How does a valve positioner work on a process controller?
How does a valve positioner work on a process controller?
How does a valve positioner work on a process controller?
Thus, when a process controller sends a command signal to a valve equipped with a positioner, the positioner receives that command signal and applies as much or as little air pressure to the actuator as needed in order to achieve that desired stem position.
How does an electronic valve position sensor work?
Electronic valve positioners, such as the Fisher model DVC6000, use an electronic sensor to detect valve stem position, a microprocessor to compare that sensed stem position against the control signal by mathematical subtraction (error = position − signal), then a pneumatic signal converter and relay (s) to send air pressure to the valve actuator.
How is a valve positioner used in an electric actuator?
Thus, a positioner circuit using a potentiometer or LVDT/RVDT sensor to detect valve stem position and a set of transistor outputs to drive the motor is necessary to make an electric actuator responsive to an analog control signal. A simple force-balance pneumatic valve positioner design appears in the following cutaway illustration:
How does the flapper nozzle control the valve actuator?
The flapper nozzle is controlled by the 3-15 psi pressure signal, the valve actuator is stable at postion maintained by a spring. For higher control action as per the pneumatic signal flapper-nozzle opens and close, which give a corresponding pneumatic pressure to the diaphragm.
How does a Fisher pneumatic balance positioner work?
The following photograph shows a close view of a Fisher model 3582 pneumatic motion-balance positioner’s mechanism: At the heart of this mechanism is a D-shaped metal ring translating bellows motion and valve stem motion into flapper (baffle) motion.
Where is the feedback on a pneumatic valve positioner?
On the left-hand side of this positioner may be seen part of the feedback mechanism: a metal bracket bolted to the valve stem connector, linking to an arm coming out of the positioner’s side.