| 摘要 |
A fire detection system has a detector for sensing optical radiation from a spark or flame or hot spot and an optical waveguide comprising an elongate hollow tube, having an inlet end portion for placement in a hostile, hazardous environment, and having an outlet end portion for emitting light rays to the detector and for placement in a benign, non-hazardous environment, and having a reflective inner surface forming a passage for transmitting the optical radiation from the tube inlet end portion to the tube outlet end portion by successive internal reflections. The elongate hollow waveguide tube is sealed at the inlet end portion by a lens which admits the optical radiation to the tube; and at the outlet end typically by the detector. The sealed tube is filled with an inert gas, such as nitrogen, which helps to maintain the reflective interior surface of the tube.
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