A programmable logic controller or PLC is a digital computer used for automation of industrial electro mechanical processes, such as control of machinery on factory assembly lines, amusement rides, or light fixtures. PLCs are used in many machines in many industries. Programmable logic controller are armored for severe conditions (such as dust, moisture, heat, cold), and have the facility for extensive input/output arrangements. These connect the PLC to sensors and actuators. PLCs read limit switches, analog process variables (such as temperature and pressure), and the positions of complex positioning systems.