Rockwell Automation FactoryTalk Transaction Manager User Guide - Manual (Page 81)

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Defining Data Points
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case of high-speed data changes). If the data is changing at a high rate, then
switch the transactions to unscheduled.
Unscheduled transactions offer better protection against stale and
mismatched data via the use of ladder logic. The controller dictates when the
data is read and it can lock values into its registers prior to triggering the
transaction. This helps prevent stale data from being read as long as the data
valid time is set to zero for a non-trigger data point.
The best way to prevent stale or mismatched data is to use unscheduled data
point blocks. All data is handled as a single unit, managed by the controller,
and parsed into separate units using the Parse function from the Transaction
Definition dialog box (double-click a transaction in the right pane of the
FactoryTalk Transaction Manager workspace). This method may also
reduce traffic on the controller network because the data is not scanned at a
constant rate.
Specifying Quality
For the FactoryTalk Live Data connectors, choose one of the bad quality
options if you want the Transaction Control Manager service or FactoryTalk
Transaction Manager service to use bad quality values. Otherwise, select
Use Substitution Option for Bad Quality on the Edit Collection Parameters
dialog box. If you do not select a bad quality value, the Transaction Control
Manager service or FactoryTalk Transaction Manager service uses one of
the substitution policies listed earlier in this chapter when it receives a bad
quality value for this data point.
If you choose to allow bad quality values, then use the QualityOf()
expression from the Expression Editor dialog box to bind the quality value
to a column in your database. In addition, the bad quality status is saved to
the Transaction Control Manager service log file or the control connector’s
log file (when using the FactoryTalk Transaction Manager service) at an
error level. The QualityOf() expression provides the following quality
values: