Rockwell Automation FactoryTalk Historian SE 3.0 UniInt Interface User Guide - Manual (Page 101)

UniInt Interface User Manual 95
A
C
Point Values
1 2 3 4
Time
1 Second Intervals
6 7 8 5
B
15
14
13
12
11
...
4
3
2
1
0
0
1
2
IF1
State
Primary
Backup
Off
Primary
Backup
Off
0
15
14
13
12
11
10
9
8
7
6
5
IF1
Heartbeat
IF2
State
IF2
Heartbeat
Active_ID
Time Action
T+0 Both interfaces are running with IF1 in
the primary role.
T+2.25 Event A: IF1 stops updating its
heartbeat point for any reason.
T+2.5 IF2 reads the active ID point and IF1‟s
heartbeat point. Both are good so IF2
discards data older than time 0.5.
T+3.5 Event B: IF2 notices that IF1‟s
heartbeat point has not updated. IF2
discards data older than Time 1.5.
T+4.5 IF2 notices that IF1 still has not
updated its heartbeat point. IF2 stops
discarding queued data.
T+5.5 IF2 notices that IF1 still has not
updated its heartbeat point.
T+5.75 Event C: IF1 resumes operation. The
active ID point is equal to IF1‟s ID, so
IF1 updates its heartbeat point and
continues operating normally.
T+6.5 IF2 notices IF1 has updated its
heartbeat point. IF2 will send the data
it has in its queue and then return to
normal backup operation.
IF1 was not collecting data from time 2.25 to
time 5.75. IF2 will send the data it received from
time 1.5 to time 6.5. This will lead to two periods
of overlapping data: from time 1.5 to time 2.25
and from time 5.75 to time 6.5.
Figure 6: Timing chart for failover when the primary interface stops updating its heartbeat
point for less than five intervals.