Audio lab · Vibration analysis
Bearing fault vibration analysis: interactive demo
An early bearing defect produces small, repetitive impacts that barely change the overall vibration level, but envelope analysis exposes them as a line at the bearing’s fault frequency. This demo simulates a machine with adjustable imbalance and an outer-race defect, then shows the waveform, the raw spectrum and the envelope spectrum against an alarm threshold.
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Vibration analysis / condition monitoring
Find a bearing fault before it shows.
What this shows: an early bearing defect barely moves the overall vibration level, but envelope analysis reveals its fault frequency.
Run the machine
Imbalance raises the line at 1× shaft speed.
Each ball strikes the defect, exciting a 3 kHz structural resonance.
Waveform, spectrum, envelope
Synthetic accelerometer · 16,384 HzAmber: raw waveform and spectrumBlue: envelope spectrumDashed: expected outer-race frequency and harmonicsRed: alarm threshold
Imbalance—
Bearing—
mg = thousandths of g; the 1× line is a peak amplitude. The outer-race line is the envelope-spectrum peak within ±2% of the expected frequency, in dB above the median envelope floor; noise alone reaches roughly +7 to +10 dB. The 1× alarm compares against the healthy 20 mg baseline.
Predictive maintenance on motors, pumps, fans and gearboxes. See vibration analysis and diagnostics.
What this experiment models
One second of synthetic acceleration at 16,384 Hz (1 Hz FFT resolution): shaft harmonics at 1×, 2× and 3×, Gaussian sensor noise (60 mg RMS) and, for the defect, decaying 3 kHz impulses repeating at the ball-pass frequency of the outer race (BPFO = 4.5 × (1 − d/D) × shaft rate for a nine-ball bearing with d/D ≈ 0.20, about 3.59× shaft speed) with about 1% random slip. The raw spectrum is a Hann-windowed FFT scaled to peak amplitude. The envelope is the magnitude of the analytic signal of the 2–4.5 kHz band (FFT band-pass), followed by a Hann-windowed FFT. Shaft speed is assumed known, as from a tachometer. Playback is the same synthetic signal, four seconds long. Real machines add speed variation, transmission paths, mounting resonances and other faults; thresholds should come from a machine’s own baseline data.
The principle
How it works
Each time a rolling element passes an outer-race defect it strikes it, and the impact rings a structural resonance, here at 3 kHz. In the raw spectrum that energy is smeared around the resonance and is easy to miss next to the shaft harmonics. Envelope analysis band-pass filters around the resonance, takes the magnitude of the analytic signal to recover the rhythm of the impacts, and computes the spectrum of that envelope. The repetition rate then appears as a line at the ball-pass frequency of the outer race (BPFO) and its harmonics.
Imbalance behaves differently: it raises the line at 1× shaft speed in the raw spectrum, so the demo tracks the two faults with separate indicators. BPFO depends on bearing geometry and shaft speed, which is why the demo assumes a known speed, as from a tachometer.
Real machines add speed variation, transmission paths and other faults, and alarm thresholds should come from each machine’s own baseline. See vibration analysis.
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More demos
All six demos on one page: the audio labVibration analysis →