Which statement best describes relay outputs in PLCs interfaces with external devices?

Which statement best describes relay outputs in PLCs interfaces with external devices?

• A. It uses a triac to switch DC loads.
• B. It uses physical relay contacts inside the module to open and close the circuit.
• C. It cannot interface with output devices.
• D. It uses transistors to switch the circuit.

Answer: (B)

Relays in PLC output modules are electromechanical switches. When the output is energized, a coil inside the module pulls in contacts that physically open or close the external circuit. This design provides galvanic isolation between the PLC and the load and lets the PLC drive higher-current or higher-voltage devices like solenoids or motors through the contactors. It’s different from solid-state switching, which uses transistors or triacs to switch the load without moving parts. So, the mechanism described is the physical relay contacts inside the module opening and closing the circuit to the external device.

Relays in PLC output modules are electromechanical switches. When the output is energized, a coil inside the module pulls in contacts that physically open or close the external circuit. This design provides galvanic isolation between the PLC and the load and lets the PLC drive higher-current or higher-voltage devices like solenoids or motors through the contactors. It’s different from solid-state switching, which uses transistors or triacs to switch the load without moving parts. So, the mechanism described is the physical relay contacts inside the module opening and closing the circuit to the external device.