Programmable Logic Controllers

Description

This textbook, now in its sixth edition, continues to be straightforward and easy-to-read, presenting the principles of PLCs while not tying itself to one manufacturer or another. Extensive examples and chapter ending problems utilize several popular PLCs, highlighting understanding of fundamentals that can be used regardless of manufacturer. This book will help you to understand the main design characteristics, internal architecture, and operating principles of PLCs, as well as Identify safety issues and methods for fault diagnosis, testing, and debugging. New to This edition:

A new chapter 1 with a comparison of relay-controlled systems, microprocessor-controlled systems, and the programmable logic controller, a discussion of PLC hardware and architecture, examples from various PLC manufacturers, and coverage of security, the IEC programming standard, programming devices and manufacturer’s software
More detail of programming using Sequential Function Charts
Extended coverage of the sequencer
More Information on fault finding, including testing inputs and outputs with an illustration of how it is done with the PLC manufacturer’s software
New case studies

A methodical introduction, with many illustrations, describing how to program PLCs, no matter the manufacturer, and how to use internal relays, timers, counters, shift registers, sequencers, and data-handling facilities
Consideration of the standards given by IEC 1131-3 and the programming methods of ladder, functional block diagram, instruction list, structured text, and sequential function chart
Many worked examples, multiple-choice questions, and problems are included, with answers to all multiple-choice questions and problems given at the end of the book

Front Cover 2
Programmable Logic Controllers 5
Copyright 6
Contents 7
Preface 11
- Prerequisite Knowledge Assumed 12
- Changes from the Fifth Edition 12
  - Aims 12
- Structure of the Book 13
Acknowledgments 14
Chapter 1: Programmable Logic Controllers 15
- 1.1 Controllers 15
  - 1.1.1 Relay-Controlled Systems 17
  - 1.1.2 Microprocessor-Controlled Systems 18
  - 1.1.3 The Programmable Logic Controller 19

Front Cover 2
Programmable Logic Controllers 5
Copyright 6
Contents 7
Preface 11
- Prerequisite Knowledge Assumed 12
- Changes from the Fifth Edition 12
  - Aims 12
- Structure of the Book 13
Acknowledgments 14
Chapter 1: Programmable Logic Controllers 15
- 1.1 Controllers 15
  - 1.1.1 Relay-Controlled Systems 17
  - 1.1.2 Microprocessor-Controlled Systems 18
  - 1.1.3 The Programmable Logic Controller 19
- 1.2 Hardware 21
- 1.3 PLC Architecture 23
  - 1.3.1 Input/Output Unit 23
  - 1.3.2 Sourcing and Sinking 25
- 1.4 PLC Systems 26
  - 1.4.1 Security 29
- 1.5 Programs 30
  - 1.5.1 The IEC Standard 31
  - 1.5.2 Programming PLCs 33
- Summary 34
- Problems 35
- Lookup Tasks 36
Chapter 2: Input/Output Devices 37
- 2.1 Input Devices 37
  - 2.1.1 Mechanical Switches 40
  - 2.1.2 Proximity Switches 43
  - 2.1.3 Photoelectric Sensors and Switches 44
  - 2.1.4 Encoders 45
  - 2.1.5 Temperature Sensors 47
  - 2.1.6 Position/Displacement Sensors 51
  - 2.1.7 Strain Gauges 52
  - 2.1.8 Pressure Sensors 54
  - 2.1.9 Liquid-Level Detectors 55
  - 2.1.10 Fluid Flow Measurement 55
  - 2.1.12 Smart Sensors 56
  - 2.1.11 Ultrasonic Proximity Sensors 56
  - 2.1.13 Sensors Ranges 57
- 2.2 Output Devices 57
  - 2.2.1 Relay 57
  - 2.2.2 Directional Control Valves 58
  - 2.2.3 Motors 60
  - 2.2.4 Stepper Motors 63
- 2.3 Examples of Applications 67
  - 2.3.1 A Conveyor Belt 67
  - 2.3.2 A Lift 67
  - 2.3.3 A Robot Control System 68
  - 2.3.4 Liquid-Level Monitoring 69
  - 2.3.5 Packages on Conveyor Belt Systems 69
- Summary 70
- Problems 71
- Lookup Tasks 75
Chapter 3: Digital Systems 77
- 3.2 Octal and Hexadecimal 78
  - 3.2.1 Octal System 79
  - 3.2.2 Hexadecimal System 80
- 3.1 The Binary System 78
- 3.3 Binary Coded Decimals 80
- 3.4 Numbers in the Binary, Octal, Hex, and BCD Systems 81
- 3.5 Binary Arithmetic 82
  - 3.5.1 Signed Numbers 83
  - 3.5.2 One's and Two's Complements 83
  - 3.5.3 Floating Point Numbers 84
- 3.6 PLC Data 85
- 3.7 Combinational Logic Systems 86
- 3.8 Sequential Logic Systems 87
  - 3.8.1 Latches 87
  - 3.8.2 Flip-Flops 89
- Summary 89
- Problems 91
- Lookup Tasks 92
Chapter 4: I/O Processing 93
- 4.1 Input/Output Units 93
  - 4.1.1 Input Units 93
  - 4.1.2 Output Units 96
- 4.2 Signal Conditioning 99
  - 4.2.1 Changing Voltage Levels 100
  - 4.2.2 Op-Amp Comparator 102
  - 4.2.3 Output Protection 103
- 4.3 Remote Connections 103
  - 4.3.1 Serial and Parallel Communications 104
  - 4.3.2 Serial Standards 105
  - 4.3.3 Parallel Standards 108
  - 4.3.4 Protocols 110
  - 4.3.5 ASCII Codes 112
- 4.4 Networks 113
  - 4.4.1 Distributed Systems 114
  - 4.4.2 Network Standards 115
- 4.5 Examples of Commercial Systems 117
  - 4.5.1 MAP 117
  - 4.5.2 Ethernet 118
  - 4.5.4 DeviceNet 119
  - 4.5.3 ControlNet 119
  - 4.5.6 PROFIBUS 120
  - 4.5.7 Factory-Floor Network 120
  - 4.5.5 Allen-Bradley Data Highway 120
- 4.6 Processing Inputs 120
- 4.7 I/O Addresses 122
- Summary 123
- Problems 124
- Lookup Tasks 127
Chapter 5: Ladder and Functional Block Programming 129
- 5.1 Ladder Diagrams 129
  - 5.1.1 PLC Ladder Programming 131
- 5.2 Logic Functions 134
  - 5.2.1 AND 134
  - 5.2.2 OR 135
  - 5.2.3 NOT 137
  - 5.2.4 NAND 138
  - 5.2.5 NOR 139
  - 5.2.6 Exclusive OR (XOR) 140
- 5.3 Latching 141
- 5.4 Multiple Outputs 141
- 5.5 Entering Programs 143
  - 5.5.1 Ladder Symbols 144
- 5.6 Function Blocks 144
  - 5.6.1 Logic Gates 144
  - 5.6.2 Boolean Algebra 149
- 5.7 Program Examples 152
  - 5.7.1 Location of Stop Switches 154
- Summary 155
- Problems 156
- Lookup Tasks 164
Chapter 6: IL, SFC, and ST Programming Methods 165
- 6.1 Instruction Lists 165
  - 6.1.1 Ladder Programs and Instruction Lists 167
  - 6.1.2 Branch Codes 169
  - 6.1.3 More Than One Rung 172
  - 6.1.4 Programming Examples 173
- 6.2 Sequential Function Charts 174
  - 6.2.1 Branching and Convergence 177
  - 6.2.2 Actions 179
  - 6.2.3 Programming a PLC 181
- 6.3 Structured Text 181
  - 6.3.1 Conditional Statements 183
  - 6.3.2 Iteration Statements 185
  - 6.3.3 Structured Text Programs 186
  - 6.3.4 Comparison with Ladder Programs 188
- Summary 188
- Problems 189
Chapter 7: Internal Relays 201
- 7.1 Internal Relays 201
- 7.2 Ladder Programs 202
  - 7.2.1 Programs with Multiple Input Conditions 202
  - 7.2.2 Latching Programs 204
  - 7.2.3 Response Time 205
- 7.3 Battery-Backed Relays 206
- 7.4 One-Shot Operation 207
- 7.5 Set and Reset 208
  - 7.5.1 Program Examples 212
- 7.6 Master Control Relay 213
  - 7.6.1 Examples of Programs 217
- Summary 218
- Problems 220
Chapter 8: Jump and Call 229
- 8.1 Jump 229
  - 8.1.1 Jumps Within Jumps 230
- 8.2 Subroutines 231
  - 8.2.1 Function Boxes 232
- Summary 235
- Problems 235
- Lookup Tasks 238
Chapter 9: Timers 239
- 9.1 Types of Timers 239
- 9.2 On-Delay Timers 240
  - 9.2.2 Cascaded Timers 242
  - 9.2.1 Sequencing 242
  - 9.2.3 On/Off Cycle Timer 244
- 9.3 Off-Delay Timers 245
- 9.4 Pulse Timers 246
- 9.5 Retentive Timers 248
- 9.6 Programming Examples 249
- Summary 250
- Problems 252
- Lookup Tasks 258
Chapter 10: Counters 259
- 10.2 Programming 259
  - 10.2.1 Counter Application 263
- 10.1 Forms of Counter 259
- 10.3 Up- and Down-Counting 265
- 10.4 Timers with Counters 266
- 10.5 Sequencer 268
- Summary 271
- Problems 272
- Lookup Tasks 280
Chapter 11: Shift Registers 281
- 11.1 Shift Registers 281
- 11.2 Ladder Programs 282
  - 11.2.1 A Sequencing Application 284
  - 11.2.2 Keeping Track of Items 284
- Summary 286
- Problems 287
- Lookup Tasks 291
Chapter 12: Data Handling 293
- 12.1 Registers and Bits 293
- 12.2 Data Handling 294
  - 12.2.1 Data Movement 294
  - 12.2.2 Data Comparison 296
  - 12.2.3 Data Selection 297
- 12.3 Arithmetic Functions 298
  - 12.3.1 Arithmetic Operations 298
- 12.4 Closed Loop Control 299
  - 12.4.1 Modes of Control 300
  - 12.4.2 Control with a PLC 302
- Summary 303
- Problems 303
- Lookup Tasks 307
Chapter 13: Designing Systems 309
- 13.1 Program Development 309
  - 13.1.1 Flowcharts and Pseudocode 309
- 13.2 Safe Systems 312
  - 13.2.1 PLC Systems and Safety 314
  - 13.2.2 Emergency Stop Relays 316
  - 13.2.3 Safety Functions 317
  - 13.2.4 Safety PLCs 318
- 13.3 Commissioning 318
  - 13.3.1 Testing Inputs and Outputs 319
  - 13.3.2 Testing Software 320
  - 13.3.3 Simulation 321
- 13.4 Fault Finding 322
  - 13.4.1 Fault Detection Techniques 322
  - 13.4.2 Program Storage 327
- 13.5 System Documentation 327
  - 13.5.1 Example of an Industrial Program 328
- Problems 350
- Summary 350
- Lookup Tasks 353
Chapter 14: Programs 355
- 14.1 Temperature Control 355
- 14.2 Valve Sequencing 361
  - 14.2.1 Cyclic Movement 361
  - 14.2.2 Sequencing 362
  - 14.2.4 Car Park Barrier Operation Using Valves 366
  - 14.2.3 Sequencing Using a Sequential Function Chart 366
  - 14.2.5 Controlled Reset of Cylinders 370
- 14.3 Conveyor Belt Control 371
  - 14.3.1 Bottle Packing 372
- 14.4 Control of a Process 378
- 14.5 A Selection Example: A Drinks Machine 381
- 14.6 A Data Comparison Example: A Fan Heater 381
- Problems 384
- Lookup Tasks 388
Appendix: Symbols 389
- Ladder Programs 389
- Function Blocks 390
  - Commonly Encountered Blocks 390
- Logic Gates 391
- Sequential Function Charts 392
- Structured Text 393
  - Operators 393
  - Conditional and Iteration Statements 394
- Instruction List (IEC 61131-3 Symbols) 393
- Answers 395
  - Chapter 2 395
  - Chapter 1 395
  - Chapter 3 396
  - Chapter 4 397
  - Chapter 5 398
  - Chapter 6 399
  - Chapter 7 401
  - Chapter 8 402
  - Chapter 9 402
  - Chapter 10 403
  - Chapter 11 404
  - Chapter 12 405
  - Chapter 13 406
  - Chapter 14 409
- Index 415

Author's affiliation

William Bolton: Formerly Lecturer, Buckingham Chilterns Unive

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