a novel method for the optimal band selection for vibration signal demodulation and comparison with the kurtogram

the narrowband amplitude demodulation of a vibration signal enables the extraction of components carrying information about rotating machine faults. however, the quality of the demodulated signal depends on the frequency band selected for the demodulation. the spectral kurtosis (sk) was proved to be a very efficient method for detection of such faults, including defective rolling element bearings and gears. although there are conditions, under which sk yields valid results, there are also cases, when it fails, e.g. in the presence of a relatively strong, non-gaussian noise containing high peaks or for a relatively high repetition rate of fault impulses. in this paper, a novel method for selection of the optimal frequency band, which attempts to overcome the aforementioned drawbacks, is presented. subsequently, a new tool for presentation of results of the method, called the protrugram, is proposed. the method is based on the kurtosis of the envelope spectrum amplitudes of the demodulated signal, rather than on the kurtosis of the filtered time signal. the advantage of the method is the ability to detect transients with smaller signal-to-noise ratio comparing to the sk-based fast kurtogram. the application of the proposed method is validated on simulated and real data, including a test rig, a simulated signal, and a jet engine vibration signal.