This clause specifies how to apply the Common Data Dictionary (IEC CDD) published as IEC/TS 62720 by the “International Electrotechnical Commission - IEC” to the EUInformation Structure.

Note - entries of the IEC CDD reference to the “common code” from UN/CEFACT Rec. 20 if one is available.

The units and their identifiers, along with their relationships, is maintained in the IEC Common Data Dictionary (CDD): https://cdd.iec.ch/cdd/iec62720/iec62720.nsf/TreeFrameset. Specific units can only be found via search. A ‘*’ as search string will return all units.

Figure 6 specifies the dialog to search for units and optionally export them.

Figure 6 – Searching Units in the IEC Common Data Dictionary

Table 21 contains a small excerpt of the relevant columns in IEC 62720:

Table 22 – Examples from the IEC CDD

Excerpt of Units from IEC/TS 62720
Code	Symbol	Name
UAA017	Ω	ohm
UAA033	°C	degree Celsius
UAA070	μN	micronewton
UAA172	J	joule
UAA539	in	inch
UAB044	in/s2	inch per second squared
UAA497	g/s	gram per second

Note – The “Code” corresponds to the data identifier of the IRDI for the CDD entry.

All units in the IEC CDD have been extracted and mapped to the EUInformation fields. The list is available here:

http://www.opcfoundation.org/UA/EngineeringUnits/IEC/IEC62720_to_OPCUA.csv

This mapping has been generated as follows:

• The namespaceUri shall be http://www.opcfoundation.org/UA/units/cdd/IEC62720
• The Code is the data identifier of the IRDI. It is represented by 3 uppercase characters and 3 digits. This code has been converted into a 32-Bit Integer and is used for the unitId. The following pseudo code specifies the conversion algorithm:

Int32 unitId = 0;Int32 c;for (i=0; i<6;i++){

c = UnitCode[i] 0x1f; unitId = unitId << 5; unitId = unitId | c;}

• The Short Name field shall be used as invariant locale for displayName. Servers can configure multiple additional locales for each displayName. However, if none of the LocaleIds specified by the Client for the Session matches these additional locales, the Server shall return the invariant locale.
• The Preferred Name field shall be used as invariant locale for description. Servers can configure multiple additional locales for each description. However, if none of the LocaleIds specified by the Client for the Session matches these additional locales, the Server shall return the invariant locale.