A programmable logic controller is a type of tiny computer that can receive data through its inputs and send operating instructions through its outputs. Fundamentally, a PLC’s job is to control a system’s functions using the internal logic programmed into it. Medium PLC will be having 64 to 1024 IOs.
Input/output (or I/O) is central to every PLC. I/O is the connection of the controller to the outside world and to the machine or process being controlled. Inputs to the PLC can be either voltages or currents representing physical variables or the status of devices such as switches, motors, or lights. A programmable logic controller (PLC) is a small, modular solid state computer with customized instructions for performing a particular task. PLCs, which are used in industrial control systems (ICS) for a wide variety of industries, have largely replaced mechanical relays, drum sequencers and cam timers.
PLC are divided into three types based on output namely Relay output, Transistor output, and Triac Output PLC. There are three basic types of controllers: on-off, proportional and PID. Depending upon the system to be controlled, the operator will be able to use one type or another to control the process.
