Siemens SIMATIC PCS 7 Function Manual page 33

The ET 200M distributed I/O device is connected as redundant DP slave to a fault-tolerant
automation system operating as the DP master via PROFIBUS DP. A redundant configuration
is achieved by installing an additional ET 200M and an additional PROFIBUS DP connection.
Note
Use only active bus modules for the ET 200M in a fault-tolerant system with PCS 7. Active bus
modules enable you to plug and pull modules in runtime.
The following figure illustrates this configuration with ET 200M. Signals from redundant sensors
can be registered.
Availability
The block diagram shows an example configuration with ET 200M without a fault.
If a fault occurs in a maximum of one signal path per redundancy node (e.g. bus line
(bus = PROFIBUS DP) in the first redundancy node and an input module (SM) in the second
redundancy node), the overall system remains operable. The connected device continues to
supply data to the central device, which remains available. If any other component in the
redundancy chain fails, however, the complete system will fail.
Fault-tolerant Process Control Systems (V8.1)
Function Manual, 11/2014, A5E34878832-AA
Fault-tolerant Solutions in PCS 7
3.1 Solutions for the I/O
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