Basic Instrument Operation and Adjusting of Control Valve Pneumatic Positioner- Instrument Training

Basic Instrument Operation and Adjusting of Control Valve Pneumatic Positioner- Instrument Training

Below is the video Explaining the Basic Instrument operation and adjusting of control valve pneumatic positioner. Today I want to explain operation and Adjustments in Pneumatic positioners. Do you know how a pneumatic positioner operates? The Pneumatic positioners operates on a force balance principal. Assume an equilibrium position. An increased control pressure will deflect the diaphragm down, compressing the feedback spring. The balance arm moves the spool in the pilot valve furnishing supply air to the actuator, while at the same time air is exhausted from actuator and is vented to atmosphere through the pilot valve. With the increased supply air, the actuator rotates (or moves linearly) moving the positioner spindle. The spindle and cam rotate, forcing the lower arm upwards compressing the feedback spring. This motion will continue until two forces are equal and the unit is an equilibrium position. Do you know how to adjust ZERO and SPAN for pneumatic positioners? Span is adjusted with the brass-colored (upper) thumb wheel located on the feedback spring. To adjust the span, always return to minimum input signal first, then loosen the locking screw and turn thumb wheel . Tighten screw when span is set. Do not allow the top of the spring to contact the spring guide . Always check zero after adjusting span. Zero is adjusted by turning the silver (lower) thumb wheel located on the lower arm or externally with a screwdriver , through the zero adjustment opening. Remember to install cover to ensure the units sealing. Now How to adjust the cam in Pneumatic positioner? With the cover and indicator removed, loosen the screw and turn the cam locking nut counterclockwise until the cam loosens. Adjust the cam as desired making sure that the ball bearing always is riding on an active lobe on the cam. To secure the cam, make sure that screw is backed out from the locking nut then finger tighten the locking nut and tighten screw. Install and adjust the indicator and reinstall cover.

Basic Instrument Operation and Adjusting of Control Valve Pneumatic Positioner- Instrument Training