Determining The Monitoring Times - Siemens SIMATIC S7-400H System Manual

9.4.2

Determining the monitoring times

Determination 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 partners and an
average communication load.
Your system profile may differ considerably from those scenarios, so observe the following
rules.
● 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
● Any increase in the number of programs executed in priority classes > 15 (in particular
● You can even undercut the calculated monitoring times in small high-performance
S7-400H
System Manual, 09/2007, A5E00267695-03
times.
those of communication blocks) automatically increases the communication delay and
cycle time extension.
systems.
Link-up and update
9.4 Time monitoring
109