Following is a description of the DataTypesdefined in this specification.

DataTypeslike String, Boolean, Doubleor LocalizedTextare defined in OPC 10000-3. Their representation is specified in OPC 10000-5.

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

Table 14RangeDataType 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 AddressSpaceis defined in Table 15

Table 15Rangedefinition

Attributes

Value

BrowseName

Range

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

Table 16EUInformationDataType 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 unitIdis not available.

displayName

LocalizedText

The displayNameof 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 AddressSpaceis defined in Table 17

Table 17EUInformationdefinition

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 18contains 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

10–3rad

mrad

MMT

millimetre

10–3m

mm

HMT

hectometre

102m

hm

KTM

kilometre

103m

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 × 10–4K/s

°F/h

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

  • The Common Codeis 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 EUInformation.namespaceUrishall 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 EUInformationstructure has been defined such that other standards bodies can incorporate their engineering unit definitions into OPC UA. If Serversuse such an approach then they shall identify this standards body by using a proper namespaceUriin 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 AddressSpaceis 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 AddressSpaceis 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,axisStepsmay be set to “Null” and in this case, the Rangelimits 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 AddressSpaceis 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 DataTypeof 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 AddressSpaceis defined in Table 27.

Table 27– XVType definition

Attributes

Value

BrowseName

XVType