A valve positioner compares the stem position of the valve actuator to what?

A valve positioner functions to ensure that the valve actuator's position aligns accurately with the desired setpoint, which is typically established by a control system. The positioner achieves this by comparing the actual position of the valve stem, often measured through a feedback mechanism, to a control signal received from the controller. This signal indicates the required position for the valve to achieve optimal control over the process, taking into account factors such as flow rates, pressure, and temperature.

By continuously measuring the stem position against the controller's output, the valve positioner can make necessary adjustments to the actuator to correct any discrepancies. This feedback loop is critical for maintaining process efficiency and stability. Therefore, the answer that indicates the valve positioner compares the stem position to the signal from the controller correctly captures the essential function of a valve positioner in automated control systems.