HISTORY OF PLC

HISTORICAL BACKGROUND SUMMARY

In 1968, a group of engineers from General Motors developed the concept of PLC with an initial specification. The PLC must be :-

1) Easy to program and reprogram
2) Easy to maintain and repair
3) More reliable in an industrial environment
4) Smaller in size than its relay equivalent
5) Cost competitive

Development of PLC

1968
The concept of PLC was developed

1969
A hardware CPU controller was used with logic instructions. It comes with 1K of memory and 128 I/O points.

1974
Using several processors within a PLC with add on timers and counters functions. Arithmetic operations are also included. This PLC has 12K of memory and 1024 I/O points.

1976
Remote I/O systems were introduced

1980
Intelligent I/O modules were developed

1983
Small low cost PLC’s were introduced

1985 onwards
With networking capabilities