Preface
W. Bolton
Technological advances in recent years have resulted in the development of the programmable logic controller (PLC) and a consequential revolution of control engineering. This book, an introduction to PLCs, aims to ease the tasks of practicing engineers coming into contact with PLCs for the first time. It also provides a basic course for students in curricula such as the English technicians' courses for Nationals and Higher Nationals in engineering, giving full syllabus coverage of the National and Higher National in Engineering units and company training programs and serving as an introduction for first-year undergraduate courses in engineering.
The book addresses the problem of various programmable control manufacturers using different nomenclature and program forms by describing the principles involved and illustrating them with examples from a range of manufacturers. The text includes:
• The basic architecture of PLCs and the characteristics of commonly used input and outputs to such systems
• A discussion of the number systems: denary, binary, octal, hexadecimal, and BCD
• A painstaking methodical introduction, with many illustrations, describing how to program PLCs, whatever 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
• To assist the reader to develop the skills necessary to write programs for programmable logic controllers, many worked examples, multiple-choice questions, and problems are included in the book, with answers to all multiple-choice questions and problems given at the end of the book
Prerequisite Knowledge Assumed
This book assumes no background in computing. However, a basic knowledge of electrical and electronic principles is desirable.
Changes from the Fourth Edition
The fourth edition of this book was a complete restructuring and updating of the third edition and includes a more detailed consideration of IEC 1131-3, including all the programming methods given in the standard, and the problems of safety, including a discussion of emergency stop relays and safety PLCs. The fifth edition builds on this foundation by providing more explanatory text, more examples, and more problems and including with each chapter a summary of its key points.
Aims
This book aims to enable the reader to:
• Identify and explain the main design characteristics, internal architecture, and operating principles of programmable logic controllers.
• Describe and identify the characteristics of commonly used input and output devices.
• Explain the processing of inputs and outputs by PLCs.
• Describe communication links involved with PLC systems, the protocols, and networking methods.
• Develop ladder programs for the logic functions AND, OR, NOR, NAND, NOT, and XOR.
• Develop ladder programs involving internal relays, timers, counters, shift registers, sequencers, and data handling.
• Develop functional block diagram, instruction list, structured text, and sequential function chart programs.
• Identify safety issues with PLC systems.
• Identify methods used for fault diagnosis, testing, and debugging.
Structure of the Book
The figure on the following page outlines the structure of the book.
Acknowledgments
I am grateful to the many reviewers of the fourth edition for their helpful feedback and comments. These included:
Dr Hongwei Zang, of Sheffield Hallam University, England
Rini de Rooij
Michael Lorello, of Pitney Bowes
Jay Dowling
Harvey P. Jones
and those many reviewers from industry.
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