Higher order spectra (HOS) are the tools in signal processing for the identification of the presence of higher harmonics in a signal which is a typical case of a non-linear dynamic behavior in mechanical systems. The breathing of a crack during shaft rotation also exhibits a non-linear behavior. The crack is known to generate 2X (twice the machine RPM) and higher harmonics in addition to 1X component in the shaft response during its rotation. Misaligned shaft also shows such feature as a crack in a shaft. The HOS have now been applied on a small rotating rig to observe its features. Results are found to be encouraging to distinguish these two faults based on a few experiments conducted on a small rig, which are presented here. The presented results though limited suggest the potential of the use of the HOS in the condition monitoring of rotating machinery.
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