References to attribute values

When configuring a PI point data reference attribute, you can use substitution parameters to reference the value of another attribute. You can use attribute value references to specify a value in the Relative Time field or in the point attribute configuration for automatically-generated PI points. The syntax is:

%@AttributeName%

where AttributeName is the name of the attribute. The @ indicates to substitute the value of the indicated attribute, rather than its name. To reference an attribute that is not a sibling of the current attribute, use the syntax described in Indirect PI point references to define the path to the desired attribute.

PI AF does not update the attribute value over time. When a substitution is used in the tag name, the value is resolved only at the time the data reference is loaded. If a substitution parameter is used to define point attributes, PI AF uses the value of the attribute at the exact time that you created or updated the data reference (see Attribute-value updates from PI point data references for more information). This value is a constant. PI AF does not evaluate that attribute value again, unless you update the data reference.

Note: The exception to this rule is a value substitution for the Relative Time, which is evaluated on every value call to the PI point data reference (see Create ranges of configurable durations).