| 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. |
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| Stakeholder | |
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| 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). |
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| Post conditions | Client knows the current value of device parameters |
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| Actors | Engineer, Expert, Observer, Operator |
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| Trigger | Whenever the data is needed |
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| Frequency | |
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| Description |
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| Step | Action |
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| Preparation | The OPC Client selects the respective offline device node |
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| 1 | OPC Client selects the online device and the parameter set of the online device. |
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| 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. |
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| 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). |
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| 4 | The DTM retrieves the current values from the device and returns them to the server. |
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| 5 | OPC Server returns the requested information to the client. |
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| 6 | OPC Client displays the parameter value (or uses it otherwise). |
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| Exceptions | Step 1, The specified parameter does not exist in the device. |
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| Requirements | |
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| Notes | |
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| Open Issues | |
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