IEC 62541-8-2020 pdf free download – OPC unified architecture – Part 8: Data access.
This part of lEC 62541 is part of the overall OPC Unified Architecture (OPC UA) standard series
and defines the information model associated with Data Access(DA). lt particularly includesadditional VariableTypes and complementary descriptions of the NodeClass es and Attributesneeded for Data Access, additional`Properties, and other information and behaviour.
The complete address space model,including all NodeClass es and Attributes is specified inIEC 62541-3.The services to detect and access data are specified in IEC 62541-4.
Normative references
The following documents are referred to in the text in such a way that some or all of their contentconstitutes requirements of this document. For dated references, only the edition cited applies.
For undated references,the latest edition of the referenced document (including anyamendments) applies.
IEC TR 62541-1,OPC Unified Architecture – Part 1: Overview and ConceptsIEC 62541-3,OPC Unified Architecture – Part 3: Address Space ModelIEC 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 inlnternational Trade , available at
https://www.unece.org/cefact/codesfortradelcodes_index.html
3Terms,definitions and abbreviated terms
3.1Terms and definitions
For the purposes of this document,the terms and definitions given in lEC TR 62541-1,IEC 62541-3, and lEC 62541-4 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the followingaddresses:
. IEC Electropedia: available at http://www.electropedia.orgl
. Iso Online browsing platform: available at http://www.iso.orglobp
3.1.1
Dataltem
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
Analogltem
Dataltem that represents 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 UAdefines a specific VariableType to identify an Analogltem . Properties describe the possible ranges of Analogltem s.
3.1.3
Discreteltem
Dataltem that represents 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 identifyDiscreteltems with two states or with multiple states.Properties specify the string values for these states.
3.1.4
Arrayltem
Dataltem that represents continuously variable physical quantities and where each individualdata 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 toidentify Arrayifem variants.
3.1.5
EngineeringUnits
units of measurement for Analogltems 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 Dataltem value and aboutthe highest and lowest value likely to be obtained in normal operation.
3.2Abbreviated terms
DAdata access
EUengineering unitUAUnified Architecture
4Concepts
Data Access deals with the representation and use of automation data in Servers.
Automation data can be located inside the Server or on l0 cards directly connected to theServer . It can also be located in sub-servers or on other devices such as controllers andinputloutput 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 withtransparent access to their automation data.
The links to automation data instances are called Dataltems . The categories of automation dataare provided is completely vendor-specific. Figure 1 illustrates how the AddressSpace of aServer may consist of a broad range of differentDataltem s.IEC 62541-8 pdf download.