Abstract: The present invention is a method and system for accurately analyzing shaft encoder signals from rotating machines. The invention reduces noise and other interferences in the encoder signals by novel means that yield an unprecedented power for extracting useful information. Signal distortion due to variation in the rotation rate of the machinery and due to FFT leakage are eliminated by acquiring digital values of the encoder signals at a set of discrete times that are determined by the properly averaged rotation rate of the shaft and requiring a fixed integer number of these discrete times per rotation of the shaft. Amplitude modulation is eliminated by proper spectral combination of left and right sidebands of the main encoder signal. Additive noise is removed by multiplying sidebands and averaging the results over a number of data records.

Abstract: The present invention provides a method and system for analyzing signals generated by rotating components that slip in a rotating machine and for detecting faults in those components. Pulses from a shaft encoder serve as an external clock in digitizing the signal data. A fixed number of data samples are thereby acquired for each complete rotation of the rotating shaft of the machine. Complex spectra are provided for data records of a fixed length with the first sample of each data record always beginning at the same point relative to the shaft angular orientation. Signal-processing means multiply pairs of signal spectral components so that the complex products produced by the data for the component of interest has a fixed phase relative to the shaft orientation.