Current status circuit for a variable frequency motor

摘要

A sensor linked with a power cable to produce a first signal in response to the presence of at least one of a sensed current and a sensed voltage within the power cable. The measuring circuit is electrically connected to the sensor to produce a second signal in response to the first signal representative of the magnitude of at least one of the sensed current and the sensed voltage within the power cable. The measuring circuit also produces a third signal in response to the first signal representative of a sensed frequency of at least one of the sensed current and the sensed voltage within the power cable. The measuring circuit includes a model of a set of predetermined relationships between a plurality of reference frequencies and a reference amplitude for each of the reference frequencies for at least one of the sensed voltage and the sensed current of the power cable. The measuring circuit compares the second signal and the third signal to the model to produce a resultant signal indicative of an alarm condition. By including the frequency of the sensed signal in the determination of whether the motor is operating properly, accurate determination of alarm conditions can be made.