Method and apparatus for monitoring of spring pack displacement of a motor-operated valve

摘要

A system for measuring spring pack displacement of a motor-operated valve (MOV) includes at least one power line having a current. The system includes a current sensor for sensing the current and providing a plurality of digital current values, and a personal computer (PC) processor for acquiring a plurality of frequency values of one or more frequency signatures from the plurality of digital current values and calculating the spring pack displacement from the plurality of frequency values. The processor may include data storage for the plurality of digital current values for at least a time interval necessary to stroke the valve stem in either an open or closed direction. The MOV may include a motor pinion gear having a motor pinion tooth-meshing frequency, a worm shaft having a rotational frequency, a worm shaft gear having plural teeth, a worm having a worm lead, a worm gear having plural teeth and a worm gear tooth-meshing frequency, and a spring pack having a displacement. The frequency signatures may include the motor pinion tooth-meshing frequency and the worm gear tooth-meshing frequency. The processor may calculate the rotational frequency of the worm shaft from the motor pinion tooth-meshing frequency divided by a number of the plural teeth of the worm shaft gear, the number of rotations of the worm shaft from the integral of the rotational frequency of the worm shaft, and the number of the plural teeth of the worm gear being meshed from the integral of the worm gear tooth-meshing frequency. The processor may also calculate the spring pack displacement from the product of the worm lead times the difference of the number of the rotations of the worm shaft less the number of the plural teeth of the worm gear being meshed.