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zero crossing

A point where a signal crosses its average; counting them estimates how fast it oscillates.

A zero crossing is a sign change of x_i - x̄; a vibration at f Hz gives about 2f crossings per second.

Examples

  • A 1 s window of the fan with 46 zero crossings means about 23 Hz, roughly 1380 rpm if the shake is once per turn.

  • Noise near the mean adds extra crossings, so a small dead band around zero is the usual fix.

See also

RMS spectral bin feature
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