In the last decade, the programmable logic controller (PLC) has become an integral part of industrial automation and computer-aided manufacturing. The PLC has changed considerably since its inception and now resembles a microprocessor, with its own architecture and programming languages. Thus an up-to-date book on this important subject is necessary. Michel’s book fills this need admirably.
The book has six chapters and a bibliography. Chapter 1, on the need for and idea of PLCs, discusses the objectives, functions, and technologies of industrial automation with simple examples. A brief discussion on PLC processors, instructions, and interfacing is followed by a brief account of the industrial constraints under which PLCs have to operate.
Chapter 2 describes the architecture of PLCs. This chapter is extraordinary. In roughly 80 pages, the author has compressed a large amount of basic information about PLCs. The chapter can be read quickly if you are a computer hardware engineer, but if you are barely familiar with how computer hardware works, this chapter will give you a quick and accurate tutorial on various aspects of PLCs. The chapter introduces the concept of a “bus,” then describes processors, registers, stacks, and the operation of central processors. Michel includes enough material on memories, the types of memories used, and the issues involved. He then goes on to discuss the processor and memory cycles, multiprocessor PLCs, and their architectures. The chapter also describes various methods of input-output used in industry, including bitwise, numerical, and analog I/O. The chapter ends with a discussion of system breakdown (called “system-security” in the text) and points to be considered in preventing breakdown. Throughout the chapter the concepts are illustrated with practical examples of PLCs manufactured in France (mainly) and the United States.
Chapter 3 covers the environment of PLCs. With the help of good illustrations and photographs of the American and French products, it describes different methods of communication between PLCs and operators. A discussion of the functions of different consoles is followed by descriptions of peripheral and auxiliary devices like simulators and printers. A brief but useful discussion on PLC networks, topologies, serial/parallel transmission, and communication closes the chapter.
Chapters 4 and 5 cover the software aspects of PLCs. They discuss how PLCs are programmed for particular industrial applications. Since each application has its own control requirements, which are affected by the program run on the PLC, it is necessary to develop languages in which one can describe the algorithms for control. Chapter 4 starts with the definition of processes, interrupts, and process creation and blocking. The author then describes graphical, literal, and future languages. Each is discussed with simple industrial examples. The coverage of logical, arithmetic, and input/output instructions is complete. Michel also covers extended instructions to describe looping, timers, counters, and so on. The chapter ends with a nice description of communication networks and various protocols, including MAP by General Motors. A brief discussion on Gould Modicon’s MODBUS network follows.
Chapter 5 is the second most interesting part of the book. It describes GRAFCET (state transition command graph), a method to represent the specifications of an automated system. GRAFCET was developed in France in 1978 and has become the prototype for PLC languages around the world. The instruction set chosen for examples is for small range machines such as the Texas 5TI. The author first discusses a small set of instructions, such as AND, OR, OUT, STORE, and COUNTER, with examples. He then extends them to more elaborate applications, which are illustrated by neat diagrams. A detailed discussion of how to use GRAFCET to describe an industrial problem and its control follows. The chapter then develops a complete example of the automation of a transfer machine with three stations, 21 inputs, and 20 outputs. Chapter 5 concludes with a discussion of GEMMA, which is used to represent procedures that make a system function, stop, or deal with breakdowns.
Chapter 6 focuses on the general aspects of PLCs. It discusses the evolution and state of the PLC market, its technical and economic aspects, evaluations of the commercial PLCs, and available choices.
The bibliography lists 26 books, surveys, reports, and theses. Most of these are in French.
This informative and nicely written book contains many good diagrams and photographs and a lot of commercial information. The translator should be commended for doing a great job. My complaints about the book are minor. It leans heavily on the French market and should have contained at least addresses of PLC manufacturers in the United States. A few more references to papers in English would have been helpful. The book is certainly useful for self-study, but it cannot be used as a textbook as there are no exercises. I recommend it highly, though it is probably not suitable for personal libraries because of the price. It will certainly become popular if the publisher makes a paperback edition available.
