
UniInt Interface User Manual 87
15
14
13
12
11
...
4
3
2
1
0
Active_ID
0
1
2
IF1
State
Primary
Backup
Off
Primary
Backup
Off
1 2 3 4
Time
B
A
0
Point Values
1 Second
Intervals
B
15
14
13
12
11
...
4
3
2
1
0
IF1
Heartbeat
IF2
State
IF2
Heartbeat
Both interfaces are running with IF1 in
the primary role.
IF2 reads the active ID point and IF1‟s
heartbeat point. Both are good so IF2
discards data in its queue older than
time 0.5.
Event A: IF1 shuts down gracefully,
setting the active ID point and its
heartbeat point to 0.
Event B: IF2 notices the active ID point
is 0 and immediately transitions to
primary, sending the data in its queue to
Historian.
Overlap data from time 0.5 to 2.8
Figure 2: Timing chart for when the primary interface gracefully shuts down and the backup
interface assumes the role of primary.
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