The component provides a logarithmic frequency axis, levels in dB against a stated reference, averaging that settles the noise floor, max hold, peak markers that read frequency and level, and a THD readout. The FFT and the window functions are provided by Smart.DSP, which applies the amplitude correction of the selected window, so the levels shown are correct for every window.
Blocks of 4096 samples arrive twenty times per second. The tone is 0.5 V peak with second and third harmonics at −40 and −46 dB, which gives a THD of about 1.1%. Compare this with the THD readout. Enable averaging to settle the noise floor, and enable max hold and sweep the tone frequency.
Change the window and observe the peak reading. A flat-top window reads amplitude to within 0.01 dB but spreads the peak in frequency; a rectangular window does the opposite. The readout reflects the selected window in both cases.
A motor at 1490 rpm (24.8 Hz) with an outer-race bearing defect at 3.57 times the shaft speed and its harmonics, over 1/f noise. Markers supplied by the application are placed at the shaft frequency and the defect frequency, so the peaks can be compared with the expected frequencies. Peaks are found on the averaged trace by prominence, so a single strong line is reported once.