UA Part 8: DataAccess - 6.6 DataTypes

6.6.1 AnnotationDataType DataType definition

This structure contains additions as explanation and specification of the physical quantity such as "relative" for a relative velocity. The structure is defined in Table 46.

Table 46 – AnnotationDataType Structure

Name	Type	Description
AnnotationDataType	structure	Subtype of Structure defined in OPC 10000-5
Annotation	String	Names the annotation to give further information about value like how it is measured or where it originates from.
Discipline	String	Gives a human readable classification of the physical quantity according to its field of application to allow grouping of values. These can be, for example, “Engineering”, “Finance” or similar.
Uri	String	Names a source for deeper description of the annotation.

Examples are given in Table 47.

Table 47 – AnnotationDataType examples

Name	Values for a linear acceleration	Values for AC voltage	Values for DC voltage	Values for AC RMS voltage
AnnotationDataType
Annotation	linear	AC	DC	RMS
Discipline	-	Electrical Engineering	Electrical Engineering	Electrical Engineering
Uri	-	https://www.britannica.com/science/alternating-current	https://www.britannica.com/science/direct-current	https://en.wikipedia.org/wiki/Root_mean_square

Its representation in the AddressSpace is defined in Table 48.

Table 48 – AnnotationDataType definition

Attribute		Value
BrowseName		AnnotationDataType
IsAbstract		False
References	NodeClass		BrowseName	DataType	TypeDefinition	Other
Subtype of the Structure defined in OPC 10000-5
Conformance Units
Data Access Quantities Base

6.6.2 LinearConversionDataType DataType definition

This structure contains a simple conversion according to the following formula. The factors (a = inititialAddend, b = multiplicand, c = divisor, d = finalAddend) are given in a Structure. X is the source value (in source unit) and f(x) the target value (in target unit). The structure is defined in Table 49.

The values of the structure can also be used for a simple inverse conversion. It can be used if a client wants to write a value to the server. The valuey1 is the value that the client wants to write to the server in the named alternative unit andx1 is the value the client actually has to write to the server instead.

Table 49 – LinearConversionDataType Structure

Name	Type	Description
LinearConversionDataType	Structure	Subtype of Structure defined in OPC 10000-5
InitialAddend	Float	The initial addend of linear conversion.
Multiplicand	Float	The multiplicand of linear conversion.
Divisor	Float	The divisor of linear conversion.
FinalAddend	Float	The final addend of linear conversion.

Its representation in the AddressSpace is defined in Table 48.

Table 50 – LinearConversionDataType Definition

Attribute		Value
BrowseName		LinearConversionDataType
IsAbstract		False
References	NodeClass		BrowseName	DataType	TypeDefinition	Other
Subtype of the Structure defined in OPC 10000-5
Conformance Units
Data Access Alternative Units

6.6.3 ConversionLimitEnum

ConversionLimitEnum indicates whether the ServerUnit can be converted. A distinction is made between NO_CONVERSION, LIMITED and UNLIMITED. NO_CONVERSION means that no conversion is allowed (e.g. for statistical values). LIMITED conversion means that either only the conversions mentioned in the AlternativeUnits are to be used or the client requires specific know-how for the conversion. UNLIMITED means the conversion is simple and possible if the client knows the UnitSystem. The enumeration is defined in Table 51.

Table 51 – ConversionLimitEnum Items

Name	Value	Description
NO_CONVERSION	0	No conversion of the value allowed (e.g. statistical value).
LIMITED	1	Conversion only permitted on the basis of the conversions specified by the server, or if the client has the appropriate domain knowledge to perform an independent conversion.
UNLIMITED	2	Conversion on the basis of the specified unit according to the rules of the source system of units (e.g. SI / ISQ) and the coding system (e.g. UCUM) is permitted.

Its representation in the AddressSpace is defined in Table 52.

Table 52 – ConversionLimitEnum Definition

Attribute		Value
BrowseName		ConversionLimitEnum
IsAbstract		False
References	NodeClass		BrowseName	DataType	TypeDefinition	Other
Subtype of the Enumeration type defined in OPC 10000-5
HasProperty	Variable		EnumStrings	LocalizedText []	PropertyType
Conformance Units
Data Access Alternative Units

6.6.4 QuantityDimension

The QuantityDimension Structure DataType describes the dimensionality of a kind of quantity in the context of a system of units. In the SI system of units, the dimensions of a kind of quantity are expressed as a product of the basic physical dimensions length (L), mass(M), time (T), current(I), absolute temperature(θ), amount of substance(N) and luminous intensityJ as

The rational powers of the dimensional exponents(α, β, γ, δ, ε, η, v), are positive, negative, or zero.

An additional dimensionless exponent is used for countable things that have no physical quantity assigned.

The QuantityDimension elements are defined in Table 53.

Table 53 – QuantityDimension DataType structure

Name	Type	Description
QuantityDimension	Structure
MassExponent	SByte	Exponent of the dimension mass for the physical quantity.
LengthExponent	SByte	Exponent of the dimension length for the physical quantity.
TimeExponent	SByte	Exponent of the dimension time for the physical quantity.
ElectricCurrentExponent	SByte	Exponent of the dimension electric current for the physical quantity.
AmountOfSubstanceExponent	SByte	Exponent of the dimension amount of substance for the physical quantity.
LuminousIntensityExponent	SByte	Exponent of the dimension luminous intensity for the physical quantity.
AbsoluteTemperatureExponent	SByte	Exponent of the dimension absolute temperature for the physical quantity.
DimensionlessExponent	SByte	Exponent for dimensionless quantities.

Its representation in the AddressSpace is defined in Table 54.

Table 54 – QuantityDimension definition

Attribute		Value
BrowseName		QuantityDimension
IsAbstract		False
References	NodeClass		BrowseName	DataType	TypeDefinition	Other
Subtype of Structure defined in OPC 10000-5.
Conformance Units
Data Access Quantities Base

For example, the dimension of the physical quantity kind

the dimension of the physical quantity kind force is

and the dimension of the physical quantity kind “things (e.g., screws) per time” is

Table 55 – QuantityDimension examples

Name	Values for speed	Values for force	Values for “things per time”
QuantityDimension
MassExponent	0	1	0
LengthExponent	1	1	0
TimeExponent	-1	-2	-1
ElectricCurrentExponent	0	0	0
AmoutOfSubstanceExponent	0	0	0
LuminousIntensityExponent	0	0	0
AbsoluteTemperatureExponent	0	0	0
DimensionlessExponent	0	0	1

The extended SI System of units includes derived units that are built as a product of base units. That makes it difficult to compare units as SI allows an unlimited number of “SI unit strings” to describe the same quantity.

All 3 are valid SI representations of the quantity “speed” and therefore share the same quantity dimensions. A specific representation of a unit is often used to express details how the unit was measured. The dimension structure makes it much easier to identify and compare the kind of quantity of EU values.