Using I/O on the S7-400H
7-32
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07
Redundant analog output modules
Redundant control of a final control element is achieved by interconnecting two
outputs of two analog output modules in parallel (1-of-2 structure)
Analog output modules
I
Final control element
Figure 7-12 Redundant analog output modules in a 1-of-2 structure
To wire the analog output module circuit shown above:
• Wire the ground lines in star pattern in order to avoid output errors (limited
common-mode suppression for the analog output modules).
Depassivation of modules
Passivated modules are reactivated by the following events:
• When fault-tolerant system starts up
• When the fault-tolerant system switches to the “Redundant” operating mode
• Following a system modification during ongoing operation
• By the function FC 451 “RED DEPA” when at least one redundant module is
passivated.
The functionality and use of FC 451 are described in the corresponding online
help.
The depassivation is performed in FB 450 “RED IN” when one of these events
occur,. When the all of modules have been depassivated, an entry is made in the
diagnostics buffer.
When you use redundant I/O in a one-way central device or one-way DP slave,
you have to depassivate the redundant modules after the station failure/return or
replacement of a defective module. You can trigger a complete depassivation with
FC 451.
Note
If a redundant module is assigned a process image partition but the corresponding
OB is not available in the CPU, the complete passivation can take approximately 1
minute.
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