Playing Well with Others

Process Analyzers Can Use OPC Xi and OPC ADI to Communicate with Control Systems

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For those end users and vendors who have standardized on the .NET framework for services and data exchange and interchange, the OPC Foundation has also recently announced the OPC Xi (Express Interface) specification. The OPC Xi interface is the result of collaboration among several OPC vendor companies from the process industry to develop an easily integrated and secure solution for a variety of plant communications, including analyzers with PC-based controls. "OPC Xi was developed with the primary goal to provide a .NET-based migration path from OPC Classic. OPC Xi may also be used as a standard .NET WCF interface for newly developed OPC servers," said Thomas Burke, OPC Foundation's president.

"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 the Microsoft Component Object Model (COM) to .Net," said one of the developers of OPC Xi, Chris Felts, product strategist with Emerson Process Management (

"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  moved from COM to .Net. COM is efficient for local server access, but it can be difficult to configure for remote server access and problematic for communication through firewalls," said another of OPC Xi's developers, Jon Brown, strategic account manager with Iconics (

"Xi provides secure communications with a firewall-friendly interface and patented security features to provide secure communications between process automation systems and higher level manufacturing execution systems (MES) and enterprise resources planning (ERP) systems. Xi increases client connectivity robustness by maintaining the state-of-the-client connection, allowing the client to reconnect quickly and easily if communications with the server become lost," said Lee Neitzel, senior technologist with Emerson Process Management. "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, including Transmission Control Protocol (TCP), Hypertext Transfer Protocol (HTTP), and Secure Hypertext Transfer Protocol (HTTPS)."

The promise of PAT is far from being realized, partly due to integration problems with disparate analyzer communication protocols. These new OPC specifications may take us a long way toward achieving the FDA's vision for PAT.  

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