined some David Herres holds a New Hampshire Master Engineering News background information on oscilloscopes, Electrician’s license and has worked as an Record. He has also written four books particularly as they have developed during electrician in the northern part of that state for published by McGraw-Hill: 2011 National the past century. In the next and many years. He has focused on writing since Electrical Code Chapter by Chapter, concluding article in this series, some 2006, having written for such magazines as Troubleshooting and Repairing Commercial exercises that illustrate the use of an ELEVATOR WORLD, Electrical Construction and Electrical Equipment, The Electrician’s Trade Demystifed and The Homeowner’s DIY Guide to Electrical Wiring, the latter published in December 2014. He holds a BA in English Literature and Composition from Hobart College of Geneva, New York.

Learning-Reinforcement Questions

Use the below learning- reinforcement questions to study for the Continuing Education Assessment Exam available online at www.elevatorbooks.com or on p. 139 of this issue. ♦ What is the principal hazard in removing a TV from its cabinet? ♦ What was the great contribution of Tektronix in the oscilloscope’s development? ♦ What was the great contribution of LeCroy in the oscilloscope’s development? ♦ What is a PCO, and what are some of its drawbacks? ♦ What is an MDO?

62 www.elevatorworld.com • May 2016 ELEVATOR WORLD Continuing Education Assessment Examination Questions Read the article “Oscilloscopes, Part One” (p. 55) and study the learning-reinforcement questions at the end of the article. To receive one hour (0.1 CEU) of continuing-education credit, answer the assessmentassessment examination examination questions questions found found below below online online at www.elevatorbooks. at www.elevatorbooks. com or fll out the ELEVATOR WORLD Continuing Education reporting Form found overleaf and submit by mail with payment. Approved for Continuing Education by NAEC for CET® and CAT®.

1. How many analog channels are usually included in a modern 7. Te Fourier Transform: oscilloscope? a. Was developed in 1920, along with triggering. a. One. b. Is quite simple mathematically. b. Two or four. c. Permits domain translation. c. Tree. d. None of these. d. Five.

2. In most modern oscilloscopes, triggering has replaced the fat 8. An oscilloscope can be damaged by heavy fault current if an screen. incorrect hookup is made. a. True. a. True. b. False. b. False.

3. Why is triggering important? 9. When is a diferential probe used? a. It reduces the cost of the oscilloscope. a. For making point-to-point measurements. b. It permits multiple channels. b. With a grounded bench-type oscilloscope. c. It permits digitization. c. When measuring the DC bus voltage in a variable- d. It stabilizes the display. frequency drive. d. All of these. 4. What was the great innovation of LeCroy Corp.? a. CRT displays. 10. A portable handheld, battery-powered oscilloscope: b. Triggering. a. May be connected to point-to-point wiring within c. Digitization. grounded equipment. d. Multichannel oscilloscopes. b. Has both sides isolated from ground. c. Is not prone to fault current due to incorrect hookup. 5. A PCO is: d. All of these. a. Less costly than a conventional oscilloscope. b. More costly than a conventional oscilloscope. c. Not prone to low transfer rates. d. Not dependent upon oscilloscope-enabling sofware.

6. A mixed-domain oscilloscope (MDO) may have time or frequency situated along its X axis. a. True. b. False.

May 2016 • ELEVATOR WORLD 139 ELEVATOR WORLD Continuing Circle correct answer. Education Reporting Form 1. a b c d 6. a b 2. a b 7. a b c d Article title: “Oscilloscopes, Part One” 3. a b c d 8. a b (EW, May 2016, p. 55). 4. a b c d 9. a b c d Continuing-education credit: Tis ar- 5. a b c d 10. a b c d ticle will earn you one contact hour (0.1 CEU) of elevator-industry continuing- Signature: ______education credit. Directions: Select one answer for Payment options: each question in the exam. Completely Check one: ❑ $35.00 – Non-subscriber course fee circle the appropriate letter. A minimum score of 80% is required to ❑ $29.75 – ELEVATOR WORLD earn credit. You can also take this test online at www.elevatorbooks. subscriber course fee com. Subscriber #: ______(Six-digit number on your print label or in your digital confrmation) Last name: ______❑ Payment enclosed First name: ______Middle initial:______(check payable to Elevator World, Inc.) CET®, CAT® or QEI number:______State License number: ______Charge to my: ❑ VISA Company name: ______❑ MasterCard Address:______City:______❑ American Express State: ______ZIP code: ______Telephone:______Fax: ______Card number: ______E-mail: ______Expiration date: ______

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