The Alarm and Conditionmodel extends the OPC UA base Eventmodel by defining various Event Typesbased on the BaseEventType. All of the Event Typesdefined in this standard can be further extended to form domain or Serverspecific Alarm and Condition Types.

Instances of Alarm and Condition Typesmay be optionally exposed in the AddressSpacein order to allow direct access to the state of an Alarm or Condition. Instances not exposed in the AddressSpacestill have a ConditionId(NodeId). This NodeIdcan be the target of references in the AddressSpaceeven though the target node does not exist in the AddressSpace. For example, an AlarmGroupmight reference a number of Conditionsthat do not exist in the AddressSpace.

The following sub clauses define the OPC UA Alarm and Condition Types. Figure 8informally describes the hierarchy of these Types. Subtypes of the LimitAlarmTypeand the DiscreteAlarmTypeare not shown.


Figure 8– ConditionType hierarchy