Figure 12 informally describes the AlarmConditionType, its sub-types and where it is in the hierarchy of Event Types.

Figure 12 - AlarmConditionType Hierarchy Model

The AlarmConditionType is an abstract type that extends the AcknowledgeableConditionType by introducing an ActiveState, SuppressedState and ShelvingState. It also adds the ability to set a delay time, re-alarm time, Alarm groups and audible Alarm settings The Alarm model is illustrated in Figure 13. This illustration is not intended to be a complete definition. It is formally defined in Table 35.

Figure 13 – Alarm Model

Table 35 – AlarmConditionType definition

Attribute	Value
BrowseName	AlarmConditionType
IsAbstract	False
References	Node Class	BrowseName	DataType	TypeDefinition	Modelling Rule
Subtype of the AcknowledgeableConditionType defined in clause 5.7.2
HasComponent	Variable	ActiveState	LocalizedText	TwoStateVariableType	Mandatory
HasProperty	Variable	InputNode	NodeId	PropertyType	Mandatory
HasComponent	Variable	SuppressedState	LocalizedText	TwoStateVariableType	Optional
HasComponent	Variable	OutOfServiceState	LocalizedText	TwoStateVariableType	Optional
HasComponent	Object	ShelvingState		ShelvedStateMachineType	Optional
HasProperty	Variable	SuppressedOrShelved	Boolean	PropertyType	Mandatory
HasProperty	Variable	MaxTimeShelved	Duration	PropertyType	Optional
HasProperty	Variable	AudibleEnabled	Boolean	PropertyType	Optional
HasProperty	Variable	AudibleSound	AudioDataType	AudioVariableType	Optional
HasComponent	Variable	SilenceState	LocalizedText	TwoStateVariableType	Optional
HasProperty	Variable	OnDelay	Duration	PropertyType	Optional
HasProperty	Variable	OffDelay	Duration	PropertyType	Optional
HasComponent	Variable	FirstInGroupFlag	Boolean	BaseDataVariableType	Optional
HasComponent	Object	FirstInGroup		AlarmGroupType	Optional
HasComponent	Variable	LatchedState	LocalizedText	TwoStateVariableType	Optional
HasAlarmSuppressionGroup	Object	<AlarmGroup>		AlarmGroupType	OptionalPlaceholder
HasProperty	Variable	ReAlarmTime	Duration	PropertyType	Optional
HasComponent	Variable	ReAlarmRepeatCount	Int16	BaseDataVariableType	Optional
HasComponent	Method	Silence	Defined in 5.8.5		Optional
HasComponent	Method	Suppress	Defined in 5.8.6		Optional
HasComponent	Method	Unsuppress	Defined in 5.8.7		Optional
HasComponent	Method	RemoveFromService	Defined in 5.8.8		Optional
HasComponent	Method	PlaceInService	Defined in 5.8.9		Optional
HasComponent	Method	Reset	Defined in 5.8.4		Optional
HasSubtype	ObjectType	DiscreteAlarmType
HasSubtype	ObjectType	LimitAlarmType
HasSubtype	ObjectType	DiscrepancyAlarmType

The AlarmConditionType inherits all Properties of the AcknowledgeableConditionType. The following states are sub-states of the True EnabledState.

ActiveState/Id when set to True indicates that the situation the Condition is representing currently exists. When a Condition instance is in the inactive state (ActiveState/Id when set to False) it is representing a situation that has returned to a normal state. The transitions of Conditions to the inactive and Active states are triggered by Server specific actions. Subtypes of the AlarmConditionType specified later in this document will have sub-state models that further define the Active state. Recommended state names are described in Annex A.

The InputNode Property provides the NodeId of the Variable the Value of which is used as primary input in the calculation of the Alarm state. If this Variable is not in the AddressSpace, a NULL NodeId shall be provided. In some systems, an Alarm may be calculated based on multiple Variables Values; it is up to the system to determine which Variable’s NodeId is used.

SuppressedState, OutOfServiceState and ShelvingState together allow the suppression of Alarms on display systems. These three suppressions are generally used by different personnel or systems at a plant, i.e. automatic systems, maintenance personnel and Operators.

SuppressedState is used internally by a Server to automatically suppress Alarms due to system specific reasons. For example, a system may be configured to suppress Alarms that are associated with machinery that is in a state such as shutdown. For example, a low level Alarm for a tank that is currently not in use might be suppressed. Recommended state names are described in Annex A.

OutOfServiceState is used by maintenance personnel to suppress Alarms due to a maintenance issue. For example, if an instrument is taken out of service for maintenance or is removed temporarily while it is being replaced or serviced the item would have the OutOfServiceState set. Recommended state names are described in Annex A.

ShelvingState suggests whether an Alarm shall (temporarily) be prevented from being displayed to the user. It is quite often used by Operators to block nuisance Alarms. The ShelvingState is defined in 5.8.10.

When an Alarm has any or all of the SuppressedState, OutOfServiceState or ShelvingState set to True, the SuppressedOrShelved property shall be set True and this Alarm is then typically not displayed by the Client. State transitions associated with the Alarm do occur, but they are not typically displayed by the Clients as long as the Alarm remains in any of the SuppressedState, OutOfServiceState or Shelved state.

The optional Property MaxTimeShelved is used to set the maximum time that an Alarm Condition may be shelved. The value is expressed as duration. Systems can use this Property to prevent permanent Shelving of an Alarm. If this Property is present it will be an upper limit on the duration passed into a TimedShelve Method call. If a value that exceeds the value of this Property is passed to the TimedShelve Method, then a Bad_ShelvingTimeOutOfRange error code is returned on the call. If this Property is present it will also be enforced for the OneShotShelved state, in that an Alarm Condition will transition to the Unshelved state from the OneShotShelved state if the duration specified in this Property expires following a OneShotShelve operation without a change of any of the other items associated with the Condition.

The optional Property AudibleEnabled is a Boolean that indicates if the current state of this Alarm includes an audible Alarm.

The optional Property AudibleSound contains the sound file that is to be played if an audible Alarm is to be generated. This file would be play/generated as long as the Alarm is active and unacknowledged, unless the silence StateMachine is included, in which case it may also be silenced by this StateMachine.

The SilenceState is used to suppress the generation of audible Alarms. Typically, it is used when an Operator silences all Alarms on a screen, but needs to acknowledge the Alarms individually. Silencing an Alarm shall silence the Alarm on all systems (screens) that it is being reported on. Not all Clients will make use of this StateMachine, but it allows multiple Clients to synchronize audible Alarm states. Acknowledging an Alarm shall automatically silence an Alarm.

The OnDelay and OffDelay Properties can be used to eliminate nuisance Alarms. The OnDelay is used to avoid unnecessary Alarms when a signal temporarily overshoots its setpoint, thus preventing the Alarm from being triggered until the signal remains in the Alarm state continuously for a specified length of time (OnDelay time). The OffDelay is used to reduce chattering Alarms by locking the Alarm indication for a certain holding period after the condition has returned to normal. I.e. the Alarm shall stay active for the OffDelay time and shall not regenerate if it returns to active in that period. If the Alarm remains in the inactive zone for OffDelay it will then become inactive.

The optional variable FirstInGroupFlag is used together with the FirstInGroup object. The FirstInGroup Object is an instance of an AlarmGroupType that groups a number of related Alarms. The FirstInGroupFlag is set on the Alarm instance that was the first Alarm to trigger in a FirstInGroup. If this variable is present, then the FirstInGroup shall also be present. These two nodes allow an alarming system to determine which Alarm in the list was the trigger. It is commonly used in situations where Alarms are interrelated and usually multiple Alarms occur. For example, vibration sensors in a turbine, usually all sensors trigger if any one triggers, but what is important for an Operator is the first sensor that triggered.

The LatchedState Object, if present, indicates that this Alarm supports being latched. The Alarm will remain with a retain bit of True until it is no longer active, is acknowledge and is reset. The Reset Method, if called while active has no effect on the Alarm and is ignored and an error of Bad_InvalidState is return on the call. The Object indicates the current state, latched or not latched. Recommended state names are described in Annex A. If this Object is provided the Reset Method must also be provided.

An Alarm instance may contain HasAlarmSuppressionGroup reference(s) to instance(s) of AlarmGroupType. Each instance is an AlarmSuppressionGroup. When an AlarmSuppressionGroup goes active, the Server shall set the SuppressedState of the Alarm to True. When all of referenced AlarmSuppressionGroups are no longer active, then the Server shall set SuppressedState to False. A single AlarmSuppressionGroup can be assigned to multiple Alarms. AlarmSuppressionGroups are used to control Alarm floods and to help manage Alarms.

ReAlarmTime if present sets a time that is used to bring an Alarm back to the top of an Alarm list. If an Alarm has not returned to normal within the provided time (from when it last was alarmed), the Server will generate a new Alarm for it (as if it just went into alarm). If it has been silenced it shall return to an un-silenced state, if it has been acknowledged it shall return to unacknowledged. The Alarm active time is set to the time of the re-alarm.

ReAlarmRepeatCount if present counts the number times an Alarm was re-alarmed. Some smart alarming system would use this count to raise the priority or otherwise generate additional or different annunciations for the given Alarm. The count is reset when an Alarm returns to normal.

Silence Method can be used to silence an instance of an Alarm. It is defined in 5.8.5.

Suppress Method can be used to suppress an instance of an Alarm. Most Alarm suppression occurs via advanced alarming, but this method allows additional access to suppress a particular Alarm instance. Additional details are provided in the definition in 5.8.6.

Unsuppress Method can be used to remove an instance of an Alarm from SuppressedState. Additional details are provided in the definition in 5.8.7.

PlaceInService Method can be used to remove an instance of an Alarm from OutOfServiceState. It is defined in 5.8.9.

RemoveFromService Method can be used to place an instance of an Alarm in OutOfServiceState. It is defined in 5.8.8.

Reset Method is used to clear a latched Alarm. It is defined in 5.8.4. If this Object is provided the LatchedState Object shall also be provided.

More details about the Alarm Model and the various states can be found in Sub clause 4.8. and in Annex E.

The AlarmGroupType provides a simple manner of grouping Alarms. This grouping can be used for Alarm suppression or for identifying related Alarms. The actual usage of the AlarmGroupType is specified where it is used.

Table 36 – AlarmGroupType Definition

Attribute	Value
BrowseName	AlarmGroupType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the FolderType defined in OPC 10000-5
AlarmGroupMember	Object	<AlarmConditionInstance>		AlarmConditionType	OptionalPlaceholder

The instance of an AlarmGroupType should be given a name and description that describes the purpose of the Alarm group.

The AlarmGroupType instance will contain a list of instances of AlarmConditionType or sub type of AlarmConditionType referenced by AlarmGroupMember references. At least one Alarm must be present in an instance of an AlarmGroupType.

The Reset Method is used reset a latched Alarm instance. It is only available on an instance of an AlarmConditionType that exposes the LatchedState. Normally, the NodeId of the Object instance is passed as the ObjectId to the Call Service. However, some Servers do not expose Condition instances in the AddressSpace. Therefore, Servers shall allow Clients to call the Reset Method by specifying ConditionId as the ObjectId. The Method cannot be called with an ObjectId of the AlarmConditionType Node.

Signature

Reset();

The parameters are defined in Table 40

Table 37 – Reset arguments

Argument	Description

Method result codes in Table 41 (defined in Call service)

Table 38 – Silence result codes

Result Code	Description
Bad_MethodInvalid	The MethodId provided does not correspond to the ObjectId provided. See OPC 10000-4 for the general description of this result code.
Bad_NodeIdInvalid	Used to indicate that the specified ObjectId is not valid or that the Method was called on the ConditionType Node. See OPC 10000-4 for the general description of this result code.
Bad_InvalidState	The Alarm instance was not latched or still active or still required acknowledgement. For an Alarm Instance to be reset it must have been in Alarm, and returned to normal and have been acknowledged prior to being reset.

Table 42 specifies the AddressSpace representation for the Reset Method.

Table 39 – Reset Method AddressSpace definition

Attribute	Value
BrowseName	Reset
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
AlwaysGeneratesEvent	ObjectType	AuditConditionResetEventType	Defined in 5.10.11

The Silence Method is used silence a specific Alarm instance. It is only available on an instance of an AlarmConditionType that also exposes the SilenceState. Normally, the NodeId of the Object instance is passed as the ObjectId to the Call Service. However, some Servers do not expose Condition instances in the AddressSpace. Therefore, Servers shall allow Clients to call the Silence Method by specifying ConditionId as the ObjectId. The Method cannot be called with an ObjectId of the AlarmConditionType Node.

Signature

Silence();

The parameters are defined in Table 40

Table 40 – Silence arguments

Argument	Description

Method result codes in Table 41 (defined in Call service)

Table 41 – Silence result codes

Result Code	Description
Bad_MethodInvalid	The MethodId provided does not correspond to the ObjectId provided. See OPC 10000-4 for the general description of this result code.
Bad_NodeIdInvalid	Used to indicate that the specified ObjectId is not valid or that the Method was called on the ConditionType Node. See OPC 10000-4 for the general description of this result code.

Comments

If the instance is not currently in an audible state, the command is ignored.

Table 42 specifies the AddressSpace representation for the Silence Method.

Table 42 – Silence Method AddressSpace definition

Attribute	Value
BrowseName	Silence
References	NodeClass		BrowseName	DataType	TypeDefinition	ModellingRule
AlwaysGeneratesEvent	ObjectType	AuditConditionSilenceEventType		Defined in 5.10.10

The Suppress Method is used to suppress a specific Alarm instance. It is only available on an instance of an AlarmConditionType that also exposes the SuppressedState. This Method can be used to change the SuppressedState of an Alarm and overwrite any suppression caused by an associated AlarmSuppressionGroup. This Method works in parallel with any suppression triggered by an AlarmSupressionGroup, in that if the Method is used to suppress an Alarm, an AlarmSuppressionGroup might clear the suppression.

Normally, the NodeId of the object instance is passed as the ObjectId to the Call Service. However, some Servers do not expose Condition instances in the AddressSpace. Therefore, Servers shall allow Clients to call the Suppress Method by specifying ConditionId as the ObjectId. The Method cannot be called with an ObjectId of the AlarmConditionType Node.

Signature

Suppress();

Method Result Codes in Table 43 (defined in Call Service)

Table 43 – Suppress result codes

Result Code	Description
Bad_MethodInvalid	The MethodId provided does not correspond to the ObjectId provided. See OPC 10000-4 for the general description of this result code.
Bad_NodeIdInvalid	Used to indicate that the specified ObjectId is not valid or that the Method was called on the ConditionType Node. See OPC 10000-4 for the general description of this result code.

Comments

Suppress Method applies to an Alarm instance, even if it is not currently active.

Table 44 specifies the AddressSpace representation for the Suppress Method.

Table 44 – Suppress Method AddressSpace definition

Attribute	Value
BrowseName	Suppress
References	NodeClass	BrowseName		DataType		TypeDefinition	ModellingRule
AlwaysGeneratesEvent	ObjectType		AuditConditionSuppressionEventType		Defined in 5.10.4

The Unsuppress Method is used to clear the SuppressedState of a specific Alarm instance. It is only available on an instance of an AlarmConditionType that also exposes the SuppressedState. This Method can be used to overwrite any suppression cause by an associated AlarmSuppressionGroup. This Method works in parallel with any suppression triggered by an AlarmSuppressionGroup, in that if the Method is used to clear the SuppressedState of an Alarm, any change in an AlarmSuppressionGroup might again suppress the Alarm.

Normally, the NodeId of the ObjectInstance is passed as the ObjectId to the Call Service. However, some Servers do not expose Condition instances in the AddressSpace. Therefore, Servers shall allow Clients to call the Unsuppress Method by specifying ConditionId as the ObjectId. The Method cannot be called with an ObjectId of the AlarmConditionType Node.

Signature

Unsuppress();

Method Result Codes in Table 43 (defined in Call Service)

Table 45 – Unsuppress result codes

Result Code	Description
Bad_MethodInvalid	The MethodId provided does not correspond to the ObjectId provided. See OPC 10000-4 for the general description of this result code.
Bad_NodeIdInvalid	Used to indicate that the specified ObjectId is not valid or that the Method was called on the ConditionType Node. See OPC 10000-4 for the general description of this result code.

Comments

Unsuppress Method applies to an Alarm instance, even if it is not currently active.

Table 44 specifies the AddressSpace representation for the Suppress Method.

Table 46 – Unsuppress Method AddressSpace definition

Attribute	Value
BrowseName	Unsuppress
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
AlwaysGeneratesEvent	ObjectType	AuditConditionSuppressionEventType	Defined in 5.10.4

The RemoveFromService Method is used to suppress a specific Alarm instance. It is only available on an instance of an AlarmConditionType that also exposes the OutOfServiceState. Normally, the NodeId of the object instance is passed as the ObjectId to the Call Service. However, some Servers do not expose Condition instances in the AddressSpace. Therefore, Servers shall allow Clients to call the RemoveFromService Method by specifying ConditionId as the ObjectId. The Method cannot be called with an ObjectId of the AlarmConditionType Node.

Signature

RemoveFromService ();

Method result codes in Table 47 (defined in Call Service)

Table 47 – RemoveFromService result codes

Result Code	Description
Bad_MethodInvalid	The MethodId provided does not correspond to the ObjectId provided. See OPC 10000-4 for the general description of this result code.
Bad_NodeIdInvalid	Used to indicate that the specified ObjectId is not valid or that the Method was called on the ConditionType Node. See OPC 10000-4 for the general description of this result code.

Comments

Instances that do not expose the OutOfService State shall reject RemoveFromService calls. RemoveFromService Method applies to an Alarm instance, even if it is not currently in the Active State.

Table 48 specifies the AddressSpace representation for the RemoveFromService Method.

Table 48 – RemoveFromService Method AddressSpace definition

Attribute	Value
BrowseName	RemoveFromService
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
AlwaysGeneratesEvent	ObjectType	AuditConditionOutOfServiceEventType	Defined in 5.10.12

The PlaceInService Method is used to set the OutOfServiceState to False of a specific Alarm instance. It is only available on an instance of an AlarmConditionType that also exposes the OutOfServiceState. Normally, the NodeId of the ObjectInstance is passed as the ObjectId to the Call Service. However, some Servers do not expose Condition instances in the AddressSpace. Therefore, Servers shall allow Clients to call the PlaceInService Method by specifying ConditionId as the ObjectId. The Method cannot be called with an ObjectId of the AlarmConditionType Node.

Signature

PlaceInService ();

Method result codes in Table 47 (defined in Call Service)

Table 49 – PlaceInService result codes

Result Code	Description
Bad_MethodInvalid	The MethodId provided does not correspond to the ObjectId provided. See OPC 10000-4 for the general description of this result code.
Bad_NodeIdInvalid	Used to indicate that the specified ObjectId is not valid or that the Method was called on the ConditionType Node. See OPC 10000-4 for the general description of this result code.

Comments

The PlaceInService Method applies to an Alarm instance, even if it is not currently in the Active State.

Table 48 specifies the AddressSpace representation for the PlaceInService Method.

Table 50 – PlaceInService Method AddressSpace definition

Attribute	Value
BrowseName	PlaceInService
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
AlwaysGeneratesEvent	ObjectType	AuditConditionOutOfServiceEventType	Defined in 5.10.12

The ShelvedStateMachineType defines a sub-state machine that represents an advanced Alarm filtering model. This model is illustrated in Figure 15.

The state model supports two types of Shelving: OneShotShelving and TimedShelving. They are illustrated in Figure 14. The illustration includes the allowed transitions between the various sub-states. Shelving is an Operator initiated activity.

In OneShotShelving, a user requests that an Alarm be Shelved for its current Active state. This type of Shelving is typically used when an Alarm is continually occurring on a boundary (i.e. a Condition is jumping between High Alarm and HighHigh Alarm, always in the Active state). The One Shot Shelving will automatically clear when an Alarm returns to an inactive state. Another use for this type of Shelving is for a plant area that is shutdown i.e. a long running Alarm such as a low level Alarm for a tank that is not in use. When the tank starts operation again the Shelving state will automatically clear.

In TimedShelving, a user specifies that an Alarm be shelved for a fixed time period. This type of Shelving is quite often used to block nuisance Alarms. For example, an Alarm that occurs more than 10 times in a minute may get shelved for a few minutes.

In all states, the Unshelve can be called to cause a transition to the Unshelve state; this includes Un-shelving an Alarm that is in the TimedShelve state before the time has expired and the OneShotShelve state without a transition to an inactive state.

All but two transitions are caused by Method calls as illustrated in Figure 14. The “Time Expired” transition is simply a system generated transition that occurs when the time value defined as part of the “Timed Shelved Call” has expired. The “Any Transition Occurs” transition is also a system generated transition; this transition is generated when the Condition goes to an inactive state.

Figure 14 – Shelve state transitions

The ShelvedStateMachineType includes a hierarchy of sub-states. It supports all transitions between Unshelved, OneShotShelved and TimedShelved.

The state machine is illustrated in Figure 15 and formally defined in Table 51.

Figure 15 – ShelvedStateMachineType model

Table 51 –ShelvedStateMachineType definition

Attribute	Value
BrowseName	ShelvedStateMachineType
IsAbstract	False
References	NodeClass	BrowseName	DataType		TypeDefinition	ModellingRule
Subtype of the FiniteStateMachineType defined in OPC 10000-5
HasProperty	Variable	UnshelveTime	Duration		PropertyType	Mandatory
HasComponent	Object	Unshelved			StateType
HasComponent	Object	TimedShelved			StateType
HasComponent	Object	OneShotShelved			StateType
HasComponent	Object	UnshelvedToTimedShelved			TransitionType
HasComponent	Object	TimedShelvedToUnshelved			TransitionType
HasComponent	Object	TimedShelvedToOneShotShelved			TransitionType
HasComponent	Object	UnshelvedToOneShotShelved			TransitionType
HasComponent	Object	OneShotShelvedToUnshelved			TransitionType
HasComponent	Object	OneShotShelvedToTimedShelved			TransitionType
HasComponent	Method	TimedShelve	Defined in Clause 5.8.10.3			Mandatory
HasComponent	Method	OneShotShelve	Defined in Clause 5.8.10.4			Mandatory
HasComponent	Method	Unshelve	Defined in Clause 5.8.10.2			Mandatory

UnshelveTime specifies the remaining time in milliseconds until the Alarm automatically transitions into the Un-shelved state. For the TimedShelved state this time is initialised with the ShelvingTime argument of the TimedShelve Method call. For the OneShotShelved state the UnshelveTime will be a constant set to the maximum Duration except if a MaxTimeShelved Property is provided.

This FiniteStateMachine supports three Active states; Unshelved, TimedShelved and OneShotShelved. It also supports six transitions. The states and transitions are described in Table 52. This FiniteStateMachine also supports three Methods; TimedShelve, OneShotShelve and Unshelve.

Table 52 – ShelvedStateMachineType transitions

BrowseName	References	BrowseName	TypeDefinition
Transitions
UnshelvedToTimedShelved	FromState	Unshelved	StateType
	ToState	TimedShelved	StateType
	HasEffect	AlarmConditionType
	HasCause	TimedShelve	Method
UnshelvedToOneShotShelved	FromState	Unshelved	StateType
	ToState	OneShotShelved	StateType
	HasEffect	AlarmConditionType
	HasCause	OneShotShelve	Method
TimedShelvedToUnshelved	FromState	TimedShelved	StateType
	ToState	Unshelved	StateType
	HasEffect	AlarmConditionType
TimedShelvedToOneShotShelved	FromState	TimedShelved	StateType
	ToState	OneShotShelved	StateType
	HasEffect	AlarmConditionType
	HasCause	OneShotShelving	Method
OneShotShelvedToUnshelved	FromState	OneShotShelved	StateType
	ToState	Unshelved	StateType
	HasEffect	AlarmConditionType
OneShotShelvedToTimedShelved	FromState	OneShotShelved	StateType
	ToState	TimedShelved	StateType
	HasEffect	AlarmConditionType
	HasCause	TimedShelve	Method

The Unshelve Method sets the instance of AlarmConditionType to the Unshelved state. Normally, the MethodId found in the Shelving child of the Condition instance and the NodeId of the Shelving object as the ObjectId are passed to the Call Service. However, some Servers do not expose Condition instances in the AddressSpace. Therefore, all Servers shall also allow Clients to call the Unshelve Method by specifying ConditionId as the ObjectId. The Method cannot be called with an ObjectId of the ShelvedStateMachineType Node.

Signature

Unshelve( );

Method Result Codes in Table 53 (defined in Call Service)

Table 53 – Unshelve result codes

Result Code	Description
Bad_ConditionNotShelved	See Table 103 for the description of this result code.

Table 54 specifies the AddressSpace representation for the Unshelve Method.

Table 54 – Unshelve Method AddressSpace definition

Attribute	Value
BrowseName	Unshelve
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
AlwaysGeneratesEvent	ObjectType	AuditConditionShelvingEventType	Defined in 5.10.7

The TimedShelve Method sets the instance of AlarmConditionType to the TimedShelved state (parameters are defined in Table 55 and result codes are described in Table 56). Normally, the MethodId found in the Shelving child of the Condition instance and the NodeId of the Shelving object as the ObjectId are passed to the Call Service. However, some Servers do not expose Condition instances in the AddressSpace. Therefore, all Servers shall also allow Clients to call the TimedShelve Method by specifying ConditionId as the ObjectId. The Method cannot be called with an ObjectId of the ShelvedStateMachineType Node.

Signature

TimedShelve(

[in] Duration ShelvingTime

);

Table 55 – TimedShelve parameters

Argument	Description
ShelvingTime	Specifies a fixed time for which the Alarm is to be shelved. The Server may refuse the provided duration. If a MaxTimeShelved Property exist on the Alarm than the Shelving time shall be less than or equal to the value of this Property.

Method Result Codes (defined in Call Service)

Table 56 – TimedShelve result codes

Result Code	Description
Bad_ConditionAlreadyShelved	See Table 103 for the description of this result code. The Alarm is already in TimedShelved state and the system does not allow a reset of the shelved timer.
Bad_ShelvingTimeOutOfRange	See Table 103 for the description of this result code.

Comments

Shelving for some time is quite often used to block nuisance Alarms. For example, an Alarm that occurs more than 10 times in a minute may get shelved for a few minutes.

In some systems the length of time covered by this duration may be limited and the Server may generate an error refusing the provided duration. This limit may be exposed as the MaxTimeShelved Property.

Table 57 specifies the AddressSpace representation for the TimedShelve Method.

Table 57 – TimedShelve Method AddressSpace definition

Attribute	Value
BrowseName	TimedShelve
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
HasProperty	Variable	InputArguments	Argument[]	PropertyType	Mandatory
AlwaysGeneratesEvent	ObjectType	AuditConditionShelvingEventType	Defined in 5.10.7

The OneShotShelve Method sets the instance of AlarmConditionType to the OneShotShelved state. Normally, the MethodId found in the Shelving child of the Condition instance and the NodeId of the Shelving object as the ObjectId are passed to the Call Service. However, some Servers do not expose Condition instances in the AddressSpace. Therefore, all Servers shall also allow Clients to call the OneShotShelve Method by specifying ConditionId as the ObjectId. The Method cannot be called with an ObjectId of the ShelvedStateMachineType Node.

Signature

OneShotShelve( );

Method Result Codes are defined in Table 58 (status code field is defined in Call Serv ice)

Table 58 – OneShotShelve result codes

Result Code	Description
Bad_ConditionAlreadyShelved	See Table 103 for the description of this result code. The Alarm is already in OneShotShelved state.

Table 59 specifies the AddressSpace representation for the OneShotShelve Method.

Table 59 – OneShotShelve Method AddressSpace definition

Attribute	Value
BrowseName	OneShotShelve
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
AlwaysGeneratesEvent	ObjectType	AuditConditionShelvingEventType	Defined in 5.10.7

Alarms can 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 LimitAlarmType is an abstract type used to provide a base Type for AlarmConditionTypes with multiple limits. The LimitAlarmType is illustrated in Figure 16.

Figure 16 – LimitAlarmType

The LimitAlarmType is 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 Alarm Types. These Properties shall be set for any Alarm limits that are exposed by the derived limit Alarm types. These Properties are 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 Property shall still be provided, but will have its AccessLevel set 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 Alarm limit. If a Server supports AdaptiveAlarming for Alarm limits, the corresponding base Alarm limit 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 AdaptiveAlarm can be reset if any algorithmic changes need to be discarded.

The Alarm limits listed may cause an Alarm to be generated when a value equals the limit or it may generate the Alarm when the limit is exceeded, (i.e. the Value is above the limit for HighLimit and below the limit for LowLimit). The exact behaviour when the value is equal to the limit is Server specific.

The Variable that is the source of the LimitAlarmType Alarm shall be a scalar. This LimitAlarmType can be subtyped if the Variable that 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 Alarm is generated,
• if all elements exceed the limit an Alarm is generated,
• the limits may also be an array, in which case if any array limit is exceeded by the corresponding source array element, an Alarm is generated.

This clause describes the state machine and the base Alarm Type behaviour for Alarm ConditionTypes with multiple mutually exclusive limits.

The ExclusiveLimitStateMachineType defines the state machine used by AlarmConditionTypes that handle multiple mutually exclusive limits. It is illustrated in Figure 17.

Figure 17 – ExclusiveLimitStateMachineType

It is created by extending the FiniteStateMachineType. It is formally defined in Table 61 and the state transitions are described in Table 62.

Table 61 – ExclusiveLimitStateMachineType definition

Attribute	Value
BrowseName	ExclusiveLimitStateMachineType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the FiniteStateMachineType
HasComponent	Object	HighHigh		StateType
HasComponent	Object	High		StateType
HasComponent	Object	Low		StateType
HasComponent	Object	LowLow		StateType
HasComponent	Object	LowToLowLow		TransitionType
HasComponent	Object	LowLowToLow		TransitionType
HasComponent	Object	HighToHighHigh		TransitionType
HasComponent	Object	HighHighToHigh		TransitionType

Table 62 – ExclusiveLimitStateMachineType transitions

BrowseName	References	BrowseName	TypeDefinition
Transitions
HighHighToHigh	FromState	HighHigh	StateType
	ToState	High	StateType
	HasEffect	AlarmConditionType
HighToHighHigh	FromState	High	StateType
	ToState	HighHigh	StateType
	HasEffect	AlarmConditionType
LowLowToLow	FromState	LowLow	StateType
	ToState	Low	StateType
	HasEffect	AlarmConditionType
LowToLowLow	FromState	Low	StateType
	ToState	LowLow	StateType
	HasEffect	AlarmConditionType

The ExclusiveLimitStateMachineType defines the sub state machine that represents the actual level of a multilevel Alarm when it is in the Active state. The sub state machine defined here includes High, Low, HighHigh and LowLow states. This model also includes in its transition state a series of transition to and from a parent state, the inactive state. This state machine as it is defined shall be used as a sub state machine for a state machine which has an Active state. This Active state could be part of a “level” Alarm or “deviation” Alarm or any other Alarm state machine.

The LowLow, Low, High, HighHigh are typical for many industries. Vendors can introduce sub-state models that include additional limits; they may also omit limits in an instance. If a model omits states or transitions in the StateMachine, it is recommended that they provide the optional Property AvailableStates and/or AvailableTransitions (see OPC 10000-5).

The ExclusiveLimitAlarmType is used to specify the common behaviour for Alarm Types with multiple mutually exclusive limits. The ExclusiveLimitAlarmType is illustrated in Figure 18.

Figure 18 – ExclusiveLimitAlarmType

The ExclusiveLimitAlarmType is formally defined in Table 63.

Table 63 – ExclusiveLimitAlarmType definition

Attribute	Value
BrowseName	ExclusiveLimitAlarmType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the LimitAlarmType defined in clause 5.8.11.
HasSubtype	ObjectType	ExclusiveLevelAlarmType	Defined in Clause 5.8.14.3
HasSubtype	ObjectType	ExclusiveDeviationAlarmType	Defined in Clause 5.8.15.3
HasSubtype	ObjectType	ExclusiveRateOfChangeAlarmType	Defined in Clause 5.8.16.3
HasComponent	Object	LimitState		ExclusiveLimitStateMachineType	Mandatory

The LimitState is a sub state of the ActiveState and has an IsTrueSubStateOf reference to the ActiveState. The LimitState represents the actual limit that is violated in an instance of ExclusiveLimitAlarmType. When the ActiveState of the AlarmConditionType is inactive the LimitState shall not be available and shall return NULL on read. Any Events that subscribe for fields from the LimitState when the ActiveState is inactive shall return a NULL for these unavailable fields.

The NonExclusiveLimitAlarmType is used to specify the common behaviour for Alarm Types with multiple non-exclusive limits. The NonExclusiveLimitAlarmType is illustrated in Figure 19.

Figure 19 – NonExclusiveLimitAlarmType

The NonExclusiveLimitAlarmType is formally defined in Table 64.

Table 64 – NonExclusiveLimitAlarmType definition

Attribute	Value
BrowseName	NonExclusiveLimitAlarmType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the LimitAlarmType defined in clause 5.8.11.
HasSubtype	ObjectType	NonExclusiveLevelAlarmType	Defined in Clause 5.8.14.2
HasSubtype	ObjectType	NonExclusiveDeviationAlarmType	Defined in Clause 5.8.15.2
HasSubtype	ObjectType	NonExclusiveRateOfChangeAlarmType	Defined in Clause 5.8.16.2
HasComponent	Variable	HighHighState	LocalizedText	TwoStateVariableType	Optional
HasComponent	Variable	HighState	LocalizedText	TwoStateVariableType	Optional
HasComponent	Variable	LowState	LocalizedText	TwoStateVariableType	Optional
HasComponent	Variable	LowLowState	LocalizedText	TwoStateVariableType	Optional

HighHighState, HighState, LowState, and LowLowState represent the non-exclusive states. As an example, it is possible that both HighState and HighHighState are in their True state. Vendors may choose to support any subset of these states. Recommended state names are described in Annex A.

Four optional limits are defined that configure these states. At least the HighState or the LowState shall be provided even though all states are optional. It is implied by the definition of a HighState and a LowState, that these groupings are mutually exclusive. A value cannot exceed both a HighState value and a LowState value simultaneously.

A level Alarm is commonly used to report when a limit is exceeded. It typically relates to an instrument – e.g. a temperature meter. The level Alarm becomes active when the observed value is above a high limit or below a low limit.

The NonExclusiveLevelAlarmType 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 NonExclusiveLevelAlarmType should be used.

The NonExclusiveLevelAlarmType is based on the NonExclusiveLimitAlarmType. It is formally defined in Table 65.

Table 65 – NonExclusiveLevelAlarmType definition

Attribute	Value
BrowseName	NonExclusiveLevelAlarmType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the NonExclusiveLimitAlarmType defined in clause 5.8.13.

No additional Properties to the NonExclusiveLimitAlarmType are defined.

The ExclusiveLevelAlarmType is a special level Alarm utilized with multiple mutually exclusive limits. It is formally defined in Table 66.

Table 66 – ExclusiveLevelAlarmType definition

Attribute	Value
BrowseName	ExclusiveLevelAlarmType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Inherits the Properties of the ExclusiveLimitAlarmType defined in clause 5.8.12.3.

No additional Properties to the ExclusiveLimitAlarmType are defined.

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.

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
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the NonExclusiveLimitAlarmType defined in clause 5.8.13.
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.

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
References	NodeClass	BrowseName	DataType	TypeDefinition	Modelling Rule
Inherits the Properties of the ExclusiveLimitAlarmType defined in clause 5.8.12.3.
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.

A Rate of Change Alarm is 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 Rate of Change Alarm becomes active when the rate at which the value changes exceeds or drops below a defined limit.

A Rate of Change is 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 Rate of Change of 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 NonExclusiveRateOfChangeAlarmType 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 this AlarmConditionType should be used

The NonExclusiveRateOfChangeAlarmType is 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.

ExclusiveRateOfChangeAlarmType is 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 Properties of the ExclusiveLimitAlarmType defined 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.

The DiscreteAlarmType is used to classify Types into Alarm Conditions where the input for the Alarm may take on only a certain number of possible values (e.g. True/False, running/stopped/terminating). The DiscreteAlarmType with sub types defined in this standard is illustrated in Figure 20. It is formally defined in Table 71.

Figure 20 – DiscreteAlarmType Hierarchy

Table 71 – DiscreteAlarmType definition

Attribute	Value
BrowseName	DiscreteAlarmType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the AlarmConditionType defined in clause 5.8.2.
HasSubtype	ObjectType	OffNormalAlarmType	Defined in Clause 5.8.15

The OffNormalAlarmType is a specialization of the DiscreteAlarmType intended to represent a discrete Condition that is considered to be not normal. It is formally defined in Table 72. This sub type is usually used to indicate that a discrete value is in an Alarm state, it is active as long as a non-normal value is present.

Table 72 – OffNormalAlarmType Definition

Attribute	Value
BrowseName	OffNormalAlarmType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition		ModellingRule
Subtype of the DiscreteAlarmType defined in clause 5.8.17.1
HasSubtype	ObjectType	TripAlarmType	Defined in Clause 5.8.17.4
HasSubtype	ObjectType	SystemOffNormalAlarmType	Defined in Clause 5.8.17.3
HasProperty	Variable	NormalState	NodeId		PropertyType	Mandatory

The NormalState Property is a Property that points to a Variable which has a value that corresponds to one of the possible values of the Variable pointed to by the InputNode Property where the NormalState Property Variable value is the value that is considered to be the normal state of the Variable pointed to by the InputNode Property. When the value of the Variable referenced by the InputNode Property is not equal to the value of the NormalState Property the Alarm is Active. If this Variable is not in the AddressSpace, a NULL NodeId shall be provided.

This Condition is used by a Server to indicate that an underlying system that is providing Alarm information is having a communication problem and that the Server may have invalid or incomplete Condition state in the Subscription. Its representation in the AddressSpace is formally defined in Table 73.

Table 73 – SystemOffNormalAlarmType definition

Attribute	Value
BrowseName	SystemOffNormalAlarmType
IsAbstract	True
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
HasSubtype	ObjectType	CertificateExpirationAlarmType	Defined in Clause 0
Subtype of the OffNormalAlarmType, i.e. it has HasProperty References to the same Nodes.

The TripAlarmType is a specialization of the OffNormalAlarmType intended to represent an equipment trip Condition. The Alarm becomes active when the monitored piece of equipment experiences some abnormal fault such as a motor shutting down due to an overload condition. It is formally defined in Table 74. This Type is mainly used for categorization.

Table 74 – TripAlarmType definition

Attribute	Value
BrowseName	TripAlarmType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the OffNormalAlarmType defined in clause 5.8.17.2.

The InstrumentDiagnosticAlarmType is a specialization of the OffNormalAlarmType intended to represent a fault in a field device. The Alarm becomes active when the monitored device experiences a fault such as a sensor failure. It is formally defined in Table 74. This Type is mainly used for categorization.

Table 75 – InstrumentDiagnosticAlarmType definition

Attribute	Value
BrowseName	InstrumentDiagnosticAlarmType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the OffNormalAlarmType defined in clause 5.8.17.2.

The SystemDiagnosticAlarmType is a specialization of the OffNormalAlarmType intended to represent a fault in a system or sub-system. The Alarm becomes active when the monitored system experiences a fault. It is formally defined in Table 74. This Type is mainly used for categorization.

Table 76 – SystemDiagnosticAlarmType definition

Attribute	Value
BrowseName	SystemDiagnosticAlarmType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the OffNormalAlarmType defined in clause 5.8.17.2.

This SystemOffNormalAlarmType is raised by the Server when the Server’s Certificate is within the ExpirationLimit of expiration. This Alarm automatically returns to normal when the certificate is updated.

Table 77 – CertificateExpirationAlarmType definition

Attribute	Value
BrowseName	CertificateExpirationAlarmType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the SystemOffNormalAlarmType defined in clause 5.8.17.3
HasProperty	Variable	ExpirationDate	DateTime	PropertyType	Mandatory
HasProperty	Variable	ExpirationLimit	Duration	PropertyType	Optional
HasProperty	Variable	CertificateType	NodeId	PropertyType	Mandatory
HasProperty	Variable	Certificate	ByteString	PropertyType	Mandatory

ExpirationDate is the date and time this certificate will expire.

ExpirationLimit is the time interval before the ExpirationDate at which this Alarm will trigger. This shall be a positive number. If the property is not provided, a default of 2 weeks shall be used.

CertificateType – See OPC 10000-12 for definition of CertificateType.

Certificate is the certificate that is about to expire.

The DiscrepancyAlarmType is commonly used to report an action that did not occur within an expected time range.

The DiscrepancyAlarmType is based on the AlarmConditionType. It is formally defined in Table 78.

Table 78 – DiscrepancyAlarmType definition

Attribute	Value
BrowseName	DiscrepancyAlarmType
IsAbstract	False
References	Node Class	BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the AlarmConditionType defined in 5.8.2.
HasProperty	Variable	TargetValueNode	NodeId	PropertyType	Mandatory
HasProperty	Variable	ExpectedTime	Duration	PropertyType	Mandatory
HasProperty	Variable	Tolerance	Double	PropertyType	Optional

The TargetValueNode Property provides the NodeId of the Variable that is used for the target value.

The ExpectedTime Property provides the Duration within which the value pointed to by the InputNode shall equal the value specified by the TargetValueNode (or be within the Tolerance range, if specified).

The Tolerance Property is a value that can be added to or subtracted from the TargetValueNode’s value, providing a range that the value can be in without generating the Alarm.

A DiscrepancyAlarmType can be used to indicate a motor has not responded to a start request within a given time, or that a process value has not reached a given value after a setpoint change within a given time interval.

The DiscrepancyAlarmType shall return to normal when the value has reached the target value.