Subscribing To Events Of An Opc Ua Server - Siemens SIMATIC ET 200AL System Manual

OPC UA communication
9.3 Using the S7-1500 as an OPC UA server
9.3.6.5

Subscribing to events of an OPC UA server

Subscribing to all events via the "Server" node
OPC UA servers provide events via the "Server" node and lower-level nodes. When OPC UA
clients subscribe to the "Server" node, they receive all events and alarms of the OPC UA
server.
The "Server" node is located in the "Objects" folder below "Root".
OPC UA servers inform OPC UA clients which event types they use (under "Root > Types >
EventTypes" in the address space).
Filter options for events
OPC UA clients can choose and only subscribe to specific nodes under the "Server" node and
thus to specific event types, for example, only the "UserProgram" node. This reduces the
number of events from the OPC UA server to program alarms.
Another way of filtering is to select the event fields, known as "Select Clause" in OPC UA
terminology.
This means that in the subscription, the OPC UA client makes a selection of the event fields in
addition to the event alarm object (e.g. the "UserProgram" node). You select the event fields
via the browse name of the corresponding field.
OPC UA also defines so-called "Where Clauses". A Where Clause in the event filter is used to
further limit the number of events that are supplied by the OPC UA server for the selected
object, for example, by filtering to a severity range.
Example client UaExpert
The example of the UaExpert OPC UA client shows how events of an OPC UA server can be
received via a subscription. Here is the most important information on the displayed
events/alarms:
• Event View is a separate view of events in addition to the Data Access View.
• The "Configuration" area contains the selected event signaling object with the fields for
the Select Clause. A configuration of Where clauses is currently not possible in UaExpert.
• In the "Events" area, "Events" tab: Corresponds to the TIA alarm view with activated "Alarm
archive" button; events of the "Information only" category and outgoing alarms are also
visible there, because UaExpert buffers them in the background for display. These events
are not visible in the "Alarms" tab.
• In the "Events" field, "Alarms" tab: Corresponds to the TIA alarm display with activated
"Current alarms" button; alarms are visible here with their status, e.g. "active"
(corresponds to "incoming") and these alarms can also be acknowledged using the
shortcut menu. Outgoing alarms are no longer visible in this view.
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Function Manual, 05/2021, A5E03735815-AJ
Communication