What is a PLC?

• A. An electronic device that controls output devices based on input signals and a user-developed program
• B. A simple switch
• C. A type of sensor
• D. A motor controller

Answer: (A)

A PLC is an electronic control device that reads input signals, runs a user-programmed set of instructions, and then controls output devices based on that logic. It processes signals from sensors and switches, executes the stored program (often written in ladder logic or similar languages), and updates actuators like relays, valves, or motors to achieve automated behavior. This combination lets you implement complex control sequences, interlocks, timing, and decision-making in a single robust unit used in automation and manufacturing. A simple switch is just a passive device with no built-in programming to decide what happens next. A sensor only provides input data without performing control actions. A motor controller focuses on managing motor speed or torque, not the broader logic of how multiple inputs should steer a process.