Rockwell Automation FactoryTalk Historian SE 3.0 UniInt Interface User Guide - Manual (Page 104)

UniInt Failover Scheme
98
Time Action
T+0 Both interfaces are running with IF1
in the primary role.
T+2.1 IF2 reads the ActiveID and IF1‟s
heartbeat. Both are good, so IF2
discards data older than time 0.1.
T+2.9 Event A, IF1‟s stops for any reason
just before updating its heartbeat.
T+3.1 Ev ent B, IF2 notices that IF1‟s
heartbeat has not updated. IF2 will
discard data older than Time 1.1.
T+4.1 IF2 notices that IF1 still has not
updated its heartbeat. IF2 stops
discarding old queued data.
T+5.1 IF2 notices that IF1 still has not
updated its heartbeat.
T+6.1 Event C, IF1 still has not updated its
heartbeat so IF2 transitions to
Primary sending all data received
from Time 1.1 and sets the ActiveID
to 2.
The time it takes for the failover to occur is slightly
more than three seconds and the amount of
overlapping data is almost two seconds from time
1.1 to time 2.9.
Figure 8: Timing Chart for the Minimum Failover Time with Maximum Overlap.