Valve positioners are used on controlling valves where accurate and rapid control is required without error or hysterises.
Positioners are generally mounted on the side-yoke or top casing of the pneumatic actuator for linear sliding stem control valves, and at/near the end-of-shaft for rotary control vales.
Control Valve Positioner Circuit
For either basic design type, “mechanical feedback linkage” connected directly to the valve’s stem provides feedback to controller.
The process controller tells the positioner to “change” position; the feedback linkage reports back to the positioner confirming that a change has occurred and gives a “sense” of the magnitude of the change in position.