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 100005. 

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.