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Using a Quantum IEC Hot Standby System
840 USE 106 00 January 2003 135
7.4 Section Transfer Control
Section Transfer Control
Section Transfer
Control
Description
A new function has been added with Concept 2.5 that allows the selection of
section(s) that will not be transferred from the Primary controller to the Standby
controller with the exception of SFC sections. SFC sections are always transferred
every scan.
A benefit of selecting section(s) to not be transferred is that it allows you to reduce
the number of IEC Hot Standby registers in the configuration and thus reduce Hot
Standby scan time. The type of sections that should be slected for non-transfers are
those that do not have to be updated for every scan, i.e., Section that loads recipe.
This new function should be used along with guidelines for optimizing an IEC
application for IEC Hot Standby Operation to reduce HSBY scan time found in
Additional Guidelines for IEC Hot Standby , p. 147
.
Using Section
Transfer Control
The use of this feature requires initial planning of your Hot Standby project to insure
that logic not requiring an update fore every scan is segregated into its own
section(s) so that they can be selected for non-transfer. Logic elements that can be
used in non-transfer sections are those that have no internal states (e.g., contacts,
coils, etc.). Logic elements that should not be used in non-transfer sections are
those that have internal states (e.g., timers, counters, etc.) since the internal state
needs to be updated on every scan.
After sections are selected for nontransfer, the number of IEC Hot Standby registers
can be reduced. To insure that you have enough IEC Hot Standby registers
configured, go to the Memory Prediction dialog to view Hot Standby Memory usage.
See
Normal Operation, p. 140
. Additionally, you can perform an analyze program
under the project menu item. If you do not have enough IEC Hot Standby registers,
then you will receive an error message. This message will indicate the minimum
number of registers needed. A safety buffer should be added to this value to
configure space for future program modifications. The reduction of the IEC Hot
Standby registers is a change in the configuration and requires a complete
download of the project (i.e. the Hot Standby process has to be stopped). Selecting
sections to be not transferred without reducing IEC Hot Standby registers has no
effect on the Hot Standby scan time.