The Evolution Of The Programmable Logic Controller

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The Evolution Of The Programmable Logic Controller

The Evolution Of The Programmable Logic Controller


The first Programmable Logic Controller (PLC) was evolved by a group of engineers at General Motors in 1968, when the company were looking for an alternate to replace complex relay control systems.

The new control scheme had to rendezvous the next requirements:

Simple programming

Program changes without scheme intervention (no interior rewiring)

Smaller, cheaper and more dependable than corresponding relay control systems

Simple, reduced cost maintenance

Subsequent development produced in a scheme, which endowed the sim- ple connection of binary signals. The obligations as to how these sig- nals were to be connected were specified in the control program. With the new schemes it became likely for the first time to contrive pointers on a screen and to document these in electronic memories.

Since then, three decades have passed, throughout which the enormous progress made in the development of microelectronics did not halt short of programmable logic controllers. For instance, even if program optimi- sation and therefore a reduction of needed recollection capacity primarily still rep- resented an significant key task for the programmer, nowadays this is hardly of any significance. Moreover, the variety of functions has developed 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 types an integral part of numerous PLCs. The next sheets in this introductory chapter summarize the basic design of a PLC simultaneously with the currently most significant jobs and applications.


Programmable logic controllers typically contain a variable number of input/output (I/O) docks, and are generally Reduced Instruction Set Computer (RISC) based. They are conceived for real-time use, and often should withstand rough environments on the shop floor. The programmable logic controller circuitry monitors the rank of multiple sensor inputs, which control yield actuators, which may be things like engine starters, solenoids, lights and exhibitions, or valves.

This controller has made a significant contribution to factory automation. Earlier automation schemes had to use thousands of one-by-one relays and cam timers. In numerous cases, a PLC permits all of the relays and timers inside a factory scheme to be replaced with a lone controller. Today, programmable logic controllers consign a broad variety of functionality, including basic relay control, shift control, process control, and complex networking, as well as being utilised in circulated control ...
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