Rockwell Automation FactoryTalk Historian SE 3.0 H2H Interface User Guide - Manual (Page 50)

Historian Point Configuration
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following table indicates the maximum length of this attribute for all the different
combinations of PI API and Historian Server versions.
PI API Historian Server Maximum Length
1.6.0.2 or higher 2.x or higher 1023
1.6.0.2 or higher Below 2.x 80
Below 1.6.0.2 2.x or higher 80
Below 1.6.0.2 Below 2.x 80
If the Historian Server version is earlier than 2.x or the PI API version is earlier than 1.6.0.2,
and you want to use a maximum
ExDesc length of 1023, you need to enable the PI SDK. See
Appendix B for information.
Unless the /tn or /ptid interface parameter is used, the extended descriptor may be used
as an alternative source tag specification by using the keyword STAG=<tag name> . The
How PItoPI Finds Source Points section explains how the interface parameters affect which
receiving tag attributes are used for mapping to the source point and the order that the
attributes are searched for a mapping.
Note that the STAG keyword must be the first four characters of the Exdesc attribute value.
No spaces can precede the STAG keyword. The STAG keyword is case insensitive. If
additional information is included after the STAG specification, the tag name must be
terminated with a comma or enclosed in double quotation marks.
If the source tag name contains a comma within it, it must be enclosed in double quotation
marks. For example,
STAG="batchreactor1,temp" is a legitimate way to define a source
tag name.
Performance Points
For UniInt-based interfaces, the extended descriptor is checked for the string
“PERFORMANCE_POINT”. If this character string is found, UniInt treats this point as a
performance point. See the section called
Scan Class Performance Points .
UserInt1
Note: If the source tag name length exceeds 80 characters, users must use the
UserInt1 attribute for source point mapping. This is due to a limitation with the PI API
programming library which supports tag names of 80 characters or less for point ID
resolution.
Unless the /tn or /tnex interface parameter is used, the UserInt1 attribute can be used to
specify the source tag point ID. The How PItoPI Finds Source Points section explains how
the interface parameters affect which receiving tag attributes are used for mapping to the
source point and the order that the attributes are searched for a mapping.
If the source tag name is longer than 80 characters then you must use this attribute to specify
the source tag point ID. This is an alternative to using the source tag name. The advantage of
using a point ID is that a tag name can change but the point ID cannot. For example, if the
source tag name is used and that name is changed, the interface point will no longer be able to
find it and will therefore not be able to collect its data. Using the source tag point ID will
prevent a tag rename from stopping data updates.