Siemens SIMATIC ET 200SP HA System Manual page 50

Plant planning
4.8 Redundancy and changes during operation
Configuration
The following figure shows an example for the connection of the sensors or actuators each with
two redundantly used input/output modules.
Figure 4-3 S7-400 H-system with sensors and actuators on module pairs (redundant signal processing)
Response to failure
The following applies when a I/O module or a channel of the two I/O modules fails (valid for
input/output and mixed modules):
The following applies when individual channels when a fault occurs:
● Error-free inputs remain available in the system.
● Error-free outputs are still controlled in the system.
Maintenance and service
In the ongoing, error-free operation, one of the following functions is possible for one I/O
module of a module pair:
● Firmware update
● Replacing a module
NOTICE
I/O modules in the I/O redundancy mode for which at least one channel is configured with
"Keep last value"
When the CPU is in "STOP" mode or the PROFINET cable is pulled, the following action are
also prohibited one after the other:
● Replacement of both I/O modules
● Firmware update for both I/O modules
Without an active connection to the CPU in "RUN" mode, the online parameter "Keep last
value" is reset in both I/O modules. Both I/O modules output the value 0.
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Sensor
ET 200SP HA Distributed I/O system
System Manual, 08/2019, A5E39261167-AD