Position Sensors

David S. Nyce is founder and owner of Revolution Sensor Company in Apex, North Carolina, US. He was formerly a Divisional General Manager and Director of Technology for the Sensors Group of MTS Systems Corporation, and was Chief Engineer or VP of Engineering at several other sensor manufacturing companies. Mr. Nyce has more than 30 years of experience developing sensors of many types for industrial, automotive, military, medical, and commercial use.

About the Author xv Preface xvii Trademarks xix About the Companion Website xxi 1 Sensor Definitions and Conventions 1 1.1 Is it a Sensor or a Transducer? 1 1.2 Position versus Displacement 5 1.3 Absolute or Incremental Reading 6 1.4 Contact or Contactless Sensing and Actuation 7 1.5 Linear/Angular Configuration 10 1.6 Position Velocity and Acceleration 11 1.7 Application versus Sensor Technology 13 1.8 Operational Lifetime 13 1.9 Questions for Review 14 References 16 2 Specifications 17 2.1 About Position Sensor Specifications 17 2.2 Measuring Range 18 2.3 Zero Span and Full Scale 18 2.4 Repeatability 21 2.5 Nonlinearity 22 2.6 Hysteresis 28 2.7 Calibrated Accuracy 31 2.8 Drift 33 2.9 What does all this Accuracy Stuff Mean to Me? 34 2.10 Temperature Effects 36 2.11 Response Time 40 2.12 Damping 42 2.13 Cross Sensitivity 44 2.14 Shock and Vibration 45 2.15 Electromagnetic Compatibility 48 2.16 High Voltage Pulse Protection 50 2.17 Power Requirements 52 2.18 Intrinsic Safety Explosion Proofing and Purging 54 2.19 Reliability 62 2.20 Questions for Review 66 3 Output Types and Communication Protocols 69 3.1 Analog Output Types 69 3.2 Digital Output Types 73 3.3 SSI 73 3.4 CANbus 80 3.5 PROFIBUS 104 3.6 HART 106 3.7 Questions for Review 117 4 Resistive/Potentiometric Sensing 119 4.1 Resistive Position Sensors 119 4.2 Resistance 120 4.3 History of Resistors and Resistive Position Sensors 122 4.4 Position Sensor Design 124 4.5 The Resistive Element 127 4.6 The Wiper 129 4.7 Linear and Rotary Mechanics 130 4.8 Signal Conditioning 131 4.9 Advantages/Disadvantages 132 4.10 Typical Performance Parameters 132 4.11 Specifications and Application 135 4.12 Manufacturers 136 4.13 Questions for Review 136 5 Cable Extension Transducers 139 5.1 Cable Extension Transducer History 139 5.2 Cable Extension Transducer Construction 140 5.3 Signal Conditioning 144 5.4 Application 144 5.5 Advantages/Disadvantages 148 5.6 Typical Performance Specifications 148 5.7 Manufacturers 149 5.8 Questions for Review 150 6 Capacitive Sensing 153 6.1 Capacitive Position Sensors 153 6.2 Capacitance 154 6.3 Dielectric Constant 157 6.4 History of Capacitive Position Sensors 158 6.5 Capacitive Position Sensor Design 159 6.6 Electronic Circuits for Capacitive Sensors 163 6.7 Guard Electrodes 169 6.8 EMI/RFI 170 6.9 Typical Performance Specifications and Application 172 6.10 Manufacturers 173 6.11 Questions for Review 173 7 Inductive Sensing 175 7.1 Inductive Position Sensors 175 7.2 Inductance 177 7.3 Permeability 182 7.4 History of Inductive Position Sensors 183 7.5 Inductive Position Sensor Design 184 7.6 The Coil and Bobbin 185 7.7 Core 188 7.8 Signal Conditioning 189 7.9 Advantages 192 7.10 Typical Application and Performance Specifications 192 7.11 Manufacturers 194 7.12 Questions for Review 194 8 The LVDT and RVDT 197 8.1 LVDT and RVDT Position Sensors 197 8.2 History of the LVDT and RVDT 198 8.3 LVDT and RVDT Position Sensor Design 199 8.4 Coils 200 8.5 Core 202 8.6 Carrier Frequency 206 8.7 Demodulation 207 8.8 Signal Conditioning 211 8.9 Synchronization 217 8.10 Calibration 219 8.11 Advantages 221 8.12 Typical Performance Specifications and Application 222 8.13 Manufacturers 224 8.14 Questions for Review 225 References 226 9 Distributed Impedance 227 9.1 Distributed Impedance Position Sensors 227 9.2 History 229 9.3 Operational Theory 229 9.4 The Distributed Impedance Sensing Element as a Transmission Line 234 9.5 Periodic Structures 235 9.6 Hybrid Waves 235 9.7 Distributed Impedance Sensor Design 236 9.8 Electronics 237 9.9 Advantages 239 9.10 Typical Performance Specifications and Applications 239 9.11 Infinite Resolution? 241 9.12 Calibration 241 9.13 Manufacturers 243 9.14 Questions for Review 243 10 The Hall Effect 247 10.1 Hall Effect Sensors 247 10.2 The Hall Effect 248 10.3 History of the Hall Effect 250 10.4 Hall Effect Position Sensor Design 251 10.5 The Hall Effect Element 254 10.6 Electronics 254 10.7 Linear Arrays 257 10.8 Advantages 258 10.9 Typical Performance Specifications and Applications 259 10.10 Manufacturers 260 10.11 Questions for Review 261 11 Magnetoresistive Sensing 263 11.1 Magnetoresistive Sensors 263 11.2 Magnetoresistance 264 11.3 History of Magnetoresistive Sensors 271 11.4 Magnetoresistive Position Sensor Design 273 11.5 The Magnetoresistive Element 275 11.6 Linear Arrays 276 11.7 Electronics 276 11.8 Advantages of Magnetoresistive Sensors 278 11.9 Typical Performance Specifications and Applications 278 11.10 Manufacturers 281 11.11 Questions for Review 281 12 Magnetostrictive Sensing 285 12.1 Magnetostrictive Sensors 285 12.2 Magnetostriction 286 12.3 History of Magnetostriction 288 12.4 Magnetostrictive Position Sensor Design 289 12.5 Waveguide 291 12.6 Position Magnet 295 12.7 Pickup Devices 299 12.8 Damp 301 12.9 Waveguide Suspension 302 12.10 Electronics 303 12.11 Angular/Rotary Magnetostrictive Sensors 307 12.12 Advantages 308 12.13 Typical Performance Specifications 309 12.14 Application 311 12.15 Manufacturers 313 12.16 Questions for Review 313 13 Encoders 315 13.1 Linear and Rotary 315 13.2 History of Encoders 315 13.3 Construction 317 13.4 Absolute versus Incremental Encoders 319 13.5 Optical Encoders 320 13.6 Magnetic Encoders 321 13.7 Quadrature 323 13.8 Binary versus Gray Code 325 13.9 Electronics 326 13.10 Advantages 328 13.11 Typical Performance Specifications and Applications 329 13.12 Manufacturers 331 13.13 Questions for Review 331 14 Optical Triangulation 335 14.1 Linear Sensing 335 14.2 History 336 14.3 Construction 337 14.4 Light Sensor 340 14.5 Electronics 343 14.6 Laser 347 14.7 Advantages 349 14.8 Typical Performance Specifications and Applications 350 14.9 Manufacturers 350 14.10 Questions for Review 351 Bibliography 353 Glossary of Sensor Terminology 355 Index 363