Rockwell Automation 1756-HIST2G FactoryTalk Historian ME 2.2 - Manual (Page 99)

5 • M ANAGING P OINTS
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point source. The point type of the trigger point does not have to be same point
type as the Output point.
The Output point is associated with the trigger point by setting the Source Tag
attribute of the Output point equal to the tag name of the trigger point. Any scan
tag referenced in the Extended Description or Scan Tag fields must not be high
speed or have a scan rate of faster than 1 second. If it does, the module will
generate an error and prevent you from saving your work in the Point Property
page. 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.
„
By writing a new value to the snapshot of the output point itself. The new value
need not be different from the previous value to trigger an output, but the
timestamp of the new value must be more recent than the previous value.
Point Attributes
The Point Property page contains three fields that are used for Trigger Input and
Output points:
„
Extended Description
„
Instrument Tag
„
Source Tag
Note that:
„
The Scan Rate is not applicable to the Trigger Input tag.
„
The Scan On drop-down menu must be set to On.
„
The trigger tag name must be in single quotes.
E XTENDED D ESCRIPTION : T RIGGER C ONDITIONS
The Extended Description field on the Point Property page is used for the trigger
condition and the keywords that indicate trigger condition: TRIG or EVENT. Ensure
that the words TRIG and EVENT are uppercase. Condition names are case-
insensitive.
The TRIG keyword:
„
Does not require any condition.
„
Has a default condition of Any.