Measurement and Control Basics, 3rd Edition - Yola

1 Measurement andControl basics , 3rd EditionThomas A. Hughes Process Control and Process Control Loops Fundamentals Temperature and Pressure Measurement Level Measurement and Control Analytical and Flow MeasurementTaken from Measurement and Control basics , Third EditionNoticeThe information presented in this publication is for the general education of the reader. Because neither the authors nor the publisher have any Control over the use of the information by the reader, both the authors and the publisher disclaim any and all liability of any kind arising out of such use. The reader is expected to exercise sound professional judgment in using any of the information presented in a particular , neither the authors nor the publisher have investigated or considered the effect of any patents on the ability of the reader to use any of the information in a particular application.

2 The reader is responsible for reviewing any possible patents that may affect any particular use of the information references to commercial products in the work are cited as examples only. Neither the authors nor the publisher endorse any referenced commercial product. Any trademarks or tradenames referenced belong to the respective owner of the mark or name. Neither the authors nor the publisher make any representation regarding the availability of any referenced commercial product at any time. The manufacturer s instructions on use of any commercial product must be followed at all times, even if in conflict with the information in this 2002 ISA The Instrumentation, Systems, and Automation SocietyAll rights reserved. Printed in the United States of America.

3 10 9 8 7 6 5 4 3 2 ISBN 1-55617-764-XNo part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the Alexander Box 12277 Research Triangle Park, NC 27709 Library of Congress Cataloging-in-Publication DataHughes, Thomas and Control basics / Thomas A. 3rd cm. -- (Resources for Measurement and Control series)Includes bibliographical references and 1-55617-764-X1. Process Control --Instruments. 2. Measuring instruments. I..H78 '7--dc212001006083 Editor s IntroductionThis mini-book is available both in downloadable form, as part of the ISA Press Digital Book Library, and bound in a print format.

4 Mini-books are small, unified volumes, from 25 to 100 pages long, drawn from the ISA catalog of reference and technical books. ISA makes mini-books available to readers who need narrowly focused information on particular subjects rather than a broad-ranging text that provides an overview of the entire subject. Each provides the most recent version of the material in some cases including revisions that have not yet been incorporated in the larger parent volume. Each has been re-indexed and renumbered so it can be used independently of the parent volume. Other mini-books on related subjects are material in this mini-book was drawn from the following ISA titles: Measurement and Control basics , 3rd Edition , by Thomas A. Hughes. Order Number: 1-55617-764-XTo order:Internet: : 919/549-8411 Fax:919/549-8288 Email: Resources for Measurement and Control Series (RMC) Measurement and Control basics , 3rd Edition (2002) Industrial Level, Pressure, and Density Measurement (1995) Industrial Flow Measurement (1990) Programmable Controllers, 3rd Edition (2001) Control Systems Documentation: Applying Symbols and Identification (1993) Industrial Data Communications.

5 Fundamentals and Applications, 3rd Edition (2002) Real-Time Control Networks (1993) Automation Systems for Control and Data Acquisition (1992) Control Systems Safety Evaluation and Reliability, 2nd Edition (1998)THIS BOOK IS DEDICATED TOmy wife Ellen, my daughter Audrey, and my mother Helene for their loveixCONTENTSABOUT THE AUTHOR xiiiPREFACE xvChapter 1 INTRODUCTION TO PROCESS Control 1 Introduction, 1 Definition of Process Control , 1 Elements of a Process Control System, 3 General Requirements of a Control System, 7 Intuitive Approach to Process Control Concepts, 9 Chapter 2 PROCESS Control LOOPS 27 Introduction, 27 Single-loop Feedback Control , 27 Time Elements of a Feedback Loop, 30 Comparison of Basic Physical Systems, 35 Dead Time Lag, 47 Advanced Control Loops, 49 Tuning Control Loops, 53 Chapter 3 ELECTRICAL AND ELECTRONIC FUNDAMENTALS 67 Introduction, 67 Fundamentals of Electricity, 67 Selecting Wire Size.

6 81 Electrical Control Devices, 87 Chapter 4 DIGITAL SYSTEM FUNDAMENTALS 93 Introduction, 93 Binary Signals and Codes, 93xTable of ContentsNumbering Systems, 94 Data Codes, 101 Binary Logic Functions, 106 Logic Function Symbols, 111 Ladder Logic Diagrams, 111 Chapter 5 PRESSURE Measurement 117 Introduction, 117 Definition of Pressure, 117 Manometers, 126 Pressure Gauges, 128 Chapter 6 LEVEL Measurement AND Control 147 Introduction, 147 Sight-type Instruments, 147 Pressure-type Instruments, 151 Electrical-type Instruments, 155 Sonic-type Instruments, 160 Radiation-type Instruments, 161 Level Switches, 165 Chapter 7 TEMPERATURE Measurement 171 Introduction, 171A Brief History of Temperature Measurement , 171 Temperature Scales, 172 Reference Temperatures, 173 Filled-System Thermometers, 175 Bimetallic Thermometers, 176 Thermocouples, 179 Resistance Temperature Detectors, 188 Thermistors, 193 Integrated-Circuit Temperature Sensors, 195 Radiation Pyrometers, 197 Chapter 8 ANALYTICAL Measurement AND Control 201 Introduction, 201 Conductivity Measurement , 201 Hydrogen-Ion Concentration (pH)

7 Measurement , 204 Density and Specific Gravity Measurement , 208 Humidity Measurement , 216 Principles of Electromagnetic Radiation, 221 Electromagnetic Spectrum, 221 Photodetectors, 224 Turbidity Analyzer, 231 Gas Analysis, 232 Analyzer Measurement Applications, 236 Table of ContentsxiChapter 9 FLOW Measurement 241 Introduction, 241 Flow Principles, 241 Flow-Measuring Techniques, 252 Chapter 10 FINAL Control ELEMENTS 275 Introduction, 275 Control Valve basics , 275AC and DC Motors, 292 Pumps, 302 Chapter 11 PROCESS Control COMPUTERS 309 Introduction, 309 History of Process Control Computers, 309 Distributed Control Systems, 315 Programmable Controllers, 318 Basic Components of PLC Systems, 320 Plantwide Computer-based System, 336 Appendix A STANDARD GRAPHICS SYMBOLS FOR PROCESS Control AND INSTRUMENTATION 341 Appendix B THERMOCOUPLE TABLES 353 Appendix C ANSWERS TO EXERCISES 357 INDEX 367xiiiABOUT THE AUTHORT homas A.

8 Hughes, a Senior Member of ISA The Instrumentation, Sys-tems, and Automation Society, has 30 years of experience in the design and installation of instrumentation and Control systems, including 20 years in the management of instrumentation and Control projects for the process and nuclear industries. He is the author of two books: Measure-ment and Control basics , 3rd Edition , (2002) and Programmable Controllers, 3rd Edition , (2001), both published by ISA. Mr. Hughes received a B. S. in engineering physics from the University of Colorado, and a in Control systems engineering from Colorado State University. He holds professional engineering licenses in the states of Col-orado and Alaska, and has held engineering and management positions with Dow Chemical, Rockwell International, EG&G Rocky Flats, Topro Systems Integration, and the International Atomic Energy Agency.

9 Mr. Hughes has taught numerous courses in electronics, mathematics, and instrumentation systems at the college level and in industry. He is cur-rently the Principal Consultant with Nova Systems Engineering Services in Arvada, third Edition of Measurement and Control basics is a thorough and com-prehensive treatment of the basic principles of process Control and mea-surement. It is designed for engineers, technicians, management, and sales personnel who are new to process Control and Measurement . It is also valuable as a concise and easy-to-read reference source on the new Edition provides expanded coverage of pressure, level, flow, temperature, analytical Measurement , and process Control computers. Material on the proper tuning of Control loops was added to Chapter 1, and expanded coverage of Control loops was added to Chapter 2.

10 Chapter 3 includes a more complete discussion of electrical and electronic funda-mentals needed in process Control and instrumentation. The discussion of the basic principles underlying pressure Measurement has been expanded to include a discussion of sensor characteristics and potentiometric-type pressure sensors. Extensive coverage was added on typical pressure transmitter applications. The discussion on level mea-surement has been increased with the addition of several common level instruments and switches such as displacers, tape floats, microwave, and radar. The chapter on temperature Measurement has been improved by adding new illustrations and a section on radiation pyrometers. Coverage of analytical Measurement and Control in Chapter 8 was increased by the addition of a section on the principles of electromagnetic radiation and its application to analytical Measurement .