Which statement describes the difference between PLC input logic and hardwired switches?

Which statement describes the difference between PLC input logic and hardwired switches?

• A. PLC can use either normally opened or normally closed logic with a single set of switch contacts
• B. PLC cannot simulate hardwired logic
• C. PLC must use separate contact for each logic state
• D. PLC always uses normally open contacts

Answer: (A)

In PLC input logic, you can decide how a switch's signal is interpreted in software, so the same physical contact can represent either normally open or normally closed behavior. By using a NO contact in the rung or by applying an inversion (or using a NC contact) in the ladder logic, the PLC can treat the input as true when the switch closes or as true when the switch opens. This flexibility means one set of switch contacts can implement either polarity without changing the hardware. In contrast, hardwired logic ties the behavior directly to the physical wiring, so you’d need different hardware (or wiring) to achieve the opposite logic.

In PLC input logic, you can decide how a switch's signal is interpreted in software, so the same physical contact can represent either normally open or normally closed behavior. By using a NO contact in the rung or by applying an inversion (or using a NC contact) in the ladder logic, the PLC can treat the input as true when the switch closes or as true when the switch opens. This flexibility means one set of switch contacts can implement either polarity without changing the hardware. In contrast, hardwired logic ties the behavior directly to the physical wiring, so you’d need different hardware (or wiring) to achieve the opposite logic.