UA Part 9: Alarms and Conditions - 5.8.17 Discrete Alarms

The DiscreteAlarmTypeis used to classify Typesinto Alarm Conditionswhere the input for the Alarmmay take on only a certain number of possible values (e.g. True/False, running/stopped/terminating). The DiscreteAlarmTypewith 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

5.8.17.2 OffNormalAlarmType

The OffNormalAlarmTypeis a specialization of the DiscreteAlarmTypeintended to represent a discrete Conditionthat 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 Alarmstate, 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 Propertyis a Propertythat points to a Variablewhich has a value that corresponds to one of the possible values of the Variablepointed to by the InputNode Propertywhere the NormalState Property Variablevalue is the value that is considered to be the normal state of the Variablepointed to by the InputNode Property. When the value of the Variablereferenced by the InputNode Propertyis not equal to the value of the NormalState Propertythe Alarmis Active. If this Variableis not in the AddressSpace, a NULL NodeIdshall be provided.

5.8.17.3 SystemOffNormalAlarmType

This Conditionis used by a Serverto indicate that an underlying system that is providing Alarminformation is having a communication problem and that the Servermay have invalid or incomplete Conditionstate in the Subscription. Its representation in the AddressSpaceis 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 Referencesto the same Nodes.

5.8.17.4 TripAlarmType

The TripAlarmTypeis a specialization of the OffNormalAlarmTypeintended to represent an equipment trip Condition. The Alarmbecomes 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 Typeis 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.

5.8.17.5 InstrumentDiagnosticAlarmType

The InstrumentDiagnosticAlarmTypeis a specialization of the OffNormalAlarmTypeintended to represent a fault in a field device. The Alarmbecomes active when the monitored device experiences a fault such as a sensor failure. It is formally defined in Table 74. This Typeis 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.

5.8.17.6 SystemDiagnosticAlarmType

The SystemDiagnosticAlarmTypeis a specialization of the OffNormalAlarmTypeintended to represent a fault in a system or sub-system. The Alarmbecomes active when the monitored system experiences a fault. It is formally defined in Table 74. This Typeis 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.

5.8.17.7 CertificateExpirationAlarmType

This SystemOffNormalAlarmTypeis raised by the Serverwhen the Server’sCertificate is within the ExpirationLimitof expiration. This Alarmautomatically 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

ExpirationDateis the date and time this certificate will expire.

ExpirationLimitis the time interval before the ExpirationDateat which this Alarmwill 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.

Certificateis the certificate that is about to expire.