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Measurement Definition
Chapter 4
For an order measurement at a given ADC FMAX, the equivalent maximum
number of revolutions can be calculated as follows:
Ex.: For a speed of 3600 rpm, FMAX = 1287:
If the speed was 60,000 RPM, then first increase the FMAX as much as is
allowed or is practicable.
For the purposes of this example, assume setting the FMAX to 4578 (the
maximum that is allowed when tracking filters are being used). Then the
equivalent number of revolutions in the tracking filter definition can be
recalculated:
When you define a tracking filter, first make sure that the tracked frequency is
well within the bandwidth (the ADC FMAX). Then adjust the number of
revolutions in the filter definition, according to the machine speed and the
configured number of FFT lines, as shown in the preceding formula.
The number of revolutions determines the bin width and the spread of the
response, side lobes. To quantify that, the following expression can be used
(where at the calculated bin width the response is approximately 3 dB down):
Rockwell Automation Publication 1444-UM001D-EN-P - June 2018
141
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