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.

image023.png

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 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.

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.

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.

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.

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.

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.