Rockwell Automation 1756-HIST2G Historian ME 2.1 - Manual (Page 117)

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Compression Maximum time (CompMax)
The compression specifications work in a similar way to the exception specifications.
Just like exception reporting, compression is a filter. The difference is that the
exception specifications determine which events should be sent to FactoryTalk
Historian ME, whereas the compression specifications determine which of the events
sent to FactoryTalk Historian ME should go into the archive.
CompMin and CompMax are limits that refer to the time between events in the
archive. A new event is not recorded if the time since the last recorded event is less
than the compression minimum time for the point. A new event is always recorded if
the time since the last recorded event is greater than or equal to the compression
maximum time.
You can adjust the compression parameters to produce efficient archive storage
without losing significant data. The compression maximum time is usually set to one
value for all points in the system. It should be large enough that a point that does not
The maximum time specification does not guarantee that a value will be written to the
archive within a certain time. The archive waits for events to be sent to it. It does not
check to see if a point has timed out. It does not 'create' new values.
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