Opc Ua Events - Siemens SIMATIC ET 200AL System Manual

OPC UA communication
9.3 Using the S7-1500 as an OPC UA server
9.3.6.2

OPC UA Events

The basic concepts for alarm processing in OPC UA are expanded on here - the basic concept
of "Events" is covered here. The terms used in the various parts of the OPC UA specification
have been retained here.
Properties of events
In the address model of the OPC UA server, as of CPU firmware version V2.9, you not only
have the option to access PLC tags (read, write) via nodes and to use methods - you can also
receive events or alarms via nodes. In OPC UA terminology, these are called "events".
An event includes an event text (Message), time stamp (Time) and event source
(SourceNode).
The information supplied with an event from the server depends on the event type. OPC UA
defines a BaseEventType in part 5 of the specification (Information Model).
Other event types that provide different alarm behavior are derived from the BaseEventType.
This type information of the different event types is visible in the address space of an OPC UA
server ("Types" folder). This also applies, for example, to the event types of "Conditions" and
"Alarms", which are discussed in the next section.
The OPC UA specification defines for the BaseEventType and for derived EventTypes which
properties (fields) of an event are mandatory and which are optional.
The following figure shows the hierarchical structure of BaseEventType.
The following sections show how specialized EventTypes are derived from the root of the
derivation hierarchy, the BaseEventType. The SIMATIC-specific derivations ensure that the
information supplied in SIMATIC with an alarm and displayed on an HMI device, for example,
can also be subscribed to by an OPC UA client in the address space of the OPC UA server.
An event itself is not available as a node in the address space. Events are only triggered by
nodes or objects that have the "Event-Notifier" property. These nodes are often also referred
to as event signaling objects. Only nodes with this property can be specified as
EventMonitoredItem in a subscription to receive corresponding events in the client.
Nodes that can trigger events with an S7-1500 CPU are objects such as "Server", the
"SimaticAlarmsAndConditions" object below it, and the three objects below that,
ProcessDiagnostics, SystemDiagnostics and UserProgram. The "EventNotifier" attribute is set
for these objects in the address space of the OPC UA server of the CPU.
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Communication