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 17.

Table 17RangeDataType structure

Name

Type

Description

Range

structure

low

Double

Lowest value in the range.

high

Double

Highest value in the range.

NOTE For some DataTypes, e.g. Int64, UInt64, or Decimal, there may be a loss in precision in the representation of the range with a Double.

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

Its representation in the AddressSpaceis defined in Table 18

Table 18Rangedefinition

Attribute

Value

BrowseName

Range

IsAbstract

False

References

NodeClass

BrowseName

DataType

TypeDefinition

Other

Subtype of Structure defined in OPC 10000-5.

Conformance Units

Base Info Range DataType

EUInformationcontains information about the EngineeringUnits.

The intention of the OPC UA standard is not to define a set of units but a way to expose units based on existing systems. Since there is not a single worldwide set of units used in all industries, the EUInformationstructure includes a separate field (the namespaceUri) to identify the system on which the exposed unit is based.

The default OPC UA mapping is based on UN/CEFACT as defined in clause 5.6.3.3, 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 URI in EUInformation.namespaceUri.

The EUInformationelements are defined in Table 19.

Table 19EUInformationDataType 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 20.

Table 20EUInformationdefinition

Attribute

Value

BrowseName

EUInformation

IsAbstract

False

References

NodeClass

BrowseName

DataType

TypeDefinition

Other

Subtype of Structure defined in OPC 10000-5.

Conformance Units

Base Info EUInformation

This clause specifies how to apply the “Codes for Units of Measurement”published by the “United Nations Centre for Trade Facilitation and Electronic Business” (see https://www.unece.org/cefact/codesfortrade/codes_index.html). This recommendation establishes a single list of code elements to represent units of the International System of Units (SI Units) like units of measure for length, mass (weight), volume and other quantities and in addition covers administration, commerce, transport, science, technology, industry etc. It provides a fixed code that can be used for automated evaluation.

Table 21contains a small excerpt of the relevant columns in the UNECE recommendation:

Table 21– Examples from the UNECE Recommendation

Excerpt from Recommendation N°. 20, Annex 1

Common Code

Name

Symbol

C81

radian

rad

C25

milliradian

mrad

MMT

millimetre

mm

HMT

hectometre

hm

KMT

kilometre

km

KMQ

kilogram per cubic metre

kg/m3

FAH

degree Fahrenheit

°F

The mapping of the UNECE common codes to EUInformation.unitId, EUInformation.displayName, and EUInformation.descriptionis available here:

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

This mapping has been generated as follows:

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;}

This structure defines float IEEE 32 bits complex value. Its elements are defined in Table 22.

Table 22– 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 23

Table 23– ComplexNumberType definition

Attribute

Value

BrowseName

ComplexNumberType

IsAbstract

False

References

NodeClass

BrowseName

DataType

TypeDefinition

Other

Subtype of Structure defined in OPC 10000-5.

Conformance Units

Data Access Complex Number

This structure defines double IEEE 64 bits complex value. Its elements are defined in Table 24.

Table 24– 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 25.

Table 25– DoubleComplexNumberType definition

Attribute

Value

BrowseName

DoubleComplexNumberType

IsAbstract

False

References

NodeClass

BrowseName

DataType

TypeDefinition

Other

Subtype of Structure defined in OPC 10000-5.

Conformance Units

Data Access DoubleComplex Number

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 26.

Table 26– 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

Its representation in the AddressSpaceis defined in Table 27.

Table 27– AxisInformation definition

Attribute

Value

BrowseName

AxisInformation

IsAbstract

False

References

NodeClass

BrowseName

DataType

TypeDefinition

Other

Subtype of Structure defined in OPC 10000-5.

Conformance Units

Data Access AxisInformationType

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 28.

Table 28– AxisScaleEnumeration values

Name

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 29.

Table 29– AxisScaleEnumeration definition

Attribute

Value

BrowseName

AxisScaleEnumeration

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 ArrayItem2Type

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 30.

Table 30– 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 31.

Table 31– XVType definition

Attribute

Value

BrowseName

XVType

IsAbstract

False

References

NodeClass

BrowseName

DataType

TypeDefinition

Other

Subtype of Structure defined in OPC 10000-5.

Conformance Units

Data Access XYArrayItemType