Table 3 shows an example of the voltage signal power spectrum analyzed by an FFT analyzer in the Excel table. PSD calculated from voltage signal power spectrum.PSD calculated from acceleration power spectrum Thus, the power spectral density (PSD) value obtained by the above method is also the efficient value (RMS value). Since the Y-axis Magnitude (cell: B16) is rms, the values in the cell from B17 to B417 are efficient values (RMS values). When entering equations shown in the E17 to E417 into the D17 to D417, the Power Spectral Density (PSD) value will appear there. In this case, the values in cells B17 to B417 are also acceleration values of each frequency component. If the Y-axis scale shows “MagLog”, the data measured with the Y-axis scale is set to Log/MagLog. As for the values from B17 to B417, they are the physical values (acceleration values) of each frequency component. The cell from A17 to A417 show frequency values from 0 Hz to 2 kHz in 5 Hz increments.Īs “Lin” is indicated in B14, it means that the data measured with the Y-axis scale is set to Lin. Since the frequency range (cell:C6) is 2000 Hz and the sampling points (cell:B7) is 1024 points, the frequency resolution becomes 5 Hz. Table 2 shows an example of the acceleration power spectrum analyzed by an FFT analyzer in the Excel table. PSD calculated from acceleration power spectrum.If you select V, PSD value is displayed as. If you select V2, the PSD value is displayed as. Our FFT analyzer has a PSD display function. When comparing the measurement results or the specifications of the target products, it is necessary to confirm whether the unit of those PSD values is or, and align the units. In this case, the unit of the square root of PSD is expressed as, , and so on. The unit of power spectral density (PSD) is expressed as in the above, but the square root of PSD sometimes is used. If the unit of the amplitude value is m/s 2, it will be, and if the unit of the amplitude value is V, it will be. The unit of power spectral density (PSD) is. Correction value at PSD for each window function The reciprocal of the correction value Hf when calculating overall (OA) and partial overall (POA) is the correction value Wf when calculating the power spectral density. Wf is the correction value for each window (window function). To display the power value per unit frequency range (1 Hz width) of the power spectrum obtained by FFT analysis, divide the power value (squared value of amplitude) by Δf.Īctually, simply dividing by Δf is not the correct value due to the window function (Hanning, flat top), thus, the power spectral density (PSD) is calculated by the following equation.
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