IEC 62541-8:2011

IEC 62541-8 ®
Edition 1.0 2011-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
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OPC unified architecture –
Part 8: Data Access
Architecture unifiée OPC –
Partie 8: Accès aux données
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IEC 62541-8 ®
Edition 1.0 2011-10
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
PRICE CODE
INTERNATIONALE
CODE PRIX Q
ICS 25.040.40; 25.100.01 ISBN 978-2-88912-727-6

– 2 – 62541-8 © IEC:2011
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms, definitions and abbreviations . 6
3.1 Terms and definitions . 6
3.2 Abbreviations . 7
4 Concepts . 7
5 Model . 8
5.1 General . 8
5.2 Variable Types . 9
5.2.1 DataItemType . 9
5.2.2 AnalogItemType . 10
5.2.3 DiscreteItemType . 11
5.3 AddressSpace Model . 12
5.4 Attributes of DataItems . 13
5.5 Property DataTypes. 14
5.5.1 Overview . 14
5.5.2 Range . 14
5.5.3 EUInformation . 14
6 Data Access specific usage of Services . 15
6.1 General . 15
6.2 PercentDeadband . 15
6.3 Data Access Status Codes . 15
6.3.1 Overview . 15
6.3.2 Operation level result codes . 15
6.3.3 LimitBits . 17
6.3.4 SemanticsChanged . 17

Figure 1 – OPC DataItems are linked to automation data . 8
Figure 2 – DataItem VariableType Hierarchy . 9
Figure 3 – Representation of DataItems in the AddressSpace . 13

Table 1 – DataItemType Definition . 9
Table 2 – AnalogItemType Definition . 10
Table 3 – DiscreteItemType Definition . 11
Table 4 – TwoStateDiscreteType Definition . 11
Table 5 – MultiStateDiscreteType Definition . 12
Table 6 – Range Data Type Structure . 14
Table 7 – Range Definition. 14
Table 8 – EUInformation Data Type Structure . 14
Table 9 – EUInformation Definition . 15
Table 10 – Operation level result codes for BAD data quality . 16
Table 11 – Operation level result codes for UNCERTAIN data quality . 16
Table 12 – Operation level result codes for GOOD data quality . 17

62541-8 © IEC:2011 – 3 –
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
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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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.
The text of this standard is based on the following documents:
FDIS Report on voting
65E/194/FDIS 65E/216/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.

– 4 – 62541-8 © IEC:2011
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.
62541-8 © IEC:2011 – 5 –
INTRODUCTION
This International Standard is the specification for developers of OPC UA applications. The
specification is a result of an analysis and design process to develop a standard interface to
facilitate the development of applications by multiple vendors that will inter-operate
seamlessly together.
– 6 – 62541-8 © IEC:2011
OPC UNIFIED ARCHITECTURE –
Part 8: Data Access
1 Scope
This part of IEC 62541 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 complemental 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 referenced documents are indispensable for the application of this document.
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, OPCUnified architecture – Part 5: Information Model
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document the terms and definitions given in IEC 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 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
NOTE 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.

62541-8 © IEC:2011 – 7 –
3.1.3
DiscreteItem
DataItems that represent data that may take on only a certain number of possible values
NOTE 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
EngineeringUnits
units of measurement for AnalogItems that represent continuously-variable physical quantities
(e.g., length, mass, time, temperature)
NOTE 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
DA Data Access
EU Engineering Unit
UA Unified Architecture
4 Concepts
Data Access deals with the representation and use of automation data in OPC UA Servers.
Automation data can be located inside the OPC UA Server or on I/O cards directly connected
to the OPC UA 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
an OPC UA server might consist of a broad range of different DataItems.

– 8 – 62541-8 © IEC:2011
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 Part 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. 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.

62541-8 © IEC:2011 – 9 –
BaseDataVariableType
Defined in
IEC 62541-5
DataItemType
AnalogItemType
DiscreteItemType
MultiState
TwoStateDiscreteType
DiscreteType
Figure 2 – DataItem VariableType Hierarchy
5.2 Variable Types
5.2.1 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 Part 3 and Part 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 Part 5; i.e the Properties of that type are inherited.
HasSubtype VariableType AnalogItemType Defined in 5.2.2
HasSubtype VariableType DiscreteItemType Defined in 5.2.3

HasProperty Variable Definition String PropertyType Optional
HasProperty Variable ValuePrecision Double PropertyType Optional

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”

– 10 – 62541-8 © IEC:2011
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 that it supports with more precision.
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.
5.2.2 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 5.2; 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

InstrumentRange defines the value range that can be returned by the instrument.
Example: InstrumentRange ::= {-9999.9, 9999.9}
The Range Data Type is specified in 5.5.2.
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 this range. Client software must be prepared to deal with this. Similarly a
client may attempt to write a value that is outside 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 5.5.3.

62541-8 © IEC:2011 – 11 –
If the item contains an array, the Properties shall apply to all elements in the array.
5.2.3 DiscreteItemType
5.2.3.1 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 5.2.3.2
HasSubtype VariableType MultiStateDiscreteType Defined in 5.2.3.3

5.2.3.2 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.
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 5.2.3; 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, the Properties will apply to all elements in the array.

– 12 – 62541-8 © IEC:2011
5.2.3.3 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 5.2.3; 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 the range of the list and robust
servers should be prepared to handle writes of illegal values.
If the item contains an array, 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 Part 3).
5.3 AddressSpace Model
DataItems are always defined as data components of other Nodes in the AddressSpace. They
are never defined by themselves. A simple example of a container for DataItems would be a
“Folder Object” but it can be an Object of any other type.
Figure 3 illustrates the basic AddressSpace model of a DataItem, in this case an AnalogItem.

62541-8 © IEC:2011 – 13 –
DataItemType
Boiler_01 (Object)
Definition
Pressure (Variable)
Attribute
AnalogItemType
Value
DataType
AccessLevel
MinimumSamplingInterval
InstrumentRange
EURange
EngineeringUnits
Definition
InstrumentRange
EURange
PropertyType
EngineeringUnits
Figure 3 – Representation of DataItems in the AddressSpace
Each DataItem is represented by a DataVariable with a specific set of Attributes. The
TypeDefinition reference indicates the type of the DataItem (in this case the AnalogItemType).
Additional characteristics of DataItems are defined using Properties. The VariableTypes in 5.2
specify which properties may exist. These Properties have been found useful for a wide range
of Data Access clients. Servers that want to disclose similar information should use the OPC-
defined Property rather than a vendor-specific one.
The above figure shows only a subset of Attributes and Properties. Other Attributes as
defined for Variables in Part 3 (e.g., Description) may also be available.
5.4 Attributes of DataItems
This subclause lists the Attributes of Variables that have particular importance for Data
Access. They are specified in detail in Part 3. The following Attributes are particularly
important for Data Access:
• Value
• DataType
• AccessLevel
• MinimumSamplingInterval
Value is the most recent value of the Variable that the server has. Its data type is defined by
the DataType Attribute. The AccessLevel Attribute defines the server’s basic ability to access
current data and MinimumSamplingInterval defines how current the data are.

– 14 – 62541-8 © IEC:2011
When a client requests the Value Attribute for reading or monitoring, the server always
returns a StatusCode (the quality and the server’s ability to access/provide the value) and,
optionally, a ServerTimestamp and a SourceTimestamp. See Part 4 for details on StatusCode
and the meaning of the two timestamps. Specific status codes for Data Access are defined in
6.3.
5.5 Property DataTypes
5.5.1 Overview
Following is a description of the data types used for Data Access properties defined in this
part.
DataTypes like String, Boolean, Double or LocalizedText are defined in Part 3. Their
representation is specified in Part 5.
5.5.2 Range
This structure defines the Range for a value. Its elements are defined in Table 6.
Table 6 – Range Data Type Structure
Name Type Description
Range structure
low Double Lowest value in the range.
high Double Highest value in the range.

Its representation in the AddressSpace is defined in Table 7
Table 7 – Range Definition
Attributes Value
BrowseName Range
5.5.3 EUInformation
This structure contains information about the EngineeringUnits. Its elements are defined in
Table 8.
The structure has been defined such that standards bodies can incorporate their engineering
unit definitions into OPC UA. Servers shall use the namespaceUri in this structure to identify
the proper organization.
Table 8 – EUInformation Data Type 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 9

62541-8 © IEC:2011 – 15 –
Table 9 – EUInformation Definition
Attributes Value
BrowseName EUInformation
6 Data Access specific usage of Services
6.1 General
Part 4 specifies the complete set of services. Those needed for the purpose of DataAccess
are in particular:
• The View service set and Query service set to detect DataItems, and their Properties.
• The Attribute service set to read or write Attributes and in particular the value Attribute.
• The MonitoredItem and Subscription service set to set up monitoring of DataItems and to
receive data change notifications.
6.2 PercentDeadband
The DataChangeFilter in Part 4 defines the conditions under which a data change notification
shall be reported. This filter contains a deadband which can be of type AbsoluteDeadband or
PercentDeadband. Part 4 already specifies the behaviour of the AbsoluteDeadband. This sub-
clause specifies the behaviour of the PercentDeadband type.
DeadbandType = PercentDeadband
For this type of deadband, the deadbandValue is defined as the percentage of the EURange.
That is, it applies only to AnalogItems with an EURange Property that defines the typical
value range for the item. This range shall be multiplied with the deadbandValue to generate
an exception limit. An exception is determined as follows:
Exception if (absolute value of (last cached value - current value) >
(deadbandValue/100.0) * ((high–low) of EURange)))
The range of the deadband is from 0,0 to 100,0 Percent. Specifying a deadbandValue outside
this range will be rejected and reported with the StatusCode Bad_DeadbandFilterInvalid (see
Table 10).
If the item is an array of values and any array element exceeds the deadbandValue, the entire
monitored array is returned.
6.3 Data Access Status Codes
6.3.1 Overview
This subclause defines additional codes and rules that apply to the StatusCode when used for
Data Access values.
The general structure of the StatusCode is specified in Part 4. It includes a set of common
operational result codes that also apply to Data Access.
6.3.2 Operation level result codes
Certain conditions under which a Variable value was generated are only valid for automation
data and in particular for device data. They are similar, but slightly more generic than the
description of data quality in the various fieldbus specifications.
In the following, Table 10 contains codes with BAD severity, indicating a failure;

– 16 – 62541-8 © IEC:2011
Remarks:
• Bad_WaitingForInitialData is defined in Part 4.

Table 11 contains codes with UNCERTAIN severity, indicating that the value has been
generated under sub-normal conditions.
Table 12 contains GOOD (success) codes.
Note again, that these are the codes that are specific for Data Access and supplement the
codes that apply to all types of data and are therefore defined in Part 4.
Table 10 – Operation level result codes for BAD data quality
Symbolic Id Description
Bad_ConfigurationError There is a problem with the configuration that affects the usefulness of the value.
Bad_NotConnected The variable should receive its value from another variable, but has never been configured to do so.
Bad_DeviceFailure There has been a failure in the device/data source that generates the value that has affected the
value.
Bad_SensorFailure There has been a failure in the sensor from which the value is derived by the device/data source.
The limits bits are used to define if the limits of the value have been reached.
Bad_NoCommunication Communications to the data source is defined, but not established, and there is no last known value
available. This status/substatus is used for cached values before the first value is received.
Bad_OutOfService The source of the data is not operational.
Bad_LastKnown OPC UA requires that the Server shall return a Null value when the Severity is Bad. Therefore, the
Fieldbus code “Bad_LastKnown” shall be mapped to Uncertain_NoCommunicationLastUsable
Bad_DeadbandFilterInvalid The specified PercentDeadband is not between 0,0 and 100,0 or a PercentDeadband is not
supported, since an EURange is not configured.
Remarks:
• Bad_WaitingForInitialData is defined in Part 4.

Table 11 – Operation level result codes for UNCERTAIN data quality
Symbolic Id Description
Uncertain_ Communication to the data source has failed. The variable value is the last value that had a good
NoCommunicationLastUsa quality and it is uncertain whether this value is still current.
ble
The server timestamp in this case is the last time that the communication status was checked. The
time at which the value was last verified to be true is no longer available.
Uncertain_ Whatever was updating this value has stopped doing so. This happens when an input variable is
LastUsableValue configured to receive its value from another variable and this configuration is cleared after one or
more values have been received.
This status/substatus is not used to indicate that a value is stale. Stale data can be detected by the
client looking at the timestamps.
Uncertain_SubstituteValue The value is an operational value that was manually overwritten.
Uncertain_InitialValue The value is an initial value for a variable that normally receives its value from another variable. This
status/substatus is set only during configuration while the variable is not operational (while it is out-
of-service).
Uncertain_ The value is at one of the sensor limits. The Limits bits define which limit has been reached. Also
SensorNotAccurate set if the device can determine that the sensor has reduced accuracy (e.g. degraded analyzer), in
which case the Limits bits indicate that the value is not limited.
Uncertain_ The value is outside of the range of values defined for this parameter. The Limits bits indicate which
EngineeringUnitsExceeded limit has been reached or exceeded.
Uncertain_SubNormal The value is derived from multiple sources and has less than the required number of GOOD
sources.
62541-8 © IEC:2011 – 17 –
Table 12 – Operation level result codes for GOOD data quality
Symbolic Id Description
Good_LocalOverride The value has been Overridden. Typically this is means the input has been disconnected and a
manually-entered value has been ”forced”.

6.3.3 LimitBits
The bottom 16 bits of the StatusCode are bit flags that contain additional information, but do
not affect the meaning of the StatusCode. Of particular interest for DataItems is the LimitBits
field. In some cases, such as sensor failure it can provide useful diagnostic information.
Servers that do not support Limit have to set this field to 0.
6.3.4 SemanticsChanged
The StatusCode also contains an informational bit called SemanticsChanged.
OPC UA Servers that implement Data Access shall set this Bit in notifications if one or several
of the following Properties changes:
• EngineeringUnits (could create problems if the client uses the value to perform
calculations);
• EURange (could change the behaviour of a Subscription if a PercentDeadband filter is
used);
• FalseState, TrueState, EnumStrings (changes can cause misinterpretation by users or
(scripting) programs).
It should not be changed for any of the other Data Access Properties.
Clients should not process the data value until they re-read the mentioned Properties
associated with the Variable.
____________
– 18 – 62541-8 © CEI:2011
SOMMAIRE
AVANT-PROPOS . 19
INTRODUCTION . 21
1 Domaine d’application . 22
2 Références normatives . 22
3 Termes, définitions et abréviations . 22
3.1 Termes et définitions . 22
3.2 Abréviations . 23
4 Concepts . 23
5 Modèle . 24
5.1 Généralités. 24
5.2 Types de Variable . 25
5.2.1 Type d’Elément de Données . 25
5.2.2 Type d’Elément Analogique . 26
5.2.3 Type d’Elément Discret . 27
5.3 Modèle d’espace d’adresse . 29
5.4 Attributs des Éléments de Données . 31
5.5 Types de Données Propriété . 31
5.5.1 Aperçu général . 31
5.5.2 Plage . 31
5.5.3 Information EU . 32
6 Utilisation particulière des Services d’Accès aux Données . 32
6.1 Généralités. 32
6.2 Pourcentage de Bande Neutre . 32
6.3 Codes d’Etats d’Accès aux Données . 33
6.3.1 Aperçu général . 33
6.3.2 Codes de résultats de niveau opérationnel . 33
6.3.3 Bits de limites . 34
6.3.4 Sémantique Modifiée . 34

Figure 1 – Éléments de Données OPC reliés aux données d’automatisation . 24
Figure 2 – Hiérarchie du Type de Variable Élément de Données . 25
Figure 3 – Représentation des Éléments de Données dans l’Espace d’Adresse . 30

Tableau 1 – Définition du Type d’Elément de Donnée . 26
Tableau 2 – Définition du Type d’Elément Analogique . 27
Tableau 3 – Définition du Type d’Elément Discret . 28
Tableau 4 – Définition du Type Discret à Deux Etats. 28
Tableau 5 – Définition du Type Discret à États Multiples . 29
Tableau 6 – Structure du Type de Données « Plage » . 31
Tableau 7 – Définition de Plage . 32
Tableau 8 – Structure du Type de Données Information EU . 32
Tableau 9 – Définition de l’Information EU . 32
Tableau 10 – Codes de résultats de niveau opérationnel MAUVAIS . 33
Tableau 11 – Codes de résultats de niveau opérationnel DOUTEUX . 34
Tableau 12 – Codes de résultats de niveau opérationnel BONS . 34
...