The digital synchronous filtering technique

An original signal processing technique, digital synchronous filtering (DSF) is described. DSF makes it possible to estimate the time history of such periodic components of the signal being analysed, the corresponding frequencies of which are integer multiples of some triggering frequency (external or defined by the signal itself). These signal components, which are not synchronous with the triggering signal, are simultaneously attenuated. The DSF is based upon the well known time domain averaging technique. The DSF is especially suitable, for example, in the analysis of vibro-acoustic signals acquired from a rotating machine observed in run-up/coast-down (i.e. non-stationary) conditions. In this paper the DSF is briefly described and properties of the resulting filters are discussed in detail. The bank of filters obtained makes it possible to estimate the averaged time courses of the periodic components of the signal (in the example presented orders of the components are no greater than six in relation to the triggering signal used). Amplitude and phase characteristics of the filters are given. Only simple fixed-point arithmetic operations were used in order to prepare the necessary software for signal processing. An example of the application of the DSF in investigations of a turbocompressor observed during the coast-down is given.