A valve positioner compares a valve stem's position against the actuator's __________?

• A. Input Signal
• B. Output Signal
• C. Feedback
• D. Temperature

Answer: (A)

A valve positioner keeps the valve moving so that the actual stem position matches the command given to the actuator. It takes the control signal that represents the desired valve opening (the input signal, typically a 4–20 mA or similar command) and compares that to how far the stem actually is, using a feedback element to sense the real position. If there’s any difference, the positioner adjusts the air supply to the actuator to move the stem until the two match. This creates a precise, responsive control loop.

That’s why the referenced comparison uses the input signal—the target reference for positioning—rather than the output signal, a temperature, or the feedback alone.