Luedeka, Neely & Graham, P.C.
Machine fault detection using slot pass frequency flux measurements
 A method for nonintrusive detection of anomalies in electric machines. A flux coil is positioned external to the motor to obtain magnetic leakage flux measurements, which are transformed to the frequency domain to obtain a flux spectrum. Asymmetry-producing faults, such as turn-to-turn stator winding shorts, produce changes in the amplitudes of individual frequencies and groups of frequencies within a defined slot pass family of frequencies of the flux spectrum. The measured amplitudes of the slot pass family of frequencies are compared to reference and trend data. Significant changes in the slot pass frequency amplitudes indicate the presence of a machine fault or other anomalous condition. Significant changes are determined by comparing individual amplitudes and groups of amplitudes of the slot pass family of frequencies to an absolute or delta threshold value. Alternatively, measured amplitudes of the slot pass frequencies can be statistically compared to trend data previously acquired for the motor to determine when a significant change in the slot pass amplitudes has occurred. 
CSI Technology, Inc.
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Stewart V. Kenneth R.
Bowers Piety