Experimental evaluation and statistical analysis of synchronous averaging

Time synchronous averaging for the extraction of periodic waveforms is a rather common processing method for rotating machinery diagnosis. By synchronizing the signal to the rotational angle of the component of interest (e.g. by using a tachometer reference signal), it is possible to perform the averaging in the angular domain, thus obtaining an angle-synchronous signal. Such an operation usually requires a resampling procedure. In this paper, the operations of averaging in time and angular domain are thoroughly discussed, referring to the main measurement and computational errors affecting the extracted waveform. The effects of uncertainty in the pulse arrival times of the reference signal on the synchronous averaging method are studied. Jittering of the reference signal affects the quality of the synchronous averaging process resulting in an attenuation of the extracted synchronous signal components, especially in the high frequency band. A theoretical analysis of the linkage between jitter model and attenuation is performed and an analytical model is proposed. The agreement of the analytical model with numerical simulations is first shown, and then an experimental case study involving the early detection of bearing damage is examined. The results are discussed in the framework of the cyclostationary signal theory.