Following is a description of the DataTypes defined in this specification.

DataTypes like String, Boolean, Double or LocalizedText are defined in OPC 10000-3. Their representation is specified in OPC 10000-5.

This structure defines the Range for a value. Its elements are defined in Table 14.

Table 14 – Range DataType structure

Name	Type	Description
Range	structure
low	Double	Lowest value in the range.
high	Double	Highest value in the range.

If a limit is not known a NaN shall be used.

Its representation in the AddressSpace is defined in Table 15

Table 15 – Range definition

Attributes	Value
BrowseName	Range

This structure contains information about the EngineeringUnits. Its elements are defined in Table 16.

Table 16 – EUInformation DataType structure

Name	Type	Description
EUInformation	structure
namespaceUri	String	Identifies the organization (company, standards organization) that defines the EUInformation.
unitId	Int32	Identifier for programmatic evaluation. −1 is used if a unitId is not available.
displayName	LocalizedText	The displayName of the engineering unit is typically the abbreviation of the engineering unit, for example ”h” for hour or ”m/s” for meter per second.
description	LocalizedText	Contains the full name of the engineering unit such as ”hour” or ”meter per second”.

Its representation in the AddressSpace is defined in Table 17

Table 17 – EUInformation definition

Attributes	Value
BrowseName	EUInformation

To facilitate interoperability, OPC UA specifies how to apply the widely accepted “Codes for Units of Measurement” published by the “United Nations Centre for Trade Facilitation and Electronic Business” (see UN/CEFACT: UNECE Recommendation N° 20). It uses and is based on the International System of Units (SI Units) but in addition provides a fixed code that can be used for automated evaluation. This recommendation has been accepted by many industries on a global basis.

The UNECE recommendation can be found here:

https://www.unece.org/cefact/codesfortrade/codes_index.html

The latest UNECE version (Rev 12. Filename = rec20_Rev12e_2016.xls, published in 2016) is available here:

http://www.unece.org/fileadmin/DAM/cefact/recommendations/rec20/rec20_Rev12e_2016.xls

The mapping of the UNECE codes to OPC UA (EUInformation.unitId) is available here:

http://www.opcfoundation.org/UA/EngineeringUnits/UNECE/UNECE_to_OPCUA.csv

Table 18 contains a small excerpt of the published Annex with Code Lists:

Table 18 – Examples from the UNECE Recommendation

Excerpt from Recommendation N°. 20, Annex 1
Common Code	Name	Conversion Factor	Symbol
C81	radian		rad
C25	milliradian	10–3 rad	mrad
MMT	millimetre	10–3 m	mm
HMT	hectometre	102 m	hm
KTM	kilometre	103 m	km
KMQ	kilogram per cubic metre	kg/m3	kg/m3
FAH	degree Fahrenheit	5/9×K	°F
J23	degree Fahrenheit per hour	1,543 210 × 10–4 K/s	°F/h

Specific columns of this table shall be used to create the EUInformation structure as defined by the following rules:

• The Common Code is represented as an alphanumeric variable length of 3 characters. It shall be used for the EUInformation.unitId. The following pseudo code specifies the algorithm to convert the Common Code into an Int32 as needed for EUInformation.unitId:

Int32 unitId = 0; Int32 c; for (i=0; i<=3;i++) {

c = CommonCode[i]; if (c == 0) break; // end of Common Code unitId = unitId << 8; unitId = unitId | c;}

• The Symbol field shall be copied to the EUInformation.displayName. The localeId field of EUInformation.displayName shall be empty.
• The Name field shall be used for EUInformation.description. If the name is copied, then the localeId field of EUInformation.description shall be empty. If the name is localized then the localeId field shall specify the correct locale.

The EUInformation.namespaceUri shall be http://www.opcfoundation.org/UA/units/un/cefact.

NOTE  It will be advantegous to use Recommendation N°. 20 as specified, because it can be programmatically interpreted by generic OPC UA Clients. However, the EUInformation structure has been defined such that other standards bodies can incorporate their engineering unit definitions into OPC UA. If Servers use such an approach then they shall identify this standards body by using a proper namespaceUri in EUInformation.namespaceUri.

This structure defines float IEEE 32 bits complex value. Its elements are defined in Table 19.

Table 19 – ComplexNumberType DataType structure

Name	Type	Description
ComplexNumberType	structure
real	Float	Value real part
imaginary	Float	Value imaginary part

Its representation in the AddressSpace is defined in Table 20

Table 20 – ComplexNumberType definition

Attributes	Value
BrowseName	ComplexNumberType

This structure defines double IEEE 64 bits complex value. Its elements are defined in Table 21.

Table 21 – DoubleComplexNumberType DataType structure

Name	Type	Description
DoubleComplexNumberType	structure
real	Double	Value real part
imaginary	Double	Value imaginary part

Its representation in the AddressSpace is defined in Table 22.

Table 22 – DoubleComplexNumberType definition

Attributes	Value
BrowseName	DoubleComplexNumberType

This structure defines the information for auxiliary axis for ArrayItemType Variables.

There are three typical uses of this structure:

1. The step between points is constant and can be predicted using the range information and the number of points. In this case, axisSteps can be set to NULL.
2. The step between points is not constant, but remains the same for a long period of time (from acquisition to acquisition for example). In this case, axisSteps contains the value of each step on the axis.
3. The step between points is not constant and changes at every update. In this case, a type like XYArrayType shall be used and axisSteps is set to NULL.

Its elements are defined in Table 23.

Table 23 – AxisInformation DataType structure

Name	Type	Description
AxisInformation	structure
engineeringUnits	EUInformation	Holds the information about the engineering units for a given axis.
eURange	Range	Limits of the range of the axis
title	Localizedtext	User readable axis title, useful when the units are %, the Title may be “Particle size distribution”
axisScaleType	AxisScaleEnumeration	LINEAR, LOG, LN, defined by AxisSteps
axisSteps	Double[]	Specific value of each axis steps, may be set to “Null” if not used

When the steps in the axis are constant, axisSteps may be set to “Null” and in this case, the Range limits are used to compute the steps. The number of steps in the axis comes from the parent ArrayItem.ArrayDimensions.

This enumeration identifies on which type of axis the data shall be displayed. Its values are defined in Table 24.

Table 24 – AxisScaleEnumeration values

Value	Description
LINEAR_0	Linear scale
LOG_1	Log base 10 scale
LN_2	Log base e scale

Its representation in the AddressSpace is defined in Table 25.

Table 25 – AxisScaleEnumeration definition

Attributes	Value
BrowseName	AxisScaleEnumeration

This structure defines a physical value relative to a X axis and it is used as the DataType of the Value of XYArrayItemType. For details see 5.3.4.3.

Many devices can produce values that can perfectly be represented with a float IEEE 32 bits but, they can position them on the X axis with an accuracy that requires double IEEE 64 bits. For example, the peak value in an absorbance spectrum where the amplitude of the peak can be represented by a float IEEE 32 bits, but its frequency position required 10 digits which implies the use of a double IEEE 64 bits.

Its elements are defined in Table 26.

Table 26 – XVType DataType structure

Name	Type	Description
XVType	structure
x	Double	Position on the X axis of this value
value	Float	The value itself

Its representation in the AddressSpace is defined in Table 27.

Table 27 – XVType definition

Attributes	Value
BrowseName	XVType