Rockwell Automation 1756-HIST2G FactoryTalk Historian ME 2.2 - Manual (Page 98)

F ACTORY T ALK H ISTORIAN ME M ODULE U SER ’ S G UIDE
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Input Points
An input point is a polled, advised, or high speed or triggered point when the data
flow is from a controller to the FactoryTalk Historian ME snapshot and archive. For
Trigger Input points, a separate trigger point must be configured. The input point is
associated with a trigger point by entering point attributes in the Extended
Description field for the input point as follows:
<keyword>=‘<trigger_tag_name>’;<condition>
where the keyword is TRIG or EVENT, trigger_tag_name is the name of the trigger
point, and condition is Any, Anychange, Nonzero, Decrement, or Increment. 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.
FactoryTalk Historian ME automatically assumes a point is trigger-based, rather than
scan-based, when the <keyword>=‘<trigger_tag_name>’;<condition> string is found
in the Extended Description field. An input is triggered when a new value is sent to
the snapshot of the trigger point.
Output Points
A point is an output (also known as a write back) point when the data is read from
from the FactoryTalk Historian ME archive to a controller. For Output points, the
timestamp of the trigger value must be greater than the timestamp of the previous
value. Output points are triggered in two ways:
„
By configuring a separate trigger point. The output point must have the same
point source as the interface, FTME. The trigger point can be associated with any
FactoryTalk Historian ME Archive
To External Data Source From External Data Source
Output points Trigger Input points
Controller
Controller
(Write back)