ExDesc (extended descriptor)

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Last UpdatedFeb 14, 2023
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The ExDesc attribute configures a variety of run-time settings, two of which are included in every interface and are described in the following table.

Note: Keywords must be specified in upper case.

Keyword	Description	Example
PERFORMANCE_POINT	When set, such point stores the amount of time, in seconds, that it takes an interface to complete a scan for a particular scan class. The lower the scan time, the better the performance.	PERFORMANCE_POINT For details, refer to the PI UniInt Framework 4.6.0 User Guide.
EVENT	An input is triggered when a new value is sent to the Snapshot of the trigger point. The new value does not need to be different than the previous Snapshot value to trigger an input, but the timestamp of the new value must be greater than (more recent than) or equal to the timestamp of the previous value. Valid trigger conditions: anychange - any change in value increment - any increase in value decrement - any decrease in value nonzero -any non-zero value Note: Not triggered by system digital states For details about defining event- driven points, refer to the PI UniInt Framework 4.6.0 User Guide.	/EVENT=sinusoid, … or /EVENT =sinusoid anychange, …

Keyword

Description

Example

PERFORMANCE_POINT

When set, such point stores the amount of time, in seconds, that it takes an interface to complete a scan for a particular scan class. The lower the scan time, the better the performance.

PERFORMANCE_POINT For details, refer to the PI UniInt Framework 4.6.0 User Guide.

EVENT

An input is triggered when a new value is sent to the Snapshot of the trigger point. The new value does not need to be different than the previous Snapshot value to trigger an input, but the timestamp of the new value must be greater than (more recent than) or equal to the timestamp of the previous value.

Valid trigger conditions:

anychange - any change in value
increment - any increase in value
decrement - any decrease in value
nonzero -any non-zero value

Note: Not triggered by system digital states

For details about defining event- driven points, refer to the PI UniInt Framework 4.6.0 User Guide.

/EVENT=sinusoid, … or

/EVENT =sinusoid anychange, …

Note: To assign values to replaceable parameters in SQL queries, you specify placeholders in the ExDesc attribute. Replaceable parameters in queries are indicated by question marks.

ExtendedDescriptor Length

Depending on the version of the PI API and the Data Archive, this interface supports an ExDesc attribute whose length is at most 80 or 1023 characters. The following table indicates the maximum length of this attribute for all the different combinations of PI API and Data Archive versions.

PI API	Data Archive	Maximum Length
PI API	Data Archive	Maximum Length
6.0.2 or later	4.370.x or later	1023
6.0.2 or later	Earlier than 3.4.370.x	80
Earlier than 1.6.0.2	4.370.x or later	80
Earlier than 1.6.0.2	Earlier than 3.4.370.x	80

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.

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