Errata exists for this version of the document.

The DiscreteAlarmType is used to classify Types into Alarm Conditions where the input for the Alarm may take on only a certain number of possible values (e.g. True/False, running/stopped/terminating). The DiscreteAlarmType with sub types defined in this standard is illustrated in Figure 20. It is formally defined in Table 71.

Figure 20 – DiscreteAlarmType Hierarchy

Table 71 – DiscreteAlarmType definition

Attribute	Value
BrowseName	DiscreteAlarmType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the AlarmConditionType defined in clause 5.8.2.
HasSubtype	ObjectType	OffNormalAlarmType	Defined in Clause 5.8.15

The OffNormalAlarmType is a specialization of the DiscreteAlarmType intended to represent a discrete Condition that is considered to be not normal. It is formally defined in Table 72. This sub type is usually used to indicate that a discrete value is in an Alarm state, it is active as long as a non-normal value is present.

Table 72 – OffNormalAlarmType Definition

Attribute	Value
BrowseName	OffNormalAlarmType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition		ModellingRule
Subtype of the DiscreteAlarmType defined in clause 5.8.17.1
HasSubtype	ObjectType	TripAlarmType	Defined in Clause 5.8.17.4
HasSubtype	ObjectType	SystemOffNormalAlarmType	Defined in Clause 5.8.17.3
HasProperty	Variable	NormalState	NodeId		PropertyType	Mandatory

The NormalState Property is a Property that points to a Variable which has a value that corresponds to one of the possible values of the Variable pointed to by the InputNode Property where the NormalState Property Variable value is the value that is considered to be the normal state of the Variable pointed to by the InputNode Property. When the value of the Variable referenced by the InputNode Property is not equal to the value of the NormalState Property the Alarm is Active. If this Variable is not in the AddressSpace, a NULL NodeId shall be provided.

This Condition is used by a Server to indicate that an underlying system that is providing Alarm information is having a communication problem and that the Server may have invalid or incomplete Condition state in the Subscription. Its representation in the AddressSpace is formally defined in Table 73.

Table 73 – SystemOffNormalAlarmType definition

Attribute	Value
BrowseName	SystemOffNormalAlarmType
IsAbstract	True
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
HasSubtype	ObjectType	CertificateExpirationAlarmType	Defined in Clause 0
Subtype of the OffNormalAlarmType, i.e. it has HasProperty References to the same Nodes.

The TripAlarmType is a specialization of the OffNormalAlarmType intended to represent an equipment trip Condition. The Alarm becomes active when the monitored piece of equipment experiences some abnormal fault such as a motor shutting down due to an overload condition. It is formally defined in Table 74. This Type is mainly used for categorization.

Table 74 – TripAlarmType definition

Attribute	Value
BrowseName	TripAlarmType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the OffNormalAlarmType defined in clause 5.8.17.2.

The InstrumentDiagnosticAlarmType is a specialization of the OffNormalAlarmType intended to represent a fault in a field device. The Alarm becomes active when the monitored device experiences a fault such as a sensor failure. It is formally defined in Table 74. This Type is mainly used for categorization.

Table 75 – InstrumentDiagnosticAlarmType definition

Attribute	Value
BrowseName	InstrumentDiagnosticAlarmType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the OffNormalAlarmType defined in clause 5.8.17.2.

The SystemDiagnosticAlarmType is a specialization of the OffNormalAlarmType intended to represent a fault in a system or sub-system. The Alarm becomes active when the monitored system experiences a fault. It is formally defined in Table 74. This Type is mainly used for categorization.

Table 76 – SystemDiagnosticAlarmType definition

Attribute	Value
BrowseName	SystemDiagnosticAlarmType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the OffNormalAlarmType defined in clause 5.8.17.2.

This SystemOffNormalAlarmType is raised by the Server when the Server’s Certificate is within the ExpirationLimit of expiration. This Alarm automatically returns to normal when the certificate is updated.

Table 77 – CertificateExpirationAlarmType definition

Attribute	Value
BrowseName	CertificateExpirationAlarmType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the SystemOffNormalAlarmType defined in clause 5.8.17.3
HasProperty	Variable	ExpirationDate	DateTime	PropertyType	Mandatory
HasProperty	Variable	ExpirationLimit	Duration	PropertyType	Optional
HasProperty	Variable	CertificateType	NodeId	PropertyType	Mandatory
HasProperty	Variable	Certificate	ByteString	PropertyType	Mandatory

ExpirationDate is the date and time this certificate will expire.

ExpirationLimit is the time interval before the ExpirationDate at which this Alarm will trigger. This shall be a positive number. If the property is not provided, a default of 2 weeks shall be used.

CertificateType – See OPC 10000-12 for definition of CertificateType.

Certificate is the certificate that is about to expire.