advance plc rework

Control engineering has evolved over time. In the past humans were the main



method for controlling a system. More recently electricity has been used for control and


early electrical control was based on relays. These relays allow power to be switched on


and off without a mechanical switch. It is common to use relays to make simple logical


control decisions. The development of low cost computer has brought the most r ecent rev-


olution, the Programmable Logic Controller (PLC). The advent of the PLC began in the


1970s, and has become the most common choice for manufacturing controls.