PLC_Theory Book.pdf

Programmable Controllers

Theory and Implementation

Second Edition

L.A. Bryan

E.A. Bryan

PROGRAMMABLE

CONTROLLERS

T HEORY AND I MPLEMENTATION

Second Edition

L. A. Bryan

E. A. Bryan

An Industrial Text Company Publication

Atlanta • Georgia • USA

Published by Industrial Text Company

First edition 1988. Second edition 1997

Printed and bound in the United States of America

03 02 01 00 99 98 97 10 9 8 7 6 5 4 3 2

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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.

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Contents

C ONTENTS

Preface ..................................................................................................... ix

About the Authors .................................................................................... x

How to Use this Book ............................................................................. xi

S ECTION 1 NTRODUCTORY C ONCEPTS

Chapter 1 Introduction to Programmable Controllers

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

Chapter 2 Number Systems and Codes

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

Chapter 3 Logic Concepts

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

S ECTION 2C OMPONENTS AND S YSTEMS

Chapter 4 Processors, the Power Supply, and Programming Devices

4-1 Introduction ............................................................................................ 82

4-2 Processors ............................................................................................... 84

4-3 Processor Scan ........................................................................................ 86

4-4 Error Checking and Diagnostics ............................................................ 92

4-5 The System Power Supply ..................................................................... 98

4-6 Programming Devices .......................................................................... 104

Chapter 5 The Memory System and I/O Interaction

5-1 Memory Overview ............................................................................... 110

5-2 Memory Types ..................................................................................... 111

5-3 Memory Structure and Capacity .......................................................... 115

5-4 Memory Organization and I/O Interaction ........................................... 119

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iii

Contents

5-5 Configuring the PLC Memory—I/O Addressing ................................. 127

5-6 Summary of Memory, Scanning, and I/O Interaction .......................... 132

5-7 Memory Considerations ....................................................................... 133

Chapter 6 The Discrete Input/Output System

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

Chapter 7 The Analog Input/Output System

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

7-9 Analog Output Data Handling .............................................................. 207

7-10 Analog Output Connections ................................................................. 213

7-11 Analog Output Bypass/Control Stations .............................................. 214

Chapter 8 Special Function I/O and Serial Communication Interfacing

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

S ECTION 3 PLC P ROGRAMMING

Chapter 9 Programming Languages

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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