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Engineering Units management
May 3, 2023
11:40, EEST
Francesco Zambon
Forum Posts: 62
Member Since:
December 20, 2021
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Good morning,

Can you please explain how to manage the measurement units (EngineeringUnits) of the analog variables (AnalogItemType) in the OPC UA standard?

I take as an example the TemperatureLimitation variable defined in the EUROMAP 82.1 standard https://www.euromap.org/euromap82-1

Variable name:


Description (File EUROMAP82.1_Release_1.01.pdf Page 18):
10.5 Temperature Limitation
Description: This setpoint is for temperature limitation of the mold circuit e.g. to protect the connected tubes or the downstream water distribution system.
Units: °C or °F
Example: 120

Question 1:
Can the EngineeringUnits node be “handled” like the LocalizedText node?
Can the OPC UA client display the TemperatureLimitation variable in the desired unit of measurement?
For example by setting the LOCALE of the client (en_US, de_DE, fr_FR, …), the server translates the LocalizedText into the desired language of the client.

Question 2:
I don’t understand the meaning of the sentence “Unit: °C or °F”.
It means that the OPC UA server can decide to display the variable in “°C” or “°F”, or that the OPC UA client can display the variable both in the unit of measure “°C” and in the unit of measure “°F”?

Question 3:
Are there other types in the OPC UA standard besides EngineeringUnits to manage units of measurement?

Thank you for your help.
Best regards.


May 3, 2023
14:05, EEST
Bjarne Boström
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April 3, 2012
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Technically it is also a “standard Property” that is optional to any Variable node: https://reference.opcfoundation.org/Core/Part3/v105/docs/5.6.2 (with some limitations). For the EUInformation Structure itself see: https://reference.opcfoundation.org/v104/Core/docs/Part8/5.6.3/.

SDK contains some help from the ” “Codes for Units of Measurement” published by the “United Nations Centre for Trade Facilitation and Electronic Business”” in in com.prosysopc.ua.stack.core.StandardEngineeringUnits. It is .. maybe not the easiest to use, but it has static methods: ‘List getAll()’, ‘EUInformation getByCommonCode(String commonCode)’ and ‘getByUnitId(int unitId)’. There are .. a lot of units, but here the StandardEngineeringUnits.DEGREE_CELSIUS and DEGREE_FAHRENHEIT are most likely the ones you look for. A “°C or °F” from a different “EUInformation”-namespace than the “https://opcfoundation.org/UA/units/un/cefact” might mean a different thing (doublecheck does the euromap say anything about this, if not I would assume it to mean this one). And it probably would be better to use the namespace+unitId instead of any displayname/desription for other than visualization purposes. But in general I would sort of say it is the same thing with localization, these are features added to the spec, but possibly like never (yet) used.

1. No, it is just extra info about the “type/kind” of the value, so here it is either °C or °F, but there are no automatic conversions (spec-wise). You can only set one of them. In the localization the locales are transmitted as part of the ActivateSession; there is nothing similar for this. In theory client can of course convert values by itself, but it would be a purely client-side thing.

2. It means the literal value given (by the server maker etc.) can either be given/set as farenheit or celcius and the EngineeringUnits Property shall be set to the same so that there is no confusion for clients which one it is. (so if you set it in celsius, you would also use StandardEngineeringUnits.DEGREE_CELSIUS as the EngineeringUnits).

3. For units of measurement, not that I know. For currency it would seem at some point this was added: https://reference.opcfoundation.org/Core/Part3/v105/docs/8.61.

May 3, 2023
16:14, EEST
Francesco Zambon
Forum Posts: 62
Member Since:
December 20, 2021
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Dear Bjarne,

Thanks for your help.

Best regards,

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