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Smoke alarm

  • US 4,021,792 A
  • Filed: 06/23/1975
  • Issued: 05/03/1977
  • Est. Priority Date: 06/23/1975
  • Status: Expired due to Term
First Claim
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1. A smoke alarm for detecting smoke in air comprising:

  • a light shielded smoke chamber defining a generally closed space having a longitudinal axis with a first and second port provided in said chamber at each end of said longitudinal axis, and having a third port disposed on an axis substantially perpendicular to said longitudinal axis, each of said ports having a baffling means for preventing the entry of light without substantially interfering with the entry of smoke through each of said ports into said chamber, at least one of said baffling means being a reticulated foam layer disposed across one of said ports, said reticulated layer having a nonporous plate disposed thereon whereby light is substantially prevented from penetrating said layer while smoke is permitted to enter said layer and aperture through the sides of said layer;

    an array of louvered apertures proximately disposed to said third aperture, said array of apertures having louvers oriented with opposite inclinations whereby smoke flowing perpendicular to said longitudinal axis of said chamber is directed toward said third aperture regardless of direction of flow;

    a flue means for directing smoke flowing parallel to said longitudinal axis of said chamber into said first and second ports;

    an incandescant bulb and lens assembly to provide a beam of collimated light said bulb thermally coupled to a heat sink at selected portions of said bulb whereby vaporized matter within said incandescant bulb is induced to condense on said selected portions of said bulb thermally coupled to said heat sink and light produced by said bulb and directed into said collimated beam is substantially unattenuated by condensation of said vaporized matter;

    a first photoelectric cell to provide an electrical response upon the irradiation by light scattered from said collimated beam, said scattered light beam scattered by smoke dispersed into said chamber;

    a second photoelectric cell to produce an electrical response upon the radiation by light from said beam;

    a power supply to provide a source of electrical power;

    a wheatstone bridge having four circuit segments coupled to said power supply and grouped in a first and second series pair said first and second series pairs being coupled in parallel, said first series pair being said first and second photoelectric cell and said second series pair being low impedance electrical resistors, one of said resistors being a low impedance variable resistor, whereby said wheatstone bridge is substantially unaffected by changes in relative humidity;

    an alarm means coupled to said wheatstone bridge for producing an alarm signal when said first photoelectric cell responds to a measured increase of light scattered from smoke within said chamber and for silencing said alarm signal when said first photoelectric cell responds to a measured decrease of light scattered from smoke within said chamber;

    a relaxation oscillator coupled to said incandescant bulb, said relaxation oscillator being triggered when said incandescant bulb becomes open circuited, whereby a fail-safe signal is produced which is distinguishable from said alarm signal; and

    a coated wire having a predetermined optical scattering coefficient to simulate the scattering of light from smoke within said chamber, said wire removably disposed in said beam by a spring means and a shaft coupled to said wire, said shaft extending from said smoke alarm to allow manual depression to dispose said wire into said beam, said spring means for encouraging said wire from said beam when said shaft is not depressed.

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