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Want to learn more? We hope you enjoy this McGraw-Hill eBook! If you’d like more information about this book, its author, or related books and websites, please click here. Fundamentals of Industrial Instrumentation and Process Control
William C. Dunn
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DOI: 10.1036/0071466932 To my wife Nadine for her patience, understanding, and many helpful suggestions during the writing of this text For more information about this title, click here
Contents
Preface xiii
Chapter 1. Introduction and Review 1 Chapter Objectives 1 1.1 Introduction 1 1.2 Process Control 2 1.3 Definitions of the Elements in a Control Loop 3 1.4 Process Facility Considerations 6 1.5 Units and Standards 7 1.6 Instrument Parameters 9 Summary 13 Problems 13
Chapter 2. Basic Electrical Components 15 Chapter Objectives 15 2.1 Introduction 15 2.2 Resistance 16 2.2.1 Resistor formulas 17 2.2.2 Resistor combinations 19 2.2.3 Resistive sensors 23 2.3 Capacitance 24 2.3.1 Capacitor formulas 24 2.3.2 Capacitor combinations 25 2.4 Inductance 26 2.4.1 Inductor formulas 26 2.4.2 Inductor combinations 27 Summary 27 Problems 28
Chapter 3. AC Electricity 31 Chapter Objectives 31 3.1 Introduction 31 3.2 Circuits with R, L, and C 32
v vi Contents
3.2.1 Voltage step 32 3.2.2 Time constants 33 3.2.3 Phase change 35 3.3 RC Filters 38 3.4 AC Bridges 39 3.5 Magnetic Forces 40 3.5.1 Magnetic fields 40 3.5.2 Analog meter 42 3.5.3 Electromechanical devices 43 Summary 44 Problems 45
Chapter 4. Electronics 47 Chapter Objectives 47 4.1 Introduction 48 4.2 Analog Circuits 48 4.2.1 Discrete amplifiers 48 4.2.2 Operational amplifiers 49 4.2.3 Current amplifiers 53 4.2.4 Differential amplifiers 54 4.2.5 Buffer amplifiers 55 4.2.6 Nonlinear amplifiers 56 4.2.7 Instrument amplifier 56 4.2.8 Amplifier applications 57 4.3 Digital Circuits 58 4.3.1 Digital signals 58 4.3.2 Binary numbers 58 4.3.3 Logic circuits 60 4.3.4 Analog-to-digital conversion 61 4.4 Circuit Considerations 63 Summary 63 Problems 64
Chapter 5. Pressure 67 Chapter Objectives 67 5.1 Introduction 67 5.2 Basic Terms 68 5.3 Pressure Measurement 69 5.4 Pressure Formulas 70 5.5 Measuring Instruments 73 5.5.1 Manometers 73 5.5.2 Diaphragms, capsules, and bellows 75 5.5.3 Bourdon tubes 77 5.5.4 Other pressure sensors 79 5.5.5 Vacuum instruments 79 5.6 Application Considerations 80 5.6.1 Selection 80 5.6.2 Installation 80 5.6.3 Calibration 81 Summary 81 Problems 82 Contents vii
Chapter 6. Level 85 Chapter Objectives 85 6.1 Introduction 85 6.2 Level Formulas 86 6.3 Level Sensing Devices 87 6.3.1 Direct level sensing 88 6.3.2 Indirect level sensing 92 6.4 Application Considerations 95 Summary 97 Problems 97
Chapter 7. Flow 99 Chapter Objectives 99 7.1 Introduction 99 7.2 Basic Terms 100 7.3 Flow Formulas 102 7.3.1 Continuity equation 102 7.3.2 Bernoulli equation 103 7.3.3 Flow losses 105 7.4 Flow Measurement Instruments 107 7.4.1 Flow rate 107 7.4.2 Total flow 111 7.4.3 Mass flow 112 7.4.4 Dry particulate flow rate 113 7.4.5 Open channel flow 113 7.5 Application Considerations 114 7.5.1 Selection 114 7.5.2 Installation 115 7.5.3 Calibration 115 Summary 115 Problems 116
Chapter 8. Temperature and Heat 119 Chapter Objectives 119 8.1 Introduction 119 8.2 Basic Terms 120 8.2.1 Temperature definitions 120 8.2.2 Heat definitions 121 8.2.3 Thermal expansion definitions 123 8.3 Temperature and Heat Formulas 124 8.3.1 Temperature 124 8.3.2 Heat transfer 124 8.3.3 Thermal expansion 126 8.4 Temperature Measuring Devices 127 8.4.1 Thermometers 127 8.4.2 Pressure-spring thermometers 129 8.4.3 Resistance temperature devices 130 8.4.4 Thermistors 131 8.4.5 Thermocouples 131 8.4.6 Semiconductors 133 viii Contents
8.5 Application Considerations 134 8.5.1 Selection 134 8.5.2 Range and accuracy 134 8.5.3 Thermal time constant 134 8.5.4 Installation 137 8.5.5 Calibration 137 8.5.6 Protection 137 Summary 138 Problems 138
Chapter 9. Humidity, Density, Viscosity, and pH 141 Chapter Objectives 141 9.1 Introduction 141 9.2 Humidity 142 9.2.1 Humidity definitions 142 9.2.2 Humidity measuring devices 146 9.3 Density and Specific Gravity 149 9.3.1 Basic terms 149 9.3.2 Density measuring devices 150 9.3.3 Density application considerations 153 9.4 Viscosity 153 9.4.1 Basic terms 153 9.4.2 Viscosity measuring instruments 154 9.5 pH Measurements 155 9.5.1 Basic terms 155 9.5.2 pH measuring devices 156 9.5.3 pH application considerations 156 Summary 157 Problems 158
Chapter 10. Other Sensors 161 Chapter Objectives 161 10.1 Introduction 161 10.2 Position and Motion Sensing 161 10.2.1 Basic position definitions 161 10.2.2 Position and motion measuring devices 163 10.2.3 Position application consideration 166 10.3 Force, Torque, and Load Cells 166 10.3.1 Basic definitions of force and torque 166 10.3.2 Force and torque measuring devices 167 10.3.3 Force and torque application considerations 170 10.4 Smoke and Chemical Sensors 170 10.4.1 Smoke and chemical measuring devices 171 10.4.2 Smoke and chemical application consideration 171 10.5 Sound and Light 171 10.5.1 Sound and light formulas 171 10.5.2 Sound and light measuring devices 173 10.5.3 Light sources 174 10.5.4 Sound and light application considerations 174 Summary 176 Problems 176 Contents ix
Chapter 11. Actuators and Control 179 Chapter Objectives 179 11.1 Introduction 179 11.2 Pressure Controllers 180 11.2.1 Regulators 180 11.2.2 Safety valves 182 11.2.3 Level regulators 182 11.3 Flow Control Actuators 183 11.3.1 Globe valve 183 11.3.2 Butterfly valve 185 11.3.3 Other valve types 185 11.3.4 Valve characteristics 186 11.3.5 Valve fail safe 187 11.4 Power Control 188 11.4.1 Electronic devices 188 11.4.2 Magnetic control devices 193 11.5 Motors 195 11.5.1 Servo motors 195 11.5.2 Stepper motors 195 11.5.3 Valve position feedback 196 11.5.4 Pneumatic feedback 196 11.6 Application Considerations 196 11.6.1 Valves 196 11.6.2 Power devices 197 Summary 198 Problems 198
Chapter 12. Signal Conditioning 201 Chapter Objectives 201 12.1 Introduction 201 12.2 Conditioning 202 12.2.1 Characteristics 202 12.2.2 Linearization 204 12.2.3 Temperature correction 205 12.3 Pneumatic Signal Conditioning 205 12.4 Visual Display Conditioning 206 12.4.1 Direct reading sensors 206 12.5 Electrical Signal Conditioning 207 12.5.1 Linear sensors 208 12.5.2 Float sensors 208 12.5.3 Strain gauge sensors 211 12.5.4 Capacitive sensors 212 12.5.5 Resistance sensors 213 12.5.6 Magnetic sensors 214 12.5.7 Thermocouple sensors 215 12.5.8 Other sensors 215 12.6 A-D Conversion 216 Summary 216 Problems 216 x Contents
Chapter 13. Signal Transmission 219 Chapter Objectives 219 13.1 Introduction 220 13.2 Pneumatic Transmission 220 13.3 Analog Transmission 220 13.3.1 Noise considerations 220 13.3.2 Voltage signals 222 13.3.3 Current signals 223 13.3.4 Signal conversion 223 13.3.5 Thermocouples 224 13.3.6 Resistance temperature devices 225 13.4 Digital Transmission 226 13.4.1 Transmission standards 226 13.4.2 Smart sensors 227 13.4.3 Foundation Fieldbus and Profibus 229 13.5 Controller 230 13.5.1 Controller operation 231 13.5.2 Ladder diagrams 232 13.6 Digital-to-Analog Conversion 235 13.6.1 Digital-to-analog converters 235 13.6.2 Pulse width modulation 236 13.7 Telemetry 237 13.7.1 Width modulation 237 13.7.2 Frequency modulation 238 Summary 239 Problems 239
Chapter 14. Process Control 241 Chapter Objectives 241 14.1 Introduction 241 14.2 Basic Terms 242 14.3 Control Modes 243 14.3.1 ON/OFF action 243 14.3.2 Differential action 244 14.3.3 Proportional action 244 14.3.4 Derivative action 246 14.3.5 Integral action 247 14.3.6 PID action 248 14.4 Implementation of Control Loops 249 14.4.1 ON/OFF action pneumatic controller 249 14.4.2 ON/OFF action electrical controller 250 14.4.3 PID action pneumatic controller 251 14.4.4 PID action control circuits 252 14.4.5 PID electronic controller 254 14.5 Digital Controllers 256 Summary 257 Problems 257
Chapter 15. Documentation and Symbols 259 Chapter Objectives 259 15.1 Introduction 259 Contents xi
15.2 System Documentation 260 15.2.1 Alarm and trip systems 260 15.2.2 Alarm and trip documentation 261 15.2.3 PLC documentation 261 15.3 Pipe and Identification Diagrams 262 15.3.1 Standardization 262 15.3.2 Interconnections 262 15.3.3 Instrument symbols 263 15.3.4 Instrument identification 264 15.4 Functional Symbols 266 15.4.1 Actuators 266 15.4.2 Primary elements 266 15.4.3 Regulators 267 15.4.4 Math functions 267 15.5 P and ID Drawings 267 Summary 269 Problems 271
Appendix A. Units 273
Appendix B. Thermocouple Tables 277
Appendix C. References and Information Resources 279
Appendix D. Abbreviations 283
Glossary 287 Answers to Odd-Numbered Questions 297 Index 311 ABOUT THE AUTHOR William Dunn has B.Sc. in physics from the University of London, graduating with honors, he also has a B.S.E.E. He has over 40 years industrial experience in management, marketing support, customer interfacing, and advanced product development in systems and microelectronic and micromachined sensor development. Most recently he taught industrial instrumentation, and digital logic at Ouachita Technical College as an adjunct professor. Previously he was with Motorola Semiconductor Product Sector working in advanced product development, designing micromachined sensors and transducers. He holds some 15 patents in sensor design, and has presented some 20 technical papers in sensor design and application.
Copyright © 2005 by The McGraw-Hill Companies, Inc. Click here for terms of use. Preface
Instrumentation and process control can be traced back many millennia. Some of the early examples are the process of making fire and instruments using the sun and stars, such as Stonehenge. The evolution of instrumentation and process control has undergone several industrial revolutions leading to the complexi- ties of modern day microprocessor-controlled processing. Today’s technological evolution has made it possible to measure parameters deemed impossible only a few years ago. Improvements in accuracy, tighter control, and waste reduc- tion have also been achieved. This book was specifically written as an introduction to modern day indus- trial instrumentation and process control for the two-year technical, voca- tional, or degree student, and as a reference manual for managers, engineers, and technicians working in the field of instrumentation and process control. It is anticipated that the prospective student will have a basic understanding of mathematics, electricity, and physics. This course should adequately pre- pare a prospective technician, or serve as an introduction for a prospective engineer wishing to get a solid basic understanding of instrumentation and process control. Instrumentation and process control involve a wide range of technologies and sciences, and they are used in an unprecedented number of applications. Examples range from the control of heating, cooling, and hot water systems in homes and offices to chemical and automotive instrumentation and process control. This book is designed to cover all aspects of industrial instrumentation, such as sensing a wide range of variables, the transmission and recording of the sensed signal, controllers for signal evaluation, and the control of the manu- facturing process for a quality and uniform product. Chapter 1 gives an introduction to industrial instrumentation. Chapters 2 through 4 refresh the student’s knowledge of basic electricity and introduce electrical circuits for use in instrumentation. Sensors and their use in the meas- urement of a wide variety of physical variables—such as level, pressure, flow, temperature, humidity, and mechanical measurements—are discussed in Chapters 5 through 10. The use of regulators and actuators for controlling pres- sure, flow, and the control of the input variables to a process are discussed in
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Copyright © 2005 by The McGraw-Hill Companies, Inc. Click here for terms of use. xiv Preface
Chapter 11. Electronics is the medium for sensor signal amplification, condi- tioning, transmission, and control. These functions are presented as they apply to process control in Chapters 12 through 14. Finally, in Chapter 15, documen- tation as applied to instrumentation and control is introduced, together with standard symbols recommended by the Instrument Society of America (ISA) for use in instrumentation control diagrams. The primary reason for writing this book was that the author felt that there was no clear, concise, and up-to-date book for prospective technicians and engi- neers which could help them understand the basics of instrumentation and process control. Every effort has been made to ensure that the book is accurate, easily readable, and understandable. Both engineering and scientific units are discussed in the book. Each chap- ter contains worked examples for clarification, with exercise problems at the end of each chapter. A glossary and answers to the odd-numbered questions are given at the end of the book.
William C. Dunn Chapter 1 Introduction and Review
Chapter Objectives This chapter will introduce you to instrumentation, the various measurement units used, and the reason why process control relies extensively on instru- mentation. It will help you become familiar with instrument terminology and standards. This chapter discusses