Rockwell Automation FactoryTalk Transaction Manager User Guide - Manual (Page 77)

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Defining Data Points
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Typically, this mode of collection is used to support a transaction that logs
data infrequently.
U
NSCHEDULED
: S
END
S
UBSCRIBED
V
ALUE
W
HENEVER
I
T
C
HANGES
This collection mode is driven by the data server and each data point is
continuously on scan at the prescribed rate. When the server detects a
change to a data point value or quality, it sends the value to the control
connector, which passes it to the Transaction Control Manager service or the
FactoryTalk Transaction Manager service. This collection mode is
event-based, not time-based.
Keep in mind that any unsolicited message sent by the controller that does not
include a change in value or quality will never be sent to FactoryTalk Transaction
Manager.
The Subscription Scan Rate sets the limit on how fast new data can arrive.
For example, if the Subscription Scan Rate is 150 milliseconds, the data
server cannot send changes faster. If the underlying data value is changing
faster, the control connector only sees the current value every 150
milliseconds.
Typically, this mode of collection is used for a transaction trigger that
executes at a high or low transition, or exceeds a valid range.
Consecutive Data Point and Data Block Support
You can quickly add multiple consecutive data points in your application.
For example, if you want to add multiple consecutive data points N7:0
through N7:6, select them from the Contents of window on the FactoryTalk
Transaction Manager FactoryTalk Data Point dialog box, and then click Add
Selected Tags to add them to the FactoryTalk data point grid.
You can create a single data point with blocked data, such as a data point that
has multiple consecutive elements. For example, if you want to create a data
point with 10 elements, type N7:0,L10. This feature applies to pure data
table files and not to structures (for example, T3:0.ACC,L8 is not
supported). The maximum size of a data block passed to the connector from