Envelope Analysis
Envelope Analysis (envelope demodulation) is a vibration signal processing technique that isolates and analyzes amplitude modulation of high-frequency machine vibration signals to detect repetitive impact pulses from faults in rolling-element bearings, gears, and rotating components. It extracts the signal envelope via bandpass filtering, rectifying, and low-pass filtering, then performs FFT to generate an envelope spectrum revealing fault frequencies obscured by noise.
In shop floor maintenance, envelope analysis is used for early detection of bearing defects like spalling or cracks by identifying characteristic defect frequencies (e.g., Ball Pass Frequency Inner/Outer Race, Ball Spin Frequency) in the envelope spectrum, even in high-noise environments. Maintenance teams select a high-frequency resonance band, apply bandpass filtering, rectify the signal, and compute the envelope FFT to pinpoint fault type and severity. In CMMS like ServiceGrid, envelope analysis data is logged as condition monitoring metrics; alerts trigger maintenance tasks when envelope amplitude exceeds thresholds or specific defect frequencies emerge.
How does envelope analysis differ from Shock Pulse Analysis (SPA)?
Envelope analysis performs frequency-domain FFT on the demodulated signal to identify individual defect frequencies, while SPA measures high-frequency pressure pulse magnitude without frequency resolution.
Why is envelope analysis independent of machine load?
Both defect frequency amplitude and background 'carpet' level attenuate equally across joints under load changes, so their ratio remains constant.
What algorithm isolates amplitude modulation in envelope analysis?
The Hilbert transform is commonly used to extract the amplitude modulation component from the carrier signal.
Can envelope analysis detect gear faults?
Yes, it detects gear tooth damage (e.g., cracking, wear) by identifying modulation patterns linked to gear mesh frequencies.