Time Sync Issue in Alarm List
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The OPC AE standard dictates that the OPC AE server send time tagged A&E.
Hence, the time is taken from the OPC AE server. Most OPC AE servers receive time tagged A&E from the PLC itself.
You did not tell what PLC you are using, but with high probability you have a PLC with a time synchronization problem. Present, or only in the past.
The Automation System Network User's Guide contains detailed information on how to synchronize the time in System 800xA - please study it. Your choice of PLC affects the settings, so do also refer to your PLC's specific user's guides.
Most OPC AE servers in 800xA are capable of "refresh", so the alarm content should refresh into the alarm list(s) once you have gotten the OPC AE server and PLC wíth correct time. A connectivity server restart should trigger a new refresh if nothing else works, but you can always start with the OPC AE server and corresponding Event Collector service provider.
"Delete" in 800xA alarm lists is not very useful when the OPC AE server support refresh, any deleted alarm will resurface at next refresh with the source OPC server. So, instead of deleting alarms, get your PLC's and OPC AE server's time straightened out. There are OPC AE clients with which you can view an OPC AE server's content. Work out the problem in the OPC AE server and 800xA alarm lists should update themselves.