National Instruments Order Analysis Toolset - Manual (Page 40)

Chapter 3 Gabor Transform-Based Order Tracking
LabVIEW Order Analysis Toolset User Manual 3-10 ni.com
Figure 3-7(c) shows the frequency-rpm spectral map. The horizontal axis
represents rpm, or rotational speed. You can map the rpm axis from the time
axis in the frequency-time spectral map by the rpm-time function. The
frequency of each order component is calculated by the following equation.
Because the relationship between rpm and frequency is a linear function,
order components appear as lines with a slope of in Figure 3-7(c).
The resonance beams appear as horizontal lines.
Applying a frequency-to-order-number transform to the frequency-rpm
spectral map generates the order-rpm spectral map, shown in Figure 3-7(d).
The order-rpm spectral map displays the order components as horizontal
lines and the resonance beams as hyperbolas.
Using the frequency-time spectral map, the frequency-rpm spectral map,
and the order-rpm spectral map, you can clearly and efficiently observe all
the order components in the entire time and rpm ranges.
Calculating Waveform Magnitude
The reconstructed time waveform of the selected order contains only a few
frequency components in a relatively short time interval. Therefore, the
reconstructed time waveform of the selected order displays like a sine
waveform in which the frequency and magnitude have been modulated.
In practical applications such as product testing for comparison with
reference curves, calculating the waveform magnitude as a function of rpm
is useful. The LabVIEW Order Analysis Toolset uses the root mean square
(RMS) of the time waveform to calculate the waveform magnitude and
correlate the sine waveform with the tachometer pulses to obtain the
waveform phase. Both the magnitude and the phase are computed in a short
time interval. By means of the time-rpm function, the LabVIEW Order
Analysis Toolset performs a time-to-rpm mapping operation to obtain the
waveform magnitude and phase as a function of rpm.
Frequency
RPM
60
------------- Order ×
=
RPM
60
-------------