IEC 62541-8:2015

IEC 62541-8 ®
Edition 2.0 2015-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
OPC Unified Architecture –
Part 8: Data Access
Architecture unifiée OPC –
Partie 8: Accès aux données
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IEC 62541-8 ®
Edition 2.0 2015-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
OPC Unified Architecture –
Part 8: Data Access
Architecture unifiée OPC –
Partie 8: Accès aux données
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 25.040.40; 35.100 ISBN 978-2-8322-2273-7

– 2 – IEC 62541-8:2015 © IEC 2015
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references. 6
3 Terms, definitions and abbreviations . 6
3.1 Terms and definitions . 6
3.2 Abbreviations and symbols . 7
4 Concepts . 7
5 Model . 8
5.1 General . 8
5.2 SemanticsChanged . 9
5.3 Variable Types . 9
5.3.1 DataItemType . 9
5.3.2 AnalogItemType . 10
5.3.3 DiscreteItemType . 11
5.3.4 ArrayItemType . 13
5.4 Address Space model . 18
5.5 Attributes of DataItems . 19
5.6 DataTypes . 20
5.6.1 Overview . 20
5.6.2 Range . 20
5.6.3 EUInformation . 20
5.6.4 ComplexNumberType . 21
5.6.5 DoubleComplexNumberType . 22
5.6.6 AxisInformation . 22
5.6.7 AxisScaleEnumeration . 23
5.6.8 XVType . 23
6 Data Access specific usage of Services . 23
6.1 General . 23
6.2 PercentDeadband . 24
6.3 Data Access status codes . 24
6.3.1 Overview . 24
6.3.2 Operation level result codes . 24
6.3.3 LimitBits . 26

Figure 1 – OPC DataItems are linked to automation data . 8
Figure 2 – DataItem VariableType hierarchy . 9
Figure 3 – Graphical view of a YArrayItem . 15
Figure 4 – Representation of DataItems in the AddressSpace . 19

Table 1 – DataItemType definition . 9
Table 2 – AnalogItemType definition . 10
Table 3 – DiscreteItemType definition . 11
Table 4 – TwoStateDiscreteType definition . 12
Table 5 – MultiStateDiscreteType definition . 12
Table 6 – MultiStateValueDiscreteType definition . 13

Table 7 – ArrayItemType definition . 14
Table 8 – YArrayItemType definition . 14
Table 9 – YArrayItem item description . 15
Table 10 – XYArrayItemType definition . 16
Table 11 – ImageItemType definition . 17
Table 12 – CubeItemType definition . 17
Table 13 – NDimensionArrayItemType definition . 18
Table 14 – Range DataType structure . 20
Table 15 – Range definition . 20
Table 16 – EUInformation DataType structure . 20
Table 17 – EUInformation definition . 20
Table 18 – Examples from the UNECE Recommendation . 21
Table 19 – ComplexNumberType DataType structure . 22
Table 20 – ComplexNumberType definition . 22
Table 21 – DoubleComplexNumberType DataType structure . 22
Table 22 – DoubleComplexNumberType definition . 22
Table 23 – AxisInformation DataType structure . 22
Table 24 – AxisScaleEnumeration values . 23
Table 25 – AxisScaleEnumeration definition . 23
Table 26 – XVType DataType structure . 23
Table 27 – XVType definition . 23
Table 28 – Operation level result codes for BAD data quality . 25
Table 29 – Operation level result codes for UNCERTAIN data quality . 25
Table 30 – Operation level result codes for GOOD data quality . 25

– 4 – IEC 62541-8:2015 © IEC 2015
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPC UNIFIED ARCHITECTURE –
Part 8: Data Access
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
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with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 62541-8 has been prepared by subcommittee 65E: Devices and
integration in enterprise systems, of IEC technical committee 65: Industrial-process
measurement, control and automation.
This second edition cancels and replaces the first edition published in 2011. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Clarified that deadband has to be between 0.0 and 100.0. Violations result in error
Bad_DeadbandFilterInvalid (6.2)
b) Added VariableTypes handling ArrayItems and DataTypes supporting this, including
complex number types. These data types are required for complex analyzer devices but
seem useful for other domains as well.

The text of this standard is based on the following documents:
CDV Report on voting
65E/381/CDV 65E/407/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 62541 series, published under the general title OPC Unified
Architecture, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – IEC 62541-8:2015 © IEC 2015
OPC UNIFIED ARCHITECTURE –
Part 8: Data Access
1 Scope
This part of IEC 62451 is part of the overall OPC Unified Architecture (OPC UA) standard
series and defines the information model associated with Data Access (DA). It particularly
includes additional VariableTypes and complementary descriptions of the NodeClasses and
Attributes needed for Data Access, additional Properties, and other information and
behaviour.
The complete address space model, including all NodeClasses and Attributes is specified in
IEC 62541-3. The services to detect and access data are specified in IEC 62541-4.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC TR 62541-1, OPC Unified Architecture - Part 1: Overview and Concepts
IEC 62541-3, OPC unified architecture - Part 3: Address Space Model
IEC 62541-4, OPC unified architecture - Part 4: Services
IEC 62541-5, OPC unified architecture - Part 5: Information Model
UN/CEFACT: UNECE Recommendation N° 20, Codes for Units of Measure Used in
International Trade, available at http://www.unece.org/cefact/recommendations/rec_index.htm
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC TR 62541-1,
IEC 62541-3, and IEC 62541-4 as well as the following apply.
3.1.1
DataItem
link to arbitrary, live automation data, that is, data that represents currently valid information
Note 1 to entry: Examples of such data are
• device data (such as temperature sensors),
• calculated data,
• status information (open/closed, moving),
• dynamically-changing system data (such as stock quotes),
• diagnostic data.
3.1.2
AnalogItem
DataItems that represent continuously-variable physical quantities (e.g., length, temperature),
in contrast to the digital representation of data in discrete items
Note 1 to entry: Typical examples are the values provided by temperature sensors or pressure sensors. OPC UA
defines a specific VariableType to identify an AnalogItem. Properties describe the possible ranges of AnalogItems.
3.1.3
DiscreteItem
DataItems that represent data that may take on only a certain number of possible values (e.g.,
OPENING, OPEN, CLOSING, CLOSED)
Note 1 to entry: Specific VariableTypes are used to identify DiscreteItems with two states or with multiple states.
Properties specify the string values for these states.
3.1.4
ArrayItem
DataItems that represent continuously-variable physical quantities and where each individual
data point consists of multiple values represented by an array (e.g., the spectral response of
a digital filter)
Note 1 to entry: Typical examples are the data provided by analyser devices. Specific VariableTypes are used to
identify ArrayItem variants.
3.1.5
EngineeringUnits
units of measurement for AnalogItems that represent continuously-variable physical quantities
(e.g., length, mass, time, temperature)
Note 1 to entry: This standard defines Properties to inform about the unit used for the DataItem value and about
the highest and lowest value likely to be obtained in normal operation.
3.2 Abbreviations and symbols
DA Data Access
EU Engineering Unit
UA Unified Architecture
4 Concepts
Data Access deals with the representation and use of automation data in Servers.
Automation data can be located inside the Server or on I/O cards directly connected to the
Server. It can also be located in sub-servers or on other devices such as controllers and
input/output modules, connected by serial links via field buses or other communication links.
OPC UA Data Access Servers provide one or more OPC UA Data Access Clients with
transparent access to their automation data.
The links to automation data instances are called DataItems. Which categories of automation
data are provided is completely vendor-specific. Figure 1 illustrates how the AddressSpace of
a Server might consist of a broad range of different DataItems.

– 8 – IEC 62541-8:2015 © IEC 2015
OPC UA Server
Root
Adressspace
with DataItems
IEC
Figure 1 – OPC DataItems are linked to automation data
Clients may read or write DataItems, or monitor them for value changes. The Services needed
for these operations are specified in IEC 62541-4. Changes are defined as a change in status
(quality) or a change in value that exceeds a client-defined range called a Deadband. To
detect the value change, the difference between the current value and the last reported value
is compared to the Deadband.
5 Model
5.1 General
The DataAccess model extends the variable model by defining VariableTypes. The
DataItemType is the base type. ArrayItemType, AnalogItemType and DiscreteItemType (and
its TwoState and MultiState subtypes) are specializations. See Figure 2. Each of these
VariableTypes can be further extended to form domain or server specific DataItems.

BaseDataVariableType
Defined in
IEC 62541-5
Type DataItemType
ArrayItemType AnalogItemType DiscreteItemType
TwoState MultiState MultiStateValue
DiscreteType DiscreteType DiscreteType

IEC
Figure 2 – DataItem VariableType hierarchy
5.2 SemanticsChanged
The StatusCode also contains an informational bit called SemanticsChanged.
Servers that implement Data Access shall set this Bit in notifications if certain Properties
defined in this standard change. The corresponding Properties are specified individually for
each VariableType.
Clients that use any of these Properties should re-read them before they process the data
value.
5.3 Variable Types
5.3.1 DataItemType
This VariableType defines the general characteristics of a DataItem. All other DataItem Types
derive from it. The DataItemType derives from the BaseDataVariableType and therefore
shares the variable model as described in IEC 62541-3 and IEC 62541-5. It is formally defined
in Table 1.
Table 1 – DataItemType definition
Attribute Value
BrowseName DataItemType
IsAbstract False
ValueRank −2 (−2 = ‘Any’)
DataType BaseDataType
References NodeClass BrowseName DataType TypeDefinition ModellingRule
Subtype of the BaseDataVariableType defined in IEC 62541-5; i.e the Properties of that type are inherited.
HasSubtype VariableType AnalogItemType Defined in 5.3.2
HasSubtype VariableType DiscreteItemType Defined in 5.3.3
HasSubtype VariableType ArrayItemType Defined in 5.3.4
HasProperty Variable Definition String PropertyType Optional
HasProperty Variable ValuePrecision Double PropertyType Optional

– 10 – IEC 62541-8:2015 © IEC 2015
Definition is a vendor-specific, human readable string that specifies how the value of this
DataItem is calculated. Definition is non-localized and will often contain an equation that can
be parsed by certain clients.
Example: Definition::= “(TempA – 25) + TempB”
ValuePrecision specifies the maximum precision that the Server can maintain for the item
based on restrictions in the target environment.
ValuePrecision can be used for the following DataTypes:
• For Float and Double values it specifies the number of digits after the decimal place.
• For DateTime values it indicates the minimum time difference in nanoseconds. For
example, a ValuePrecision of 20 000 000 defines a precision of 20 ms.
The ValuePrecision Property is an approximation that is intended to provide guidance to a
Client. A Server is expected to silently round any value with more precision that it supports.
This implies that a Client may encounter cases where the value read back from a Server
differs from the value that it wrote to the Server. This difference shall be no more than the
difference suggested by this Property.
5.3.2 AnalogItemType
This VariableType defines the general characteristics of an AnalogItem. All other AnalogItem
Types derive from it. The AnalogItemType derives from the DataItemType. It is formally
defined in Table 2.
Table 2 – AnalogItemType definition
Attribute Value
BrowseName AnalogItemType
IsAbstract False
ValueRank −2 (−2 = ‘Any’)
DataType Number
References NodeClass BrowseName DataType TypeDefinition ModellingRule
Subtype of the DataItemType defined in 5.3.1 i.e the Properties of that type are inherited.
HasProperty Variable InstrumentRange Range PropertyType Optional
HasProperty Variable EURange Range PropertyType Mandatory
HasProperty Variable EngineeringUnits EUInformation PropertyType Optional

The following paragraphs describe the Properties of this VariableType. If the analog item’s
Value contains an array, the Properties shall apply to all elements in the array.
InstrumentRange defines the value range that can be returned by the instrument.
Example: InstrumentRange::= {-9999.9, 9999.9}
Although defined as optional, it is strongly recommended for Servers to support this Property.
Without an InstrumentRange being provided, Clients will commonly assume the full range
according to the DataType.
The Range Data Type is specified in 5.6.2.
EURange defines the value range likely to be obtained in normal operation. It is intended for
such use as automatically scaling a bar graph display.
Sensor or instrument failure or deactivation can result in a returned item value which is
actually outside of this range. Client software must be prepared to deal with this possibility.
Similarly a Client may attempt to write a value that is outside of this range back to the server.

The exact behaviour (accept, reject, clamp, etc.) in this case is Server-dependent. However,
in general Servers shall be prepared to handle this.
Example: EURange::= {-200.0,1400.0}
See also 6.2 for a special monitoring filter (PercentDeadband) which is based on the
engineering unit range.
EngineeringUnits specifies the units for the DataItem’s value (e.g., DEGC, hertz, seconds).
The EUInformation type is specified in 5.6.3.
Important note: Understanding the units of a measurement value is essential for a uniform
system. In an open system in particular where servers from different cultures might be used, it
is essential to know what the units of measurement are. Based on such knowledge, values
can be converted if necessary before being used. Therefore, although defined as optional,
support of the EngineeringUnits Property is strongly advised.
OPC UA recommends using the “Codes for Units of Measurement” (see UN/CEFACT:
UNECE Recommendation N° 20). The mapping to the EngineeringUnits Property is specified
in 5.6.3.
EXAMPLE OF UNIT MIX-UP: In 1999, the Mars Climate Orbiter crashed into the surface of Mars. The main reason
was a discrepancy over the units used. The navigation software expected data in newton second; the company who
built the orbiter provided data in pound-force seconds. Another, less expensive, disappointment occurs when
people used to British pints order a pint in the USA, only to be served what they consider a short measure.
The StatusCode SemanticsChanged bit shall be set if any of the EURange (could change the
behaviour of a Subscription if a PercentDeadband filter is used) or EngineeringUnits (could
create problems if the client uses the value to perform calculations) Properties are changed
(see section 5.2 for additional information).
5.3.3 DiscreteItemType
5.3.3.1 General
This VariableType is an abstract type. That is, no instances of this type can exist. However, it
might be used in a filter when browsing or querying. The DiscreteItemType derives from the
DataItemType and therefore shares all of its characteristics. It is formally defined in Table 3.
Table 3 – DiscreteItemType definition
Attribute Value
BrowseName DiscreteItemType
IsAbstract True
ValueRank −2 (−2 = ‘Any’)
DataType BaseDataType
References NodeClass BrowseName DataType TypeDefinition ModellingRule
Subtype of the DataItemType defined in 5.2; i.e the Properties of that type are inherited.
HasSubtype VariableType TwoStateDiscreteType Defined in 5.3.3.2
HasSubtype VariableType MultiStateDiscreteType Defined in 5.3.3.3
HasSubtype VariableType MultiStateValueDiscreteType Defined in 5.3.3.4

5.3.3.2 TwoStateDiscreteType
This VariableType defines the general characteristics of a DiscreteItem that can have two
states. The TwoStateDiscreteType derives from the DiscreteItemType. It is formally defined in
Table 4.
– 12 – IEC 62541-8:2015 © IEC 2015
Table 4 – TwoStateDiscreteType definition

Attribute Value
BrowseName TwoStateDiscreteType
IsAbstract False
ValueRank −2 (−2 = ‘Any’)
DataType Boolean
References NodeClass BrowseName DataType TypeDefinition ModellingRule
Subtype of the DiscreteItemType defined in 5.3.3; i.e the Properties of that type are inherited.
HasProperty Variable TrueState LocalizedText PropertyType Mandatory
HasProperty Variable FalseState LocalizedText PropertyType Mandatory

TrueState contains a string to be associated with this DataItem when it is TRUE. This is
typically used for a contact when it is in the closed (non-zero) state.
for example: "RUN", "CLOSE", "ENABLE", "SAFE“, etc.
FalseState contains a string to be associated with this DataItem when it is FALSE. This is
typically used for a contact when it is in the open (zero) state.
for example: "STOP", "OPEN", "DISABLE", "UNSAFE“, etc.
If the item contains an array, then the Properties will apply to all elements in the array.
The StatusCode SemanticsChanged bit shall be set if any of the FalseState or TrueState
(changes can cause misinterpretation by users or (scripting) programs) Properties are
changed (see section 5.2 for additional information).
5.3.3.3 MultiStateDiscreteType
This VariableType defines the general characteristics of a DiscreteItem that can have more
than two states. The MultiStateDiscreteType derives from the DiscreteItemType. It is formally
defined in Table 5.
Table 5 – MultiStateDiscreteType definition
Attribute Value
BrowseName MultiStateDiscreteType
IsAbstract False
ValueRank −2 (−2 = ‘Any’)
DataType UInteger
References NodeClass BrowseName DataType TypeDefinition ModellingRule
Subtype of the DiscreteItemType defined in 5.3.3; i.e the Properties of that type are inherited.
HasProperty Variable EnumStrings LocalizedText[] PropertyType Mandatory

EnumStrings is a string lookup table corresponding to sequential numeric values (0, 1, 2, etc.)
Example:
”OPEN”
”CLOSE”
”IN TRANSIT” etc.
Here the string “OPEN” corresponds to 0, “CLOSE” to 1 and “IN TRANSIT” to 2.
Clients should be prepared to handle item values outside of the range of the list; and robust
servers should be prepared to handle writes of illegal values.
If the item contains an array then this lookup table shall apply to all elements in the array.

NOTE The EnumStrings property is also used for Enumeration DataTypes (for the specification of this DataType,
see IEC 62541-3).
The StatusCode SemanticsChanged bit shall be set if the EnumStrings (changes can cause
misinterpretation by users or (scripting) programs) Property is changed (see section 5.2 for
additional information).
5.3.3.4 MultiStateValueDiscreteType
This VariableType defines the general characteristics of a DiscreteItem that can have more
than two states and where the state values (the enumeration) does not consist of consecutive
numeric values (may have gaps) or where the enumeration is not zero-based. The
MultiStateValueDiscreteType derives from the DiscreteItemType. It is formally defined in
Table 6.
Table 6 – MultiStateValueDiscreteType definition

Attribute Value
BrowseName MultiStateValueDiscreteType
IsAbstract False
ValueRank Scalar
DataType Number
References NodeClass BrowseName DataType TypeDefinition ModellingRule
Subtype of the DiscreteItemType defined in 5.3.3; i.e the Properties of that type are inherited.
HasProperty Variable EnumValues See IEC 62541-3 Mandatory
HasProperty Variable ValueAsText See IEC 62541-3 Mandatory

EnumValues is an array of EnumValueType. Each entry of the array represents one
enumeration value with its integer notation, a human-readable representation, and help
information. This represents enumerations with integers that are not zero-based or have gaps
(e.g. 1, 2, 4, 8, 16). See IEC 62541-3 for the definition of this type. MultiStateValueDiscrete
Variables expose the current integer notation in their Value Attribute. Clients will often read
the EnumValues Property in advance and cache it to lookup a name or help whenever they
receive the numeric representation.
MultiStateValueDiscrete Variables can have any numeric Data Type; this includes signed and
unsigned integers from 8 to 64 Bit length.
The numeric representation of the current enumeration value is provided via the Value
Attribute of the MultiStateValueDiscrete Variable. The ValueAsText Property provides the
localized text representation of the enumeration value. It can be used by Clients only
interested in displaying the text to subscribe to the Property instead of the Value Attribute.
5.3.4 ArrayItemType
5.3.4.1 General
This abstract VariableType defines the general characteristics of an ArrayItem. Values are
exposed in an array but the content of the array represents a single entity like an image.
Other DataItems might contain arrays that represent for example several values of several
temperature sensors of a boiler.
ArrayItemType or its subtype shall only be used when the Title and AxisScaleType Properties
can be filled with reasonable values. If this is not the case DataItemType and subtypes like
AnalogItemType, which also support arrays, shall be used. The ArrayItemType is formally
defined in Table 7.
– 14 – IEC 62541-8:2015 © IEC 2015
Table 7 – ArrayItemType definition
Attribute Value
BrowseName ArrayItemType
IsAbstract True
ValueRank 0 (0 = OneOrMoreDimensions)
DataType BaseDataType
References NodeClass BrowseName DataType TypeDefinition ModellingRule
Subtype of the DataItemType defined in 5.3.1; i.e the Properties of that type are inherited.
HasSubtype VariableType YArrayItemType Defined in 5.3.4.2
HasSubtype VariableType XYArrayItemType Defined in 5.3.4.3
HasSubtype VariableType ImageItemType Defined in 5.3.4.4
HasSubtype VariableType CubeItemType Defined in 5.3.4.5
HasSubtype VariableType NDimensionArrayItemType Defined in 5.3.4.6
HasProperty Variable InstrumentRange Range PropertyType Optional
HasProperty Variable EURange Range PropertyType Mandatory
HasProperty Variable EngineeringUnits EUInformation PropertyType Mandatory
HasProperty Variable Title LocalizedText PropertyType Mandatory
HasProperty Variable AxisScaleType AxisScaleEnumeration PropertyType Mandatory

InstrumentRange defines the range of the Value of the ArrayItem.
EURange defines the value range of the ArrayItem likely to be obtained in normal operation. It
is intended for such use as automatically scaling a bar graph display.
EngineeringUnits holds the information about the engineering units of the Value of the
ArrayItem.
For additional information about InstrumentRange, EURange, and EngineeringUnits see the
description of AnalogItemType in 5.3.2.
Title holds the user readable title of the Value of the ArrayItem.
AxisScaleType defines the scale to be used for the axis where the Value of the ArrayItem
shall be displayed.
The StatusCode SemanticsChanged bit shall be set if any of the InstrumentRange, EURange,
EngineeringUnits or Title Properties are changed (see 5.2 for additional information).
5.3.4.2 YArrayItemType
YArrayItemType represents a single-dimensional array of numerical values used to represent
spectra or distributions where the x axis intervals are constant. YArrayItemType is formally
defined in Table 8.
Table 8 – YArrayItemType definition
Attribute Value
BrowseName YArrayItemType
IsAbstract False
ValueRank 1
DataType BaseDataType
ArrayDimensions {0} (0 = UnknownSize)
References NodeClass BrowseName DataType TypeDefinition ModellingRule
Subtype of the ArrayItemType defined in 5.3.4.1

HasProperty Variable XAxisDefinition AxisInformation PropertyType Mandatory

The Value of the YArrayItem contains the numerical values for the Y-Axis. Engineering Units
and Range for the Value are defined by corresponding Properties inherited from the
ArrayItemType.
The DataType of this VariableType is restricted to SByte, Int16, Int32, Int64, Float, Double,
ComplexNumberType and DoubleComplexNumberType.
The XAxisDefinition Property holds the information about the Engineering Units and Range for
the X-Axis.
The StatusCode SemanticsChanged bit shall be set if any of the following five Properties are
changed: InstrumentRange, EURange, EngineeringUnits, Title or XAxisDefinition (see 5.2 for
additional information).
Figure 3 shows an example of how Attributes and Properties may be used in a graphical
interface.
Magnitude response (dB)
–10
–20
–30
–40
–50
–60
–70
–80
–90
0 5 10 15 20
Frequency (kHz)
IEC
Figure 3 – Graphical view of a YArrayItem
Table 9 describes the values of each element presented in Figure 3.
Table 9 – YArrayItem item description
Attribute / Property Item value
Description Magnitude Response (dB)
axisScaleType AxisScaleEnumeration.LINEAR 0
InstrumentRange.low -90
InstrumentRange.high 5
EURange.low -90
EURange.high 2
EngineeringUnits.namespaceUrl http://www.opcfoundation.org/UA/units/un/cefact
EngineeringUnits.unitId 2N
EngineeringUnits.displayName “en-us”, “dB”
EngineeringUnits.description “en-us”, “decibel”
Title Magnitude
XAxisDefinition.EngineeringUnits.namespaceUrl http://www.opcfoundation.org/UA/units/un/cefact
XAxisDefinition.EngineeringUnits.unitId kHz
XAxisDefinition.EngineeringUnits.displayName “en-us”, “kHz”
XAxisDefinition.EngineeringUnits.description “en-us”, kilohertz”
Magnitude (dB)
– 16 – IEC 62541-8:2015 © IEC 2015
Attribute / Property Item value
XAxisDefinition.Range.low 0
XAxisDefinition.Range.high 25
XAxisDefinition.title “en-us”, “Frequency”
XAxisDefinition.axisScaleType AxisScaleEnumeration.LINEAR_0
XAxisDefinition.axisSteps null

Interpretation notes:
• Not all elements of this table are used in the graphic.
• The X axis is displayed in reverse order, however, the XAxisDefinition.Range.low shall
be lower than XAxisDefinition.Range.high. It is only a graphical representation that
reverses the display order.
• There is a constant X axis
5.3.4.3 XYArrayItemType
XYArrayItemType represents a vector of XVType values like a list of peaks, where XVType.x
is the position of the peak and XVType.value is its intensity. XYArrayItemType is formally
defined in Table 10.
Table 10 – XYArrayItemType definition
Attribute Value
BrowseName XYArrayItemType
IsAbstract False
ValueRank 1
DataType XVType (defined in 5.6.8)
References NodeClass BrowseName DataType TypeDefinition ModellingRule
Subtype of the ArrayItemType defined in 5.3.4.1

HasProperty Variable XAxisDefinition AxisInformation PropertyType Mandatory

The Value of the XYArrayItem contains an array of structures (XVType) where each structure
specifies the position for the X-Axis (XVType.x) and the value itself (XVType.value), used for
the Y-Axis. Engineering units and range for the Value are defined by corresponding Properties
inherited from the ArrayItemType.
XAxisDefinition Property holds the information about the Engineering Units and Range for the
X-Axis.
The axisSteps of XAxisDefinition shall be set to NULL because it is not used.
The StatusCode SemanticsChanged bit shall be set if any of the InstrumentRange, EURange,
EngineeringUnits, Title or XAxisDefinition Properties are changed (see 5.2 for additional
information).
5.3.4.4 ImageItemType
ImageItemType defines the general characteristics of an ImageItem which represents
...