Mitsubishi Electric MELSEC Q Series Reference Manual page 266

(c) When the redundant system is a normal station
Th = Tsw + SS × 2 [ms]
Th: Cyclic data retention time
Tsw: System switching time of Redundant CPU
SS: Sequence scan time of Redundant CPU
*1 For details, refer to the following.
QnPRHCPU User's Manual (Redundant System)
Normal station
Station No.1
System A
1
CPU scan time
Data sent from
0)
station No.1 to
another station
Control system
System A
System B
Standby system
System B
CPU scan time
Data sent from
station No.2 to
another station
Data received
at another
station from
station No.1 or 2
264
Communication error station
Power
down
1)
Standby system
Cyclic transmission delay time
0)
Cyclic data retention time
*1
*1
Control system
System switching time
2
1)
2)
1)
5
3 4
3) 4)
Cyclic transmission delay time
2) 3)
4)