| The paper deals with the evaluation of the Root Mean Square (RMS) indices of signals with linearly variable magnitude by using Wavelet Packet Transform (WPT) and Fast Fourier Transform (FFT). Firstly there is presented a synthesis of employed techniques and previous results of the authors with respect to synthetically generated singleharmonic signals. The signals had linearly decreasing/increasing magnitude M. M varies according to a constant slope G. The studied absolute difference between the final and initial values of M belongs to the set {2,5, 5, 7.5 and 10}% from the initial M. Results of the RMS evaluation by using both FFT and WPT in a single harmonic approach are recalled, focusing on the maximum absolute values of percent relative errors. New studies are presented now, firstly considering randomly generated synthetic multiharmonic signals. Three cases are considered, corresponding to harmonic orders belonging to 3 distinct ranges: 3…9, 31…39 and respectively 3…40. The errors associated to the use of FFT and WPT are evaluated for them. Two real multi-harmonic signals are afterward analyzed. Small differences were noticed between the values yielded by FFT and WPT for the total RMS as compared to those computed with Riemann sums. The differences between the RMS yielded by FFT and WPT are also evaluated and discussed. |
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