Rockwell Automation FactoryTalk Historian SE 3.0 UniInt Interface User Guide - Manual (Page 97)

UniInt Interface User Manual 91
1 2 3 4
Time
B
A
Point Values
1 Second
Intervals
C
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+2.5 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: the active ID point on the
data source is changed from 1 to
2.
T+3 Event B: IF1 reads the active ID
point and IF2‟s heartbeat point.
IF2‟s heartbeat is good and the
active ID has changed to a 2, so
IF1 immediately transitions to
backup.
T+3.5 Event C: IF2 notices that the
active ID point on the data source
is 2 and immediately transitions to
primary. The data in its queue and
any new data are sent to
Historian.
Overlap data from time 0.5 to 3.
Figure 4: Timing chart for a manual failover to the backup interface.