Introduction to Programmable Logic Controllers

INTRODUCTION TO PROGRAMMABLE LOGIC CONTROLLERS Second Edition

by

Gary Dunning

Introduction to Programmable Logic Controllers, Second Edition by Gary Dunning Business Unit Director: Alar Elken

Executive Marketing Manager: Maura Theriault

Production Editor: Barbara L. Diaz

Acquisitions Editor: Mark Huth

Channel Manager: Mona Caron

Art/Design Coordinator: Rachel Baker

Development: Dawn Daugherty

Executive Production Manager: Mary Ellen Black

Cover Design: Cummings Advertising/Art, Inc

COPYRIGHT  2002 by Delmar, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license Printed in the United States of America 1 2 3 4 5 XXX 05 04 02 01 00 For more information contact Delmar, 3 Columbia Circle, PO Box 15015, Albany, NY 12212-5015. Or find us on the World Wide Web at http://www.delmar.com ALL RIGHTS RESERVED. Portions of this work  1998. No part of this work covered by the copyright hereon may be reproduced or used in any form or by any means graphic, electronic, or mechanical, including photocopying, recording, taping, Web distribution or information storage and retrieval systems without written permission of the publisher.

For permission to use material from this text or product, contact us by Tel (800) 730-2214 Fax (800) 730-2215 www.thomsonrights.com Library of Congress Cataloging-in-Publication Data Dunning, Gary. Introduction to programmable logic controllers / by Gary Dunning. 2nd ed. p. cm. Includes index. ISBN 0-7668-1768-7 (alk. paper) 1. Programmable controllers. I. Title. TJ223.3.3.P76 D86 2001 629.8 9 dc21

00-047578

NOTICE TO THE READER Publisher does not warrant or guarantee any of the products described herein or perform any independent analysis in connection with any of the product information contained herein. Publisher does not assume, and expressly disclaims, any obligation to obtain and include information other than that provided to it by the manufacturer. The reader is expressly warned to consider and adopt all safety precautions that might be indicated by the activities herein and to avoid all potential hazards. By following the instructions contained herein, the reader willingly assumes all risks in connection with such instructions. The Publisher makes no representation or warranties of any kind, including but not limited to, the warranties of fitness for particular purpose or merchantability, nor are any such representations implied with respect to the material set forth herein, and the publisher takes no responsibility with respect to such material. The publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or part, from the readers use of, or reliance upon, this material.

TA B L E OF CON TE N TS Preface ix Acknowledgments

xi

Part I CHAPTER 1

Introduction to PLCs

Welcome to the World of Programmable Logic Controllers. . . . . . . .

What Is a Programmable Logic Controller (PLC)? . . . . . . Where Did the PLC Come From? . . . . . . . . . . . . . . . Why Use a PLC? . . . . . . . . . . . . . . . . . . . . . . . . What Makes a PLC Work? . . . . . . . . . . . . . . . . . . . How Do PLCs Know What They Are Supposed to Do? . . . How Do Instructions Get into the PLC’s Memory? . . . . . Innovations Incorporated into the Programmable Controller Introduction to Fixed and Modular PLC Hardware . . . . . The Central Processing Unit . . . . . . . . . . . . . . . . . . CHAPTER 2

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4 5 6 8 8 9 11 16 23

Micro Programmable Logic Controllers . . . . . . . . . . . . . . . . . .

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Overview of Selected Micro PLCs . . . . . . . . . . . . GE Fanuc Automation VersaMax Controllers . . . . . . . GE Fanuc Automation Series 90 Micro PLC . . . . . . . The Mitsubishi FX2N Super Micro . . . . . . . . . . . . Omron’s CPM1A Series Micro PLC . . . . . . . . . . . . Rockwell Automation’s MicroLogix 1000 Microcontroller Rockwell Automation’s MicroLogix 1500 Microcontroller Siemens Simatic S7-200 Micro PLC. . . . . . . . . . . . CHAPTER 3

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57

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Programming a Programmable Controller . . . . . . . . . . . . . . . . . . . . . . . . . . .

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33 33 37 39 44 45 46 50

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Handheld Programming Terminals . . . . . . . . . . . . . . . . . Desktop Personal Computers (PCs) and PLC Programming . . . . Notebook Personal Computers and PLC Programming . . . . . . Windows CE-based Handheld Personal Computers . . . . . . . . Industrial Computers. . . . . . . . . . . . . . . . . . . . . . . . . Industrial Monitors . . . . . . . . . . . . . . . . . . . . . . . . . . Open PLC Systems. . . . . . . . . . . . . . . . . . . . . . . . . . The IEC 1131-3 Programming Standard . . . . . . . . . . . . . . Soft PLC or Open-architecture Control . . . . . . . . . . . . . . . One Step Further: Production Data from PLC to Office Databases

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58 63 68 71 73 77 77 78 88 88 iii

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TABLE OF CONTENTS

CHAPTER 4

Number Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Number System Characteristics . . . . . . . . . . . . . . . . . . The Decimal Number System . . . . . . . . . . . . . . . . . . . Decimal Place Values. . . . . . . . . . . . . . . . . . . . . . . . Binary and Binary-coded Decimal Numbers . . . . . . . . . . . Binary Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . Bit Position and Weighting . . . . . . . . . . . . . . . . . . . . . Binary Coding . . . . . . . . . . . . . . . . . . . . . . . . . . . Binary-coded Decimal (BCD) Numbers . . . . . . . . . . . . . BCD Number Representation of Numbers Between 10 and 99 . BCD Representation of the Decimal Numbers 100 through 999 BCD Representation of Four-digit Decimal Values. . . . . . . . Applications of BCD . . . . . . . . . . . . . . . . . . . . . . . . The Octal Number System. . . . . . . . . . . . . . . . . . . . . Valid Octal Numbers . . . . . . . . . . . . . . . . . . . . . . . . Octal-to-decimal Conversion . . . . . . . . . . . . . . . . . . . Binary-to-octal Conversion . . . . . . . . . . . . . . . . . . . . Octal-to-binary Conversion . . . . . . . . . . . . . . . . . . . . The Hexadecimal Number System . . . . . . . . . . . . . . . . CHAPTER 5

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96 97 97 98 98 99 100 102 105 106 106 106 108 108 109 110 111 111

Introduction to PLC Operation. . . . . . . . . . . . . . . . . . . . . . .

119

The Digital Concept . . . . . . . . . . . . . . . . . . . Analog Signals . . . . . . . . . . . . . . . . . . . . . . The Binary Concept . . . . . . . . . . . . . . . . . . . Binary Data Representation . . . . . . . . . . . . . . . Correlation of 16-bit Words to Input Signals . . . . . . The Input Status File . . . . . . . . . . . . . . . . . . . The Output Status File . . . . . . . . . . . . . . . . . . Input and Output Status Files and Fixed PLCs . . . . . Differentiating One I/O Screw Terminal from Another. Sixteen-point I/O Modules with Decimal Addressing . I/O Interaction with the Input and Output Status Files Fixed PLC I/O Addressing When I/O Is Expanded . . PLC Memory and How It Is Used. . . . . . . . . . . . Data Formats . . . . . . . . . . . . . . . . . . . . . . . PLC System Memory . . . . . . . . . . . . . . . . . . PLC Application Memory . . . . . . . . . . . . . . . . CHAPTER 6

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153

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Introduction to Logic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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120 121 122 123 124 128 129 131 133 135 137 140 141 141 145 146

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Conventional Ladders versus PLC Ladder Logic. What is Logic? . . . . . . . . . . . . . . . . . . . Overview of Logic Functions . . . . . . . . . . . Series—The AND Logic Function . . . . . . . . .

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153 156 157 158

TABLE OF CONTENTS

Three-input AND Logic . . . . . . . . . . Parallel Circuits—The OR Logic Function NOT Logic . . . . . . . . . . . . . . . . . Analysis of Rung #1 . . . . . . . . . . . . Analysis of Rung #2 . . . . . . . . . . . . Parallel NOT Logic . . . . . . . . . . . . . Exclusive OR Logic . . . . . . . . . . . . Analysis of Exclusive OR Logic . . . . . . Combinational Logic . . . . . . . . . . . . Priority of Logic Elements . . . . . . . . . CHAPTER 7

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160 162 164 165 165 166 167 168 169 170

Input Modules. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

177

Input Modules . . . . . . . . . . . . . . . . . . . . Discrete Input Module. . . . . . . . . . . . . . . . Discrete AC Input Module . . . . . . . . . . . . . AC Input Module Specifications. . . . . . . . . . . DC Input Modules . . . . . . . . . . . . . . . . . . Sinking and Sourcing. . . . . . . . . . . . . . . . . DC Input Module Operation . . . . . . . . . . . . DC Sinking Input Module Specifications . . . . . . Solid-state Sensor Interface to DC Input Modules . A Final Note on Sinking and Sourcing. . . . . . . . Analog Inputs . . . . . . . . . . . . . . . . . . . . . Specialty Modules . . . . . . . . . . . . . . . . . . CHAPTER 8

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178 180 180 183 189 190 194 195 198 200 200 208

Output Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

215

Discrete Output Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transistor-Transistor Logic (TTL) Output Modules . . . . . . . . . . . . . . . . Relay Output Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Module Selection Considerations . . . . . . . . . . . . . . . . . . . . . . . . . Choosing the Proper Output Module . . . . . . . . . . . . . . . . . . . . . . . Isolated Output Modules. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Interposing Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Surge Suppression and Output Modules . . . . . . . . . . . . . . . . . . . . . High-density I/O Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Analog Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Emergency-stop Switches and PLC Applications. . . . . . . . . . . . . . . . . I/O Modules in Hazardous Locations . . . . . . . . . . . . . . . . . . . . . . . Hardware Considerations Before Installing PLCs in Class 1, Division 2, Areas

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216 221 221 226 227 228 228 230 231 231 232 234 235

Putting Together a Modular PLC. . . . . . . . . . . . . . . . . . . . . .

241

Racks, Chassis, or Baseplates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Local, or Base, PLC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

242 248

CHAPTER 9

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vi

TABLE OF CONTENTS

Local Expansion . . . . . . . . . . . . . Remote I/O Expansion . . . . . . . . . . PLC Networking . . . . . . . . . . . . . Selection and Placement of I/O Modules Power Supply Selection . . . . . . . . . I/O Racks and Expansion . . . . . . . .

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248 249 251 251 253 263

CHAPTER 10 PLC Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

275

The Processor’s Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Processor’s Operating System . . . . . . . . . . . . . . . . . . . . . . . . . Processor Scanning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Omron CQM1 Operating Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . The Watchdog Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Processor Ports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The RS-232C Communication Standard . . . . . . . . . . . . . . . . . . . . . . Serial Communication Between a Personal or Industrial Computer and the PLC Interfacing to non-RS-232 PLC Processors . . . . . . . . . . . . . . . . . . . . . Processor-operating Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . On-line Editing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Battery Backup for the Processor’s Volatile Memory . . . . . . . . . . . . . . . . Lithium Battery Handling and Disposal . . . . . . . . . . . . . . . . . . . . . . Nonvolatile Memory: EEPROM . . . . . . . . . . . . . . . . . . . . . . . . . . Passwords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Allen-Bradley SLC 500 Modular Processors . . . . . . . . . . . . . . . . . . Rockwell Automation’s Logix 5550 Controller . . . . . . . . . . . . . . . . . . . The General Electric Series 90-30 Processors . . . . . . . . . . . . . . . . . . . Choosing the Correct Processor for an Application . . . . . . . . . . . . . . . . .

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276 276 279 281 283 285 287 288 292 292 295 295 297 298 299 301 308 310 318

CHAPTER 11 Processor Data Organization . . . . . . . . . . . . . . . . . . . . . . . .

327

SLC 500 Files. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Data Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . User-defined Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

328 330 339

CHAPTER 12 The Basic Relay Instructions . . . . . . . . . . . . . . . . . . . . . . . .

347

Part II

PLC Instructions

Bit, or Relay, Instructions . . . . . . . . . The Normally Open Instruction . . . . . . The Output Instruction . . . . . . . . . . Modular SLC 500 Instruction Addressing The Normally Closed Instruction . . . . . The One-shot Instruction . . . . . . . . .

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348 348 349 350 352 354

TABLE OF CONTENTS

vii

The Output-latching Instruction. . . . . . . . . . . . . . . . . . . . . . . . . . . . The Negated Output Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . Internal Bit-type Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

356 359 359

CHAPTER 13 Understanding Relay Instructions and the Programmable Controller

Input Modules. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Interfacing a Start-stop Push-button Station to a Programmable Controller User Program Development for a Start-stop, Push-button Interface . . . . Motor Starter Circuits and the Overload Contacts . . . . . . . . . . . . . . Special Considerations for PLC Control of Motor Starters . . . . . . . . . .

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371 374 381 382

CHAPTER 14 Documenting Your PLC System . . . . . . . . . . . . . . . . . . . . . .

387

Why Add Documentation to User Program? . . . . . . . . . . Information to Include in PLC Documentation . . . . . . . . Documentation and Software Packages . . . . . . . . . . . . . Types of Documentation . . . . . . . . . . . . . . . . . . . . . Adding Documentation When Developing a New Application

CHAPTER 15 Timer and Counter Instructions . . . . . . . . . . . . . . . . . . . . . .

409

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388 388 390 391 397

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Timer Instructions . . . . . . . . . . SLC 500 Timers . . . . . . . . . . . The On-delay Timer Instruction . . . The Off-delay Timer Instruction. . . The Retentive Timer Instruction . . The Reset Instruction . . . . . . . . PLC Counter Instructions . . . . . . Allen-Bradley SLC 500 Counters . . How Counters Work . . . . . . . . . The Count-up Instruction . . . . . . The Count-down Instruction . . . . The High-speed Counter Instruction The Counter Reset Instruction . . . The Clear Instruction . . . . . . . . Combining Timers and Counters . .

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367

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410 410 413 415 416 418 418 420 422 423 424 426 426 427 428

CHAPTER 16 Comparison and Data-Handling Instructions . . . . . . . . . . . . . . .

435

Comparison Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Data-handling Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Logical Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

436 440 452

CHAPTER 17 Sequencer Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . .

467

The Sequencer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sequencer Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

468 468

viii

TABLE OF CONTENTS

The SLC 500 Sequencer Output Instruction . . . . . . . . . . . . . . . . Programming the Sequencer Output Instruction . . . . . . . . . . . . . . Multiple Sequencers and File Designation . . . . . . . . . . . . . . . . . Applying Hexadecimal Numbers and Masks With SLC 500 Programming Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mask Data Representation . . . . . . . . . . . . . . . . . . . . . . . . . .

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469 475 476

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477 480

APPENDIX A Instruction Set Reference. . . . . . . . . . . . . . . . . . . . . . . . . .

485

APPENDIX B Status File Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . .

491

APPENDIX C Applying Hexadecimal Numbers in PLC Masking Applications . . . . .

495

Glossary Index

499 511

PRE FA CE Welcome to the world of programmable logic controllers. Since their development in the early 1970s, programmable logic controllers (PLCs) have literally taken control of practically every modern manufacturing process. The second edition text has been brought up to date, providing the latest possible information on and introduction to PLC products. We have added PLC information and pictures from AEG Schneider Automation/Square D-Modicon and Mitsubishi Electric Automation, Inc. A new chapter two introduces the newer and smaller micro and pico PLCs. Also, this second edition presents explanatory pictures in two colors. This way the specific object referred to in the text is highlighted for easy understanding. The accompanying lab manual has been updated from Rockwell Automation’s older APS programming software to the current RSLogix 500 Windows programming software. All chapters and lab exercises were developed to be an easy-to-understand introduction to the world of PLCs. Developed as a first quarter or semester introductory textbook, Introduction to Programmable Logic Controllers, Second Edition, discusses the top players in today’s PLC market and their products, including Rockwell Automation/Allen-Bradley, General Electric, Mitsubishi, Omron, Schneider Automation, and Siemens. The text was developed to be as generic as possible. Although separate, the lab manual’s hands-on programming exercises were developed for the Allen-Bradley SLC 500 and MicroLogix family of PLCs using RSLogix 500 Windows software. This book was developed for electrical technicians, maintenance personnel, machine design engineers, and individuals selling PLCs in today’s ever-changing manufacturing environment. Students will quickly learn the basics of today’s modern PLCs. Because the PLC is an industrial computer, many electricians and technicians are apprehensive about diving into the world of computers and the associated, seemingly foreign, terminology. This text is developed for these individuals. These new terms are explained in plain English so those new to the world of PLCs will feel comfortable. For additional help in understanding PLC terminology, you will find a comprehensive glossary near the end of the book. Topics covered will include exploring what a PLC is, operation, usage, instructions, applications, hardware selection and configuration, introductory programming examples and exercises, and some troubleshooting hints. The accompanying lab manual will give the student hands-on programming and hookup exercises. Students will configure different PLCs, set up the RSLinx drivers to communicate from a personal computer to the PLC, select proper modules, and calculate power supply loading. A lab exercise will walk students through a motor starter interface to an SLC 500 PLC along with issues in converting conventional ladder start-stop into PLC logic, separation of I/O, and proper instruction selection. Programming exercises will provide hands-on experience developing simple programs that incorporate basic instructions up to and including timers, counters, and sequencers. This textbook is organized in the following manner: ix

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PREFACE

Chapter

Chapter Title

Chapter Description

1

Welcome to the World of Programmable Logic Controllers

Provides an introduction to what programmable controllers are and why and where they are used.

2

Micro Programmable Logic Controllers

Introduces the student to the world of the new and smaller micro and pico PLCs.

3

Programming a Programmable Controller

Describes the available options for programming a programmable controller.

4

Number Systems

Covers the basics of numbers and number systems used with PLCs.

5

Introduction to PLC Operation

Chapter five introduces the basic operating principles of the PLC.

6

Introduction to Logic

Describes the basic logic functions and how they relate to programmable controllers.

7

Input Modules

Describes the basic input modules available, selecting the correct module and basic module interface.

8

Output Modules

Describes the basic output modules available, selecting the correct module and basic module interface.

9

Putting Together a Modular PLC

Introduces the basic considerations when putting together a modular PLC. The chapter reviews power calculations for configuring rack I/O modules and power supply selection.

10

PLC Processors

Introduces the PLC processor and its capabilities, features, and basic operation.

11

Processor Data Organization

Introduces program and data organization inside a PLC processor.

12

The Basic Relay Instructions

Describes the basic instructions used in developing PLC ladder programs.

13

Understanding Relay Instructions and the Programmable Controller Input Modules

Describes the use of relay instructions and considerations when interfacing to real-world input devices.

14

Documenting Your PLC System

Introduces documentation features available when using PLC ladder program development software.

15

Timer and Counter Instructions

Describes timer and counter instructions. Specifically introduces the Allen-Bradley SLC 500 timer and counter instructions.

16

Comparison and Data-Handling Instructions

Introduces data handling and comparison instructions. Specifically covers the SLC 500 instructions.

17

Sequencer Instructions

Introduces the sequencer instructions. Specifically covers the SLC 500 instructions.

Appendix A

A quick reference to the SLC 500 instruction set.

Appendix B

A quick reference to the SLC 500 status file.

Appendix C

Reviews how hexadecimal numbers are used in masking applications.

Glossary

A comprehensive list of defined PLC terms.

A C K NOWL E D GM E N TS I wish to thank my wife, Jean, for her endless hours of typing, proofreading, spell checking, figure development, and art. Thanks to my son, Joe, for his art work for Figures 4-9, 4-13, 4-15, and 4-16. Developing any major technical textbook requires a substantial amount of technical information. We are greatly thankful to the following corporations who provided literature, manuals, and art along with the technical support necessary to complete this project. AEG Schneider Automation/Square D-Modicon Allen-Bradley, a Rockwell Automation business ASAP Inc., Chagrin Falls, Ohio GE Fanuc Automation Mitsubishi Electric Automation, Inc. Omron Electronics, Inc. Siemens Energy & Automation Inc. Along with Delmar, I would like to express appreciation to the following reviewers for their encouragement and suggestions during the preparation of this manuscript: Keith Elliott Rockingham Community College Wentworth, NC

William Shepherd Owens Community College Perrysburg, OH

Ron Meyer Central Community College Doniphan, NE

Daniel Lewis James Rumsey Technical College Bunker Hill, WV

Paul F. Owens San Juan College Aztec, NM

Michael Brumbach York Technical College Rock Hill, SC

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