ExDesc

Length

Depending on the version of the PI API and the PI Data Archive, this interface supports Tag attributes whose length is at most 255 or 1023 characters. The following table indicates the maximum length of this attribute for all the different combinations of PI API and PI Data Archive versions.

If the PI Data Archive version is earlier than 3.4.370.x or the PI API version is earlier than 1.6.0.2, and you want to use a maximum tag length of 1023, you need to enable the PI SDK.

The ExDesc is used to specify multiple configuration items. This field is used to specify if the optional Quality and Severity tags are to be configured. Also this field is used to identify the attribute(s) to be stored. Finally, this field is used to identify the vendor specific attributes (0- n) to be stored. Multiple parameters may be specified, each separated by a comma.

Configuring Severity and Quality Tags

Use the ExDesc attribute to configure the optional Quality (/QY) and Severity (/SY) tags associated with conditional event tags only (where the location3 field of the PI Tag contains a 2). These tags are built by the interface when this field contains the directive. These tags will not be deleted if the parent PI tag is deleted, instead Scan-Off will be written. If the ExDesc of the parent tag is edited and one or both directives are removed the tags will not be deleted and the interface will write Scan-Off for those tags.

For example, to store the quality attribute of the event in PI, include /QY in the ExDesc field. The interface will create the tag at start-up with a _QY suffix on the PI tag name. For example, if the PI tagname is Boiler1LevelAlarm, then the tag name for the quality tag is Boiler1LevelAlarm_QY.

The PI OPCAE interface conforms to the OPC Data Access standard. The OPC Data Access standard uses Fieldbus quality flags. The interface translates those quality flags to the closest approximation within the PI System State table, OPC_AE_QUAL (built by the interface).

The low 8 bits of the Quality flags are currently defined in the form of three bit fields: Quality, Sub-status and Limit status. The 8 Quality bits are arranged as follows:

QQSSSSLL

Good Quality

Not Used by OPC

Questionable

To store the Severity tag the interface creates this tag at start-up with a _SY suffix on the PI tag name. For example, to store the severity attribute of the event in PI, include /SY in the ExDesc field. If the PI tagname is Boiler1LevelAlarm, then the tag name for the severity tag is Boiler1LevelAlarm_SY.

The severity is a 4-byte integer in a range set by the server, which is normally a value from 1 to 1000.

Attribute PI Tag Identity

When storing all events/alarms attributes in separate PI tags, use the argument /att and the appropriate value(s) in the table below to identify the attribute to be stored. Using the /att allows the flexibility of what attribute(s) are stored for a particular alarm/event. A single attribute can be configured (e.g. /att=COND) or multiple attributes (e.g. /att=EVC,SUB,MES). The keywords are listed in the table below and are not case-sensitive:

Note: When specifying multiple attributes the order stored is the same as the table above

Using VSA1…VSAn in the Attribute PI Tag Identity

The VSA specification in the /att is a relative offset into the actual VSA offset specified by the /evc command parameter (Command-line parameters). Consider the following Attribute PI Tag Identity when the startup command line contains the event category definition

/evc1=1,601,602,603,604,605 or the equivalent entry exists in the Interface Configuration Utility:

When /att=COND,VSA602,VSA604,VSA605 is specified then those specific VSAs are archived.

Note: VSAs requested in this field must be configured either manually in the startup batch file or by the Interface Configuration Utility. Verify correct configuration of the /evc command argument to ensure correct behavior.

Using SRC in the Attribute PI Tag Identity

This feature may be used at anytime, although it is most useful when ‘/ALL’ has been specified in the instrumenttag (see section InstrumentTag). It is designed to add the source name to archived data so that when ALL events are archived to this point, events from different sources can be distinguished. Area events, however, have no source. For area events, the interface will attempt to retrieve the area name for use in place of the source name.

Note: The /ALL tag configuration without additional attributes is designed for testing purposes and should NOT be used in a production environment

Vendor-Specific Attributes Identity

Because vendor-specific attributes are different between systems and event categories, it can sometimes be useful to label the attributes. This field can be used to ‘name’ a specific VSA attribute. This enhances the support for alarms and events client tools, such as PI-AlarmView, when identifying the attributes for display. For example, if vendor attribute 1 is the ‘Area’ then to identify it in the PItag, set the ExDesc to /vsa1=”Area”. This can be used by client tools to display the field name along with the value for this attribute.

Example use of the ExDesc

Below is an example of configuring the ExDesc attribute with the quality tag, severity tag, PI tag identity and vendor attributes identity.

/QY,/SY,/att=sub, /VSA1="Alarm Name"