User Guide User Manual

FactoryTalk Historian To Historian Interface User Guide 43
modes. It is not possible for PI2 to have two values with the same timestamp.
InstrumentTag
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.
Length
Depending on the version of the PI API and the Historian Server, this Interface supports an
InstrumentTag attribute whose length is at most 32 or 1023 characters. The 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
32
Below 1.6.0.2
2.x or higher
32
Below 1.6.0.2
Below 2.x
32
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 InstrumentTag length of 1023, you need to enable the PI
SDK. See Appendix B for information.
Unless the /tn, /tnex, or /ptid interface parameter is used, the InstrumentTag can be
used to specify the source tag. The ExDesc and Tag attributes can also be used for source tag
name definition. The UserInt1 attribute can be used to specify source tag by point ID
instead of 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.
The interface checks the InstrumentTag attribute first. If the InstrumentTag is empty,
the extended descriptor is checked for STAG=<tagname> at the beginning of the ExDesc
value. That is, the ExDesc attribute must begin with the „STAG‟ keyword. If neither
InstrumentTag nor ExDesc has a tag name, the UserInt1 attribute is checked for the
source tag point ID. Finally if none of these three attributes identify a source point, the
receiving tag name is used for the source tag name.
ExDesc
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.
Length
Depending on the version of the PI API and the Historian Server, this Interface supports an
Extended Descriptor attribute whose length is at most 80 or 1023 characters. The