238 Rockwell Automation Publication 1444-UM001D-EN-P - June 2018
Chapter 9 Trend and Transient Capture
Dynamic Data
To include TWF and FFT data with the transient data, enable the
measurements on the FFT Page of each channel. The FFT and TWF saved are
as defined on the FFT Pages but with a maximum TWF size of 2048 points
and a maximum FFT size of 900 lines.
When the TWF sample size or FFT line size that is specified on the FFT Page
is larger than can be accommodated in the Transient Buffer, the lower sizes are
applied only to the Transient data. All other uses remain as specified. The
TWF and FFT saved to the Transient Buffer is always at the same sample rate
and FMAX specified by the signal source.
Sampling during a Transient Event
During a transient event, while the reference speed remains between the low
and high-speed thresholds, the executing buffer updates at prescribed delta
RPM
(1)
and delta time triggers. For startups, delta RPM updates trigger only in
the increasing speed direction while for coast downs, delta RPM updates
trigger in either increasing or decreasing speed directions.
• Independent delta RPM and delta time triggers can be defined for
startup and coast down.
• If the delta RPM is set to 0, then no samples are taken on speed change.
• The delta RPM triggers can be set from 1…1000 RPM, or 0 if disabled,
and the delta time triggers from 1…3600 seconds (1 hour).
• A discrete data record is saved on each trigger.
• A dynamic data record is captured on every tenth trigger, and considers
both delta RPM and delta TIME triggers.
Transient
Buffer Storage
TWF
Samples
FFT Lines
Base FFT Lines Decimation
None Alternate Path
(2)
Primary Path
(3)
Not available
(1)
4096 1600 1800 1000 600
Available 2048 800 900 500 300
1024 400 450 250 150
512 200 225 125 75
256 100 112 67 32
(1) When the TWF or FFT is defined at this level, the data that is written to the Transient buffer is reduced to the 2048 TWF samples and
equivalent FFT lines. Data retains the same sample rate and FMAX.
(2) Or if -60 dB filter is applied (Aeroderivative Measurement Type)
(3) And the standard -24 dB/octave filter is applied
(1) The module evaluates speed at 96 millisecond intervals. Consequently, measurements are not necessarily captured at precisely
the specified delta RPM.
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