National Instruments Order Analysis Toolset - Manual (Page 20)

Chapter 2 Order Analysis
© National Instruments Corporation 2-5 LabVIEW Order Analysis Toolset User Manual
Figure 2-3. PC Fan Running at Constant Speed
The bottom plot in Figure 2-3 depicts the tachometer pulses and the signal
from an accelerometer mounted on the PC fan. The plot on the left in
Figure 2-3 illustrates a conventional power spectrum based on the fast
Fourier transform (FFT). The upper-right plot in Figure 2-3 shows the
frequency-time spectral map computed from the short-time Fourier
transform (STFT) with a 1,024-point Hanning window. Because of the
constant rotational speed of the fan during data acquisition, you can
identify several peaks in both the power spectrum and the frequency-time
spectral map. The peaks indicate different orders and appear in the
frequency-time spectral map as white lines.
STFT Spectrum
570
500
450
400
350
300
250
200
150
100
50
0
F
requency (Hz)
31.9 31.9 31.9