Siemens SIMATIC S7-400H Manual page 96

Communications
Redundancy
block diagram
Figure 7-3
Redundancy
block diagram
Figure 7-4
Failure behavior
Only a double error within a fault-tolerant system (e.g. CPUa1 and CPa2 in a
system) in the case of a two-fiber ring leads to total failure of communications
between the redundant systems concerned (refer to Figure 7-3).
Should a double error occur on a redundant electrical bus system – for example,
CPUa1 and CPb2 – this results in total failure of communications between the
systems involved (refer to Figure 7-4).
7-10
Fault-tolerant system a Fault-tolerant system b
CP
CPU CPU
a1
a1 b1
OLM
OLM
Fault-tolerant
system a
OLM/
CPUa1 CPa1
Bus1
OLM/
CPUa2 CPa2
Bus2
Example of Redundancy with Fault-Tolerant System and Redundant Ring
Fault-tolerant system a
CPU CP
a1 a1
Fault-tolerant system a
CPUa1 Bus1
CPa1
CPUa2 CPa2 Bus2
Example of Redundancy with Fault-Tolerant System and Redundant Bus
System
S7-400H Programmable Controller Fault-Tolerant Systems
CP
b1
OLM
OLM
System bus as optical two-
fiber ring
Fault-tolerant system b
CPb1
CPUb1
CPb2
CPUb2
1-out-of-2 redundancy
Fault-tolerant system b
CPU CP
b1 b1
Fault-tolerant system b
CPb1
CPUb1
CPb2
CPUb2
Bus1
Bus2
A5E00068197-04