__________ are used to control machines and other industrial applications with a computer instead of using relay logic.

• A. Programmable logic controllers
• B. Robots
• C. Sensors
• D. Programs

Answer: (A)

Programmable logic controllers are used to control machines and other industrial applications with a computer instead of using relay logic. A PLC is a rugged, purpose-built controller that continuously reads input signals from sensors, runs user-written logic, and updates outputs to actuators in real time. This replaces the hard-wired relay logic of older systems with software that can be easily modified, expanded, or integrated with other equipment. PLCs support ladder logic and other programming styles, timers, counters, and data handling, enabling complex control sequences and easier diagnostics. They also offer modular I/O, fault checking, and communication capabilities to connect with other devices and networks, which simplifies maintenance and scalability. Historically, relay-based control required extensive wiring and was difficult to change; PLCs reduce wiring, allow quick reprogramming, and centralize control. While robots and sensors play roles in automation, and programs are the instructions, the device that performs the control with a computer-based approach is the programmable logic controller.