Rockwell Automation FactoryTalk Historian SE 3.0 Live Data Interface User Guide - Manual (Page 30)

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FactoryTalk Historian Live Data Interface User Guide
24
SourceTag
An output point is associated with a trigger point by setting the SourceTag
attribute of the output point equal to the tag name of the trigger point.
For more information, see Output Points (page 25).
Compression Testing
For each data point, you can set the following attributes to configure its
compression testing specification:
Compression
Deviation
(CompDev)
Specifies in engineering units how much a value may differ from the
previous value before it is considered to be a significant value. As a
rule of thumb, set CompDev to the precision of the data source or
hardware (instrument). Set it a little “loose” to err on the side of
collecting, rather than losing data. After collecting data for a while, go
back and check the data for your most important tags and adjust
CompDev, if necessary.
Note: Setting the CompDev attribute value too low causes
too little data compression and wastes space in the archive.
Setting the value too high causes loss of useful data. For most
flows, pressures, and levels, use a deviation specification of
1% or 2% of Span. For temperatures, the deviation should
usually be 1 or 2 degrees.
Compression
Minimum
(CompMin)
A point is archived if the elapsed time since the previous time the
point was saved is greater than or equal to the minimum time and the
value has changed by more than the deviation. For data points
associated with interfaces that send exception reports, set CompMin
to 0.
Compression
Maximum
(CompMax)
A point is archived if the elapsed time since the previous time the
point was saved is greater than the maximum time. The
recommended maximum time specification is one work shift (for
example, 8 hours). Duplicate values will be archived if the elapsed
time exceeds CompMax. You typically set CompMax to the same value
for all points in the system.
For information on compression testing, refer to "Exception Reporting and
Compression Testing" in the FactoryTalk Historian SE Server Reference Guide ,