Time-frequency approach to extraction of selected second-order cyclostationary vibration components for varying operational conditions

In this paper, the authors propose a method for extracting second-order cyclostationary components from a vibration signal. For a known cyclic frequency, the proposed algorithm allows to estimate the amount of energy of each cyclic component of interest in the time-frequency domain. In this way, the resulting representation contains only the chosen second-order cyclostationary component that manifests itself as a number of carrier frequencies modulated by the harmonic signal of selected frequency. A significant advantage of the proposed algorithm is that it allows extracting of desired components from vibration signals generated by the machinery operating under variable load and speed. The energy of vibrations generated by operating machinery depends mostly on the load. Since this information appears to be very useful in signal interpretation, its preservation is crucial in the extraction process. Because the load variation is frequently connected with the variation of the machine rotational speed, proposed method permits limited fluctuations of the speed.