Bolton Programmable Logic Controllers

6. Auflage 2015
ISBN: 978-0-08-100353-4
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, 424 Seiten

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

Former Lecturer at Buckingham Chilterns University College, High Wycombe, UK, and now retired, William Bolton has worked in industry and academia as a senior lecturer in a college of technology, a member of the Nuffield Advanced Physics team, an adviser to a British government aid project in Brazil on technical education, as a UNESCO consultant in Argentina and Thailand, and as Head of Research and Development at the Business and Technician Education Council. He has written many engineering textbooks, including Mechatronics, 4th ed., Engineering Science, 5th ed., Higher Engineering Science, 2nd ed., Mechanical Science, 3rd ed., and Instrumentation and Control Systems.

Autoren/Hrsg.

Bolton, William

Inhaltsverzeichnis

1;Front Cover;1
2;Programmable Logic Controllers;4
3;Copyright;5
4;Contents;6
5;Preface;10
5.1;Prerequisite Knowledge Assumed;11
5.2;Changes from the Fifth Edition;11
5.2.1;Aims;11
5.3;Structure of the Book;12
6;Acknowledgments;13
7;Chapter 1: Programmable Logic Controllers;14
7.1;1.1 Controllers;14
7.1.1;1.1.1 Relay-Controlled Systems;16
7.1.2;1.1.2 Microprocessor-Controlled Systems;17
7.1.3;1.1.3 The Programmable Logic Controller;18
7.2;1.2 Hardware;20
7.3;1.3 PLC Architecture;22
7.3.1;1.3.1 Input/Output Unit;22
7.3.2;1.3.2 Sourcing and Sinking;24
7.4;1.4 PLC Systems;25
7.4.1;1.4.1 Security;28
7.5;1.5 Programs;29
7.5.1;1.5.1 The IEC Standard;30
7.5.2;1.5.2 Programming PLCs;32
7.6;Summary;33
7.7;Problems;34
7.8;Lookup Tasks;35
8;Chapter 2: Input/Output Devices;36
8.1;2.1 Input Devices;36
8.1.1;2.1.1 Mechanical Switches;39
8.1.2;2.1.2 Proximity Switches;42
8.1.3;2.1.3 Photoelectric Sensors and Switches;43
8.1.4;2.1.4 Encoders;44
8.1.5;2.1.5 Temperature Sensors;46
8.1.6;2.1.6 Position/Displacement Sensors;50
8.1.7;2.1.7 Strain Gauges;51
8.1.8;2.1.8 Pressure Sensors;53
8.1.9;2.1.9 Liquid-Level Detectors;54
8.1.10;2.1.10 Fluid Flow Measurement;54
8.1.11;2.1.11 Ultrasonic Proximity Sensors;55
8.1.12;2.1.12 Smart Sensors;55
8.1.13;2.1.13 Sensors Ranges;56
8.2;2.2 Output Devices;56
8.2.1;2.2.1 Relay;56
8.2.2;2.2.2 Directional Control Valves;57
8.2.3;2.2.3 Motors;59
8.2.4;2.2.4 Stepper Motors;62
8.3;2.3 Examples of Applications;66
8.3.1;2.3.1 A Conveyor Belt;66
8.3.2;2.3.2 A Lift;66
8.3.3;2.3.3 A Robot Control System;67
8.3.4;2.3.4 Liquid-Level Monitoring;68
8.3.5;2.3.5 Packages on Conveyor Belt Systems;68
8.4;Summary;69
8.5;Problems;70
8.6;Lookup Tasks;74
9;Chapter 3: Digital Systems;76
9.1;3.1 The Binary System;77
9.2;3.2 Octal and Hexadecimal;77
9.2.1;3.2.1 Octal System;78
9.2.2;3.2.2 Hexadecimal System;79
9.3;3.3 Binary Coded Decimals;79
9.4;3.4 Numbers in the Binary, Octal, Hex, and BCD Systems;80
9.5;3.5 Binary Arithmetic;81
9.5.1;3.5.1 Signed Numbers;82
9.5.2;3.5.2 One's and Two's Complements;82
9.5.3;3.5.3 Floating Point Numbers;83
9.6;3.6 PLC Data;84
9.7;3.7 Combinational Logic Systems;85
9.8;3.8 Sequential Logic Systems;86
9.8.1;3.8.1 Latches;86
9.8.2;3.8.2 Flip-Flops;88
9.9;Summary;88
9.10;Problems;90
9.11;Lookup Tasks;91
10;Chapter 4: I/O Processing;92
10.1;4.1 Input/Output Units;92
10.1.1;4.1.1 Input Units;92
10.1.2;4.1.2 Output Units;95
10.2;4.2 Signal Conditioning;98
10.2.1;4.2.1 Changing Voltage Levels;99
10.2.2;4.2.2 Op-Amp Comparator;101
10.2.3;4.2.3 Output Protection;102
10.3;4.3 Remote Connections;102
10.3.1;4.3.1 Serial and Parallel Communications;103
10.3.2;4.3.2 Serial Standards;104
10.3.3;4.3.3 Parallel Standards;107
10.3.4;4.3.4 Protocols;109
10.3.5;4.3.5 ASCII Codes;111
10.4;4.4 Networks;112
10.4.1;4.4.1 Distributed Systems;113
10.4.2;4.4.2 Network Standards;114
10.5;4.5 Examples of Commercial Systems;116
10.5.1;4.5.1 MAP;116
10.5.2;4.5.2 Ethernet;117
10.5.3;4.5.3 ControlNet;118
10.5.4;4.5.4 DeviceNet;118
10.5.5;4.5.5 Allen-Bradley Data Highway;119
10.5.6;4.5.6 PROFIBUS;119
10.5.7;4.5.7 Factory-Floor Network;119
10.6;4.6 Processing Inputs;119
10.7;4.7 I/O Addresses;121
10.8;Summary;122
10.9;Problems;123
10.10;Lookup Tasks;126
11;Chapter 5: Ladder and Functional Block Programming;128
11.1;5.1 Ladder Diagrams;128
11.1.1;5.1.1 PLC Ladder Programming;130
11.2;5.2 Logic Functions;133
11.2.1;5.2.1 AND;133
11.2.2;5.2.2 OR;134
11.2.3;5.2.3 NOT;136
11.2.4;5.2.4 NAND;137
11.2.5;5.2.5 NOR;138
11.2.6;5.2.6 Exclusive OR (XOR);139
11.3;5.3 Latching;140
11.4;5.4 Multiple Outputs;140
11.5;5.5 Entering Programs;142
11.5.1;5.5.1 Ladder Symbols;143
11.6;5.6 Function Blocks;143
11.6.1;5.6.1 Logic Gates;143
11.6.2;5.6.2 Boolean Algebra;148
11.7;5.7 Program Examples;151
11.7.1;5.7.1 Location of Stop Switches;153
11.8;Summary;154
11.9;Problems;155
11.10;Lookup Tasks;163
12;Chapter 6: IL, SFC, and ST Programming Methods;164
12.1;6.1 Instruction Lists;164
12.1.1;6.1.1 Ladder Programs and Instruction Lists;166
12.1.2;6.1.2 Branch Codes;168
12.1.3;6.1.3 More Than One Rung;171
12.1.4;6.1.4 Programming Examples;172
12.2;6.2 Sequential Function Charts;173
12.2.1;6.2.1 Branching and Convergence;176
12.2.2;6.2.2 Actions;178
12.2.3;6.2.3 Programming a PLC;180
12.3;6.3 Structured Text;180
12.3.1;6.3.1 Conditional Statements;182
12.3.2;6.3.2 Iteration Statements;184
12.3.3;6.3.3 Structured Text Programs;185
12.3.4;6.3.4 Comparison with Ladder Programs;187
12.4;Summary;187
12.5;Problems;188
13;Chapter 7: Internal Relays;200
13.1;7.1 Internal Relays;200
13.2;7.2 Ladder Programs;201
13.2.1;7.2.1 Programs with Multiple Input Conditions;201
13.2.2;7.2.2 Latching Programs;203
13.2.3;7.2.3 Response Time;204
13.3;7.3 Battery-Backed Relays;205
13.4;7.4 One-Shot Operation;206
13.5;7.5 Set and Reset;207
13.5.1;7.5.1 Program Examples;211
13.6;7.6 Master Control Relay;212
13.6.1;7.6.1 Examples of Programs;216
13.7;Summary;217
13.8;Problems;219
14;Chapter 8: Jump and Call;228
14.1;8.1 Jump;228
14.1.1;8.1.1 Jumps Within Jumps;229
14.2;8.2 Subroutines;230
14.2.1;8.2.1 Function Boxes;231
14.3;Summary;234
14.4;Problems;234
14.5;Lookup Tasks;237
15;Chapter 9: Timers;238
15.1;9.1 Types of Timers;238
15.2;9.2 On-Delay Timers;239
15.2.1;9.2.1 Sequencing;241
15.2.2;9.2.2 Cascaded Timers;241
15.2.3;9.2.3 On/Off Cycle Timer;243
15.3;9.3 Off-Delay Timers;244
15.4;9.4 Pulse Timers;245
15.5;9.5 Retentive Timers;247
15.6;9.6 Programming Examples;248
15.7;Summary;249
15.8;Problems;251
15.9;Lookup Tasks;257
16;Chapter 10: Counters;258
16.1;10.1 Forms of Counter;258
16.2;10.2 Programming;258
16.2.1;10.2.1 Counter Application;262
16.3;10.3 Up- and Down-Counting;264
16.4;10.4 Timers with Counters;265
16.5;10.5 Sequencer;267
16.6;Summary;270
16.7;Problems;271
16.8;Lookup Tasks;279
17;Chapter 11: Shift Registers;280
17.1;11.1 Shift Registers;280
17.2;11.2 Ladder Programs;281
17.2.1;11.2.1 A Sequencing Application;283
17.2.2;11.2.2 Keeping Track of Items;283
17.3;Summary;285
17.4;Problems;286
17.5;Lookup Tasks;290
18;Chapter 12: Data Handling;292
18.1;12.1 Registers and Bits;292
18.2;12.2 Data Handling;293
18.2.1;12.2.1 Data Movement;293
18.2.2;12.2.2 Data Comparison;295
18.2.3;12.2.3 Data Selection;296
18.3;12.3 Arithmetic Functions;297
18.3.1;12.3.1 Arithmetic Operations;297
18.4;12.4 Closed Loop Control;298
18.4.1;12.4.1 Modes of Control;299
18.4.2;12.4.2 Control with a PLC;301
18.5;Summary;302
18.6;Problems;302
18.7;Lookup Tasks;306
19;Chapter 13: Designing Systems;308
19.1;13.1 Program Development;308
19.1.1;13.1.1 Flowcharts and Pseudocode;308
19.2;13.2 Safe Systems;311
19.2.1;13.2.1 PLC Systems and Safety;313
19.2.2;13.2.2 Emergency Stop Relays;315
19.2.3;13.2.3 Safety Functions;316
19.2.4;13.2.4 Safety PLCs;317
19.3;13.3 Commissioning;317
19.3.1;13.3.1 Testing Inputs and Outputs;318
19.3.2;13.3.2 Testing Software;319
19.3.3;13.3.3 Simulation;320
19.4;13.4 Fault Finding;321
19.4.1;13.4.1 Fault Detection Techniques;321
19.4.2;13.4.2 Program Storage;326
19.5;13.5 System Documentation;326
19.5.1;13.5.1 Example of an Industrial Program;327
19.6;Summary;349
19.7;Problems;349
19.8;Lookup Tasks;352
20;Chapter 14: Programs;354
20.1;14.1 Temperature Control;354
20.2;14.2 Valve Sequencing;360
20.2.1;14.2.1 Cyclic Movement;360
20.2.2;14.2.2 Sequencing;361
20.2.3;14.2.3 Sequencing Using a Sequential Function Chart;365
20.2.4;14.2.4 Car Park Barrier Operation Using Valves;365
20.2.5;14.2.5 Controlled Reset of Cylinders;369
20.3;14.3 Conveyor Belt Control;370
20.3.1;14.3.1 Bottle Packing;371
20.4;14.4 Control of a Process;377
20.5;14.5 A Selection Example: A Drinks Machine;380
20.6;14.6 A Data Comparison Example: A Fan Heater;380
20.7;Problems;383
20.8;Lookup Tasks;387
21;Appendix: Symbols;388
21.1;Ladder Programs;388
21.2;Function Blocks;389
21.2.1;Commonly Encountered Blocks;389
21.3;Logic Gates;390
21.4;Sequential Function Charts;391
21.5;Instruction List (IEC 61131-3 Symbols);392
21.6;Structured Text;392
21.6.1;Operators;392
21.6.2;Conditional and Iteration Statements;393
22;Answers;394
22.1;Chapter 1;394
22.2;Chapter 2;394
22.3;Chapter 3;395
22.4;Chapter 4;396
22.5;Chapter 5;397
22.6;Chapter 6;398
22.7;Chapter 7;400
22.8;Chapter 8;401
22.9;Chapter 9;401
22.10;Chapter 10;402
22.11;Chapter 11;403
22.12;Chapter 12;404
22.13;Chapter 13;405
22.14;Chapter 14;408
23;Index;414

Leseproben

Chapter 1 Programmable Logic Controllers
Abstract
This chapter is an introduction to control systems, starting with a discussion of relay-controlled systems before discussing the programmable logic controller (PLC) and its general function, hardware forms, and internal architecture. PLCs are widely used for a range of automation tasks in such areas as industrial processes in manufacturing. The IEC standard 61131 is outlined. This overview is followed by more detailed discussion in the following chapters. Keywords Relay-controlled systems. Programmable logic controller IEC 61131 This chapter is an introduction to the programmable logic controller (PLC) and its general function, hardware forms, and internal architecture. PLCs are widely used for a range of automation tasks in areas such as industrial processes in manufacturing. This overview is followed by more detailed discussion in the following chapters. For a summary of the history, development, features, and comparison with other control systems, see the Wikipedia entry for Programmable logic controller. 1.1 Controllers
What type of task might a control system handle? It might be required to control a sequence of events, maintain some variable constant, or follow some prescribed change. For example, the control system for an automatic drilling machine (Figure 1.1a) might be required to start lowering the drill when the workpiece is in position, start drilling when the drill reaches the workpiece, stop drilling when the drill has produced the required depth of hole, retract the drill, and then switch off and wait for the next workpiece to be put in position before repeating the operation. Another control system (Figure 1.1b) might be used to control the number of items moving along a conveyor belt and direct them into a packing case. The inputs to such control systems might come from switches being closed or opened; for example, the presence of the workpiece might be indicated by it moving against a switch and closing it, or other sensors such as those used for temperature or flow rates. The controller might be required to run a motor to move an object to some position or to turn a valve, or perhaps a heater, on or off. Figure 1.1 An example of a control task and some input sensors: (a) an automatic drilling machine; (b) a packing system. What form might a controller have? For the automatic drilling machine, we could wire up electrical circuits in which the closing or opening of switches would result in motors being switched on or valves being actuated. Thus, as a result, we might have a relay (Figure 1.2) closing or opening contacts which, in turn, switches on the current to a motor and causes the drill to rotate (Figure 1.3). Another switch might be used to activate a relay and switch on the current to a pneumatic or hydraulic valve, which results in pressure being switched to drive a piston in a cylinder and so results in the workpiece being pushed into the required position. Such electrical circuits would have to be specific to the automatic drilling machine. For controlling the number of items packed into a packing case, we could likewise wire up electrical circuits involving sensors and motors. However, the controller circuits we devised for these two situations would be different. In the “traditional” form of control system, the rules governing the control system and when actions are initiated are determined by the wiring. When the rules used for the control actions are changed, the wiring has to be changed. Figure 1.2 A basic relay. Figure 1.3 A control circuit. 1.1.1 Relay-Controlled Systems
Relay-controlled systems are hard-wired systems. Figure 1.2 shows the basic elements of a simple relay. When a current is switched on to flow through the relay solenoid, normally-closed (NC) contacts open and normally-open (NO) contacts close. These contacts can be used to give control in a system. As an illustration consider a relay being used to operate a pneumatic or hydraulic valve, this then results in pressure being applied to drive a piston to move a workpiece. We can represent the situation by a control drawing. Figure 1.4 shows the standard symbols used for relays and Figure 1.5 shows the control drawing with the vertical lines representing the power rails and the horizontal lines to systems connected between them. The sequence of events is read from the top horizontal line downwards. Thus, in the top line of Figure 1.5(a), when the Off–On switch is closed, the relay is activated. This closes the contacts on the second line and so the solenoid valve is switched on. A more usual control drawing is shown in Figure 1.5(b) which has the relay switched on by a momentary NO push-button switch. This closes two sets of contacts. Contacts 1 latch the push button switch so that when the push stops there is still connection of power to the relay. Contacts 2 switch on the solenoid valve. The relay, and hence power to the solenoid valve, is switched off when the normally closed push-button switch is pressed. The control drawings are obviously only part of the control system as there will need to be further lines for when the solenoid valve has moved the workpiece the required distance so that it stops its action. Figure 1.4 Relay symbols. Figure 1.5 Relay-controlled system control drawings. Figure 1.6 shows another example of a relay control system. When the start push button is closed, the relay coil is switched on and latches the push button switch so that the relay remains on until the stop push button is pressed. The relay closes the NO contacts and opens the NC contacts. As a result, the green light is switched on and the red light switches off. When the stop push button is pressed, the current to the relay coil is switched off. This results in the NO contacts opening and the NC contacts closing and so the green light going off and the red light comes on. The next stage in the relay circuit might be a motor that is switched on by NO contacts, so the green light indicates when the motor is running and the red light when it is off. Figure 1.6 Relay circuit to control red and green lights. 1.1.2 Microprocessor-Controlled Systems
Instead of hardwiring each control circuit for each control situation, we can use the same basic system for all situations if we use a microprocessor-based system and write a program to instruct the microprocessor how to react to each input signal from, say, switches and give the required outputs to, say, motors and valves. Thus we might have a program of the form: If switch A closes Output to motor circuit If switch B closes Output to valve circuit By changing the instructions in the program, we can use the same microprocessor system to control a wide variety of situations. As an illustration, the modern domestic washing machine uses a microprocessor system. Inputs to it arise from the dials used to select the required wash cycle, a switch to determine that the machine door is closed, a temperature sensor to determine the temperature of the water, and a switch to detect the level of the water. On the basis of these inputs the microprocessor is programmed to give outputs that switch on the drum motor and control its speed, open or close cold and hot water valves, switch on the drain pump, control the water heater, and control the door lock so that the machine cannot be opened until the washing cycle is completed. 1.1.3 The Programmable Logic Controller
A programmable logic controller (PLC) is a special form of microprocessor-based controller that uses programmable memory to store instructions and to implement functions such as logic, sequencing, timing, counting, and arithmetic in order to control machines and processes (Figure 1.7). It is designed to be operated by engineers with perhaps a limited knowledge of computers and computing languages. They are not designed so that only computer programmers can set up or change the programs. Thus, the designers of the PLC have preprogrammed it so that the control program can be entered using a simple, rather intuitive form of language (see Chapter 4). The term logic is used because programming is primarily concerned with implementing logic and switching operations; for example, if A or B occurs, switch on C; if A and B occurs, switch on D. Input devices (that is, sensors such as switches) and output devices (motors, valves, etc.) in the system being controlled are connected to the PLC. The operator then enters a sequence of instructions, a program, into the memory of the PLC. The controller then monitors the inputs and outputs according to this program and carries out the control rules for which it has been programmed. Figure 1.7 A programmable logic controller. PLCs have the great advantage that the same basic controller can be used with a wide range of control systems. To modify a control system and the rules that are to be used, all that is necessary is for an operator to key in a different set of instructions. There is no need to rewire. The result is a flexible, cost-effective system that can be used with control systems, which vary...