The ConditionType defines all general characteristics of a Condition. All other ConditionTypes derive from it. It is formally defined in Table 9. The False state of the EnabledState shall not be extended with a sub state machine.
Table 9 – ConditionType definition
Subtype of the BaseEventType defined in OPC 10000-5
|HasSubtype||ObjectType||DialogConditionType||Defined in Clause 5.6.2|
|HasSubtype||ObjectType||AcknowledgeableConditionType||Defined in Clause 5.7.2|
|HasComponent||Method||Disable||Defined in Clause 5.5.4||Mandatory|
|HasComponent||Method||Enable||Defined in Clause 5.5.5||Mandatory|
|HasComponent||Method||AddComment||Defined in Clause 5.5.6||Mandatory|
|HasComponent||Method||ConditionRefresh||Defined in Clause 5.5.7||None|
|HasComponent||Method||ConditionRefresh2||Defined in Clause 5.5.8||None|
The ConditionType inherits all Properties of the BaseEventType. Their semantic is defined in OPC 10000-5. SourceNode Property identifies the ConditionSource. See 5.12 for more details. If the ConditionSource is not a Node in the AddressSpace, the NodeId is set to NULL. The SourceNode Property is the Node, which the Condition is associated with, it may be the same as the InputNode for an Alarm, but it may be a separate node. For example, a motor, which is a Variable with a Value that is an RPM, may be the ConditionSource for Conditions that are related to the motor as well as a temperature sensor associated with the motor. In the former the InputNode for the High RPM Alarm is the value of the Motor RPM, while in the later the InputNode of the High Alarm would be the value of the temperature sensor that is associated with the motor.
ConditionClassId specifies in which domain this Condition is used. It is the NodeId of the corresponding subtype of BaseConditionClassType. See 5.9 for the definition of ConditionClass and a set of ConditionClasses defined in this standard. When using this Property for filtering, Clients have to specify all individual subtypes of BaseConditionClassType NodeIds. The OfType operator cannot be applied. BaseConditionClassType is used as class whenever a Condition cannot be assigned to a more concrete class.
ConditionClassName provides the display name of the subtype of BaseConditionClassType.
ConditionSubClassId specifies additional class[es] that apply to the Condition. It is the NodeId of the corresponding subtype of BaseConditionClassType. See 5.9.6 for the definition of ConditionClass and a set of ConditionClasses defined in this standard. When using this Property for filtering, Clients have to specify all individual sub types of BaseConditionClassType NodeIds. The OfType operator cannot be applied. The Client specifies a NULL in the filter, to return Conditions where no sub class is applied. When returning Conditions, if this optional field is not available in a Condition, a NULL shall be returned for the field.
ConditionSubClassName provides the display name[s] of the ConditionClassType[s] listed in the ConditionSubClassId.
ConditionName identifies the Condition instance that the Event originated from. It can be used together with the SourceName in a user display to distinguish between different Condition instances. If a ConditionSource has only one instance of a ConditionType, and the Server has no instance name, the Server shall supply the ConditionType browse name.
BranchId is NULL for all Event Notifications that relate to the current state of the Condition instance. If BranchId is not NULL, it identifies a previous state of this Condition instance that still needs attention by an Operator. If the current ConditionBranch is transformed into a previous ConditionBranch then the Server needs to assign a non-NULL BranchId. An initial Event for the branch will generated with the values of the ConditionBranch and the new BranchId. The ConditionBranch can be updated many times before it is no longer needed. When the ConditionBranch no longer requires Operator input the final Event will have Retain set to False. The retain bit on the current Event is True, as long as any ConditionBranches require Operator input. See 4.4 for more information about the need for creating and maintaining previous ConditionBranches and Clause B.1 for an example using branches. The BranchId DataType is NodeId although the Server is not required to have ConditionBranches in the Address Space. The use of a NodeId allows the Server to use simple numeric identifiers, strings or arrays of bytes.
Retain when True describes a Condition (or ConditionBranch) as being in a state that is interesting for a Client wishing to synchronize its state with the Server’s state. The logic to determine how this flag is set is Server specific. Typically, all Active Alarms would have the Retain flag set; however, it is also possible for inactive Alarms to have their Retain flag set to TRUE.
In normal processing when a Client receives an Event with the Retain flag set to False, the Client should consider this as a ConditionBranch that is no longer of interest, in the case of a “current Alarm display” the ConditionBranch would be removed from the display.
EnabledState indicates whether the Condition is enabled. EnabledState/Id is True if enabled, False otherwise. EnabledState/TransitionTime defines when the EnabledState last changed. Recommended state names are described in Annex A.
A Condition’s EnabledState effects the generation of Event Notifications and as such results in the following specific behaviour:
- When the Condition instance enters the Disabled state, the Retain Property of this Condition shall be set to False by the Server to indicate to the Client that the Condition instance is currently not of interest to Clients. This includes all ConditionBranches if any branches exist.
- When the Condition instance enters the enabled state, the Condition shall be evaluated and all of its Properties updated to reflect the current values. If this evaluation causes the Retain Property to transition to True for any ConditionBranch, then an Event Notification shall be generated for that ConditionBranch.
- The Server may choose to continue to test for a Condition instance while it is Disabled. However, no Event Notifications will be generated while the Condition instance is disabled.
For any Condition that exists in the AddressSpace the Attributes and the following Variables will continue to have valid values even in the Disabled state; EventId, Event Type, Source Node, Source Name, Time, and EnabledState. Other Properties may no longer provide current valid values. All Variables that are no longer provided shall return a status of Bad_ConditionDisabled. The Event that reports the Disabled state should report the Properties as NULL or with a status of Bad_ConditionDisabled. When enabled, changes to the following components shall cause a ConditionType Event Notification:
- Severity (inherited from BaseEventType)
- Comment This may not be the complete list. Sub-Types may define additional Variables that trigger Event Notifications. In general, changes to Variables of the types TwoStateVariableType or ConditionVariableType trigger Event Notifications.
Quality reveals the status of process values or other resources that this Condition instance is based upon. If, for example, a process value is “Uncertain”, the associated “LevelAlarm” Condition is also questionable. Values for the Quality can be any of the OPC StatusCodes defined in OPC 10000-8 as well as Good, Uncertain and Bad as defined in OPC 10000-4. These StatusCodes are similar to but slightly more generic than the description of data quality in the various field bus specifications. It is the responsibility of the Server to map internal status information to these codes. A Server that supports no quality information shall return Good. This quality can also reflect the communication status associated with the system that this value or resource is based on and from which this Alarm was received. For communication errors to the underlying system, especially those that result in some unavailable Event fields, the quality shall be Bad_NoCommunication error.
Events are only generated for Conditions that have their Retain field set to True and for the initial transition of the Retain field from True to False.
LastSeverity provides the previous severity of the ConditionBranch. Initially this Variable contains a zero value; it will return a value only after a severity change. The new severity is supplied via the Severity Property, which is inherited from the BaseEventType.
Comment contains the last comment provided for a certain state (ConditionBranch). It may have been provided by an AddComment Method, some other Method or in some other manner. The initial value of this Variable is NULL, unless it is provided in some other manner. If a Method provides as an option the ability to set a Comment, then the value of this Variable is reset to NULL if an optional comment is not provided.
ClientUserId is related to the Comment field and contains the identity of the user who inserted the most recent Comment. The logic to obtain the ClientUserId is defined in OPC 10000-5.
The NodeId of the Condition instance is used as ConditionId. It is not explicitly modelled as a component of the ConditionType. However, it can be requested with the following SimpleAttributeOperand (see Table 10) in the SelectClause of the EventFilter:
Table 10 – SimpleAttributeOperand
|typeId||NodeId||NodeId of the ConditionType Node|
|attributeId||IntegerId||Id of the NodeId Attribute|