The crest factor is also referred to as the peak-to-average ratio, or the the peak-to-average power ratio, for a waveform. It is the ratio between the peak amplitude of a waveform and the RMS value, as shown in the following equation:
C = Peak amplitude
RMS Value
The crest factor can be an important parameter in signals that have periodic or random spikes dispersed throughout the signal.
A machine with an out of balance condition will produce a pure sinusoidal wave as shown in Figure 1. If the waveform has a peak amplitude of 10, the crest factor is calculated as:
C = Peak amplitude = 10 = 1.414
RMS Value 10 x 0.707
If the same machine, described above, had a bearing fault that is causing periodic impacting, the signal may look like the waveform in Figure 2. This waveform has a much higher crest factor because its peak amplitude is much greater, while the RMS value of the signal does not increase significantly.
If the same machine, described above, had a bearing fault that is causing periodic impacting, the signal may look like the waveform in Figure 2. This waveform has a much higher crest factor because its peak amplitude is much greater, while the RMS value of the signal does not increase significantly.