OpcShelvedStateMachineNode Class

Namespace: Opc.UaFx
Assemblies: Opc.UaFx.Advanced.dll

Defines a specialization of the OpcFiniteStateMachineNode which implements a sub-state machine that represents an advanced alarm filtering model.

C#

public class OpcShelvedStateMachineNode : OpcFiniteStateMachineNode, IOpcNode, IOpcNodeInfo

Inheritance Object › OpcNode › OpcInstanceNode › OpcObjectNode › OpcStateMachineNode › OpcFiniteStateMachineNode › OpcShelvedStateMachineNode

Implements IOpcNode, IOpcNodeInfo

The state model supports two types of Shelving: OneShotShelving and TimedShelving. This 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 high high 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(OpcContext) can be called to cause a transition to the unshelve state; this includes un-shelving an alarm that is in the timed shelve state before the time has expired and the one shot shelve state without a transition to an inactive state.

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.