PLC stands for programmable logic controller
PLC is an abbreviation for programmable logic controller. Up until about 1980 in industry, motors, valves and other aggregates were controled with contactors, which are large relays. This kind of electrical connection was complicated and expensive to change. Then came PLC and brought a huge change with it: software development became part of automation technology. A PLC is a small computer which does not have either a keyboard or screen. The task of PLC is to create certain logical links by using switch and sensor signals, and by giving certain signals to the outputs. These outputs are forwarded to the contactors, valves, etc. For example, a connection is if when ‘button pushed’ and ‘light barrier free’ then motor on’. This PLC control is programmed on a normal PC with a development environment suitable for the PLC. The language of the first PLC is similar to an assembler. Nowadays, C and PASCAL are also available as PLC languages.
PLC lets machines communicate with each other
If the program or parts of it are finished being created, it is easy to transfer it to PLC. Again and again, PLC learned to communicate with other PLC, bar code readers, printers and PCs. This was a historical quantum leap, because from now on machines could not remain stubborn and difficult, but instead became flexible “thoughtful” and could communicate with one another. Nowadays, PLC control can work with data produced by other computers. In contrast to (earlier) hardware “wiring”, today most machine control is done via software. This makes them much more flexible and able to offer significantly more features.
You can find more information on PLC on Wikipedia: https://en.wikipedia.org/wiki/Programmable_logic_controller