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The 1st Programmable Logic Controller (PLC) originated by a group of engineers at General Motors, when the company were looking for an alternative to substitute 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 empowered the simple connection of binary signals. The requirements as to how these kinds of 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 ascreen and to file these in electronic memories.Since then, during which the enormous progress made in the development of microelectronics did not end shortof programmable logic controllers.
For instance, even if program optimization and thus a reduction of required memory capacity initially still represented an important key task for the programmer, nowadays this is hardly of any magnitude.Furthermore, the range of characteristics has grown considerably in process visualization, analogue processing or even the use of a PLC as a controller. Nowadays, the support of these capabilities forms an integral part of many PLCs.So this was the reason why PLC was used and introduced to market
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