One function of a PLC input interface module is to

• A. Accept signals from field devices and convert them into signals that can be used by the processor
• B. Generate output signals
• C. Store programs
• D. Provide power

Answer: (A)

Reading external field signals and turning them into PLC‑readable data is what an input interface module does. It takes signals from sensors and switches, then conditions and translates those signals so the processor can interpret them—often converting voltage or current levels, isolating the signals for protection, and sometimes debouncing or filtering to ensure clean, reliable readings. The processor then sees simple digital states (on/off) or numerical values representing the sensed quantity.

This is distinct from an output module, which drives actuators, from memory that stores programs, and from the power supply that provides operating power. For example, a digital input might read a door switch as a high/low, while an analog input could convert a 4–20 mA temperature sensor signal into a usable numeric value for the processor.