Getting a complete picture: the value of alternate signal processing methods

While time waveforms and FFT spectra are important ways to visualize vibration data, they only tell a part of the story. Running vibration signals through multiple processing methods provides more ways to analyze the signal and more ways to measure deviations from the “norm”. Here are some examples of alternate processing methods.

Envelope detection

Repetitive bearing and gear mesh activity create vibration signals of much lower amplitude and higher frequencies than rotational and structural vibration signals. These lower signals may be hidden by the machine’s rotational and structural
vibration noise.

Envelope detection filters out low frequency rotational signals and enhances the bearing’s repetitive impact type signals to focus on repetitive events in the bearing defect frequency range (for example, repetitive bearing and gear tooth vibration signals).

This measurement method has proven to be a successful indicator of a major class of machine problems. Faults in roller element bearings, defective teeth in gear boxes, paper mill felt discontinuities and electric motor/stator problems are all applications for acceleration enveloping.

Phase measurement

Phase is a measurement, not a processing method. Phase measures the angular difference between a known mark on a rotating shaft and the shaft’s vibration signal. This relationship provides valuable information on vibration amplitude levels, shaft orbit and shaft position and is very useful for balancing and analysis purposes.

High frequency detection (HFD)

HFD provides early warning of bearing problems. The high frequency detection (HFD) processing method displays a numerical overall value for high frequency vibration generated by small flaws occurring within a high frequency band pass (5 to 60 kHz).