Time Response - Siemens SIMATIC S7-400H System Manual

Link-up and update
12.4 Time monitoring
12.4.1

Time response

Time response during link-up
The influence of link-up operations on your plant's control system should be kept to an
absolute minimum. The current load on your automation system is therefore a decisive factor
in the increase of link-up times. The time required for link-up is in particular determined by
● the communication load
● the cycle time
The following applies to no-load operation of the automation system:
Link-up runtime = size of load memory and work memory in MB × 1 s + base load
The base load is a few seconds.
Whenever your automation system is subject to high load, the memory-specific share may
increase up to 1 minute per MB.
Time response during updating
The update transfer time is determined by the number and overall length of modified data
blocks, rather than by the modified volume of data within a block. It is also determined by the
current process status and communication load.
As a simple approximation, we can interpret the maximum inhibit time to be configured for
priority classes > 15 as a function of the data volume in the work memory. The volume of
code in the work memory is irrelevant.
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System Manual, 03/2012, A5E00267695-11
S7-400H