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5.8 Alarm model ToC Previous Next

5.8.15 Deviation Alarm ToC Previous Next

5.8.15.1 Overview ToC

A deviation Alarm is commonly used to report an excess deviation between a desired set point level of a process value and an actual measurement of that value. The deviation Alarm becomes active when the deviation exceeds or drops below a defined limit.

For example, if a set point had a value of 10, a high deviation Alarm limit of 2 and a low deviation Alarm limit of -1 then the low sub state is entered if the process value drops below 9; the high sub state is entered if the process value raises above 12. If the set point were changed to 11 then the new deviation values would be 10 and 13 respectively. The set point can be fixed by a configuration, adjusted by an Operator or it can be adjusted by an algorithm, the actual functionality exposed by the set point is application specific. The deviation Alarm can also be used to report a problem between a redundant data source where the difference between the primary source and the secondary source exceeds the included limit. In this case, the SetpointNode would point to the secondary source.

5.8.15.2 NonExclusiveDeviationAlarmType ToC Model

The NonExclusiveDeviationAlarmType is a special level Alarm utilized 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 then an instance of NonExclusiveDeviationAlarmType should be used.

The NonExclusiveDeviationAlarmType is based on the NonExclusiveLimitAlarmType. It is formally defined in Table 67.

Table 67 – NonExclusiveDeviationAlarmType definition

Attribute Value
BrowseName NonExclusiveDeviationAlarmType
IsAbstract False

Subtype of the NonExclusiveLimitAlarmType defined in clause 5.8.13.

References NodeClass BrowseName DataType TypeDefinition ModellingRule
HasProperty Variable SetpointNode NodeId PropertyType Mandatory
HasProperty Variable BaseSetpointNode NodeId PropertyType Optional

The SetpointNode Property provides the NodeId of the set point used in the deviation calculation. In cases where the Alarm is generated by an underlying system and if the Variable is not in the AddressSpace, a NULL NodeId shall be provided.

The BaseSetpointNode Property provides the NodeId of the original or base setpoint. The value of this node is the value of the setpoint to which an AdaptiveAlarm can be reset if any algorithmic changes need to be discarded. The value of this node usually contains the originally configured set point.

5.8.15.3 ExclusiveDeviationAlarmType ToC Model

The ExclusiveDeviationAlarmType is utilized with multiple mutually exclusive limits. It is formally defined in Table 68.

Table 68 – ExclusiveDeviationAlarmType definition

Attribute Value
BrowseName ExclusiveDeviationAlarmType
IsAbstract False

Inherits the Properties of the ExclusiveLimitAlarmType defined in clause 5.8.12.3.

References NodeClass BrowseName DataType TypeDefinition Modelling Rule
HasProperty Variable SetpointNode NodeId PropertyType Mandatory
HasProperty Variable BaseSetpointNode NodeId PropertyType Optional

The SetpointNode Property provides the NodeId of the set point used in the Deviation calculation. If this Variable is not in the AddressSpace, a NULL NodeId shall be provided.

The BaseSetpointNode Property provides the NodeId of the original or base setpoint. The value of this node is the value of the set point to which an AdaptiveAlarm can be reset if any algorithmic changes need to be discarded. The value of this node usually contains the originally configured set point.

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