Siemens SIMATIC ET 200AL, System Manual

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OPC UA communication
9.3 Using the S7-1500 as an OPC UA server
Communication
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Function Manual, 05/2021, A5E03735815-AJ
Requirement
• Alarms and Conditions is activated
• Event subscriptions are set up in the OPC UA client
Principle
The following figure shows a simplified process for temporarily storing ProgramAlarms to
make them available again at another time for the OPC UA Alarms and Condition System. The
nodes mentioned in the caption are visible in the following image of the address model.
① Number of active alarms is too high to make all alarms accessible via OPC UA Alarms and Conditions
② Overloads alarm (overload alarm) is triggered. This overload alarm is active until the following situation occurs:
•
No more alarms are pending for the OPC UA Alarms and Conditions system (OutstandingProgramAlarms = 0)
and
• Number of alarms in the OPC UA Alarms and Conditions system < Hysteresis-cleaned maximum value for OPC
UA alarms (= MaxAlarmsInQueue - OverloadHysteresis)
Alarms that are not available in the OPC UA Alarms and Conditions system due to the overload situation are buff-
ered by the CPU as "OutstandingAlarms".
③ When an OPC UA client executes the ConditionRefresh method, not only are all alarm objects of the relevant sub-
scription synchronized, but also the alarms outstanding for OPC UA Alarms and Conditions (OutstandingAlarms) are
transferred to the Alarms and Conditions memory area - until the maximum number of alarms is reached. "Oldest"
alarms are transferred first. After that every subscription to these alarms receives the transferred alarms - not only
the OPC UA client that called the ConditionRefresh method.
④ The OPC UA client controls the handling of pending alarms via the information of the Overloads nodes.