Importance

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Abstract

A method for approximating a stem thrust difference during the operation of a motor operated valve combination includes the steps of sensing the stem thrust of the motor operated valve combination as a function of time during valve closing at a first time. From the sensed information, the rate of thrust build-up is determined after the onset of wedging during valve closing at the first time. The real electrical power of the motor is then sensed as a function of time during valve closing at a second time which is subsequent to the first time. The rate of real motor power build-up after the onset of wedging during valve closing at the second time is determined from the sensed information. The ratio of thrust change to power change is approximated by dividing the rate of thrust build-up after the onset of wedging at the first time by the rate of real motor power build-up after the onset of wedging at the second time. The power difference is noted between two selected locations on the trace of real electrical motor power as a function of time at the second time, the two selected locations being those for which it is desired to approximate the thrust difference. The two selected locations are not limited as to whether either or both is before or after the onset of wedging. Then the thrust difference at the second time between the two selected locations is approximated by multiplying the noted power difference between them by the approximated ratio of thrust change to power change at the second time.

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First Claim