The Programmable Logic Controller (PLC) is a ruggedized industrial computer that is specifically designed for the reliable control of manufacturing processes and machinery. PLCs are the workhorses of industrial automation, used in assembly lines, robotic devices, and process control systems. They are engineered to operate in harsh factory environments, withstanding extreme temperatures, humidity, vibration, and electrical noise. The primary function of a PLC is to read input signals from various sensors and switches (e.g., proximity sensors, push buttons, temperature sensors), execute a user-written control program based on these inputs, and then actuate output devices like motors, solenoids, lights, or relays.
What distinguishes PLCs from general-purpose computers is their focus on real-time I/O (Input/Output) control and their extreme reliability. The most common programming language used for PLCs is Ladder Logic, a graphical language that mimics the appearance of electrical relay schematics, making it intuitive for plant technicians and electricians. In a system involving a programmable power supply, a PLC might act as the master controller. It could, for example, read a barcode from a product, then command the power supply (via an interface like CC-Link or PROFINET) to apply a specific voltage sequence to test the product, and finally read the measurement results to determine if the product passes or fails.