Almost unified
Mark T. Hoske, Editor-in-Chief -- Control Engineering, 1/1/2007
Those using automation to transfer data need to embrace OPC Unified Architecture (UA) to increase security and data integration, suggests Dave Emerson, principal systems architect, U.S. Development Center, Yokogawa Corp. of America. OPC Foundation tools, though sometimes frustrating, have done industrial automation a world of good, acting as a universal translator, utility, and data pipe to send information from one place to another. UA use avoids point-to-point interfaces and hundreds of low-level drivers. OPC tools reduce costs by eliminating a tangle of interfaces, allowing easier upgrades. Emerson updated UA progress at Yokogawa's Technology Innovations Fair and 7th Annual User Conference, held Nov. 29-Dec. 1, 2006, in Houston.
OPC's new architecture—based on Web services, XML, and service-oriented architecture (SOA)—is needed because current OPC specifications are based on Microsoft DCOM, which doesn't work well with firewalls. UA adds more complex and structured data, reliability, security, performance, platform neutrality (Java, embedded platforms, and middleware beyond Microsoft offerings), and backward compatibility (with UA wrappers for DCOM clients and servers). At present, multiple OPC servers (DA, A&E, HDA) do not enable information integration. UA also offers integration with more applications, such as MES and ERP, to be a better IT citizen, providing glue among various layers of devices and software in the plant, enterprise, and supply chain, Emerson suggests.
Wisely, the new architecture includes third-party certification and a certification lab to improve reliability and confidence for plug-and-play use, addressing prior vendor self-testing compatibility concerns. More buy-in is expected through upcoming companion documentation, as industry groups define OPC UA “transports.” IEC, ISA, MIMOSA are working on information model specifications. Subscription update features include keep-alive, and heartbeat messages. Redundancy features, not in the original specification, also are being worked into UA.
The 11-part UA specification is comprehensive, covering: 1) concepts, 2) security, 3) address space, 4) services, 5) information model, 6) mappings, 7) profiles, 8) data access, 9) alarms and conditions, 10) programs, and 11) historical access. OPC Foundation released the first 10 parts of the UA specification to members in 2006 through November, and was continuing work on part 11 into December. The UA effort began in 2003. OPC Foundation has 400 member companies with more than 40 end-users participating. Encouraging greater participation in UA's continuing development will aid industry implementation.
For related reading, search unified architecture or OPC Foundation atop www.controleng.com.
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