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12.4 Time monitoring
S7-400H
System Manual, 03/2012, A5E00267695-11
159
12.4.2 Determining the monitoring times
Calculation using STEP 7 or formulas
STEP 7 automatically calculates the monitoring times listed below for each new
configuration. You can also calculate these times using the formulas and procedures
described below. They are equivalent to the formulas provided in STEP 7.
● Maximum cycle time extension
● Maximum communication delay
● Maximum inhibit time for priority classes
● Minimum I/O retention time
You can also start automatic calculation of monitoring times with Properties CPU > H
Parameters in HW Config.
Monitoring time accuracy
Note
The monitoring times determined by STEP 7 or by using formulas merely represent
recommended values.
These times are based on a fault-tolerant system with two communication peers and an
average communication load.
Your system profile may differ considerably from those scenarios, therefore the following
rules must be observed.
● The cycle time extension factor may increase sharply at a high communication load.
● Any modification of the system in operation may lead to a significant increase in cycle
times.
● Any increase in the number of programs executed in priority classes > 15 (in particular
processing of communication blocks) automatically increases the communication delay
and cycle time extension.
● You can even undercut the calculated monitoring times in small plants with high-
performance requirements.
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