Having covered industrial protocols like Ethernet/IP, Modbus, DeviceNet etc, in this article let us cover the OPC-UA (Open Platform Communications Unified Architecture) standard. This powerful industrial communication protocol has been revolutionizing the way industries communicate and exchange data over the past decade gaining wide acceptance.
The OPC-UA standard is a comprehensive, vendor-independent, and platform-neutral communication protocol that enables seamless data exchange between various industrial devices, systems, and applications. It was developed by the OPC Foundation, a non-profit organization dedicated to the advancement of open connectivity in industrial automation.
OPC-UA is designed to provide a unified and secure way for diverse systems and devices to communicate, regardless of their underlying hardware or software platforms. It offers a robust and flexible architecture that can be adapted to a wide range of industrial applications, from manufacturing and process control to building automation and energy management.
The OPC-UA standard has its roots in the earlier OPC Classic specifications, which were developed in the 1990s to address the challenges of proprietary communication protocols in industrial automation. As technology evolved, industry recognized the need for a more modern, scalable, and secure communication solution, leading to the development of the OPC-UA standard.
The OPC-UA standard was first introduced in 2006 and has since undergone continuous development and refinement. Over the years, it has gained widespread adoption across various industries, becoming a de facto standard for industrial communication and data exchange. The specifications were standardized as IEC 62541.
One of the key milestones in the evolution of OPC-UA was the introduction of the Pub/Sub (Publish-Subscribe) communication model in 2017 from version 1.04. This addition expanded the capabilities of the standard, enabling more efficient and flexible data exchange between devices and applications.
The OPC-UA standard is renowned for its comprehensive set of features that make it a powerful and versatile communication protocol. Some of the key features of OPC-UA include:
Platform-independence: OPC-UA is designed to be platform-neutral, allowing seamless communication between devices and systems running on different hardware and software platforms. Vendor-neutrality: The standard is not tied to any specific vendor or manufacturer, enabling interoperability between a wide range of industrial products and solutions. Security: OPC-UA incorporates robust security features, including authentication, encryption, and authorization, ensuring the confidentiality and integrity of data exchange. Scalability: The standard can be scaled to support a wide range of applications, from small-scale systems to large-scale industrial networks. Service Oriented: By design, it is a service-oriented architecture, providing clear separation of network and application and exposing capabilities via API. Information modeling: OPC-UA provides a comprehensive information modeling framework that allows for the structured representation of industrial data and processes. Extensibility: The standard is designed to be extensible, allowing for the addition of new features and functionalities as the industry evolves.The OPC-UA standard maps to the various layers of the Open Systems Interconnection (OSI) reference model, providing a structured and well-defined communication framework. Here's how OPC-UA maps to the OSI layers:
OPC-UA OSI Layer Mapping
This layered approach allows OPC-UA to leverage the capabilities of the underlying network infrastructure while providing a standardized and consistent communication framework for industrial applications. On top of the transport layer, OPC-UA defines the data representation and information encoding model based on the Object-Oriented Programming concept. As this is a large article by itself, we will cover this in upcoming articles.
Being communication protocol independent, the OPC-UA standard supports multiple transport protocols, allowing for flexibility and adaptability to various industrial environments and requirements. The primary transport protocols used in OPC-UA include:
TCP/IP: OPC-UA supports the widely used Transmission Control Protocol/Internet Protocol (TCP/IP) for reliable and connection-oriented data exchange. HTTPS: The standard also supports secure communication over the Hypertext Transfer Protocol Secure (HTTPS) protocol, providing enhanced security for data transmission. UDP: The User Datagram Protocol (UDP) is another transport option in OPC-UA, offering a connectionless and efficient data transfer mechanism, particularly for real-time applications.In addition to these, protocols like WebSockets, AMQP, MQTT etc are supported. The choice of transport protocol depends on the specific requirements of the industrial application, such as the need for reliability, security, or real-time performance.
OPC-UA follows a client-server communication model, where clients (e.g., HMIs, SCADA systems, or other industrial applications) request data or services from servers (e.g., PLCs, RTUs, or other industrial devices). The client-server communication in OPC-UA is based on a request-response paradigm, where the client sends a request to the server, and the server responds with the requested data or service. This communication model is compatible with many existing protocols and thus can be extended to the OPC-UA domain with thin gateways.
OPC-UA also supports advanced features, such as session management, subscription-based data reporting, and event handling, which enhance the flexibility and responsiveness of client-server communication.
In addition to the client-server communication model, the OPC-UA standard also supports the Publish-Subscribe (Pub/Sub) communication model. The Pub/Sub model enables more efficient and scalable data exchange, particularly in scenarios where multiple clients or applications need to consume the same data from a server or device.
In the Pub/Sub model, publishers (e.g., industrial devices or servers) make data available to subscribers (e.g., HMIs, SCADA systems, or other applications) without the need for direct client-server interactions. Subscribers can then subscribe to specific data topics or events, and the publishers will automatically push the data to the subscribers as it becomes available.
The Pub/Sub communication in OPC-UA provides several benefits, such as reduced network load, improved real-time performance, and the ability to support complex data distribution scenarios.
The OPC-UA standard defines a set of profiles that specify the required functionality and features for different types of industrial applications and devices. Built on top of the OPC-UA Information models, these profiles help ensure interoperability and facilitate the integration of OPC-UA-compliant systems and devices.
Some of the key OPC-UA profiles include:
Micro Embedded Device Profile: Designed for small, resource-constrained devices, such as sensors and actuators. Client Profile: Specifies the requirements for OPC-UA client applications. Server Profile: Defines the requirements for OPC-UA server implementations. Data Access Profile: Focuses on the exchange of real-time process data. Alarms and Conditions Profile: Enables the communication of alarms, events, and condition monitoring information.OPC-UA standard defines many such profiles broadly covering most of the application scenarios needed for any industrial needs.
The OPC-UA standard has a wide range of applications across various industrial sectors, including:
Manufacturing and Process Control: OPC-UA enables seamless communication between PLCs, HMIs, SCADA systems, and other industrial automation equipment, facilitating real-time monitoring, control, and optimization of manufacturing processes. Building Automation: OPC-UA is used in building management systems to integrate and control various building systems, such as HVAC, lighting, and security. Energy Management: The standard is employed in energy generation, distribution, and consumption systems, allowing for efficient monitoring, control, and optimization of energy resources. Asset Management: OPC-UA supports the integration of asset management systems, enabling remote monitoring, predictive maintenance, and lifecycle management of industrial equipment and machinery. Logistics and Supply Chain: The standard is used in logistics and supply chain applications to facilitate the exchange of data between different systems, such as warehouse management, transportation, and inventory tracking.OPC-UA foundation provides reference implementation on various underlying languages such as ANSI C, C++, Java etc. in a quiet permissive license that can be readily used. In addition to these, there are numerous third-party offerings, including those from Embien, that can help bring existing system to this technology.
In this comprehensive guide, we have explored the OPC-UA standard in depth, covering its history, features, technical details, and various applications. While this is just a high-level introduction to the standard, we will explore the same in detail in one of our upcoming articles.
Profibus is a fieldbus communication standard that allows devices to exchange data in real-time, enabling seamless communication between various components in an automated system.
