Crest Factor

The Crest Factor (CF) is a fundamental metric in vibration analysis, defined as the ratio of the peak amplitude of a time waveform to its root mean square (RMS) value. This dimensionless ratio serves as an indicator of the severity of transient or impulsive events in a vibration signal. It provides valuable insight into the presence and progression of impacting phenomena, which are typically associated with mechanical faults such as rolling element bearing defects, gear tooth damage, and cavitation in pumps.

In a purely sinusoidal waveform, such as one representing ideal machine operation without any impulsive activity, the peak amplitude is related to the RMS by a constant factor of approximately 1.414 . Therefore, a crest factor of 1.41 is indicative of a clean sinusoidal waveform with no significant impacting. Values of the crest factor greater than 1.41 suggest the presence of non-sinusoidal, high-energy transients or impacts within the time waveform. These can originate from repetitive mechanical shocks due to defects or degradation in components. In practical condition monitoring, elevated crest factors can be an early warning sign of degradation, often preceding clear signs in the frequency domain.

Figure depicts a waveform with a crest factor of 3.55, which is significantly higher than the sinusoidal baseline. This elevated CF indicates a high level of impacting in gear box teeth, which in this case correlates with advanced gear or rolling element bearing wear. The sharp, high-amplitude transients in the time waveform are characteristic of repeated impacts from defective gear surfaces.

In summary, the crest factor offers a fast, computationally simple method to assess impacting in machinery and is a valuable supplement to other vibration analysis techniques. It is particularly effective for early detection of bearing faults, gear damage, and cavitation—faults that may otherwise remain undetected in standard spectrum analysis.