System Switching; System Switching Method - Mitsubishi Electric MELSEC iQ-R-R00CPU User Manual

37.1

System Switching

This function switches the systems between the control system and the standby system to continue operation of the
redundant system when a failure or an error occurs in the control system. The systems can also be switched manually by a
user for debugging or maintenance.

System switching method

The following two methods are available for system switching: automatic system switching (automatically performed by a
system) and manual system switching (performed by a user).
The following table lists the system switching types, causes, and priority of when multiple causes are simultaneously
generated.
System switching type System switching cause
Automatic system switching Power-off, reset, hardware failure of the CPU module
Stop error of the CPU module
System switching request from a network module
Manual system switching System switching request by the SP.CONTSW instruction
System switching request from the engineering tool
• When multiple system switching causes are simultaneously generated, the systems are switched according to the cause
with higher priority. The switching cause determined according to the priority is stored in the event history and SD1643
(System switching cause).
• The manual system switching is requested for the control system CPU module.
The systems are not switched even when the CPU module is set to the STOP state. They are switched when
any of the above system switching causes is generated.
Priority
High 1

2

3
Low
4
5
37 FUNCTIONS
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37.1 System Switching
37