Real-time capable OPC UA
Until now, OPC UA has had its limitations when it comes to complex processes with real-time requirements. That's why the OPC Foundation is working on two extensions that will give the OPC UA communication standard real-time capability, by using a time-sensitive network and publish-subscribe model. We sat down with Matthias Damm, head of the OPC Foundation's pub/sub working group at Unified Automation to find out what these expansions will mean for the future of industrial networking. B&R introduced its first pub/sub-enabled product in the spring of 2016. Sebastian Sachse, technology manager of B&R's Open Automation business unit, reveals the company's underlying motivation.
Matthias, what's the reason for developing the pub/sub expansion for the OPC UA specification?
Matthias Damm: Today, OPC UA is fast – but not deterministic in terms of automation. For the applications where OPC UA is currently being used, the emphasis is on delivering data reliably without any loss of information. When it comes to communication between controllers, real-time capability becomes much more important. With the publish-subscribe model, data exchange is a lot closer to what you get with a real-time system. Combine the publish-subscribe model with a real-time network – Ethernet with the TSN expansion – and what you get is real-time capable OPC UA.
What advantages does the pub/sub expansion bring to OPC UA?
Damm: OPC UA has been working with a client/server mechanism. A client requests information and receives a response from a server. The transfer takes place asynchronously. This system has its limitations in cases when there are many nodes on the network. The publish-subscribe model extends the communication spectrum of OPC UA. The pub/sub enables one-to-many and many-to-many communication. It allows developers to define a fixed time window in which the data is to be exchanged. This covers new applications that cannot be optimally solved with client/server technology.
Sebastian, why has B&R chosen to get involved in the pub/sub working group?
Sebastian Sachse: The OPC Foundation's TSN and pub/sub working groups have greatly accelerated the spread of OPC UA into industrial applications. OPC UA is now entering into areas where cyclic communication with real-time requirements is fundamental. B&R has a lot of experience in these areas, so we saw a chance to make an active contribution. By pooling expertise with other partner companies, we're helping to create the best technology possible.
What impact will the OPC UA expansions have on the future of industrial networking?
Damm: When you build a plant that includes machines with different automation technology and fieldbus systems, it's historically been difficult to get them to work together at the control level. Today's model of OPC makes it much easier to implement communication across these multi-vendor lines.
So what's the added benefit of the publish-subscribe model?
Damm: When you have a very large, decentralized architecture, one-to-many and many-to-many communication through publish/subscribe gives you a huge advantage in terms of speed. This is a fundamental requirement for integrated systems such as packaging lines.
How far along is the pub-sub specification?
Damm: At the moment we have a stable draft version that includes the majority of the definitions. In projects like this, it's important to have pilot implementations occurring in tandem with development of the specification. At the Hannover Messe in April, we already had various manufacturers presenting the first demo applications. We expect the specification to be completed by the end of 2016.
Sebastian, B&R introduced the first pub/sub-enabled field device for OPC UA at the Hannover Messe exhibition. Why are you working on a field device so soon?
Sachse: As Matthias said, early implementation helps accelerate the specification process. The practical experience gained on testing equipment flows right back into the working groups and is incorporated into the specification. Getting to market early also gives us a head start and allows us to serve our customers at a very early stage.
What kind of applications is the field device designed for?
Sachse: The bus controller is perfect for factory automation and can be used there for almost any purpose. The new pub-sub model distributes data particularly efficiently and allows connections to the cloud via any Ethernet infrastructure. This is helpful whether you're retrofitting an existing plant or building a new one.
What development goals has B&R set for itself with regard to OPC UA?
Sachse: OPC UA has already had a significant impact on the industry and continues to spread quickly. In the short term, B&R's priorities are completing the specifications for pub/sub and TSN and integrating them into relevant products. Beyond that, as OPC UA conquers new areas of application, B&R will play an active role in those developments as well. Essentially, we share the goal of the OPC Foundation itself: To establish OPC UA as the open standard for IIoT communication from the sensor to the cloud.
Are customers requesting additional OPC UA products?
Sachse: Our customers are fully on board with OPC UA technology and are already designing machinery and plants accordingly. The many new possibilities and functions it offers are inspiring new ideas for potential applications. With our products, we'll be helping them turn those ideas into reality.