PLC or Programmable Logic Controller is well known control system used in the industries. They are used basically in electrotechnical industries for assembly lines and robotic devices. It is familiar for its used in the jagged digital computers. Deviceslike hard wired relays, timers and sequencers are replaced by PLC. It provides flexibility asit can be used in harsh environments and can withstand heat, cold, dust and moisture. PLC is coded using ladder log (a visual programming language). The programme is written on a computer and is fed to the microprocessor through a PLC cable. PLC uses a non-volatile memory to store the codes to retain them.
The use of PLC’s has been evolved for processing the analog signals and PID control. It has several advantages over relays because it is cost effective and user friendly. Not just that it is easy to program, maintain and troubleshoot.