A Rateof Change Alarmis commonly used to report an unusual change or lack of change in a measured value related to the speed at which the value has changed. The Rateof Change Alarmbecomes active when the rate at which the value changes exceeds or drops below a defined limit.

A Rateof Changeis measured in some time unit, such as seconds or minutes and some unit of measure such as percent or meter. For example, a tank may have a High limit for the Rateof Changeof its level (measured in meters) which would be 4 meters per minute. If the tank level changes at a rate that is greater than 4 meters per minute then the High sub state is entered.

The NonExclusiveRateOfChangeAlarmTypeis a special level Alarmutilized with one or more non-exclusive states. If for example both the High and HighHigh states need to be maintained as active at the same time this AlarmConditionTypeshould be used

The NonExclusiveRateOfChangeAlarmTypeis based on the NonExclusiveLimitAlarmType. It is formally defined in Table 69.

Table 69– NonExclusiveRateOfChangeAlarmType definition

Attribute	Value
BrowseName	NonExclusiveRateOfChangeAlarmType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the NonExclusiveLimitAlarmType defined in clause 5.8.13.
HasProperty	Variable	EngineeringUnits	EUInformation	PropertyType	Optional

EngineeringUnits provides the engineering units associated with the limits values. If this is not provided the assumed Engineering Unit is the same as the EU associated with the parent variable per second e.g. if parent is meters, this unit is meters/second.

ExclusiveRateOfChangeAlarmTypeis utilized with multiple mutually exclusive limits. It is formally defined in Table 70.

Table 70– ExclusiveRateOfChangeAlarmType definition

Attribute	Value
BrowseName	ExclusiveRateOfChangeAlarmType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Inherits the Propertiesof the ExclusiveLimitAlarmTypedefined in clause 5.8.12.3.
HasProperty	Variable	EngineeringUnits	EUInformation	PropertyType	Optional

EngineeringUnits provides the engineering units associated with the limits values. If this is not provided the assumed Engineering Unit is the same as the EU associated with the parent variable per second e.g. if parent is meters, this unit is meters/second.