VectoraLab Lab

What is Envelope Analysis? Envelope analysis (also called amplitude demodulation or high-frequency resonance technique) is one of the most powerful methods for detecting early bearing and gear defects. How it Works: 1. Bandpass filter the raw vibration signal around a resonance frequency (typically 5-20 kHz for bearings) 2. Rectify the filtered signal (take absolute value) 3. Low-pass filter to extract the amplitude envelope 4. Apply FFT to the envelope signal What to Look For in the Envelope Spectrum: • BPFO: Outer race defect frequency (most common) • BPFI: Inner race defect frequency • BSF: Ball spin frequency • FTF: Cage (fundamental train) frequency • Sidebands around these frequencies indicate modulation Advantages: • Detects faults much earlier than broadband RMS • Works when fault energy is hidden in noise • Identifies specific bearing fault type Filter Band Selection: • Bearing: 5–20 kHz typical carrier • Gear: around gear mesh frequency • Use kurtosis maximization to find best band Important: Envelope analysis results must be interpreted alongside bearing geometry (BPFO/BPFI), trend data, and other indicators. A peak at BPFO alone does not confirm a fault without additional evidence.