Principles of Measurement Systems Fourth Edition John P. Bentley Emeritus Professor of Measurement Systems University of Teesside PEARSON Prentice Hall Harlow, England London New York Boston San Francisco Toronto Sydney Singapore Hong Kong Tokyo Seoul Taipei New Delhi Cape Town Madrid Mexico City Amsterdam Munich Paris Milan
Contents Preface to the fourth edition Acknowledgements XI xiii Part A General Principles The General Measurement System 3 1.1 Purpose and performance of measurement systems - 3 1.2 Structure of measurement systems 4 1.3 Examples of measurement systems 5 1.4 Block diagram symbols 7 Static Characteristics of Measurement System Elements 9 2.1 Systematic characteristics 9 2.2 Generalised model of a system element 15 2.3 Statistical characteristics 17 2.4 Identification of static characteristics - calibration 21 The Accuracy of Measurement Systems in the Steady State 35 3.1 Measurement error of a system of ideal elements 35 3.2 The error probability density function of a system of non-ideal elements 36 3.3 Error reduction techniques 41 Dynamic Characteristics of Measurement Systems 51 4.1 Transfer function G(s) for typical system elements 51 4.2 Identification of the dynamics of an element 58 4.3 Dynamic errors in measurement systems 65 4.4 Techniques for dynamic compensation 70 Loading Effects and Two-port Networks 77 5.1 Electrical loading 77 5.2 Two-port networks 84 Signals and Noise in Measurement Systems 97 6.1 Introduction 97 6.2 Statistical representation of random signals 98 6.3 Effects of noise and interference on measurement circuits 107 6.4 «Noise sources and coupling mechanisms 110 6.5 Methods of reducing effects of noise and interference 113
viii CONTENTS 7 Reliability, Choice and Economics of Measurement Systems 125 7.1 Reliability of measurement systems 125 7.2 Choice of measurement systems 140 7.3 Total lifetime operating cost 141 Part B Typical Measurement System Elements 8 Sensing Elements 8.1 Resistive sensing elements 8.2 Capacitive sensing elements 8.3 Inductive sensing elements 8.4 Electromagnetic sensing elements 8.5 Thermoelectric sensing elements 8.6 Elastic sensing elements 8.7 Piezoelectric sensing elements 8.8 Piezoresistive sensing elements 8.9 Electrochemical sensing elements 8.10 Hall effect sensors 9 Signal Conditioning Elements 9.1 Deflection bridges 9.2 Amplifiers 9.3 A.C. carrier systems 9.4 Current transmitters 9.5 Oscillators and resonators 10 Signal Processing Elements and Software 10.1 Analogue-to-digital (A/D) conversion 10.2 Computer and microcontroller systems 10.3 Microcontroller and computer software 10.4 Signal processing calculations 11 Data Presentation Elements 11.1 Review and choice of data presentation elements 11.2 Pointer-scale indicators 11.3 Digital display principles 11.4 Light-emitting diode (LED) displays 11.5 Cathode ray tube (CRT) displays 11.6 Liquid crystal displays (LCDs) 11.7 Electroluminescence (EL) displays 11.8 Chart recorders 11.9 Paperless recorders 11.10 Laser printers 149 149 160 165 170 172 177 182 188 190 196 205 205 214 224 228 235 247 247 260 264 270 285 285 287 289 292 295 299 302 304 306 307
CONTENTS ix Part C Specialised Measurement Systems 12 Flow Measurement Systems 12.1 Essential principles of fluid mechanics 12.2 Measurement of velocity at a point in a fluid 12.3 Measurement of volume flow rate 12.4 Measurement of mass flow rate 12.5 Measurement of flow rate in difficult situations 13 Intrinsically Safe Measurement Systems 13.1 Pneumatic measurement systems 13.2 Intrinsically safe electronic systems 14 Heat Transfer Effects in Measurement Systems 14.1 Introduction 14.2 Dynamic characteristics of thermal sensors 14.3 Constant-temperature anemometer system for fluid velocity measurements 14.4 Katharometer systems for gas thermal conductivity and composition measurement 15 Optical Measurement Systems 15.1 Introduction: types of system 15.2 Sources 15.3 Transmission medium 15.4 Geometry of coupling of detector to source 15.5 Detectors and signal conditioning elements 15.6 Measurement systems 16 Ultrasonic Measurement Systems 16.1 Basic ultrasonic transmission link 16.2 Piezoelectric ultrasonic transmitters and receivers 16.3 Principles of ultrasonic transmission 16.4 Examples of ultrasonic measurement systems 17 Gas Chromatography 17.1 Principles and basic theory 17.2 Typical gas chromatograph 17.3 Signal processing and operations sequencing 18 Data Acquisition and Communication Systems 18.1 Time division multiplexing 18.2 Typical data acquisition system 18.3 Parallel digital signals 18.4 Serial digital signals 18.5 Error detection and correction 18.6 Frequency shift keying 18.7 Communication systems for measurement 313 313 319 321 339 342 351 353 362 367 367 369 374 378 385 385 387 393 398 403 409 427 427 428 436 447 461 461 465 468 475 476 477 478 479 487 490 493
X CONTENTS 19 The Intelligent Multivariable Measurement System 503 19.1 The structure of an intelligent multivariable system 503 19.2 Modelling methods for multivariable systems 507 Answers to Numerical Problems 515 Index 521