Rockwell Automation Publication 1444-UM001D-EN-P - June 2018
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Trend and Transient Capture
Chapter 9
Trend Buffer
The trend buffer is composed of 640 records that are sampled at the low-
resolution rate and that overwrite in a circular, first-in-first-out manner. The
buffer updates continuously when the module is in RUN mode.
Dynamic Buffer
Similar to the discrete measurement buffer, the trend function can also hold a
buffer of dynamic data records. The dynamic data buffer is composed of 64
records, each containing a time waveform and/or FFT for each channel, as
defined on the FFT page.
The Dynamic Buffer update rate is set in minutes and seconds to a minimum
(fastest) rate of 0.1 seconds, to a maximum (slowest) rate of 546 minutes, 59.0
seconds. Seconds can be entered with a resolution to 0.1 (100 milliseconds).
Dynamic data records are sampled in the same manner as the Low-Resolution
discrete data, by using its own 100 millisecond multiplier. However, regardless
of the multiplier setting, how fast dynamic data updates depend on module
performance, which is a function of module configuration and circumstances.
IMPORTANT
The discrete data is not processed from the same TWF or FFT that is captured
in the dynamic data buffer.
• FFT derived measurements (FFT Bands) are processed from an
independent FFT. The DSP of the module calculates the independent FFT,
specifically for that purpose. See
. This FFT is different
than the one defined on the FFT page and calculated in the
microprocessor of the module.
• Non-FFT derived measurements, such as Overall, 1x magnitude, DC
values are processed from the data stream, with possible different
filtering, sampling, or integration selections, so also do not necessarily
correlate with the captured TWF or FFT. See