Operation Modes Of The Redundant System - Mitsubishi Electric MELSEC iQ-R-R00CPU User Manual

26.5

Operation Modes of the Redundant System

A redundant system operates in one of the following two modes.
Operation mode
Backup mode
Separate mode
A redundant system is started in the backup mode. To switch the operation mode, use the engineering tool. ( Page 438
Operation Mode Change)
The following table describes differences between the backup mode and the separate mode.
Item
Program operation
System switching
Tracking transfer
Memory copy from
control system to
standby system
System consistency
check
Program execution type
Interrupt program
execution enable/disable
status
I/O refresh
Link refresh
Writing data to the
programmable controller
Remote operation
function
Time synchronization
26 BASIC CONCEPT
408
26.5 Operation Modes of the Redundant System
Description
A mode used to normally operate the redundant system.
When an error or failure has occurred in the control system, the standby system is switched to the control system to continue the
operation. Even if a system failure has occurred in the control system, the standby system of the redundant system continues the
operation because data is transferred from the control system to the standby system at every scan.
A mode used to maintain the redundant system without stopping controls.
In separate mode, the control system CPU module and the standby system CPU module can execute different programs. The
program of the standby system can be modified and the operation of the program can be checked with the data tracked from the
control system while the system is being controlled in the control system.
Backup mode
The control system executes programs.
The standby system CPU module executes programs according
to "Both Systems Program Executions Setting" in "Program
Setting" of "CPU Parameter". With the default setting, the
standby system does not execute programs.
To switch the mode to the backup mode, refer to the following.
Page 439 Mode switching to the backup mode
Automatic system switching and manual system switching are
supported.
Data is transferred according to "Tracking Setting" of "CPU
Parameter".
The following copy operations can be performed.
• Automatic memory copy
• Memory copy with the engineering tool
• Memory copy with the special relay and special register
The system consistency check is performed.
■When the operation mode is changed to the backup mode
The control system and the standby system take over their
execution types before the operation mode change.
■When the operation mode is changed to the backup mode
The control system and the standby system take over their
execution enable status before the operation mode change.
Whether or not to refresh the output (Y) of the standby system
depends on "Standby System Output Setting" of "CPU
Parameter".
With the default setting, the output (Y) of the standby system is
not refreshed.
Data is not transferred from devices of the CPU module in the
standby system to link devices.
Data can be written to both systems. Or, data can be written to
only a system specified in the connection destination setting.
Remote operations can be performed on both systems.
Time of the standby system is synchronized with that of the
control system.
Separate mode
Both of the control system and the standby system execute
programs.
To switch the mode to the separate mode, refer to the following.
Page 438 Mode switching to the separate mode
Only manual system switching is supported.
Data is transferred according to "Tracking Setting" of "CPU
Parameter".
However, the following data causes tracking transfer to stop.
• Local devices, local labels
• Special relay, special register
• PID control instruction information
• Signal flow memory
The following copy operations can be performed.
• Memory copy with the engineering tool
• Memory copy with the special relay and special register
The system consistency check is not performed.
■When the operation mode is changed to the separate mode
The control system and the standby system operate differently.
• The control system takes over its execution type before the
operation mode change.
• The standby system operates in the execution type specified
by the CPU parameter.
■When the operation mode is changed to the separate mode
The control system and the standby system operate differently.
• The control system takes over its execution enable status
before the operation mode change.
• The standby system disables execution of interrupt programs.
Even though "Standby System Output Setting" has been set to
"Disable" in "CPU Parameter", the output (Y) of the standby
system is enabled.
Data is transferred from devices of the CPU module in the
standby system to only the link special relay (SB) and link
special register (SW). (Except for CC-Link)
Data is written to only a system specified in the connection
destination setting.
Remote operation with the engineering tool can be performed
only on a system specified in the connection destination setting.
Time of both systems is not synchronized.