Siemens SIMATIC ET 200AL, System Manual

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OPC UA communication
9.5 Tips and recommendations
Communication
Function Manual, 05/2021, A5E03735815-AJ
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9.5.1 Rules for subscriptions
The following rules apply to subscriptions:
•
Group subscriptions in the client according to different sampling and publishing intervals
and distribute the monitored elements (variables) to these groups.
Example: Create a subscription for longer publishing intervals (e.g. 5 seconds) and a
subscription for shorter publishing intervals (e.g. 0.1 second).
• Disable unneeded subscriptions.
Reason: The "Deactivated" subscription mode reduces resource consumption.
• Consider the maximum number of monitored items of subscriptions for the corresponding
S7-1500 CPU.
The information can be found in the technical specification of the respective CPU. The
information is based on a sampling / publishing interval of 1 second.
You can find additional information in the FAQ 109755846
( https://support.industry.siemens.com/cs/us/en/view/109755846 ).
• Select the same sampling and publishing intervals for the OPC UA client and for the
OPC UA server.
• Avoid arrays and structures as elements of subscriptions – if the process allows.
Reason: If even one value of an array/structure changes, the entire structure is transferred,
creating an unnecessary communication load.
• Occasional non-compliance with the required sampling rate is acknowledged by the OPC
UA server of the S7-1500 CPU according to OPC UA specification with a "GoodOverload"
error code, see also TIA Portal Help. Different OPC UA clients handle "Good" error codes
unequal to "0" differently. Consider this behavior and, if needed, reduce the
communication load according to the measures described above.
See also
Settings of the server for subscriptions (Page 224)