Determination Of The Monitoring Times - Siemens SIMATIC S7-400H Manual

Link-up and Update
Time behavior during the update
The transfer time during updating depends on the number and overall length of the
modified data blocks; it does not depend on the modified volume of data within a
block. It is also dependent on the current process
state and on the communication load.
In a simplified view, the max. blocking time to be configured for priority
classes > 15 can be seen as a function of the volume of data in the main memory.
The volume of code in the main memory is irrelevant.
5.3.2

Determination of the Monitoring Times

Determining with STEP7 or using formulas
There are two ways in which you can determine the monitoring times:
using the "Calculate..." button on the "H Parameters" tab of the Properties
window of the CPU in HWCONFIG (refer to the online Help)
by using the formulas and steps described below. They are equivalent to the
formulas used in STEP7.
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.
5-18
S7-400H Programmable Controller Fault-Tolerant Systems
A5E00068197-04