Remote switch uses no-power fiber-optic lin

-October 10, 1996

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Remote switch uses no-power fiber-optic link

Shyam Tiwari, IGKAR, Kalpakkam, India

  The heavy-duty switching device in Figure 1 counts the number of products manufactured and rolled out of a production line per hour. The switch is useful for counting rolling heavy objects or materials weighing one to several thousand kilograms. It generates one pulse per product (no false outputs generated) and provides a count rate as high as 3600 parts per hour. The switch uses a low-cost, commercial, piezoelectric gas lighter, commonly used for kitchen or gas-grill burners. A rolling object in the production line triggers the device, and a simple fiber-optic link transmits the ignition event to a receiver.

  The flash corona of the gas lighter couples to a multimode, fused-silica optical fiber; other types of low-cost fibers work equally well. The light flash transmits through the fiber-optic link over the large distances commonly encountered in the manufacturing industry. Because the piezoelectric lighter needs no external power, the device works without a power source. The switch converts the mechanical energy from the rolling mass into a high-voltage pulse, which, in turn, generates a microsecond-duration light flash. Until the rolling object releases the trigger, no new flashes can appear; thus, you obtain one flash per material count. The system uses a commercially available photodetector and simple event-counter hardware, along with a PC-based data-acquisition system. The gas-lighter flash tip and the optical fiber are enclosed in a glass cavity filled with dry air for protection against environmental effects. (DI #1935)

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