Unsolicited Trigger
Event-based triggers have a dependency list of trigger tags. The trigger fires whenever there is a data change for the trigger tag. Quality changes of the trigger tag will cause a new raw sample and therefore the trigger will fire. Value changes of the trigger tag occur when the tag exceeds the collector compression (if you enabled collector compression).
The calculation is processed each time any tag in the dependency list changes. If you have multiple tags in the list and they change even one millisecond apart, then you will have multiple events and the calculation formula will be processed for each.
- Deletion of a tag that is in the dependency list.
- Re-addition of a tag in the dependency list.
The calculation time of an event-based calculation is the timestamp of the sample in the trigger tag that caused the firing. The values of all other tags in the formula are interpolated forward to this time so that the timestamps of all input tags are the same. Even though these are sequential events, they have the same timestamp. The calculation time becomes the timestamp for the sample stored in the destination tag.
Event-based triggers have a collection interval. The Calculation Collector notifies the archiver not to send notification of changes to trigger tags any faster than the collection interval setting.