Rockwell Automation FactoryTalk Historian SE 3.0 UniInt Interface User Guide - Manual (Page 99)

UniInt Interface User Manual 93
B
A
C
Point Values
B
1 2 3 4
Time
1 Second
Intervals
31
30
29
…
18
17
-
14
13
...
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
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 older than time 0.5.
T+3 Event A: IF1 updates its heartbeat to 30
because it has lost its connection to the
Historian Server. When the connection
to Historian is lost, the heartbeat for the
interface increments between 17-31
and then back to 17. In this example
the primary interface copy heartbeat
was at 13 for IF1, so the next heart beat
will be 30 if the connection to Historian
is lost.
T+3.5 Event B: IF2 reads the active ID point
and IF1‟s heartbeat point. IF2 still has a
good connection to Historian, so it
transitions to primary and sets the
active ID point to 2.
T+4 Event C: IF1 reads the active ID point
and notices the change to a 2. IF1
immediately transitions to backup.
Overlap data from time 0.5 to 4
Figure 5: Timing chart for failover when the primary interface loses its connection with the
Historian Server.