National Instruments Order Analysis Toolset - Manual (Page 29)

Chapter 2 Order Analysis
LabVIEW Order Analysis Toolset User Manual 2-14 ni.com
After acquiring angle samples with either hardware or software, you can
perform a Fourier transform on the angle samples to analyze them. Because
the time domain has changed into the angle domain, the frequency domain
now becomes the order domain. You can separate and observe the order
components through either the STFT spectrum or the order spectrum,
which is actually the FFT spectrum.
Figure 2-10 shows the spectrum of angle samples.
Figure 2-10. Spectrum of Angle Samples
In Figure 2-10, the Angle Samples plot shows the signal sampled at a
constant angle-interval. The Order Spectrum plot shows the order spectrum
obtained by performing a FFT on the angle samples. In the Order Spectrum
plot, significant peaks appear at each order. The Order vs. Rev plot shows
the result of a STFT on the angle samples, where an order axis is used
instead of a frequency axis. Each horizontal white line in the Order vs. Rev
plot indicates the strong power at an integer order.
Order Spectrum
10
8
6
4
2
0
Order vs. Rev
1.0
0.5
0.0
–0.5
–1.0
0 200 400 600 800 1000 1200 1400
Revolution
Amplitude
Order
Angle Samples