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7.5 Cyclic Data Retention Time for System Switching in a
Redundant System
This section gives calculation formulas for cyclic data retention time that is taken when a system switching occurs in a
redundant system.
(1) When the control system power supply module is faulty or powered off or
when the control system CPU is faulty or reset
(a) When a redundant system is the control station and "System switching time of
Redundant CPU (Tsw) < Control station switching time (Csw)" is met
*1 For details, refer to the following.
QnPRHCPU User's Manual (Redundant System)
Th = Csw+ SS [ms]
Th: Cyclic data retention time
Tsw: System switching time of Redundant CPU
*1
Csw: Control station switching time = 20 + Constant link scan set value ( Page 201, Section 6.3.6 (1))
SS: Sequence scan time of Redundant CPU
*1
1
0)
1)
0)
2
3
4
5
6
3)
4) 5)
6)
1)
3) 4) 5)
Control station Communication error station
Power
down
System A
CPU scan time
Data sent from
station No.1 to
another station
System A
System B
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
Control system
Control system
Standby system
Standby system
System switching time
Normal station
Control station
switching time
Sub-control station
Cyclic transmission
delay time
Cyclic transmission delay time
Cyclic data retention time
Station No.1
Station No.2
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