Rockwell Automation FactoryTalk Historian SE 3.0 UniInt Interface User Guide - Manual (Page 30)

Historian Point Configuration
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example, to write a value to a register in a PLC, one would use an output point. Each
interface has its own rules for determining whether a given point is an input point or an
output point. There is no de facto Historian point attribute that distinguishes a point as an
input point or an output point.
Outputs are triggered for UniInt-based interfaces. That is, outputs are typically not scheduled
to occur on a periodic basis. There are two mechanisms for triggering an output.
As of UniInt 3.3.4, event conditions can be placed on triggered outputs. The conditions are
specified using the same event condition keywords in the extended descriptor as described
under ―Trigger-Based Inputs.‖ The only difference is that the trigger tag is specified with the
SourceTag attribute instead of with the ―event‖ or ―trig‖ keywords. Otherwise, the behavior
of event conditions described under ‗Trigger-Based Inputs‖ is identical for output points. For
output points, event conditions are specified in the extended descriptor as follows:
event_condition
Trigger Method 1 (Recommended)
For trigger method 1, a separate trigger point must be configured. The output point must have
the same point source as the interface. The trigger point can be associated with any point
source, including the point source of the interface. Also, the point type of the trigger point
does not need to be the same as the point type of the output point.
The output point is associated with the trigger point by setting the SourceTag attribute of the
output point equal to the tag name of the trigger point. An output is triggered when a new
value is sent to the Snapshot of the trigger point. The new value does not need to be different
than the previous value that was sent to the Snapshot to trigger an output, but the timestamp
of the new value needs to be more recent than the previous value. If no error is indicated,
then the value that was sent to the trigger point is also written to the output point with the
same timestamp as the trigger point. If the output is unsuccessful, then an appropriate digital
state that is indicative of the failure is usually written to the output point. If an error is not
indicated, the output still may not have succeeded because the interface may not be able to
tell with certainty that an output has failed.
Trigger Method 2
For trigger method 2, a separate trigger point is not configured. To trigger an output, write a
new value to the Snapshot of the output point itself. The new value does not need to be
different than the previous value to trigger an output, but the timestamp of the new value
must be more recent than the previous value.
Trigger method 2 may be easier to configure than trigger method 1, but trigger method 2 has
a significant disadvantage. If the output is unsuccessful, there is no tag to receive a digital
state that is indicative of the failure, which is very important for troubleshooting.