Rockwell Automation Publication 1441-UM003A-EN-P - May 2011
21
FRF Frequency Response Function Extension Module
Chapter
2
Num of Lines
Sets the number of lines of resolution for the FFT. The
Acquisition time information box changes accordingly.
When set to Automatic, the FRF module automatically
chooses the number of lines after three trial hits. This
uses a Uniform window if possible and automatically
increases the lines of resolution to accommodate the
decay time.
If this cannot be achieved, then Force/Exponential is
automatically selected. This function is optimized to
work for frequency ranges between 200 Hz and 4 kHz.
If you select Automatic at a frequency range outside this
band, the algorithm attempts to auto select, but may not
achieve good results.
400 (default)
Windowing
Sets the FFT window type to Uniform or Force/
Exponential.
Force-Exp (default)
Uniform
Num of Averages
Sets the number of FFT averages.
5 (default)
Accept/Reject
When performing a hammer test, the setting Accept/
Reject to Manual displays a dual time trace and
presents the choice to accept or reject control. Setting it
to Automatic, automatically rejects overloaded data and
double impacts.
Manual (default)
Automatic
Invert Phase
Applies a 180° phase offset to the measured data. It is
used when the accelerometer or hammer needs to be
inverted at a measurement position.
Off (default)
On
Save To
You can save to the Internal memory or to the Secure
Digital (SD) card.
Internal (default)
Card
Good Coherence
Enter the threshold at which the FRF plot changes from
red (bad coherence) to green (good coherence).
80% (default)
Table 2 - FRF Analysis Set-up Parameters
Parameter
Description
Value/Comments
