Rockwell Automation FactoryTalk Historian SE 3.0 UniInt Interface User Guide - Manual (Page 89)

UniInt Interface User Manual 83
Failover ID
In a failover interface installation, each copy of the interface has its own unique positive
integer identifier. This identifier is referred to as the failover ID and is specified with
the interface startup parameter, /UFO_ID=n.
Failover Update Interval
The failover update interval determines the rate at which UniInt updates the heartbeat
points, how long it takes for the interface to failover, and how much overlapping data may be
sent to Historian. The optional /UFO_Interval startup parameter specifies the failover
update interval for unsolicited failover control tags. Each copy of the interface may define
the failover update interval as specified by the /UFO_Interval=i. However, both
interface copies participating in failover must use the same value, i, specified by the
/UFO_Interval=i parameter. The failover update interval, i, is specified in milli-
seconds with the default being 1000 milli-seconds or 1 second. The valid range for the
failover update interval is 50 – 20000 milli-seconds.
The /UFO_Interval startup parameter can only be used with unsolicited input interface
failover control tags. If the interface supports scan based input data and the interface failover
tags are defined as scan based input tags, the update interval is then defined by the scan class
to which the control tags belong.
Heartbeat Point
The heartbeat point is used to indicate that the interface is functioning. This point is
updated once every failover update interval. If the interface is connected to the Historian
Server, the value of the heartbeat point will be incremented by UniInt from 1 – 15 and then
wraps around to a value of 1 again. If the connection to the Historian Server is lost, the value
of the heartbeat point will be incremented from 17 – 31 and then wrap around to a value of
17 again. Once the connection to the Historian Server is restored, the heartbeat values will
revert back to the 1 – 15 range. During a normal shutdown process, the heartbeat value will
be set to zero.
Hot Failover
In a hot failover configuration, the interface copy that is in a backup role collects and queues
data in parallel to the interface that is in the primary role. The interface in the backup role
does not send the data collected to Historian. However, if a failover were to occur, the
interface would immediately send its data to Historian. This mode of failover eliminates loss
of data for a single point of failure.