National Instruments Order Analysis Toolset - Manual (Page 28)

Chapter 2 Order Analysis
© National Instruments Corporation 2-13 LabVIEW Order Analysis Toolset User Manual
Resampling
Resampling is a widely used method of order analysis. Figure 2-9
illustrates the resampling method.
Figure 2-9. Resampling
In the resampling method, time-samples are converted to angle samples.
The time-samples are samples of the physical signal that are equally spaced
in time. The angle samples are samples that are equally spaced in the
rotation angle.
You can acquire angle samples with either hardware or software. The
hardware solution uses an encoder or a multiplied tachometer signal to
trigger the analog-to-digital conversion, which ensures a sampling process
spaced equally in the rotation angle. The hardware solution requires
additional hardware devices and a tracking anti-aliasing filter.
Software programs designed to acquire angle samples complete the
following steps to acquire the angle samples.
1. Collects the measured signal and the tachometer signal at some
constant rate.
2. Uses interpolation or curve fitting to determine the instantaneous shaft
angle at intermediate points between the tachometer pulses.
3. Calculates the sampling time at the desired shaft-angular increment.
4. Uses interpolation to obtain new samples at the desired time.
Sample at Constant Time Frequency
Sample at Constant Angle Order