TR Get a Quote

Time Waveform and FFT Spectrum Simulator

Spectrum and time waveform are two views of the same signal. Bearing impacts stay small in the spectrum yet show up as sharp peaks and high kurtosis in the waveform. Change the components and watch both views respond.

Component amplitudes (mm/s peak)
Outer-race bearing damage
Overall vibration —mm/s RMS
Peak
— mm/s
Crest factor (band above 10X)
—
Kurtosis (band above 10X)
—
Signal character
—
BPFO
—
Δf
—

Time waveform (lines: each revolution)

FFT spectrum (Hann)

These tools are intended for preliminary assessment and training. Decisions on critical equipment should be based on on-site measurement and expert evaluation.

How to use

  1. Choose speed and Fmax.

  2. Add 1X for unbalance, 2X for misalignment, 3X and higher for looseness, and a 0.42–0.48× subsynchronous component for oil whirl.

  3. Raise the impact severity to see bearing damage stand out in the waveform and kurtosis.

Theory & formulas

Overall RMS from the time record is √(Σx²/N), consistent with the root-sum-square of the spectrum components.

Crest factor is peak/RMS: 1.41 for a sine; above 3–4 indicates an impulsive source.

Kurtosis is 3 for Gaussian noise; bearing impacts sharpen the signal and push it above 4. Because large shaft-rate sine waves mask the impacts, crest factor and kurtosis are computed on the band above 10× running speed (high-pass filtered). As damage spreads, kurtosis can drop again.

Bearing impacts excite structural resonance; the spectrum shows BPFO-spaced sidebands in the resonance region and a BPFO line at low frequency. That is why envelope analysis is used.

Frequently asked questions

Why is the bearing frequency small in the spectrum?

Impact energy spreads over a wide band and the resonance region, so the BPFO line stays small. The time waveform, crest factor, kurtosis and envelope spectrum are more sensitive for early detection.