Introduction to Instrumentation, Sensors, and Process Control For a listing of related titles from Artech House, turn to the back of this book Introduction to Instrumentation, Sensors, and Process Control William C Dunn artechhouse.com Library of Congress Cataloging-in-Publication Data Dunn, William C Introduction to instrumentation, sensors, and process control/William C Dunn p cm —(Artech House Sensors library) ISBN 1-58053-011-7 (alk paper) Process control Detectors I Title II Series TS156.8.D86 2005 670.42'7—dc22 2005050832 British Library Cataloguing in Publication Data Dunn, William C Introduction to instrumentation, sensors, and process control —(Artech House sensors library) Engineering instruments Electronic instruments Process control I Title 681.2 ISBN-10: 1-58053-011-7 Cover design by Cameron Inc © 2006 ARTECH HOUSE, INC 685 Canton Street Norwood, MA 02062 All rights reserved Printed and bound in the United States of America No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without permission in writing from the publisher All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized Artech House cannot attest to the accuracy of this information Use of a term in this book should not be regarded as affecting the validity of any trademark or service mark International Standard Book Number: 1-58053-011-7 10 Contents Preface Acknowledgment CHAPTER Introduction to Process Control xv xvi 1.1 Introduction 1.2 Process Control 1.2.1 Sequential Process Control 1.2.2 Continuous Process Control 1.3 Definition of the Elements in a Control Loop 1.4 Instrumentation and Sensors 1.4.1 Instrument Parameters 1.5 Control System Evaluation 1.5.1 Stability 1.5.2 Regulation 1.5.3 Transient Response 1.6 Analog and Digital Data 1.6.1 Analog Data 1.6.2 Digital Data 1.6.3 Pneumatic Data 1.6.4 Smart Sensors 1.7 Process Facility Considerations 1.8 Summary Definitions References 1 2 5 9 9 10 10 10 10 11 11 12 12 14 CHAPTER Units and Standards 15 2.1 Introduction 2.1.1 Units and Standards 2.2 Basic Units 2.3 Units Derived from Base Units 2.3.1 Units Common to Both the English and SI Systems 2.3.2 English Units Derived from Base Units 2.3.3 SI Units Derived from Base Units 2.3.4 Conversion Between English and SI Units 15 15 16 16 16 16 18 18 v vi Contents 2.3.5 Metric Units not Normally Used in the SI System 2.4 Standard Prefixes 2.5 Standards 2.5.1 Physical Constants 2.5.2 Standards Institutions 2.6 Summary References 20 21 22 22 22 23 23 CHAPTER Basic Electrical Components 25 3.1 Introduction 3.2 Circuits with R, L, and C 3.2.1 Voltage Step Input 3.2.2 Time Constants 3.2.3 Sine Wave Inputs 3.3 RC Filters 3.4 Bridge Circuits 3.4.1 Voltage Dividers 3.4.2 dc Bridge Circuits 3.4.3 ac Bridge Circuits 3.5 Summary References 25 25 25 27 28 32 34 34 34 38 39 40 CHAPTER Analog Electronics 41 4.1 Introduction 4.2 Analog Circuits 4.2.1 Operational Amplifier Introduction 4.2.2 Basic Op-Amp 4.2.3 Op-Amp Characteristics 4.3 Types of Amplifiers 4.3.1 Voltage Amplifiers 4.3.2 Converters 4.3.3 Current Amplifiers 4.3.4 Integrating and Differentiating Amplifiers 4.3.5 Nonlinear Amplifiers 4.3.6 Instrument Amplifiers 4.3.7 Input Protection 4.4 Amplifier Applications 4.5 Summary References 41 41 41 42 42 45 45 50 52 53 54 55 57 57 58 58 CHAPTER Digital Electronics 59 5.1 Introduction 5.2 Digital Building Blocks 5.3 Converters 59 59 61 Contents vii 5.3.1 Comparators 5.3.2 Digital to Analog Converters 5.3.3 Analog to Digital Converters 5.3.4 Sample and Hold 5.3.5 Voltage to Frequency Converters 5.4 Data Acquisition Devices 5.4.1 Analog Multiplexers 5.4.2 Digital Multiplexers 5.4.3 Programmable Logic Arrays 5.4.4 Other Interface Devices 5.5 Basic Processor 5.6 Summary References 62 64 68 72 72 74 74 74 75 75 75 76 77 CHAPTER Microelectromechanical Devices and Smart Sensors 79 6.1 Introduction 6.2 Basic Sensors 6.2.1 Temperature Sensing 6.2.2 Light Intensity 6.2.3 Strain Gauges 6.2.4 Magnetic Field Sensors 6.3 Piezoelectric Devices 6.3.1 Time Measurements 6.3.2 Piezoelectric Sensors 6.3.3 PZT Actuators 6.4 Microelectromechanical Devices 6.4.1 Bulk Micromachining 6.4.2 Surface Micromachining 6.5 Smart Sensors Introduction 6.5.1 Distributed System 6.5.2 Smart Sensors 6.6 Summary References 79 80 80 80 81 82 84 86 87 88 88 89 91 94 95 96 96 97 CHAPTER Pressure 99 7.1 Introduction 7.2 Pressure Measurement 7.2.1 Hydrostatic Pressure 7.2.2 Specific Gravity 7.2.3 Units of Measurement 7.2.4 Buoyancy 7.3 Measuring Instruments 7.3.1 Manometers 7.3.2 Diaphragms, Capsules, and Bellows 7.3.3 Bourdon Tubes 99 99 99 100 101 103 105 105 106 108 viii Contents 7.3.4 Other Pressure Sensors 7.3.5 Vacuum Instruments 7.4 Application Considerations 7.4.1 Selection 7.4.2 Installation 7.4.3 Calibration 7.5 Summary Definitions References 109 110 111 111 112 112 113 113 114 CHAPTER Level 115 8.1 Introduction 8.2 Level Measurement 8.2.1 Direct Level Sensing 8.2.2 Indirect Level Sensing 8.2.3 Single Point Sensing 8.2.4 Level Sensing of Free-Flowing Solids 8.3 Application Considerations 8.4 Summary References 115 115 115 118 124 125 126 128 128 CHAPTER Flow 129 9.1 Introduction 9.2 Fluid Flow 9.2.1 Flow Patterns 9.2.2 Continuity Equation 9.2.3 Bernoulli Equation 9.2.4 Flow Losses 9.3 Flow Measuring Instruments 9.3.1 Flow Rate 9.3.2 Total Flow 9.3.3 Mass Flow 9.3.4 Dry Particulate Flow Rate 9.3.5 Open Channel Flow 9.4 Application Considerations 9.4.1 Selection 9.4.2 Installation 9.4.3 Calibration 9.5 Summary Definitions References 129 129 129 131 132 134 136 136 142 144 144 145 145 145 147 147 147 148 148 Contents ix CHAPTER 10 Temperature and Heat 149 10.1 Introduction 10.2 Temperature and Heat 10.2.1 Temperature Units 10.2.2 Heat Energy 10.2.3 Heat Transfer 10.2.4 Thermal Expansion 10.3 Temperature Measuring Devices 10.3.1 Expansion Thermometers 10.3.2 Resistance Temperature Devices 10.3.3 Thermistors 10.3.4 Thermocouples 10.3.5 Pyrometers 10.3.6 Semiconductor Devices 10.4 Application Considerations 10.4.1 Selection 10.4.2 Range and Accuracy 10.4.3 Thermal Time Constant 10.4.4 Installation 10.4.5 Calibration 10.4.6 Protection 10.5 Summary Definitions References 149 149 149 151 153 155 157 157 160 161 162 164 165 166 166 166 167 168 168 168 169 169 170 CHAPTER 11 Position, Force, and Light 171 11.1 Introduction 11.2 Position and Motion Sensing 11.2.1 Position and Motion Measuring Devices 11.2.2 Position Application Considerations 11.3 Force, Torque, and Load Cells 11.3.1 Force and Torque Introduction 11.3.2 Stress and Strain 11.3.3 Force and Torque Measuring Devices 11.3.4 Strain Gauge Sensors 11.3.5 Force and Torque Application Considerations 11.4 Light 11.4.1 Light Introduction 11.4.2 EM Radiation 11.4.3 Light Measuring Devices 11.4.4 Light Sources 11.4.5 Light Application Considerations 11.5 Summary Definitions References 171 171 171 176 177 178 178 181 183 186 186 186 186 188 188 189 190 190 191 316 Glossary Indirect level-measuring device A device that extrapolates the level from the measurement of another variable (e.g., liquid level from a pressure measurement) Integral action The action designed to correct for long term loads −3 Ionization gauge A low pressure sensor (