ApplicationNo. 05/621338 filed on 10/10/1975
US Classes:250/373, With means to transmission-test contained fluent material340/630, Photoelectric356/434, Photoelectric (e.g., sequential viewing)356/439, Contained356/51INFRARED AND ULTRAVIOLET
ExaminersPrimary: Smith, Alfred E.
Assistant: Grigsby, T. N.
Attorney, Agent or Firm
International ClassesG08B 17/103 (20060101)
G01N 21/53 (20060101)
G01N 21/47 (20060101)
AbstractCollimated ultraviolet light radiation at wavelengths of 2537A and 3129A is alternately directed across the space to be monitored for smoke indicative of a fire. A "cats eye" mirror at the far side of the monitored space returns the ultraviolet rays to a photomultiplier detector adjacent the light source. Smoke, for example pine smoke having a particle mean diameter of 1.4 to 3.0 micrometers, will attenuate the shorter wavelength beam much more than the longer wavelength beam. Approximately 1.3 times greater attenuation is inflicted on the 2537A beam than on the 3129A by the pine smoke. Thus, returning beam signals having this ratio of signal levels will provide an indication of a pine fire. Particles of a different diameter intercepting the beam will produce a different ratio of attenuated signals.