Rockwell Automation 1756-HIST2G FactoryTalk Historian ME 2.2 - Manual (Page 95)

5 • M ANAGING P OINTS
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Span Value - value for the difference between the top of the range and the bottom
of the range. It is required for all numeric data type points.
„
Zero Value - indicates the lowest value possible. A zero is required for all
numeric data type points.
E XCEPTION F ILTERING P OINT P ROPERTIES
The FactoryTalk Historian ME exception-reporting specification determines when to
send data to the Snapshot subsystem. The exception-reporting specification consists
of a deviation (Exception Deviation), a minimum time (Exception Min), and a
maximum time (Exception Max).
The Exception Filtering section contains the following fields:
C OMPRESSION F ILTERING P OINT P ROPERTIES
When a new Snapshot arrives, the previous one is evaluated according to the
compression specifications to see if it is a significant event. If so, it is sent to the
Event Queue. If not, it is discarded. The result is that only significant data is written
to the archive. This process is called compression.
The Compression Filtering section contains the following fields:
Field Description Default Value
Exception Min Specifies the minimum time span between
exceptions, expressed as dd hh mm ss. 0 seconds
Exception Max Specifies the maximum time span between
exceptions, expressed as dd hh mm ss. 10 minutes
Exception
Deviation Specifies in engineering units how much a
value may differ from the previous value
before it is considered to be a significant
value. 0.25 engineering
units
Field Description
Compression On This flag should be turned ON for all real-time points in the
system.
With compression OFF, every value sent to the Snapshot
subsystem is saved in the archive.