How the PI to PI Interface finds source points
- Last UpdatedOct 06, 2025
- 3 minute read
- PI System
- PI to PI Interface 3.10.3
- Interfaces
When the PI to PI Interface loads a point, the interface must identify the source point from which data will be collected. In other parts of this manual, this process is referred to as mapping the interface point to a source point.
The interface uses four receiving point attributes as possible links to the source point: InstrumentTag, ExDesc, UserInt1, and Tag.
However, the PI to PI Interface /tn, /tnex , and /ptid parameters exclude one or more of these attributes from mapping to the source point. For most interface instances, none of these parameters are used. The following table summarizes the effect of these parameters on the search for either source point tag name or point ID.
The actual implementation of the search is described below the table.
|
Interface command line parameters |
Search order for attribute containing source point tag name or ID |
||
|---|---|---|---|
|
/tn |
/tnex |
/ptid |
|
|
No |
No |
No |
|
|
No |
No |
Yes |
UserInt1 attribute contains source point ID. (Illegal configuration if source Data Archive-level failover is configured.) |
|
No |
Yes |
No |
|
|
No |
Yes |
Yes |
Tag of the interface point is also source point tag name. |
|
Yes |
No |
No |
|
The interface performs the following steps to find the source point:
-
If the /tn, /tnex , and /ptid command line parameters are not specified, and the InstrumentTag attribute is not a zero-length string, the InstrumentTag value contains the source tag name and the search ends. Otherwise, proceed to step 2.
If the /tn and /ptid command line parameters are not specified and the ExDesc attribute begins with case-insensitive “STAG” followed by zero or more spaces followed by “=”, the source tag name is extracted from the remainder of the ExDesc value (as described in the following paragraph) and the search ends. Otherwise, proceed to step 3.
-
To extract the source tag name, the interface ignores any spaces following the “=”. If the next character is not a double quotation mark ("), it is the first character of the source tag name which extends to the first comma or to the end of the ExDesc attribute. If the first non-space following the “=” is a double quotation mark, the source tag name begins with the following character and extends to the first double quotation mark or to the end of the ExDesc attribute. The interface extracts the source tag name from ExDesc and the search ends.
-
If no /tn parameter and no /tnex command line parameter and either the UserInt1 attribute is greater than zero or the /ptid parameter is present, the UserInt1 attribute is the source point ID and the search ends. Otherwise, proceed to the step 4. If the search ends in this step and either the UserInt1 attribute is not greater than zero or the interface is configured for source Data Archive-level failover, the interface rejects the point.
-
The source point tag name is the same as the receiving tag name.
The search for the source point ends with either a source tag name or source point ID. If the source tag name or point ID does not exist, the interface puts the point into an error state and logs a message.