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In viewing the Valve Signature curve two things pop out at you. (1) There is no pressure spike at the open end, thus, no designation that a hard stop had been reached. And (2), the upscale data plot flattens out. It appears that the valve continues to move with no increase in force (actuator pressure). In studying the trace closer, one sees that the pressure stalls out at approximately 24 psig.
In viewing the Dynamic Error Band (DEB) plot, no anomalies are seen. The DEB stays constant throughout the full stroke and there is a hint that the mechanical stops had been reached.
The clue of the problem is in the Valve Signature curve. Because the travel continued to move even though the pressure reading stalled at some value indicates that, yes the force continued to increase and thus the actuator pressure had to continue climbing. What could cause this? Well a failed travel sensor could provide a wrong pressure reading but I don’t believe that is true in this case because of the pressure at which the measurement stopped (24 psig). In the Instrument Configuration, one specifies the operating pressure range. This allows for increased accuracy in the pressure readings (i.e. a 20 psig range has better accuracy then say the 100 psig range). It just so happens that the software allows for pressure readings of up to 125% of the range selected. Guess what, 24 psig is 125% of the "up to 20 psig" range in the configuration field. By changing the configuration pressure range to the next field of "21 to 35 psig" and rerunning the test, the anomaly (flattening) was eliminated. The new test showed the supply to be 30 psig, which exceeded the 125% rule of the 20 psig range originally selected. |
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