ExDesc

ExDesc is used to pass in a source tag name:

STAG=<sourcetagname>

Source tag name

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 >. Refer to the section in this manual How the PI to PI Interface finds source points for information on 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.

Note: If event-based update tags are added to the interface and the interface is configured for source PI Server failover it may result in unexpected behavior. For example the interface may get into a loop where it fails over after history recovery. It may print debug messages saying that source PI status tag has value out of range (istat=0). Removing any event-based tags (ExDesc attribute with Event=<tag>) from the interface will resolve this issue. PItoPI does not support event-based updates.