TP301 Festo Didactic B-1 Chapter 1 The PLC in automation technology 1.1 Introduction The first Programmable Logic Controller (PLC) was developed by a group of engineers at … … Motors in 1968, when the company were looking for an alternative to replace complex relay control systems. The new control system had to meet the following requirements:* Simple programming* Program changes without system intervention(no internal rewiring)* Smaller, cheaper and more reliable than corresponding relay control systems* Simple, …

The PLC in automation technology 1.1 Introduction The first Programmable Logic Controller (PLC) was developed by a group of engineers at General Motors in 1968, when the company were looking for an alternative to replace complex relay control systems. The new control system had to meet the following requirements: * Simple programming * Program changes without system intervention (no internal rewiring) * Smaller, cheaper and more reliable than corresponding relay control systems * Simple, low cost maintenance Subsequent development resulted in a system, which enabled the simple connection of binary signals. The requirements as to how these signals were to be connected were specified in the control program. With the new systems it became possible for the first time to plot signals on a screen and to file these in electronic memories. Since then, three decades have passed, during which the enormous progress made in the development of microelectronics did not stop short of programmable logic controllers. For instance, even if program optimisation and thus a reduction of required memory capacity initially still represented an important key task for the programmer, nowadays this is hardly of any significance. Moreover, the range of functions has grown considerably. 15 years ago, process visualisation, analogue processing or even the use of a PLC as a controller, were considered as Utopian. Nowadays, the support of these functions forms an integral part of many PLCs. The following pages in this introductory chapter outline the basic design of a PLC together with the currently most important tasks and applications. 1.2 Areas of application of a PLC Every system or machine has a controller. Depending on the type of technology used, controllers can be divided into pneumatic, hydraulic, electrical and electronic controllers. Frequently, a combination of different technologies is used. Furthermore, differentiation is made between hard-wired programmable (e.g. wiring of electro-mechanical or electronic components) and programmable logic controllers. The first is used primarily in cases, where any reprogramming by the user is out of the question and the job size warrants the development of a special controller. Typical applications for such controllers can be found in automatic washing machines, video cameras, and cars. However, if the job size does not warrant the development of a special controller or if the user is to have the facility of making simple or independent program changes, or of setting timers and counters, then the use of a universal controller, where the program is written to an electronic memory, is the preferred option. The PLC represents such a universal controller. It can be used for different applications and, via the program installed in its memory, provides the user with a simple means of changing, extending and optimising control processes.

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