The ABCs of OPC UA: Everything You Need to Understand
OPC Unified Architecture, also known as OPC UA, was developed in the mid-2000s as a TCP/IP-based protocol with the ability to share data at the control system level in real-time with high reliability and efficiency.
As I discuss the details of OPC UA, you might be wondering how you could fully grasp this concept. There is an amazing RealPars course, OPC UA: Learn the Basics, that offers comprehensive lessons on this topic.
Key Features of OPC UA
OPC Classic opened the door for control system applications to share data quickly with minimal configuration. It was first released in 1996. This method was based on the Microsoft Distributed Component Object Model or DCOM services for client-server communications.
While DCOM has some authentication features built-in, it is not fully secure, hard to configure, and usually requires operator intervention to correct when a failure occurs.
In order to correct these issues, and to provide a more robust and secure method for exchanging data, the OPC UA architecture, was developed.
OPC UA makes it possible to exchange process data, alarms and events, and historical data all from one client and server application. The original OPC UA specification was released in 2006.
OPC UA is not based upon DCOM, but rather on a protocol stack built on top of the well-known TCP/IP protocol, the backbone of Ethernet, and the internet.
This structure opened up a lot of possibilities for managing data in “blocks”, rather than just pieces of data based upon an individual tag item.
OPC UA is a client-server-based application. The OPC UA server provides access to its data by exposing its data objects to an OPC UA client, such as an HMI application.
The OPC UA interface is defined through configuration. An OPC UA application on the client subscribes to the data objects in the OPC UA server. These subscriptions are comprised of one or more data links to objects in the server that are used to request data from the server.
OPC UA Subscriptions
Each configured OPC UA subscription has properties that request data such as:
- DisplayName, which is the data object or tag,
- Tag Value,
- Quality or Status,
- Timestamp of the OPC UA Server and Client,
- Data Type, and
- Subscription ID
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A typical OPC UA subscription link has this format:
The link will point the OPC UA client directly to the OPC UA server at the location configured in the link.
Notice that the link identifies the PC name, IP address, and TCP port number at which the OPC UA server can be reached.
The OPC UA TCP protocol uses essentially the same link structure as for an internet link. This gives OPC UA clients the ability to directly discover, address, and subscribe to data in the OPC UA server over any Ethernet network.
It makes OPC UA independent of the operating system, making it truly platform-independent.
This allows OPC UA to be embedded in small devices, such as PLCs, operator terminals, handheld configuration devices, and smart appliances. Because some of these devices are physically easy to access, security is paramount.
OPC UA has built-in security measures like encryption, authentication, and authorization. Since OPC UA is based on the familiar TCP/IP protocol, its use can be extended to all industries and applications. If an ethernet connection can be made to the device, OPC UA can potentially be used!
OPC UA Architecture
To use OPC UA in my control system, you need OPC UA Server software to connect to the data sources, such as PLCs, application computers, and HMI stations.
You also need OPC UA Client software to interact with the OPC UA server and to set up subscriptions for periodic data access. This data will be used to store the collected data for use on HMI screens, historical databases, alarm loggers, PLCs, or other applications.
OPC UA can run on desktops, laptops, tablets, microcontrollers, and even in the cloud. Some manufacturers have embedded OPC UA servers directly into their PLC hardware. An example is the Siemens S7-1500 PLC.
The OPC UA base software installation is made up of a binary TCP-based protocol, plus a method for allowing the OPC UA Server to be “discovered” by other computer applications across the network.
It also includes application authentication, other security features, and data methods to access devices such as PLCs.
The OPC UA Client software can be loaded on the same PC as the OPC UA Server, on a different machine on the same network, or on a PC anywhere on the internet or in the cloud.
Because the OPC UA Client will use TCP and Internet browsing protocols to connect to the OPC UA Server, the OPC UA Client can literally be located anywhere.
OPC UA is a vital component of the fourth industrial revolution, or Industry 4.0. The Industrial Internet of Things, known as IIoT, is all about access to data and making data available to those users that require it. This is exactly what the OPC UA data subscription feature is all about!
As I have described, OPC UA is an efficient, secure, and feature-rich protocol for accessing data from a wide variety of devices, running various operating systems, in various locations.
A manufacturing company can use OPC UA to collect and store data from various plant sites in different locations connected by the internet or private intranet.
A major application for OPC UA will remain the subscription of data by HMI and data historian applications from PLC, DCS, and Building Automation controllers.
OPC UA is often the only mechanism that HMI systems can access data from vendor-supplied equipment like chillers, boilers, compressors, lab equipment, and single-use pharmaceutical processing skids.
Future of OPC UA
Because OPC UA is based on the TCP/IP Ethernet stack, as Ethernet evolves, so will OPC UA. That means that OPC UA will be able to take advantage of advances in cybersecurity measures such as encryption.
Efforts like the collaboration between OPC UA and TSN (Time-Sensitive Networking) will lead to creating comprehensive solutions by merging the strengths of different technology standards.
OPC UA is positioned to be the cornerstone for IIoT communications solutions for manufacturing systems, providing seamless data integration across devices, machines, and systems.
Software developers are realizing the value of adding OPC UA to their out-of-the-box solutions for integration with various cloud platforms, with the potential for making data storage, analysis, and retrieval more efficient.
And that concludes our discussion of OPC UA. If you're eager to dive deeper and truly master these concepts, don't forget to check out OPC UA: Learn the Basics.
This course will provide you with a comprehensive understanding, along with practical exercises to solidify your knowledge. Thank you for your time, and happy learning!