Siemens SIMATIC ET 200AL System Manual page 1434

Requirement
In the OPC UA properties of the CPU, the option "Subscriptions: Sampling time errors" (OPC
UA > Server > Diagnostics) is selected.
Error-free subscription
In the case of an OPC UA subscription to various elements (such as tags), the OPC UA server
of the SIMATIC S7-1500 must check the elements for value changes at specified intervals
(sampling interval). This check, referred to as "sampling", requires some time, which depends
on the number and the data type of the items. After the sampling is completed and a
publishing request has been received, the server sends the elements to the client.
Figure 9-55
Subscription with error
If there are too many elements in the queue, there may be an overload of the communication
stack. The CPU cannot check all elements in the given sampling interval and must therefore
skip the next sampling job.
In this case, the CPU sends the status code "GoodOverload" (0x002F0000) per element, even
though the elements were not checked. The meaning of the status code according to IEC
61131-3 is as follows: "Sampling has slowed down due to resource limitations".
①
Figure 9-56
See also FAQ 109763090 (https://support.industry.siemens.com/cs/ww/en/view/109763090).
See also
Settings of the server for subscriptions (Page 224)
Communication
Function Manual, 05/2021, A5E03735815-AJ
Error-free subscription
Sampling job is skipped
Subscription with error
OPC UA communication
9.3 Using the S7-1500 as an OPC UA server
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