THE COMPARISON OF VIBRATION SIGNALS’ TIME-FREQUENCY ANALYSIS BETWEEN EMD-BASED HT AND WT METHOD IN ROTATING MACHINERY

The method of empirical mode decomposition (EMD) based Hilbert Transformation(HT) is that, first, separate the series data to components with different time scale, say, intrinsic mode function (IMF), using EMD, then apply the Hilbert transformation to every IMFs. The result of the method is the spectrum of the method. The method and algorithm was explained in detail. Emulation and oil film whirling vibration signals were analyzed using the method. The decomposed signals profiles were revealed by IMFs figure. After applied Hilbert transformation to the signals IMFs, the time-frequency and marginal spectrums were obtained. The Wavelet Transformation (WT) method was applied to the signals also. The components of the signals were gained by using wavelet decomposition method. After applied continue wavelet transformation to the signal, the WT-based time-frequency and marginal spectrums were acquired. Compared the two time-frequency method in the domain of time, time-frequency and frequency show that, The EMD-based HT time-frequency analysis of the vibration signal is more sharp and clear than the WT-baseds ,and the WT-baseds frequencies were confused somewhat. The conclusion was deduced that the EMD-based HT time-frequency analysis method is better than the WT-baseds in the field of vibration signals processing in rotating machinery.