Rockwell Automation FactoryTalk Historian SE 3.0 UniInt Interface User Guide - Manual (Page 95)

UniInt Interface User Manual 89
1 2 3 4 5 6 7 8
Time
B
D
D
A
C
0
Point Values
1 Second Intervals
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
...
4
3
2
1
0
IF1
Heartbeat
IF2
State
IF2
Heartbeat
Active_ID
Time Action
T+0 Both interfaces are running with IF1
in the primary role.
T+2.1 Event A: IF1 stops updating its
heartbeat point.
T+3.5 Event B: IF2 notices that IF1‟s
heartbeat has not updated. IF2 will
discard data older than Time 1.5.
T+4.5 Event C: IF2 notices that IF1 still
has not updated its heartbeat. IF2
stops discarding old queued data.
T+6.5 Event D: IF1 still has not updated
its heartbeat so IF2 transitions to
Primary sending all data received
from Time 1.5.
Two things should be apparent in this figure.
The time it takes for the failover to occur is
slightly less than four and one half seconds
and the amount of overlapping data is just
over one half second.
Figure 3: Timing chart when the primary interface stops updating its heartbeat tag.