Crest factor and kurtosis contributions to identify defects inducing periodical impulsive forces

Many mechanical defects generate periodical impulsive excitation forces which excite structural resonances and the mounted resonance frequency transducer. In order to characterise the time signals induced by such defects, specific indicators such as the crest factor and kurtosis need to be used. The root mean square value, which only characterises the signal energy, and not its shape, does not give information about the origin of the excitation. These two shape indicators are used currently in the monitoring of rotating machinery and are not always used correctly. By using a simple model the properties and the limitations of these indicators are demonstrated and illustrated with real examples. (C) 1997 Academic Press Limited.