Which type of logic element uses a control relay?

• A. Memory
• B. Output
• C. Input
• D. Switch

Answer: (C)

A control relay functions as the interface bringing an external condition into the logic as a usable signal. The coil is energized by the input condition, and its contacts switch to provide a signal that the logic can read. This role—taking sensing or environmental conditions and turning them into a processing signal—fits with the input element category. Memory stores information, and outputs drive loads or actuate devices, but a control relay’s primary job in this context is to supply the logic with an input signal. So the type of logic element that uses a control relay is the input element.