IEC 62769-5-2021 Field device integration (FDI) – Part 5: Information Model.
4 Overview of OPC Unified Architecture
4.1 General The main use case for OPC standards is the online data exchange between devices and HMI or SCADA systems. In this use case, the device data is provided by an OPC server and is consumed by an OPC client integrated in the HMI or SCADA system. OPC provides functionality to browse through a hierarchical namespace containing data items and to read, write and monitor these items for data changes. Numeric identifiers for NodeIds are defined in Annex A. OPC UA incorporates features like Data Access, Alarms and Historical Data via platform independent communication mechanisms and generic, extensible and object-oriented modelling capabilities for the information a system wants to expose.
The current version of OPC UA defines an optimized binary TCP protocol for high- performance intranet communication as well as a mapping to Web Services. The abstract service model does not depend on a specific protocol mapping and allows adding new protocols in the future. Features like security, access control and reliability are directly built into the transport mechanisms. Based on the platform independence of the protocols, OPC UA servers and clients can be directly integrated into devices and controllers.
The OPC UA information model provides a standard way for Servers to expose Objects to Clients.
Objects in OPC UA terms are composed of other Objects, Variables and Methods. OPC UA also allows relationships to other Objects to be expressed. The set of Objects and related information that an OPC UA Server makes available to Clients is referred to as its AddressSpace. The elements of the OPC UA Object Model are represented in the AddressSpace as a set of Nodes described by Attributes and interconnected by References. OPC UA defines various classes of Nodes to represent AddressSpace components, most importantly Objects, Variables, Methods, ObjectTypes, DataTypes and ReferenceTypes. Each NodeClass has a defined set of Attributes.
Objects are used to represent components like folders, Devices or Networks. An Object is associated to a corresponding ObjectType that provides definitions for that Object. Variables are used to represent values. Two categories of Variables are defined: Properties and DataVariables. Properties are Server-defined characteristics of Objects, DataVariables and other Nodes. Properties are not allowed to have Properties defined for them. An example for Properties of Objects is the Manufacturer Property of a Device. DataVariables represent the contents of an Object. DataVariables may have component DataVariables. This is typically used by Servers to expose individual elements of arrays and structures. This document uses DataVariables mainly to represent the Parameters of Devices.
4.2 Overview of OPC UA Devices The OPC Unified Architecture for Devices (DI) (IEC 62541 -1 00) standard is an extension of the overall OPC Unified Architecture standard series and defines information models associated with Devices. IEC 62541 -1 00 describes three models that build upon each other as follows:
• The (base) Device Model is intended to provide a unified view of devices irrespective of the underlying device protocols.
• The Device Communication Model adds Network and Connection information elements so that communication topologies can be created.IEC 62769-5 pdf download.