Importance

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Abstract

A valve position controller tuning method avoids impact of friction in valve positioner tuning by building a dynamic model of a valve positioner from a monotonic open-loop response of a valve stem position to a change in valve position controller output. To this end, a model form is selected based on the type of pneumatic actuator and relay that controls valve flow modulating of member motion, and the valve position controller is operated in an open-loop mode. The method includes changing a valve position controller output signal to cause the valve positioner to move a valve flow modulating member, connected to valve positioner, monotonically from one stuck position to another stuck position immediately after a motion in that same direction. When a valve stem position reaches a position threshold, a first valve stem position change and a corresponding time change are measured. The method includes measuring valve stem position changes at times that depend on the first measured time change. Using the measured results, valve positioner response parameters are calculated for the selected model form from which valve position controller tuning constants are calculated.

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First Claim