What Is A Programmable Logic Controller?

A programmable logic controller (PLC) is an industrial computer designed to monitor inputs from various sensors and switches, execute a control program, and manage outputs to devices like motors and valves in real time, ensuring the seamless operation of factories and other industrial settings. Unlike general-purpose computers, PLCs are built to withstand harsh environments, operate on a deterministic cycle, and maintain high uptime without frequent reboots. They evolved from complex relay systems to software-based controllers, with the Modicon 084 recognized as the first PLC, which replaced relay logic with a software approach while retaining a familiar visual style for electricians. PLCs are essential in discrete, real-time control applications and are programmed using languages defined by the IEC 61131-3 standard, including Ladder Logic, Function Block Diagram, and Structured Text. While PLCs excel in specific control tasks, they are increasingly integrated with computer vision systems to handle perception tasks, such as quality inspection, by reading results from vision models as sensor inputs, allowing for enhanced automation without altering the core PLC control logic.