Envelope Analysis
Envelope Analysis can be used for diagnostics/investigation of machinery where faults have an amplitude modulating effect on the characteristic frequencies of the machinery. Examples include faults in gearboxes, turbines and induction motors. Envelope Analysis is also an excellent tool for diagnostics of local faults like cracks and spallings in Rolling Element Bearings (REB).
Envelope Detection or Amplitude Demodulation is the technique of extracting the modulating signal from an amplitude-modulated signal. The result is the time history of the modulating signal. This signal may be studied/interpreted as it is in the time domain or it may be subjected to a subsequent frequency analysis. Envelope Analysis is the FFT (Fast Fourier Transform) frequency spectrum of the modulating signal.
Uses
- Amplitude demodulation, that is, detection of the spectral and temporal representation of the modulating signal
- Spectral (how frequent) and temporal (where in a cycle) identification of the occurrences of impulsive events in rotating machinery
Common Applications
- Roller-bearing elements: identification of cracks in inner race, outer race or roller defects
- Gear boxes: identification of cracked or broken teeth from impulsive modulation of the tooth-meshing frequency
- Turbine blades: identification of broken or distorted blades from modulation of the bladepassing frequency
- Induction motors: identification of broken or cracked rotor bars, or bad soldering from modulation of slot harmonics by twice the slip frequency
- Reciprocating machinery: determination of precise point (in time) in the cycle of impulsive events like valve openings/closings or combustion
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