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Demodulation of vibration signal to detect faults in machinery has been a prominent prevalent technique that is discussed by a number of authors. This paper deals with the demodulation of the current signal of an induction motor driving a multistage gearbox for its fault detection. This multistage gearbox has three gear ratios, and thus, three rotating shafts and their corresponding gear mesh frequencies (GMFs). The gearbox is loaded electrically by a generator feeding an electrical resistance bank. Amplitude demodulation and frequency demodulation are applied to the current drawn by the induction motor for detecting the rotating shaft frequencies and GMFs, respectively. Discrete wavelet transform is applied to the demodulated current signal for denoising and removing the intervening neighboring features. Spectrum of a particular level, which comprises the GMFs, is used for gear fault detection. Index Terms--Current, demodulation, fault diagnosis, gears, wavelet transforms.

06-0909 Kar, C., and A.R. Mohanty. Multistage gearbox condition monitoring using motor current signature analysis and Kolmogorov-Smirnov test. Journal of Sound and Vibration (United Kingdom) 290(1,2):337-368, Feb. 21, 2006 (www. [...]

Kar, C., and A.R. Mohanty. Monitoring gear vibrations through motor current signature analysis and wavelet transform. Mechanical Systems and Signal Processing (United Kingdom) 20(1):158-187, Jan. 2006 (mssp@harcourt.com). KEYWORDS: gearboxes, gears, [...]

A new signal processing technique; i.e., a corrected multi‐resolution Fourier transform (MFT), is proposed for health monitoring of a multistage gearbox. It is inferred from the study that MFT coefficients of vibration and current signals can predict a consistent trend in the energy level possessed by the gear mesh frequencies with an increase in the severity of defects and, hence, can be useful in gearbox health monitoring.