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Processor-aided fire detector

  • US 4,254,414 A
  • Filed: 03/22/1979
  • Issued: 03/03/1981
  • Est. Priority Date: 03/22/1979
  • Status: Expired due to Term
First Claim
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1. A system for detecting a threat of fire in a frequently changing environment and discriminating against false alarms comprising:

  • means for sampling ambient air to detect an average amount of particulate matter in the environment, said sampling means including;

    duct means for conveying a common flow of said ambient air;

    a chamber coupled to said duct means for collecting samples of said ambient air;

    siphoning means coupled between said duct means and said chamber for abstracting said samples of the ambient air;

    suctioning means coupled between said chamber and said duct means for returning the samples of the ambient air to said common flow in said duct means; and

    means for forcing said ambient air through said duct means at a rate of speed, said rate being increased as the particulate matter increases within said chamber to more vigorously sample the ambient air and to determine an average amount of said particulate matter in the environment, said increased rate being decreased as the increased particulate matter decreases within said chamber, said means for forcing the ambient air using different rates of speed for determining a required time for environmental conditions within said chamber to be similar to environmental conditions outside the chamber, such that the required time effectively averages the environmental conditions within the chamber to determine if the environmental conditions outside the chamber present a threat of fire;

    two or more sensing means disposed within said sampling means for converting the amount of said particulate matter into electrical signals whose amplitudes are representative of the density of the particulate matter, a first of said sensing means feeding its signals to said means for forcing the ambient air for changing said rate of speed; and

    signal processing means for receiving said electrical signals from said two or more sensing means to monitor information comprising a change in the amplitudes of said signals as indications of the progressive and regressive levels of a threat of fire, said signal processing means for storing the information over successive time intervals, and comprising subsequently stored information with previously stored information to determine a rate at which the amounts of particulate matter in the environment increase and decrease, and instantaneous magnitude of the particulate matter in the environment, and a duration of time during which said amounts of particulate matter exist in the environment,said system determing a normal environmental condition over a period of time and distinguishing a short-term abnormal environmental condition from a long-term threat of fire.

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