Monitoring Time Accuracy; Use Of Redundant Input And Output Modules - Siemens SIMATIC S7-400H Manual

Linking and Synchronizing

Monitoring time accuracy

Note
The monitoring times determined by STEP7 or by using the formulas merely
represent a recommendation.
They are based on a fault-tolerant system with two communication peers and an
average communication load.
Since your system profile may vary sharply from this assumption, you must take
note of the following rules.
• The rise in scan cycle time can increase sharply at a high communication load.
• If you perform changes to your system while it is operating, the rise in scan
cycle time can increase appreciably as a result.
• The more program scanning (especially processing of communication blocks)
you perform in priority classes > 15, the higher the communication delay and
scan cycle time delay might grow.
• You can even undercut the calculated monitoring times in small systems with
high performance requirements.

Use of redundant input and output modules

Notice
If you have redundant I/O modules and have taken this into account in your
program accordingly, you might have to add a premium to the calculated
monitoring times, so that surging does not occur at the output modules.
A premium is required only if you operate modules redundantly from the following
table.
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Automation System S7-400H Fault-tolerant Systems
A5E00068197-07