Introduction to Programmable Logic Controllers

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INTRODUCTION TO

PROGRAMMABLE LOGIC

CONTROLLERS

Second Edition

by

Gary Dunning

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Introduction to Programmable Logic Controllers, Second Edition by Gary Dunning

Business Unit Director: Alar Elken

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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.

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

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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

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PREFACE

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 infor-mation on and introduction to PLC products. We have added PLC inforinfor-mation 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 re-ferred 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 devel-oped to be an easy-to-understand introduction to the world of PLCs.

Developed as a first quarter or semester introductory textbook, Introduction to

Pro-grammable Logic Controllers, Second Edition, discusses the top players in today’s PLC

market and their products, including Rockwell Automation/Allen-Bradley, General Elec-tric, 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 ex-ercises 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 manufactur-ing environment. Students will quickly learn the basics of today’s modern PLCs. Because the PLC is an industrial computer, many electricians and technicians are apprehen-sive about diving into the world of computers and the associated, seemingly foreign, ter-minology. 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:

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x PREFACE

Chapter Chapter Title Chapter Description 1 Welcome to the World of

Programmable Logic Controllers Provides an introduction to what programmable controllers are and whyand where they are used. 2 Micro Programmable Logic

Controllers Introduces the student to the world of the new and smaller micro andpico PLCs. 3 Programming a Programmable

Controller Describes the available options for programming a programmablecontroller. 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. Specificallycovers 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.

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ACKNOWLEDGMENTS

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 Fig-ures 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 litera-ture, 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 William Shepherd

Rockingham Community College Owens Community College Wentworth, NC Perrysburg, OH

Ron Meyer Daniel Lewis

Central Community College James Rumsey Technical College Doniphan, NE Bunker Hill, WV

Paul F. Owens Michael Brumbach San Juan College York Technical College Aztec, NM Rock Hill, SC