A Programmable Logic Controller (PLC) is an industrial computer control system that has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, machines, robotic devices, or any activity that requires high reliability, ease of programming, and process fault diagnosis. PLCs were first developed in the automobile manufacturing industry to provide flexible, rugged, and easily programmable controllers to replace hard-wired relay logic systems. The functionality of the PLC has evolved over the years to include sequential relay control, motion control, process control, and more.
A PLC is an input-output system, which means that each unit both accepts inputs and controls outputs. It takes in inputs, whether from automated data capture points or from human input points such as switches or buttons, and based on its programming, the PLC then decides whether or not to change the output. A PLC’s outputs can control a huge variety of equipment, including motors, solenoid valves, lights, switchgear, safety shut-offs, and many others.
PLCs are flexible and robust control solutions, adaptable to almost any application. They can monitor and record run-time data such as machine productivity or operating temperature, automatically start and stop processes, generate alarms if a machine malfunctions, and more. PLCs are an example of a hard real-time system since output results must be produced in response to input conditions within a limited time, otherwise unintended operation will result.
