PLC Programming: Introduction to Programmable Logic Controllers

Accelerat ing t he world's research.
INTRODUCTION TO
PROGRAMMABLE LOGIC
CONTROLLERS Second Edition
Introduction to Programmable Logic
Controllers, Se...
Gerardo Balto
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INTRODUCTION TO
PROGRAMMABLE LOGIC
CONTROLLERS
Second Edition
by
Gary Dunning
Introduction to Programmable Logic Controllers, Second Edition
by Gary Dunning
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COPYRIGHT  2002 by Delmar, a division of Thomson Learning, Inc.
Thomson Learning is a trademark used herein under license
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1 2 3 4 5 XXX 05 04 02 01 00
For more information contact Delmar,
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ALL RIGHTS RESERVED. Portions of this work  1998.
No part of this work covered by the copyright hereon may
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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
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 O F 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
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6
8
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11
16
23
Micro Programmable Logic Controllers . . . . . . . . . . . . . . . . . .
31
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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Programming a Programmable Controller . . . . . . . . . . . . . . . . .
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33
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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
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iii
iv
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
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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
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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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95
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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
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165
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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
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 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 KNOW L E D GME 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
xi