Allen-Bradley 1444-TSCX02-02RB User Manual page 145

Table 30 - FFT
Parameter Values
Enable TWF Data Enable (checked) / Disabled (not
Storage checked)
Number of Select from:
Samples • 256
• 512
• 1024
• 2048
• 4096
• 8192
Enable FFT Data Enable (checked) / Disabled (not
Storage checked)
Number of Select the number of lines for the FFT.
Spectrum Lines
Decimation
None Alternate
Path
1800 1000
900 500
450 250
225 125
(1) Or if the Measurement Type (See
Configuration Page) is either of the
aeroderivative selections.
Signal Detection Select from:
• Peak
• Peak to Peak
• RMS
Comment
Select the checkbox to save the time waveform (TWF). The module saves the TWF to any defined Trend buffers,
and makes the most recent sample available for external access.
Tip: External access to "Live" TWF and FFT data, as defined on this page, requires that the TWF and/or FFT be
enabled here.
Clear the checkbox so the waveform does not save.
FFT processing requires that the module measure a TWF using the TWF attributes defined on this properties
page); however, saving the FFT does not require saving the TWF. If you do not choose to save the TWF, the module
discards it after the calculating the FFT.
Select the number of samples to be captured in the TWF. While this TWF and the TWF that the module uses to
calculate the FFT begin with the same sample, it is not necessary that they have the same number of samples.
Therefore the Number of Spectrum Lines (for the FFT) is not related to this Number of Samples (for the TWF).
Select the checkbox to make the module process and save the FFT so it is available to be read externally from the
module. The module also saves the FFT in the Trend buffers.
Tip: External access to "Live" TWF and FFT data, as defined on this page, requires that the TWF and/or FFT be
enabled here, AND that Dynamic Data be enabled on the TREND page.
Clear the checkbox so the FFT does not process in the module.
The available number of FFT Lines that are displayed depends on the signal source and if the measurement is
decimated (the FMAX is lower than the ADC out FMAX).
Primary
(1)
Path
600
300
150
75
Hardware
Select the scaling (detection) method for the FFT line (bin) values.
An FFT is calculated from a set of samples that contain many signal cycles of the various signals that are present.
While the shape of the waveform reflects the interaction between the various signal components, it isn't possible
to discern, from an FFT, the "true" deflection of a signal. The amplitude results from the FFT are representative
RMS values that are calculated from the whole sample set. One result is calculated that can be presented as RMS,
or (scaled) peak, or (scaled) peak to peak for each discrete frequency line or bin.
Rockwell Automation Publication 1444-UM001D-EN-P - June 2018
Measurement Definition Chapter 4
145