Control Valve Positioner Cam Characteristics

[From:] [Author:admin] [Date:11-08-15] [Hit:]


Cam is part of positioner that could make the actuator stroke (not valve inherent characteristic, i.e. linier plug, equal% plug, or quick opening plug) becomes linear, equal percentage, or quick opening. For example, our control valve has a linear inherent characteristic plug, with adjust the cam we could get the equal percentage or quick opening actuator stroke.

If our valve inherent characteristic are already equal percentage, then the cam adjusted to have equal percentage characteristic, the stroke of the valve will make the flow will be more equal percentage. With this configuration, if our valve inherent characteristic is linear, then we will get equal percentage stroke. If our valve inherent characteristic is quick opening, then we will get more closely to linear flow characteristic.

The default choice will always linear cam characteristics since it just the info of the original valve design. Later on, if we found any adjustment required in the field due to bad controllability of process dynamic and needed to change the valve opening vs flow characteristic to equal% or quick opening, we can just simply adjust it.


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