A programmable logic controller (PLC) or programmable controller is a digital computer used for automation. It is a device which uses a programmable memory for user oriented instructions for implementing specific function. PLCs are used in many industries and machines.Instead of achieving the desired control or automation through physical wiring of control devices, in PLC it is achieved through a program or say software
1) The main difference from other computers is that PLCs are armored for severe conditions (such as dust, moisture, heat, cold) and have the facility for extensive input/output (I/O) arrangements.
2)PLCs read or senses limit switches, analog process variables (such as temperature and pressure), and the positions of complex positioning systems.
3)PLCs operate electric motors, pneumatic or hydraulic cylinders, magnetic relays, solenoids or analog outputs.