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Chapter1
Programmable Controllers
Theory and Implementation
Second Edition
L.A. Bryan
E.A. Bryan
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PROGRAMMABLE
CONTROLLERS
T HEORY AND I MPLEMENTATION
Second Edition
L. A. Bryan
E. A. Bryan
An Industrial Text Company Publication
Atlanta • Georgia • USA
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© 1988, 1997 by Industrial Text Company
Published by Industrial Text Company
All rights reserved
First edition 1988. Second edition 1997
Printed and bound in the United States of America
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Reproduction or translation of any part of this work beyond
that permitted by Sections 107 and 108 of the 1976 United
States Copyright act are unlawful.
Requests for permission, accompanying workbooks, or
further information should be addressed to:
Industrial Text and Video Company
1950 Spectrum Circle
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(800) PLC-TEXT
Library of Congress Cataloging-in-Publication Data
Bryan, L.A.
Programmable controllers: theory and implementation/L.A. Bryan,
E.A. Bryan.—2nd ed.
p. cm.
Includes index.
ISBN 0-944107-32-X
1. Programmable controllers. I. Bryan, E.A. II. Title.
TJ223.P76B795 1997
629.8'9—dc21 96-49350
CIP
Due to the nature of this publication and because of the different applications of
programmable controllers, the readers or users and those responsible for applying the
information herein contained must satisfy themselves to the acceptability of each
application and the use of equipment therein mentioned. In no event shall the publisher
and others involved in this publication be liable for direct, indirect, or consequential
damages resulting from the use of any technique or equipment herein mentioned.
The illustrations, charts, and examples in this book are intended solely to illustrate the
methods used in each application example. The publisher and others involved in this
publication cannot assume responsibility or liability for actual use based on the
illustrative uses and applications.
No patent liability is assumed with respect to use of information, circuits, illustrations,
equipment, or software described in this text.
Industrial Text & Video Company 1-800-752-8398
www.industrialtext.com
Contents
C ONTENTS
Preface ..................................................................................................... ix
About the Authors .................................................................................... x
How to Use this Book ............................................................................. xi
1-1 Definition ................................................................................................. 4
1-2 A Historical Background .......................................................................... 5
1-3 Principles of Operation ........................................................................... 10
1-4 PLCs Versus Other Types of Controls ................................................... 13
1-5 PLC Product Application Ranges .......................................................... 22
1-6 Ladder Diagrams and the PLC ............................................................... 24
1-7 Advantages of PLCs ............................................................................... 26
2-1 Number Systems .................................................................................... 34
2-2 Number Conversions .............................................................................. 41
2-3 One’s and Two’s Complement ............................................................... 43
2-4 Binary Codes .......................................................................................... 46
2-5 Register Word Formats .......................................................................... 50
3-1 The Binary Concept ............................................................................... 56
3-2 Logic Functions ...................................................................................... 57
3-3 Principles of Boolean Algebra and Logic .............................................. 64
3-4 PLC Circuits and Logic Contact Symbology ......................................... 68
4-1 Introduction ............................................................................................ 82
4-2 Processors ............................................................................................... 84
4-4 Error Checking and Diagnostics ............................................................ 92
4-5 The System Power Supply ..................................................................... 98
4-6 Programming Devices .......................................................................... 104
5-1 Memory Overview ............................................................................... 110
5-2 Memory Types ..................................................................................... 111
5-3 Memory Structure and Capacity .......................................................... 115
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Contents
5-5 Configuring the PLC Memory—I/O Addressing ................................. 127
5-7 Memory Considerations ....................................................................... 133
6-1 Introduction to Discrete I/O Systems ................................................... 138
6-2 I/O Rack Enclosures and Table Mapping ............................................ 139
6-3 Remote I/O Systems ............................................................................. 146
6-4 PLC Instructions for Discrete Inputs .................................................... 147
6-5 Types of Discrete Inputs ...................................................................... 150
6-6 PLC Instructions for Discrete Outputs ................................................. 162
6-7 Discrete Outputs ................................................................................... 165
6-8 Discrete Bypass/Control Stations ......................................................... 177
6-9 Interpreting I/O Specifications ............................................................. 178
6-10 Summary of Discrete I/O ..................................................................... 182
7-1 Overview of Analog Input Signals ....................................................... 186
7-2 Instructions for Analog Input Modules ................................................ 187
7-3 Analog Input Data Representation ....................................................... 189
7-4 Analog Input Data Handling ................................................................ 196
7-5 Analog Input Connections .................................................................... 199
7-6 Overview of Analog Output Signals .................................................... 201
7-7 Instructions for Analog Output Modules ............................................. 201
7-8 Analog Output Data Representation .................................................... 203
7-10 Analog Output Connections ................................................................. 213
7-11 Analog Output Bypass/Control Stations .............................................. 214
8-1 Introduction to Special I/O Modules .................................................... 218
8-2 Special Discrete Interfaces ................................................................... 220
8-3 Special Analog, Temperature, and PID Interfaces ............................... 224
8-4 Positioning Interfaces ........................................................................... 233
8-5 ASCII, Computer, and Network Interfaces .......................................... 248
8-6 Fuzzy Logic Interfaces ......................................................................... 255
8-7 Peripheral Interfacing ........................................................................... 260
9-1 Introduction to Programming Languages ............................................. 276
9-2 Types of PLC Languages ..................................................................... 276
9-3 Ladder Diagram Format ....................................................................... 282
9-4 Ladder Relay Instructions .................................................................... 289
9-5 Ladder Relay Programming ................................................................. 298
9-6 Timers and Counters ............................................................................ 306
9-7 Timer Instructions ................................................................................ 308
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