232 Rockwell Automation Publication 1444-UM001D-EN-P - June 2018
Chapter 9 Trend and Transient Capture
The Trend Page is used to configure both the Trend and the Alarm Capture
functions.
Discrete Data Buffers
The trend definition includes selections that are associated with discrete and
dynamic data.
Dynamic data refers to time waveforms and FFT. Discrete data are any single
value data, including DC measurements, speeds, and values that are processed
from a dynamic signal such as overall or 1x magnitude.
The module updates data to the discrete buffer at two different rates:
• High-Resolution ALARM buffer
The Alarm Buffer includes 320 discrete data records that update at a
fixed rate of approximately 100 milliseconds.
The update rate can vary, from the defined 100 milliseconds, as higher
priority processor demands take precedence. These variations can occur
as routine functions, dependent on configuration, or as a consequence of
circumstance; any higher priority immediate processor demands such as
an action taken on alarm or a host data request.
• Low-Resolution TREND buffer
The Trend Buffer includes 640 discrete data records. The update rate is
set in minutes and seconds to a minimum (fastest) rate of 0.1 seconds,
and to a maximum (slowest) rate of 54 minutes, 59.0 seconds. Seconds
can be entered with a resolution of 0.1 (100 milliseconds).
Low-Resolution samples are updated independent of the High-
Resolution data. Therefore, even if the timers were to trigger at the same
millisecond, the measurements read to the two buffers can be different.
This result occurs because the measurement tasks of the module execute
at a higher priority than buffer management.
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