Rockwell Automation FactoryTalk Transaction Manager User Guide - Manual (Page 136)

●
●
●
●
●
FactoryTalk Transaction Manager User Guide
136
B
UFFERING
I
N THE
F
ACTORY
T
ALK
T
RANSACTION
M
ANAGER
C
ONTROL
C
ONNECTOR
The FactoryTalk Transaction Manager control connector maintains a copy
of the data. Data servers, which may have separate copies of the data, send
changed values to the control connector. Once in the control connector, the
data is either sent to the FactoryTalk Transaction Manager service
(unscheduled data points) or is buffered until it is requested (scheduled data
points). Unscheduled data points that are sent to the FactoryTalk
Transaction Manager service are used in currently running transactions or as
transaction triggers, or they are used to update the current value table of the
FactoryTalk Transaction Manager service. If the data points are not
immediately needed, they can be overwritten before the data is used. This
will appear to cause data loss.
Scheduled data points are only used when a transaction is executed.
Scheduled data points are stored in the control connector until the
FactoryTalk Transaction Manager service requests them. If the transaction
executes slower than the data is changing in the controller, then data may be
overwritten in the control connector’s buffer. In some circumstances, lost
data is acceptable (for example, where a temperature is recorded every five
minutes but fluctuates every few seconds). The control connector is aware of
every change while the FactoryTalk Transaction Manager service is only
aware of the value that is current every five minutes.
B UFFERING I N THE T RANSACTION C ONTROL M ANAGER S ERVICE
The Transaction Control Manager service has a local data point cache that
contains the current values for every data point and the time the value was
collected. If the Data Valid option that you set on the FactoryTalk Data Point
Definition dialog box is set to zero, data is not requested from the
FactoryTalk Live Data server because this server automatically provides
updated data values when they change (hence, the values for the Transaction
Control Manager services are always correct). Transactions buffer their own
values and only request those values from the Transaction Control Manager
service master value table when the Data Valid timeout has occurred. An
exception to this rule is Device- Scheduled points, which are read from the