Where are Programmable Logic Controllers used in real world applications?
PLCs are used anywhere that you previously would have used relay logic. Unitary PLCs are the low end of complexity and are used for simple applications like controlling a pair of pumps where you want to alternate from one to the other under low demand or start both if one can’t keep up. Modular PLCs are used when you need more inputs and/or outputs than a unitary device provides. We use Modular PLCs to monitor safety devices and limits on several large diesel generators, a major gantry crane and several large high voltage motors. Rack Mounted PLCs can be either Unitary or modular and allow ease of change out in the event of a problem and centralized control for large installations where a number of individual devices are required. An example would be PLCs for controlling a bank of elevators in a major office building.
