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dataPAC User’s Guide
Chapter 4 - Off Route Analysis with the dataPAC
Here is an example of a zoomed in Orders Based spectrum measurement. Notice the
“smearing” of the lines.
Setting Up an Off Route Orders Track Spectrum Measurement
The dataPAC supports the specification and collection of a spectrum with an Fmax defined
in terms of number of orders for a varying machine speed.
As explained above, with orders tracking, the sampling rate is not fixed during the
collection period. Instead, the time spacing between the samples may be constantly varying
so that a fixed number of samples per shaft revolution is collected. The X axis of the time
waveform is no longer measured in seconds, but instead it is measured in degrees or shaft
position. From this, the corresponding spectral information is no longer measured in Hz or
CPM, but instead it is measured in orders.
You use the Frequency Unit parameter to accomplish orders based FFT collection. If you
select Orders Track, the frequency maximum can vary during the data acquisition. Orders
track eliminates the non-synchronous frequencies from the spectrum.
Notice that when you select Orders Track, your Frequency Max selections are in multiples
of running speed, such as 4X or 10X.
To collect Orders Track spectra, you must use a reference input for a trigger, such as a laser
tachometer. Note that when you select Orders Track, Trigger Control changes to Positive
Slope.
There are two parameter requirements for implementing this feature. The Fmax value must
fall within the range of 10 to 5000 Hz, and the machine speed may not vary by more than
10% during the measurement collection.
Orders tracking analysis can be used effectively to diagnose the vibrations of variable speed
machines. The orders tracking yields data in the revolution domain, not the time domain. In
an orders spectrum, signals that are periodic in the revolution domain appear as peaks and
orders or harmonic components remain fixed in their position through speed changes. This
is a clear advantage when comparing the characteristics of variable speed machines over a
period of time.
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