Rockwell Automation Publication 1444-UM001D-EN-P - June 2018 335
CIP Objects Appendix A
The FFT returned can be some fraction of the raw processed FFT where the
specific fraction is made appropriate to the filtering that is applied, which is
based on module configuration. Selections in the SpecialRequest byte of the
FFT data request record specify this control. Bits 3 and 4 of the ucDataSelect
byte indicate the proportion of the filtered data that is returned. Use the
following to adjust the number of lines that are based on the applied filtering.
Determine the factor per the preceding table, then calculate the number of
lines configured:
The FMAX, in Hz, can then be calculated as follows:
Bit Factor
43
001.000
010.375
100.625
111.125
Nc =
Nr
Factor
FMAX (Hz) =
Nr - 1
SamplePeriodInSec* 2.56* Nc
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