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

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Street, Thomas T., Alexander, John I.
• Primary Examiner(s): Brigance, Gerald L.
• Application Number:
  US06/023,043
• Time in Patent Office: 712 Days
• Field of Search: 340/627, 340/628, 340/629, 340/630, 73/28, 235/92 PC, 235/92 EV, 364/555
• US Class Current: 340/627
• CPC Class Codes: G08B 17/00 Fire alarms; Alarms responsive to explosion
• CPC Class Codes: G08B 17/10 Actuation by presence of smoke or gases , e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means
• CPC Class Codes: G08B 17/113 Constructional details

Abstract

A fire detection system which includes an environmental sampling assembly upled to a programmable digital processor for detecting a threat of fire and reducing the occurrences of false alarms in a changing environment. The sampling assembly comprises a network of air ducts, a chamber, two sensors, and an exhaust fan. The processor includes two analog-to-digital (A/D) converters, a multiplexed digital summer, short and long-term storage mediums, a signal magnitude comparator, logic circuitry, and a timing generator. The fan continuously draws ambient air through the air ducts and the chamber. Sensors within the chamber sample the air. If the sensors detect particulates of combustion in the air, the sensors provide electrical signals of varying amplitudes, which amplitudes depend on the number and sizes of the particulates being sampled, to the A/D converters of the processor. One of the sensors also feeds its signals to the fan motor for increasing the speed of the fan, thereby clearing the chamber and drawing air through the chamber at a faster rate for a more vigorous sampling of the environment. The processor may be programmed to suit a specific environment. It monitors the amplitudes of the signals from the assembly and the rate and duration of changes in the amplitudes by comparing signal samples at successive intervals of time. The processor activates a four-level, visual alarm which indicates the progression or regression of a threat of fire.

Claims

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.

2. The system of claim 1 wherein said two or more sensing means includes first and second sensors oppositely disposed within said chamber, each of said sensors converting the density of said particulate matter into said electrical signals.

3. The system of claim 1 wherein said means for forcing said air through said duct means includes a fan, said fan being driven by a control circuit which receives said electrical signal from said first sensing means and increases said rate of speed as the particulate matter increases within said chamber, said increased rate of speed being decreased as the increased particulate matter decreases within said chamber.

4. The system of claim 1 wherein said signal processing means includes:

analog-to-digital converter means for receiving and digitizing the electrical signals from said sensing means over successive intervals of time;

multiplexed digital summer means for receiving and summing outputs of said analog-to-digital converter means for each of said intervals of time;

interval-magnitude logic means for receiving and decoding the amplitude of the output of said multiplexed digital summer means to represent a percentage of the maximum possible amplitude of said output of said multiplexed digital summer means;

short-term storage means for successively receiving and storing the output of said multiplexed digital summer means for one of said intervals of time;

magnitude comparator means for comparing the magnitude of the output of said short-term storage means with the output of said multiplexed digital summer means to determine if the amplitude of said signals from said sensing means increases, is constant, or decreases;

long-term storage means for receiving and storing the output of said magnitude comparator means for a number of most recent successive intervals of time;

trend-decision logic means for receiving the output of said magnitude comparator means and counting each determination of increase, remain constant, and decrease in amplitude of the signals from the sensing means to form an average count of the amplitude of said signals, and for decoding said average count to represent the tendency of the amplitude of said signals to increase, decrease or remain constant; and

threat-decision logic means for receiving the outputs from said interval-magnitude logic means, said long-term storage means, and said trend-decision logic means, and for activating an alarm system, having a number of levels of alarm, to indicate increasing and decreasing amounts of said particulate matter in the environment, said amounts corresponding to an increasing and decreasing threat of fire.