<MonitoredItemCreateRequest>

The <MonitoredItemCreateRequest> and </MonitoredItemCreateRequest> elements define an item that you want the OPC UA server to monitor and return notifications to the Probe for OPC UA when requested. A notification can indicate a change in the data associated with the monitored item, or the occurrence of an event.

The <MonitoredItemCreateRequest> and </MonitoredItemCreateRequest> elements contain the following child elements:

<ItemToMonitor> </ItemToMonitor>

Specify an item to monitor. See <ItemToMonitor>.

<MonitoringMode> </MonitoringMode>

Specify the type of monitoring to carry out on the item. In this release of the probe, use the value of Reporting_2.

<RequestedParameters> </RequestedParameters>

Specify the parameters that define the type of monitoring that the probe requires. See <RequestedParameters>.

<ItemToMonitor>

The <ItemToMonitor> and </ItemToMonitor> elements define an element in the OPC UA server's address space that the probe wants to be monitored.

The <ItemToMonitor> and </ItemToMonitor> elements contain the following child elements:

<NodeId> </NodeId>

Specify the unique identifier of the node in the OPC UA server's address space.

<AttributeId> </AttributeId>

Specify the data type of the attribute within the node that the OPC UA server is to monitor.

The OPC UA standard defines the values for node identifiers and data type attributes.

<RequestedParameters>

The <RequestedParameters> and </RequestedParameters> elements define the details of what is to be monitored and how.

The <RequestedParameters> and </RequestedParameters> elements contain the following child elements:

<ClientHandle> </ClientHandle>

Specify a unique identifier for this monitored item. The identifier is an integer. The probe uses this value to match notifications with the appropriate node.

<SamplingInterval> </SamplingInterval>

Specify the frequency, in milliseconds, that the OPC UA server is to sample the monitored item. The following list describes the valid values:

  • 0: Indicates that the server is to use the fastest practical rate for sampling the monitored item.
  • -1: Indicates that the server is to use the default sampling interval that was defined during the creation of the Subscription. The RequestedPublishingInterval property contains this default sampling interval.
Note: if you provide a negative number for the content of this element, the probe treats it as being -1.

<Filter> </Filter>

Specify an optional filter to use to determine when the monitored item generates a notification. See <Filter>.

<QueueSize> </QueueSize>

Specify the requested size of the queue to hold notifications from the monitored item. Notifications remain in the queue until sent to the probe in response to a Publish request.

The values 0 and 1 have special meaning, depending on the type of notification that is generated. For data change notifications, 1 and 0 cause the server to use the default queue size of one. For event notifications, 0 causes the server to use the default queue entry. A value of 1 causes the OPC UA server to use the minimum queue size.

<DiscardOldest> </DiscardOldest>

Specify the policy that the OPC UA server is to follow should the queue of notifications become full. The following list describes the valid values:

  • false: The OPC UA server discards notifications that are generated after the queue becomes full.
  • true: The OPC UA server discards the oldest notification in the queue to make way for each new notification that arrives.

<Filter>

The <Filter> and </Filter> elements are optional and define a filter that determines when the monitored item generates a notification.

The <Filter> </Filter> element pair contain the following child elements:

<TypeId> </TypeId>

Identify the type of filter and contains a single child element pair: <Identifer> and </Identifer>. The <Identifer> and </Identifer> elements contain an identifier for the type of filter, and can be one of the following values:

  • i=723: Use this value for a data change filter.
  • i=726: Use this value for an event filter.

<Body> </Body>

Contain the body of the filter that defines the conditions for generating a notification. The <Body> </Body> elements contain one of the following child elements:

  • For data change items: <DataChangeFilter> and </DataChangeFilter>. The OPCUaDataChange.xml configuration file delivered with the probe provides examples of these elements.
  • For event items: <EventFilter> and </EventFilter>. The OPCUaEvent.xml configuration file delivered with the probe provides examples of these elements.

For more information, see: