False alarm resistant fire detector with improved performance
First Claim
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1. A fire detector having a low rate of generating false alarms, comprising:
- a CO2 fire detector module;
a smoke detector module adapted to measure a second property that is indicative of the presence of a fire;
an AND gate, having an output, having a first input connected to an output of the CO2 fire detector and having a second input connected to an output of the smoke detector module;
a clock, connected to the smoke detector module, for measuring a duration of each interval in which the smoke detector measures a smoke level exceeding a preselected smoke threshold level; and
alarm means, responsive to an output of the clock and the output of the AND gate, for producing an alarm if either of the following criteria are met;
the output of the clock exceeds a preselected clock threshold level, thereby indicating that the smoke level has exceeded the preselected smoke threshold level for longer than a preselected interval;
orthe output of the AND gate is high, indicating that a fire has been detected by both the CO2 detector and the smoke detector.
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Abstract
A fire detector having a greatly reduced frequency of generating false alarms. An AND gate is responsive to outputs from first and second fire detector modules that are responsive to the detection of first and second characteristics of a fire, respectively, to signal the detection of a fire if both of these characteristics have been detected. At least one override path is included to enable the occurrence of a particular type of fire to be signaled that would not otherwise be signaled by the output of said AND gate.
50 Citations
7 Claims
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1. A fire detector having a low rate of generating false alarms, comprising:
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a CO2 fire detector module; a smoke detector module adapted to measure a second property that is indicative of the presence of a fire; an AND gate, having an output, having a first input connected to an output of the CO2 fire detector and having a second input connected to an output of the smoke detector module; a clock, connected to the smoke detector module, for measuring a duration of each interval in which the smoke detector measures a smoke level exceeding a preselected smoke threshold level; and alarm means, responsive to an output of the clock and the output of the AND gate, for producing an alarm if either of the following criteria are met; the output of the clock exceeds a preselected clock threshold level, thereby indicating that the smoke level has exceeded the preselected smoke threshold level for longer than a preselected interval;
orthe output of the AND gate is high, indicating that a fire has been detected by both the CO2 detector and the smoke detector.
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2. A fire detector having a low rate of generating false alarms, comprising:
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a CO2 detector; a smoke detector; and a logic circuit for generating a fire alarm when either of the following criteria are met; the CO2 detector and the smoke detector detect two different conditions indicative of the occurrence of a fire at the same time;
ora temporal rate of change of carbon dioxide concentration exceeds a preselected threshold. - View Dependent Claims (3, 4)
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5. A method for generating a fire alarm, comprising the steps of:
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detecting carbon dioxide concentration; detecting a second condition indicative of the occurrence of a fire; and signaling the occurrence of a fire when either of the following conditions is met; carbon dioxide concentration and the second condition are both indicative of the occurrence of a fire;
orthe temporal rate of change of carbon dioxide concentration exceeds a preselected threshold. - View Dependent Claims (6, 7)
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Specification