The post AutoQuiz: What Is the Purpose of a Valve Positioner? first appeared on the ISA Interchange blog site.
This automation industry quiz question comes from the ISA Certified Control Systems Technician (CCST) program. Certified Control System Technicians calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables. Click this link for more information about the CCST program.
a) for control valves with bodies over 2 inches (5 cm) in order to overcome actuator spring forces
b) for control valves that are constructed of carbon steel or bronze
c) for control valves that are experiencing a large degree of hysteresis
d) for split-body control valves
e) none of the above
Answer A is not correct. The use of positioners is not dependent upon valve size.
Answer B is not correct. Use of a valve positioner is not related to the materials of construction of a valve.
Answer D is not correct. Use of a valve positioner is not related to the valve body type.
The correct answer is C. A positioner adjusts the pneumatic output to a valve actuator so that the requested position of the valve from a controller is achieved. A valve positioner can correct for any valve inaccuracies with regard to the controller demand signal versus the actual valve stem position, regardless of the amount of valve travel change or direction of valve travel.
Reference: Goettsche, L.D. (Editor), Maintenance of Instruments and Systems, 2nd Edition
Source: ISA News