Alarmscan be modelled with multiple exclusive sub-states and assigned limits or they may be modelled with nonexclusive limits that can be used to group multiple states together.

The LimitAlarmTypeis an abstract type used to provide a base Typefor AlarmConditionTypeswith multiple limits. The LimitAlarmTypeis illustrated in Figure 16.

image019.png

Figure 16– LimitAlarmType

The LimitAlarmTypeis formally defined in Table 60.

Table 60– LimitAlarmType definition

Attribute

Value

BrowseName

LimitAlarmType

IsAbstract

False

References

NodeClass

BrowseName

DataType

TypeDefinition

ModellingRule

Subtype of the AlarmConditionType defined in clause 5.8.2.

HasSubtype

ObjectType

ExclusiveLimitAlarmType

Defined in Clause 5.8.12.3

HasSubtype

ObjectType

NonExclusiveLimitAlarmType

Defined in Clause 5.8.13

HasProperty

Variable

HighHighLimit

Double

PropertyType

Optional

HasProperty

Variable

HighLimit

Double

PropertyType

Optional

HasProperty

Variable

LowLimit

Double

PropertyType

Optional

HasProperty

Variable

LowLowLimit

Double

PropertyType

Optional

HasProperty

Variable

BaseHighHighLimit

Double

PropertyType

Optional

HasProperty

Variable

BaseHighLimit

Double

PropertyType

Optional

HasProperty

Variable

BaseLowLimit

Double

PropertyType

Optional

HasProperty

Variable

BaseLowLowLimit

Double

PropertyType

Optional

Four optional limits are defined that configure the states of the derived limit AlarmTypes. These Propertiesshall be set for any Alarmlimits that are exposed by the derived limit Alarmtypes. These Propertiesare listed as optional but at least one is required. For cases where an underlying system cannot provide the actual value of a limit, the limit Propertyshall still be provided, but will have its AccessLevelset to not readable. It is assumed that the limits are described using the same Engineering Unit that is assigned to the variable that is the source of the Alarm. For Rate of change limit Alarms, it is assumed this rate is units per second unless otherwise specified.

Four optional base limits are defined that are used for AdaptiveSAlarming. They contain the configured Alarmlimit. If a Serversupports AdaptiveAlarmingfor Alarmlimits, the corresponding base Alarmlimit shall be provided for any limits that are exposed by the derived limit Alarm types. The value of this property is the value of the limit to which an AdaptiveAlarmcan be reset if any algorithmic changes need to be discarded.

The Alarmlimits listed may cause an Alarmto be generated when a value equals the limit or it may generate the Alarmwhen the limit is exceeded, (i.e. the Value is above the limit for HighLimitand below the limit for LowLimit). The exact behaviour when the value is equal to the limit is Serverspecific.

The Variablethat is the source of the LimitAlarmType Alarmshall be a scalar. This LimitAlarmTypecan be subtyped if the Variablethat is the source is an array. The subtype shall describe the expected behaviour with respect to limits and the array values. Some possible options:

  • if any element of the array exceeds the limit an Alarmis generated,
  • if all elements exceed the limit an Alarmis generated,
  • the limits may also be an array, in which case if any array limit is exceeded by the corresponding source array element, an Alarmis generated.