Update 2: OPC Xi is now called OPC .NET 3.0.
Original post: In the Control magazine article, Playing Well with Others, Editor in Chief Walt Boyes describes how process analyzers can use OPC Xi and OPC ADI to better communicate with control systems. These communications standards help address challenges that Walt articulates:
On-line analyzers vary from simple pH meters to complex hydrocarbon analyzers and online scanning electron microscopes (SEMs), and they speak different languages. An at-line analyzer can be completely different from the on-line analyzer sitting next to it because they were designed to meet different specifications, to do different jobs, and to communicate in completely different ways.
In an earlier post, OPC Express Interface (OPC Xi) Technical Overview Slidecast, Emerson’s Lee Neitzel described the OPC Xi standard and how application developers and process manufacturing IT staff could use this standard to connect applications and devices together.
The article has a succinct overview of how OPC Xi works that was adapted from a whitepaper, Introduction to Express Interface (Xi). This whitepaper, written by Lee and DeltaV product strategist, Chris Felts, summarizes the OPC Xi standard:
Xi is a new Microsoft .NET based interface designed for secure and reliable access to real-time and historical process automation system data. Xi provides a standard, .Net based interface for “classic” OPC server functionality, OPC Data Access (DA), OPC Alarms & Events (A&E) and OPC Historical Data Access (HDA) and represents a natural progression of Microsoft communication technology from Microsoft Component Object Model (COM) to .Net.
The OPC Xi standard addressed the legacy issue with the original OPC Data Access standard:
Xi provides the same functionality as the classic OPC servers while addressing some of the known shortcomings of classic OPC. The classic OPC servers are based on COM communications, which was state of the art when the OPC specifications were created, but since the introduction of OPC DA in 1996, Microsoft has moved from COM to .Net communications. COM is efficient for local server access but can be difficult to configure for remote server access and problematic for communication through firewalls.
The whitepaper highlights the underlying technology platform in OPC Xi:
Xi is based on Windows Communication Foundation (WCF), the latest communications technology available from Microsoft. Using WCF, a Xi server is able to offer industry standard communication protocols, such as the Transmission Control Protocol (TCP), the Hypertext Transfer Protocol (HTTP) and Secure Hypertext Transfer Protocol (HTTPS).
If you’re a developer or process manufacturing IT professional, you may want to visit the Express Interface web site for specifications, demonstration code, and other development-related information.
Update: I spoke with the OPC Foundation’s Marketing VP, Manny Mandrusiak. The development tools on the Express Interface site mentioned in the last paragraph above will be moving over to the OPC Foundation site. I’ll update this post with the new link when the transition occurs.
