Storing event attributes

Events have attributes that contain important information about the alarm or event. Some attributes are standard for all OPC AE servers, and some are vendor specific attributes that are unique to individual servers. There are 2 mechanisms used to store these attributes. The first is to store attributes in a PI tag based on the default set by the interface. These attributes are stored in a PI string tag. Quality and severity attributes associated with conditional events are optional and stored in separate tags. Event attributes are limited to 32 attributes per event category.

Below is the standard mechanism for storing alarms and events attributes for Simple, Tracking and Conditional types:

Simple Events

Simple events are events that store information about a single event such as a system or device failure. Simple event attributes are stored in a single string tag, separated by the pipe character (|), in the order listed below.

1. EventCategory

2. Severity

3. Message

4. OPC States – Enabled/Active/Acked/AckReqd

5. Vendor specific attribute(s) (optional) – VSA(1); …VSA(n)

Tracking Events

Tracking events represent occurrences with changes directed from an OPC AE client with an object in the OPC AE server. An example of a tracking event would be logging of the operator when changes are made to a process point. Tracking event attributes are stored in a single string tag, separated by the pipe character (|), in the order listed below.

6. EventCategory

7. Severity

8. Message

9. OPC States – Enabled/Active/Acked/AckReqd

10. AckReqd

11. OperatorID

12. Vendor-specific attribute(s) (optional) – VSA(1); …VSA(n)

Condition-related Events

Condition-related events are stored as string tags and represent changes into and out of process states. An example of a condition-related event would be a Temperature Alarm transitioning into a state of High Alarm. All event related information is stored in a single string tag and is separated by the pipe character (|). The Quality and Severity tags are created by the interface during start-up if configured in the ExDesc using the /QY and/or /SY options (Optional – See ExDesc

13. Conditions

14. Sub-Conditions

15. Message

16. ActorID

17. OPC States – Enabled/Active/Ackd

18. AckReqd

19. Vendor-specific attribute(s) (optional) – VSA(1);…VSA(n)

20. Quality – tag (Optional – See ExDesc)

21. Severity – tag (Optional – See ExDesc)

The second mechanism used to store alarms and events is to allow the selection of attribute(s) to be stored (Attribute PI Tag Identity).