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Shared intelligence guides control system

An open automation infrastructure uses Ethernet to transmit information

By David J. Bak, International Editor -- Design News, October 18, 1999

Grenoble, France-To provide security functions throughout one of its industrial sites near here, Hewlett-Packard has implemented a control system architecture based on programmable logic controllers (PLCs). Designed to end dependence on a centralized system, and to limit cable lengths, the new system is organized around a "distributed intelligence" concept. A critical component to its success proved to be Schneider Electric's OPC Factory Server (OFS), the first product of Schneider's Transparent Factory™ open automation infrastructure.

Hewlett-Packard's d'Eybens manufacturing site processes masses of strategic and confidential information requiring high building security. Prior to installing the new architecture, HP used a centralized control system running on an industrial PC fitted with various I/O cards. Cables linked these I/O cards to the five buildings on the managed site via a star configuration.

"After ten years of operation," says HP Systems Engineer Jack Abisset, "we were faced with a huge mass of cables running over several kilometers--a veritable octopus, impossible to manage as the documentation got more out of date as it grew." Abisset adds that the power supply would often be cut off during storms. As the organization was centralized, such faults meant a complete breakdown. "The overall philosophy had to be rethought," he explains, "not to mention our need to solve the Y2K problem."

For architectural simplicity, all information supplied to the supervisor travels over the site’s Ethernet TCP/IP network. Communication between the PLCs and the supervisor depends on Schneider Electric’s OPC (OLE for Processor Control) Factory Server, based on the standard OLE/COM interface from Microsoft.

The chosen architecture. The new system integrates Schneider Premium PLCs with PC Vue supervisory software by Arc Informatique. It features two identical system stations with full redundancy functionality built into the PC Vue software. One station operates as the running system for the security teams; the other is used for system administration by a maintenance service technician. These two stations, both of which run the PC Vue software, link to the company Ethernet data network.

A master PLC resides in each of the five buildings. To reach isolated points, a second PLC links to the master by a Fipio network. "This local network never leaves the building," Abisset points out. "We made every effort to only install it where necessary in view of our need to keep cable lengths short."

These PLCs have the main task of forwarding the data collected in the buildings (temperature, tank levels, etc.) back to the supervisor database using the company Ethernet. As Abisset explains, "Our idea was to use our own means of communication, as we are familiar with it. But that solution was only made possible by the fact that Schneider could offer an Ethernet coupler that was fully TCP/IP compatible.

OPC technology. Communication between PLCs and the supervisor is via OFC server, the OPC client/server architecture developed by Schneider Electric, with the client (developed by Arc Informatique) installed physically on the PCs running the supervisor. Without OPC, it would have been necessary to program a server station in each building with special purpose communications controllers.

Because the new system embraces market standards, it gives HP uncommon modularity. This, in turn, has enabled the company to increase the number and type of points monitored in the buildings. The system already has more than 700 inputs/outputs with a goal of 1,000. Another fundamental feature is the openness this kind of solution offers. In effect, using the TCP/IP protocol makes it possible to envision new perspectives such as remote site supervision, or the ability to network security information from all Hewlett-Packard manufacturing sites.

Additional details…Contact Schneider Electric's OPC Factory Server, One High St., North Andover, MA 01845, (978) 975-9054.

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