A solid-state relay is commonly used for PLC I/O to allow the controller to be reprogrammed without rewiring.

• A. It’s used for measurement
• B. Only used in DC
• C. True
• D. False

Answer: (C)

Solid-state relays provide fast, wear‑free switching with electrical isolation between the PLC and field devices. Because the wiring between the PLC I/O points and the field loads can stay the same, you can reassign or reprogram which outputs drive which loads without physically rewiring. The SSRs handle the switching under software control, so changing the PLC program changes the control logic without touch-up to the wiring. This is a practical reason SSRs are favored in PLC I/O, offering reliability and easy reconfiguration. They’re not primarily about measurement, and they can be used for different load types depending on the SSR, but the core idea—reprogramming with no rewiring—is why the statement is true.