A Programmable Logic Controller (PLC) works by continuously reading inputs, processing them based on a pre-written program, and sending outputs to control machines or processes. In simple terms, it acts as the brain of an automation system. The PLC receives signals from input devices like sensors, switches, or buttons, checks the conditions defined in the program, and decides what action to take — such as turning ON a motor, activating an alarm, or opening a valve.
The PLC works in a repeating cycle called the scan cycle, which has three main steps — Read, Execute, and Write. First, it reads all input signals. Next, it executes the logic written in the programming language (like Ladder Diagram or Function Block Diagram). Finally, it updates the outputs according to the results. This cycle runs many times per second, allowing real-time control. So, a PLC works by continuously monitoring inputs, executing logic, and controlling outputs to keep industrial machines running safely and efficiently.