6 OPC UA for Compressed Air Systems Information Model ToC Previous Next

6.6 Alarms and Conditions ToC Previous Next

Most CASParts have an optional FunctionalGroup with the default BrowseName Events. This FunctionalGroup provides Objects for common alarms and conditions. In total four conditions are defined: EmergencyStop, Service, Shutdown, and Warning. An OptionalPlaceholder Object <Event> with the TypeDefinition ConditionType is defined. If a manufacturer or system integrator adds additional alarms or conditions to a CASPart, <Event> shall be used. When instantiating <Event>, a concrete subtypes of the abstract ConditionType has to be used as TypeDefinition. To comply with Annex B of OPC 10000-9 – Part 9: Alarms and Conditions, a CASPart must have a HasCondition reference for each instantiated condition using the condition instance as TargetNode and the CASPart as SourceNode.

A manufacturer or system integrator may add custom alarms and conditions targeting specific Variables or Objects of a CASPart. In that case, the Variable or Object is the SourceNode and the condition instance is the TargetNode. If such an alarm or condition is created, the CASPart shall have a HasEventSource reference with the CASPart as SourceNode and the Variable or Object as TargetNode.

EXAMPLE A high limit alarm is needed for the Temperature Quantity at the process fluid inlet of a dryer. The Object InletTemperatureHighLimitAlarm using the ExclusiveLimitAlarmType as TypeDefinition is created as child of the Events Object of the dryer instance. A HasCondition reference is created with the Temperature Quantity as SourceNode and the InletTemperatureHighLimitAlarm as TargetNode. The dryer receives a HasEventSource reference to the Temperature Quantity.

To further comply with Annex B of OPC 10000-9, the Compressed Air System Object shall be the TargetNode of a HasNotifier reference, originating at the OPC UA Server Object. The Compressed Air System Object shall have a HasNotifier reference for each CASPart which instantiates alarms or conditions.

Every instantiated Component shall have at least one appropriate GeneratesEvent reference targeting the NAMUR NE 107 alarms defined in OPC 10000-100. These are CheckFunctionAlarmType, FailureAlarmType, MaintenanceRequiredAlarmType, and OffSpecAlarmType.

6.6.1 Severity ToC Previous Next

As defined by OPC 10000-5, all events shall have a severity assigned to them. This specification specifies specific severity ranges for some events. If no specific severity or severity range is provided for a defined event or condition, the manufacturer or integrator may choose from the default OPC UA range. The chosen severity when assigning it to a condition or event shall match the following categorization.

Table 10 – Severity Categorization

Severity Lower limit Upper limit
HIGH 801 1000
MEDIUM HIGH 601 800
MEDIUM 401 600
MEDIUM LOW 201 400
LOW 1 200

Figure 13 shows examples on how alarms and conditions shall be used in a Compressed Air System.

readme_files/image018.png Figure 13 – Alarms and Conditions

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