Rockwell Automation FactoryTalk Transaction Manager User Guide - Manual (Page 76)

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FactoryTalk Transaction Manager User Guide
76
Selecting a Collection Mode
For FactoryTalk data points, you can select the collection mode type. This
section provides more detail about the following types of data point
collection for FactoryTalk control connectors:
 Scheduled
 Device Scheduled
 Unscheduled
S
CHEDULED
: M
AINTAIN THE
C
URRENT
S
UBSCRIBED
V
ALUE
During scheduled collection mode, each data point is continuously on scan
at a configurable rate. The data server sends any change in value or quality
to the control connector. The control connector retains the current value in a
buffer and provides it to the FactoryTalk Transaction Manager service when
it is requested. The Transaction Control Manager service also buffers this
data internally and uses it as needed.
The data server reads the value of the data point at the Subscription Scan
Rate that is set on the FactoryTalk Data Point dialog box; if a new value is
found, it is sent to the data client. If the value has not changed in the data
server, no data is transferred. Thus network bandwidth is not used to
transmit the same value between the data server and the control connector.
Typically, this type of collection mode is used to support a transaction that
logs data constantly and rapidly (for example, logging a data point every
second while an assembly line is running).
D
EVICE
S
CHEDULED
: R
EQUEST THE
C
URRENT
V
ALUE
F
ROM THE
D
EVICE
During device scheduled collection mode, each data point is not on scan and
data is not buffered in the control connector or data server. The data server
reads directly from the device. Each value is read from the controller only
when the Transaction Control Manager service or FactoryTalk Transaction
Manager service requests it from the control connector. The value is then
retrieved from the controller and passed to the control connector.