Toward the use of wavelet scalograms in the diagnostic analysis of rotating machinery transient data

Analysis of the vibration data has historically, and in practice today, been accomplished primarily using Fourier analysis which allows the diagnostician to review vibrational amplitudes and corresponding periodic frequencies generated by the machine. The most common application of Fourier analysis provides very limited information about the frequency content versus time, as these data are lost during the transform. This article presents a comparison analysis between Fourier transform and the wavelet transform, presented via the multilevel wavelet graphical presentation, or scalogram, on startup data from a large, vertical power plant pump driven by an electric motor. Wavelet scalograms also provide interesting and unexpected information such as frequency undulations during startup as well as intermittency of specific frequency components. As each method has its strengths and limitations, using the two methods together potentially provides a more complete picture of the vibration characteristics of the machine. Results of these analyses are presented with subsequent diagnostic analyses.