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Fiber Optics Monitors Emergency Systems

Photonics Spectra
Sep 1999
Robert C. Pini

To help guarantee the reliability of its emergency power system, San Jose International Airport in California is using a fiber optic network to monitor its backup generators. More than 10 million people pass through the airport annually, and they depend on the lighting and communications systems to operate. If the utility grid drops into a black hole, the airport can switch on its four emergency generators, assuring passengers' safety. In those cases, the emergency system cannot be allowed to fail.

Previously, the generators could not be monitored through a single control system. Airport managers recognized the need to automate the monitoring through a central control point.

The present system does just that, tying together the generators across a network of data-gathering nodes that transmit information along a fiber optic cable -- and over the sprawling facility -- to a control center that also monitors critical building systems.

"Fiber optics was clearly the best choice," said Chris Smith, vice president of business development at Electronic Systems USA in Louisville, Ky., which contracted with the airport to do the improvements. The firm designs, manufactures and installs building control systems for commercial, institutional and industrial needs.

"We don't need the bandwidth [of fiber optics], but we need the security," Smith said. Fiber optics is immune to the electromagnetic noise that can interfere with high-speed data transmission over copper wires, he explained. Moreover, copper wires installed in underground conduits are susceptible to voltage surges from nearby electrical equipment or lightning strikes. Such a surge could cut communication between the control center and equipment, making it impossible to start the generators when they are needed most.

Smart communication

Smith turned to Raytheon Commercial Electronics' Control-By-Light Div. for the network system. "Raytheon's product is designed specifically to function with LonWorks," he said. The LonWorks technology, which was developed by Echelon Corp. of Palo Alto, Calif., is an open standard protocol that makes it possible for smart devices to communicate even if they were made by different manufacturers. The system at San Jose uses a network with about 30 nodes that transmit data over the fiber. Routers regenerate digital signals and convert them to be carried on copper wire.

When a node sends a message, it sends it around the network both ways. That increases reliability, fault tolerance and safety, explained Smith. In the event of a fiber break, the message still can reach its destination, and the system alerts an operator automatically.

At the airport, superintendent Jim Harvey said he is satisfied with the system, which has worked smoothly during power failures since it was installed in June.

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