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Notification :
A message which reports the current value of the changed property as well as the current state of the objects Status Flag property if it exists. The notification also contains the number of seconds remaining to the subscription. Confirmed notifications require a response from the COV client.
18.7. Discussion and Limitations of COV
General Discussion
There are some intrinsic problems with event or change reporting systems.
In our experience it is fairly common to learn that a well configured system failed to deliver the critical information only after a significant failure. We learn the hard way that we polled for data too slowly, the logger was offline when the notification was sent or that the logger was swamped with data because of the failure of incoming feed. With this in mind we draw your attention to some if the issues you should consider.
18.6. Change Criteria
The change criteria are based on the type of subscription
Subscribe to the object :
Either of these changes trigger notification
1) If the status flags change at all
2) If the Present Value changes
- Binary, Life Safty and Multistate Objects : any change to Present Value
- Analog, Loop and Pulse Objects: change by COV_Increment
Subscribe to a property :
Either of these changes trigger notification
1) If the status flags change at all (if the object has status flags)
2) If the Property Value changes
- Property is of type REAL : change by COV_Increment ( which may be defined in the subscription or may be the native increment defined in the device).
- Property is of some other type: any change to Present Value
18.7. Discussion and Limitations of COV
General Discussion
There are some intrinsic problems with event or change reporting systems.
In our experience it is fairly common to learn that a well configured syst