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5.3 The System Switching Function
5.3.1 System Switching Method
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(1) Automatic System Switching
In automatic system switching, the redundant CPU determines if a system switching
is necessary and automatically switches the control system and standby system.
2 types of automatic system switching are available: automatic system switching
when a fault occurs in the control system, and system switching requested by the
network module.
(a) System switching when a fault occurs in the control system
In the redundant system, the standby system CPU module monitors the control
system operating status.
When the control system is in any of the following status and is not able to
continue the redundant system control, the standby system CPU module switches
to the control system and continues the redundant system control.
• A stop error occurs in the control system CPU module
• The control system is powered OFF
• The control system CPU module is reset
If a continuation error occurs in the control system CPU module, system switching
will not occur.
Diagram 5.23 shows the processes that take place if a stop error occurs in the
control system CPU module:
Diagram 5.23 System switching operations when a control system error occurs
Automatic switching
Control system Error
System A - Control System
System B - Standby System
Tracking cable
System A -
(Control System -->
Standby System)
System B -
Standby System -->
Control System
Tracking cable
Begin Control
fault
fault
Stop Error has
occurred
System A
Control
system
fault
System B
Standby
system
Control
system
RUN
(Execute program)
Normal Standby
RUN
(Stop program)
RUN
(Execute program)
Standby
system
Stop Error
System
switching