___ can be connected to the input terminals of a programmable controller.

• A. A pushbutton switch
• B. A foot switch
• C. NC contacts of a timing relay
• D. Any of these

Answer: (D)

Input terminals on a programmable controller are meant to sense simple on/off signals created by switch contacts. Any device that can close or open a circuit to the input can feed a signal to the PLC. A pushbutton switch is the classic example: when pressed, it closes and the PLC sees a logic input. A foot switch works the same way, providing a hands-free active signal. The NC (normally closed) contacts of a timing relay also act as a switch; depending on the relay’s state, they can either pass or block current to the PLC input, producing the desired logic once wired correctly. As long as the voltage/current levels meet the input module’s specifications and the wiring matches the intended logic (NO vs NC), all of these can be connected to PLC inputs. That’s why the correct choice is that any of these can be connected.