OPC UA: Interoperability Through Evolution

OPC is changing.

Aw 2428 0911 Tech
For 10 years, OPC (originally for Ole for Process Control, now simply OPC, a connectivity standard) has been the dominant communications standard for transferring data between devices on the shop floor and engineering‑level systems. In January 2004, the OPC Foundation began work on OPC Unified Architecture (OPC UA), a major revision to the standard that synchronizes OPC with ongoing advances in industrial automation.

The purpose of OPC has always been to increase the interoperability of industrial automation system components by standardizing communications among them. That purpose remains the same, but OPC UA improves on classic OPC in five important ways.

One: In classic OPC, real‑time data access, historical data access, and alarms and events are actually separate specifications that must be implemented separately. This results in duplicated programming work. OPC UA is a single, unified specification. Common tasks such as connecting and name‑space generation only need to be implemented once.

Two: Classic OPC is based on component object model (COM)/distributed COM (DCOM), an object model developed by Microsoft. OPC UA is independent of any vendor or platform. Its more flexible architecture uses Web Services and is not constrained by any single, underlying object model.

Three: OPC UA extends standardization down into embedded systems where classic OPC cannot reach.

Four: OPC UA extends standardization into higher levels of the enterprise. OPC UA can interface with business decision‑supporting software such as enterprise resource planning (ERP) systems using complex data types, whereas classic OPC cannot.

Five: OPC UA has built‑in, standardized security capabilities and can navigate through firewalls and across domains in a way that classic OPC can do only with the aid of proprietary add‑on software.

Baker’s dozen

The full, public domain specification for OPC UA will consist of 13 parts; the OPC Foundation has released 12 of these parts to industry ready to serve as the basis for product development. Eric Murphy, manager of OPC marketing at industrial connectivity supplier MatrikonOPC (www.matrikonopc.com), Edmonton, Alberta, Canada, and also a member of the OPC Foundation’s Technical Advisory Council, explains the release process. “From the OPC Foundation’s point of view,” says Murphy, “no part of the OPC UA specification is released until the specification document is complete, the working sample code has been developed, and a verification procedure is in place that can establish that the code is continuing to work in the field.”

To date, companies that have developed OPC UA clients, servers or both include ABB, Beckhoff Automation GmbH, Canary Labs, Iconics, MatrikonOPC, OSIsoft and Siemens AG.

Given the scope of OPC UA and of industrial automation generally, it is not surprising that OPC UA products vary considerably in the effort and knowledge needed to develop them. “A lot of the OPC UA early-adopter products were originally built to the classic OPC standard,” says MatrikonOPC’s Murphy. “Many of these can be made to talk OPC UA over Web Services with existing, verified code—wrappers, proxies, and other migration tools—available from the OPC Foundation. Others require vendor‑created code, and these go through additional verification.”

However, the full potential of OPC UA to take part in turning raw data into real knowledge is just beginning. “Full,
enterprise‑level OPC UA products that tie real‑time data, history, alarms and events, and a rich‑informational model are in the early stages of development,” says Murphy.

The trend for this kind of integration seems clear. Rob McGreevy, vice president of platforms and applications at U.K.-based automation supplier Invensys Operations Management Group (www.invensys.com), describes the OPC landscape: “The way that industrial automation is evolving depends on structured data. A lot of our customers have a diverse set of control systems and data sources. That’s what’s most interesting to us, and that’s what OPC UA will address.”

Marty Weil, martyweil@charter.net, is a freelance writer who covers manufacturing and automation.


Invensys Operations Management Group

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