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UnitId
January 21, 2016
18:49, EET
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aSaunders925
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I’m evaluating using the OpcUaJavaSDK and I have a question about UnitId usage. I need to map the engineering units (EUInformation) returned from a Opc UA server to the way engineering units are defined in our system. I was planning on using the UnitId value as a key to do the mapping, but it doesn’t appear that I can count on this, as the Quickstart/DataAccessServe r has UnitId = 0 for all engineering unit (EUInformation) served up..
Suggestions?

January 22, 2016
9:12, EET
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Heikki Tahvanainen
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Hello,

According to specification part 8, the unitId should be -1 if the unitId is not available. Is there some sensible value in the namespaceUri field? I suppose that many sampleservers don’t yet offer realistic engineeringUnits or unitId information.

Br,
Heikki Tahvanainen

January 22, 2016
11:56, EET
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aSaunders925
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(EUInformation) EUInformation: EUInformation
NamespaceUri=http://opcfoundation.org/Quickstarts/DataAccess
UnitId=0
DisplayName=liters/sec

I’m using the sample server application from the opcfoundation.org web site.

January 22, 2016
12:57, EET
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Heikki Tahvanainen
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Hi,

If UnitId=0 consistently means liters/sec, then it’s easy to map this particular engineering unit based on that information. However, if I understood correctly then the actual problem is that the Quickstart/DataAccessServer uses UnitId=0 regardless of EUInformation. In that case of course you cannot use the UnitId information. Pages 15 and 16 from OPC UA Specification part 8 version 1.03 cover how UnitIds should be used.

If you want to map the engineering units of the Quickstart/DataAccessServer to engineering units defined in your system then you might use the information in DisplayName and Description fields of the EUInformation structure. The downside of this approach is that this mapping does not work with other OPC UA servers which might have different DisplayNames and Descriptions.

Br,
Heikki

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