Programmable Logic Controllers: Programming Methods and Applications

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Most textbooks related to programmable controllers start with the basics of ladder logic, Boolean algebra, contacts, coils and all the other aspects of learning to program PLCs. However, once they get more deeply into the subject, they generally narrow the field of view to one particular manufacturer's unit (usually one of the more popular brands and models), and concentrate on programming that device with it's capabilities and peculiarities. This is worthwhile if the desire is to learn to program that unit. However, after finishing the PLC course, the student will most likely be employed in a position designing, programming, and maintaining systems using PLCs of another brand or model, or even more likely, many machines with many different brands and models of PLC. It seems to the authors that it would be more advantageous to approach the study of PLCs using a general language that provides a thorough knowledge of programming concepts that can be adapted to all controllers. This language would be based on a collection of different manufacturer types with generally the same programming technique and capability. Although it would be impossible to teach one programming language and technique that would be applicable to each and every programmable controller on the market, the student can be given a thorough insight into programming methods with this general approach which will allow him or her to easily adapt to any PLC encountered. Therefore, the goal of this text is to help the student develop a good general working knowledge of programmable controllers with concentration on relay ladder logic techniques and how the PLC is connected to external components in an operating control system. In the course of this work, the student will be presented with real world programming problems that can be solved on any available programmable controller or PLC simulator. Later chapters in this text relate to more advanced subjects that are more suitable for an advanced course in machine controls. The authors desire that this text not only be used to learn programmable logic controllers, but also that this text will become part of the student’s personal technical reference library. Readers of this text should have a thorough understanding of fundamental ac and dc circuits, electronic devices (including thyristors), a knowledge of basic logic gates, flip flops, and Boolean algebra, and college algebra and trigonometry. Although a knowledge of calculus will enhance the understanding of PID controls, it is not required in order to learn how to properly tune a PID.