Rockwell Automation FactoryTalk Historian SE 3.0 UniInt Interface User Guide - Manual (Page 93)

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
Time Action
T+0 Both interfaces are running with IF1 in
the primary role.
T+2.5 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.
T+2.8 Event A: IF1 shuts down gracefully,
setting the active ID point and its
heartbeat point to 0.
T+3.5 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.