It is formally defined in Table 38.
Table 38 – UnitType definition
|
Attribute |
Value |
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|
BrowseName |
UnitType |
||||
|
IsAbstract |
True |
||||
|
References |
NodeClass |
BrowseName |
DataType |
TypeDefinition |
Other |
|
Subtype of the BaseObjectType defined in OPC 10000-5 |
|||||
|
HasProperty |
Variable |
Symbol |
LocalizedText |
PropertyType |
M |
|
HasProperty |
Variable |
Description |
LocalizedText |
PropertyType |
O |
|
HasProperty |
Variable |
UnitSystem |
String |
PropertyType |
M |
|
HasProperty |
Variable |
Discipline |
String |
PropertyType |
O |
|
Conformance Units |
|||||
|
Data Access Quantities Base |
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The DisplayName Attribute of each instance shall provide the name of the unit, e.g. “second”, “degree Celsius” or “square metre”. This matches the “description” field of the EUInformation structure (see 5.6.3.3).
The Symbol Property is used for the symbol of the unit (e.g. "h" for hour or "m/s" for meter per second). If no symbol is defined for the unit, the DisplayName Attribute shall be used as symbol. Symbol matches the “displayName” field of the EUInformation structure (see 5.6.3.3).
The Description Property is used to expose a more verbose explanation.
The UnitSystem Property describes the system of units (e.g. ISQ) in which the unit is specified. If any of the well known systems defined in Table 39 is used, the acronym in the column “UnitSystem” shall be used for the value of this Property.
Table 39 – Non-exhaustive list of well-known systems of units
|
UnitSystem |
System of units |
|
ISQ |
International System of Quantities (ISO/IEC 80000) Fully covers and thus replaces SI (ISO1000) |
|
USCS |
US Customary Unit System |
|
ISU |
British imperial system of units |
|
MSU |
Myanmar Units of measurement |
|
TROY |
Troy units of weight |
|
CGS |
centimetre–gram–second system of units |
|
GAUSS |
Gaussian System of units |
|
FPS |
foot–pound–second system of units |
Syntax References: Instances of the UnitType can identify the unit in a specific external reference work using HasDictionaryEntry References – see 6.3.2.