Glossary · Process instrumentation and analytical measurement
Valve positioner
Also known as: Positioner, Digital valve positioner
German: Stellungsregler
In process automation, a valve positioner is a device mounted on a control valve actuator that compares the setpoint from the control system with the measured valve stem position and adjusts the actuator, usually pneumatically, until the valve reaches the required position.
- Process instrumentation
- Process industry
In one sentence
A valve positioner compares the setpoint with the actual valve position and adjusts the actuator until the control valve reaches it.
Example
A digital valve positioner receives a 4–20 mA setpoint, positions the steam valve accordingly and reports the actual position and valve diagnostics via HART.
How it applies
- Engineering: Positioners overcome friction and process forces and improve control accuracy. The fail action on loss of signal or air (open, closed or hold) is determined by the actuator and positioner design and must suit the process.
- Commissioning: An automatic initialization adapts the positioner to the actuator and stroke. Check stroke direction, characteristic and end positions.
- Maintenance: Digital positioners record diagnostics such as friction, deviation and travel, which support Predictive maintenance of valves.
- Safety: When a valve is part of a safety instrumented function, the positioner's behavior on trip must be assessed; a positioner is not automatically suitable to perform the safety action.
- Documentation: Record the fail action, the initialization data and the configured characteristic in the valve data and maintenance documentation.