Karthikeyan Mahalingam, Cypress Semiconductor and Immanuel Rathinam, iWave Systems
EETimes 11/17/2010 5:04 PM EST
A Programmable Logic Controller (PLC) is a specialized computing system widely used to control real-time industrial processes and assemblies. The block diagram of a generic PLC is shown in Figure 1.
The PLC scans the states of inputs and controls the states of outputs through a CPU. The user program that has the control logic for CPU is stored in program memory. Examples of inputs are switches, push buttons, and sensors like those used to sense proximity, temperature, pressure, etc. Examples of outputs are relays, valves, solenoid, actuator, motor, fans, alarm, etc. There may also be a communication interface to other terminals in the system.