Annex B (informative) Use cases ToC Previous

B.7 Read parameters ToC Previous Next

B.7.2 Use case: Read online data ToC Previous Next

Use Case Read online parameters  
Description A software or user requests device parameter (the current values in the device) from a DTM. The OPC UA client collects this information by reading device parameter from the online set provided according to the FDT OPC UA information model.  
Preconditions Device node is available in OPC UA Server and the Client already knows the ParameterIds of the Parameters to read (may have been retrieved according to use case B4.2).  
Post conditions Client knows the current value of device parameters  
Actors Engineer, Expert, Observer, Operator  
Trigger Whenever the data is needed  
  Step Action
  Preparation The OPC Client selects the respective offline device node
  1 OPC Client selects the online device and the parameter set of the online device.
  2 OPC Client executes Read-Service (one or multiple times) with the list of identifiers for the respective device parameters (list of ParameterIds) and the list of AttributeIds for Value and (at least once) for DateType.
  3 OPC Server requests the requested attributes (e.g. value) of the parameter which are specified in the Read-Request from the DTM (instance data set).
  4 The DTM retrieves the current values from the device and returns them to the server.
  5 OPC Server returns the requested information to the client.
  6 OPC Client displays the parameter value (or uses it otherwise).
Exceptions Step 1, The specified parameter does not exist in the device.  
Open Issues    

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