Rockwell Automation FactoryTalk Historian SE 3.0 UniInt Interface User Guide - Manual (Page 38)

Interface Operation
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However, the interface specific documentation must be consulted to determine the exact
manner in which time is handled.
UTC time is defined here as the number of seconds since January 1, 1970 00:00:00 in
Greenwich, England. As of version 3.1.3, UniInt uses the UTC time of the Historian Server
node instead of the UTC time of the local interface node. Ideally, the UTC times of the
server and interface nodes are the same because UTC time is the same in every time zone.
However, there is normally some drift between clock times.
If an interface supports DCS timestamps, the DCS timestamp must not be more than
10 minutes ahead of the Historian Server time because Historian cannot archive events that
occur more than 10 minutes in the future.