Look At What Makes OPC Usable

OPC, a standard for device communication, has become a widely used technology for communicating data among devices manufactured by many different suppliers.

It is so old, in technology terms, though, that the underlying technology from Microsoft, the Redmond, Wash., software giant, is about to lose support. OPC-Unified Architecture, or OPC UA, has been in development for several years as a technology to move the venerable standard into the modern technological world.

Much has been written about the technology and the benefits of OPC UA (see, for example, www.automationworld.com/primers-6189), so much so, in fact, that sometimes users are confused. "Classic" OPC was built upon Microsoft's Component Object Model (COM) and Distributed COM (DCOM). Microsoft and the rest of the technology world have moved to adopt eXtensible Markup Language (XML), with the software supplier incorporating it within its .Net technology. The OPC Foundation has responded with development of OPC.Net for those who are developing in a Microsoft.Net environment, along with OPC UA for those looking for a complete embedded implementation.

Leaders of OPC Foundation member companies recently stressed to Automation World that much of the discussion surrounding these different "flavors" of OPC misses the point—that many suppliers work together to make the standard more useful for users. They specifically cited the three annual Interoperability Workshops where a group of suppliers bring their products to a location and try to connect to each other's devices. These are held in North America, Europe and Asia, in order to attract as wide a variety of members as possible. OPC Foundation Director of Certification and Compliance Nathan Pocock, who has also had experience as a supplier, likened the sessions to a free-for-all where one company takes its client and connects to other suppliers' servers and so on, iteratively. "It's pretty informal, but kind of like the same thing users would do," Pocock adds.

The OPC Foundation also hosts developers' conferences to help suppliers develop robust OPC implementations. Developers learn such things as how to wrap older products based on COM into a UA implementation. They also learn how to use compliance testing tools, build an OPC client and server, troubleshoot problems and model information. A recent mid-October class attracted 25 developers.

Compliance testing arrives

The big news emanating from the Scottsdale, Ariz., headquarters of the OPC Foundation is the start-up of a compliance-testing lab. Headed by Pocock, this first iteration will test members' products for compliance to the OPC UA equivalent of OPC DA (data acquisition). The Foundation released the first version of the UA test suite in September, so all members have had access to the requirements and test methodologies before submitting products. The tools are based on Javascript, so suppliers can take the tools and write their own advanced testing to help them prepare for future iterations of the test.

Tests for compliance use the same tool that vendors have had. Tests are conducted similarly to the way they are done at the Interoperability workshops, with some additional value added. "We have the capability to do the same thing as the workshop," says Pocock. "Lots of members have donated products to the lab that have become reference products. After we check for interoperability, then comes robustness checking. We try to crash the product using whatever ways we can find, such as injecting bad information, trying to cram in invalid ‘garbage' to test for buffer overruns, disconnecting cables or killing an OPC server to see if the client crashes or if it can resume. We then check for performance. Say a vendor claims to support 100,000 tag changes per second. We'll check that. Then we evaluate overall usability by checking out the documentation, installation/uninstall capabilities. So, once the ‘gold seal of approval' is applied, users know it's been through the wringer," he concludes.

Gary Mintchell, gmintchell@automationworld.com, is Editor in Chief of Automation World.

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