PLCs replace which type of hardwired devices?

PLCs replace which type of hardwired devices?

• A. Relay coils and contacts
• B. Microprocessors
• C. Sensors
• D. Actuators

Answer: (A)

PLCs replace relay-based logic used in older control circuits. In hardwired control, the logic is built from relay coils and their contacts wired together to perform sequencing and interlocks. A PLC uses a ladder-logic style program that mimics that same relay behavior: inputs are evaluated, rungs determine which outputs should energize, and the corresponding outputs drive actuators. So the PLC effectively substitutes the physical relay coils and contacts with software-controlled coils, while sensors provide inputs and actuators respond to the PLC outputs. The other options don’t fit because microprocessors are what make up the PLC itself, sensors supply data, and actuators are the devices driven by the PLC, not the hardware that the PLC replaces in legacy systems.

PLCs replace relay-based logic used in older control circuits. In hardwired control, the logic is built from relay coils and their contacts wired together to perform sequencing and interlocks. A PLC uses a ladder-logic style program that mimics that same relay behavior: inputs are evaluated, rungs determine which outputs should energize, and the corresponding outputs drive actuators. So the PLC effectively substitutes the physical relay coils and contacts with software-controlled coils, while sensors provide inputs and actuators respond to the PLC outputs. The other options don’t fit because microprocessors are what make up the PLC itself, sensors supply data, and actuators are the devices driven by the PLC, not the hardware that the PLC replaces in legacy systems.