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MELSEC-Q
3 SPECIFICATIONS
3.3.4 Output holding time during system switching in the multiplexed remote I/O network for
redundant system
In the multiplexed remote I/O network for redundant system, if an error occurs in the
multiplexed remote master station of the control system, the multiplexed remote sub-
master station of the standby system takes over the control of remote I/O stations. At
the time of system switching, remote I/O stations hold the outputs (data).
The output holding time of remote I/O stations during system switching differs with the
reason of system switching. In addition, it is affected by the CPU system switching
time and the switching time between a multiplexed remote master station and a
multiplexed remote sub-master station.
The following shows the calculation formula of output holding time for each reason for
system switching.
(1) When a power failure or CPU module stop error occurs
(a) CPU system switching time < System switching time from the multiplexed
remote master station to the multiplexed remote sub-master station
Standby system control system CPU
Output holding time of remote I/O station
A power failure has occurred on the control system
SS
Ds2
Toh
Control system standby system CPU
[Output holding time (Toh)]
Toh = Ds2 + SS [ms]
Ds2: Switching time from the multiplexed remote master station to the
multiplexed remote sub-master station [ms]
SS: Scanning time of the redundant CPU [ms]