Chapter 1

PLC Introduction

1.1 Introduction

A group of engineers General Motors in 1968 was developed the first Programmable Logic Controller (PLC), when the companies were in search of an alternative to substitute complex relay control systems. The new control system had to meet the following requirements:

Consequent development resulted in a system, which allowed the binary signals simple connection. The conditions as to how these signals were to be linked were identified in the control program. It became feasible for the first time to plan signals on a display and to file these in electronic memories in this new systems. Three decades have left behind, during which the massive progress developed in the microelectronics development did not stop short of PLC. For example, even if program optimization and hence a reduction of required capacity of memory firstly still characterized a vital key task for the programmer, currently this is hardly of any importance. Furthermore, the functions range has grown significantly. Some years ago, analogue processing, process visualization or even the PLC utilization as a controller, were considered as Utopian. Presently, these functions support forms a fundamental part of many PLCs.


1.2 Areas of application of a PLC

Every machine or system has a controller. Dependent on the technology type used, controllers can be separated into hydraulic, pneumatic, electronic and electrical controllers. Often, a mixture of different technologies is applied. Moreover, differentiation is created between hard-wired programmable (e.g. wiring of electro-mechanical or electronic components) and PLCs. The initial is utilized principally in cases, where any reprogramming by the user is out of the query and the task size guarantees the development of a special controller.

Characteristic applications for such controllers can be found in cars, video cameras, and automatic washing machines. Nevertheless, if the task size does not guarantee the development of a special controller or if the user is to include the facility of setting timers and counters, or of making easy or independent program changes, then a universal controller use, where the program is written to a memory of electronic, is the ideal option? The PLC stands for such a universal controller. It can be applied for different applications and, through the program installed in its memory, offers the user with an easy means of changing, expanding and optimizing control processes... Read more this article by email