26 REDUNDANT FUNCTION
26.2 System Switching
385
26
Precautions
The following describes the precautions on system switching.
*1 When the both systems are simultaneously turned on in a redundant system with redundant extension base unit, if a stop error occurs
during initial processing of the control system, the standby system also detects the stop error, and the system switching fails.
Item Description Reference
Error in the redundant function
module
• When an error has been detected on the redundant function module, the control system
and standby system continue operating without being switched.
• When a communication error has been detected in the communications between the
redundant function module and a CPU module, the systems are switched.
Page 386 Error in the
redundant function module
When both systems operate as
standby systems
• If a communication error has occurred due to a tracking cable error during system
switching, both systems may operate as standby systems.
• If a WDT error or a hardware failure of the CPU module has occurred in the control
system while a stop error exists in the standby system, both systems operate as
standby systems.
Page 386 When both
systems operate as
standby systems
When both systems operate as
control systems
If the tracking cable and the network cable that is connected to the network module
(control system or standby system) are simultaneously pulled out or disconnected, both
systems may operate as control systems.
In addition, if the tracking cable and the extension cable connected to the main base unit
of the control system are simultaneously pulled out or disconnected (if double failures
occur in one system), both systems may operate as control systems due to system
switching.
In this case, connect the tracking cable again. After a stop error has occurred in the
system B, power off and on or reset the system B.
Scan time monitoring function During system switching, scan time monitoring with the watchdog timer is interrupted.
Thus, in a scan in which the systems are switched, no error is detected even if the scan
time monitoring time has elapsed.
A time taken for system switching does not need to be considered in the scan time
monitoring time (WDT) setting.
System switching disabled by online
change
In a redundant system, the manual system switching is disabled during an online change. Page 386 System
switching disabled by
online change
Operation of an event execution
type program
When "ON of bit data (TRUE)" has been specified in the trigger type and the systems are
switched before tracking transfer of device data, an event execution type program does
not operate in the new control system.
When the cable for the network
module is disconnected
If a network module cable is disconnected, the systems may not be switched depending
on the timing of error detection on the control system and the timing on the standby
system.
Page 387 When the cable
for the network module is
disconnected
System switching during initial
processing/initial processing (when
switched to RUN)
• When a system switching cause has been generated during initial processing or initial
processing (when switched to RUN) on the control system, the systems are switched
after the initial processing or initial processing (when switched to RUN).
*1
• When a system switching cause has been generated during initial processing or initial
processing (when switched to RUN) on the standby system, whether the systems are
switched or not depends on the system switching cause.
Page 387 System
switching during initial
processing/initial
processing (when switched
to RUN)
CC-Link control at system switching When the master operating station is switched with a program by using the CC-Link
standby master function, the CC-Link control can be continued even after system
switching.
MELSEC iQ-R CC-Link
System Master/Local
Module User's Manual
(Application)
To Next Page
Loading...
