Abstract A fire detector senses the change in a physical parameter indicative of a fire such as smoke, heat or the like and produces detection pulses in synchronism with an oscillator circuit when the change in the physical parameter exceeds a predetermined amount. A counting means counts the detection pulses and produces an output which triggers an alarm circuit when a predetermined number of consecutive detection pulses are counted. The count of the counting means is reset by a reset means whenever the detection pulses are nonconsecutive, that is, whenever an oscillator pulse is received without receipt of a corresponding detection pulse. By this means intermittent changes in the physical parameter which indicate some false alarm signal rather than a real fire do not produce the required number of consecutive detection pulses and do not set off the alarm circuit. On the other hand when a real fire occurs the circuit always counts detection pulses from the beginning of the detection of a fire because the counting means is reset each time a series of consecutive detection pulses less than the predetermined number ends.
Inventors
👤 Yukio Yamauchi
Bibliographic Details
Application Number—
JurisdictionUS
Data Sourcegoogle_patents
Last Synchronized2026-10-26 00:40
CPC Classifications
G; G08; G08B; G08B29/00; G08B29/18; G08B29/185
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
183 words
A count discriminating fire detection system comprising, in combination; an oscillator circuit for generating oscillating pulses at a predetermined frequency; a fire detection means connected to said oscillator circuit for detecting a change of more than a predetermined amount in a physical parameter indicative of a fire for producing detection pulses synchronous with said oscillating pulses; a counting means having an input terminal connected to said fire detection means and a reset terminal, for counting said detection pulses for producing an output upon counting a predetermined number said detection pulses and for resetting said counting upon application of a signal to said reset terminal; a reset means having a first input terminal connected to said fire detection means, a second input terminal connected to said oscillator circuit and an output terminal connected to said reset terminal of said counting means, for applying a signal to said reset terminal of said counting means upon receiving an oscillator pulse without receiving a detection pulse; and an alarm circuit connected to said counting means for producing a fire alarm when said counting means produces an output.
Claim 2
Dependent Claim
183 words
A count discriminating fire detection system comprising, in combination; an oscillator circuit for generating oscillating pulses at a predetermined frequency; a fire detection means connected to said oscillator circuit for detecting a change of more than a predetermined amount in a physical parameter indicative of a fire for producing detection pulses synchronous with said oscillating pulses; a counting means having an input terminal connected to said fire detection means and a reset terminal, for counting said detection pulses for producing an output upon counting a predetermined number said detection pulses and for resetting said counting upon application of a signal to said reset terminal; a reset means having a first input terminal connected to said fire detection means, a second input terminal connected to said oscillator circuit and an output terminal connected to said reset terminal of said counting means, for applying a signal to said reset terminal of said counting means upon receiving an oscillator pulse without receiving a detection pulse; and an alarm circuit connected to said counting means for producing a fire alarm when said counting means produces an output.
Claim 3
Dependent Claim
74 words
A fire detection system according to claim 1, wherein said fire detection means comprises: a fire sensor for detecting a change of more than a predetermined amount in a physical parameter indicative of a fire for producing a d.c. output; and an AND gate having a first input connected to said oscillator circuit and a second input connected to said fire sensor for converting said d.c. output of said fire sensor into detection pulses.
Claim 4
Dependent Claim
25 words
A fire detection system according to claim 1, wherein said reset means comprises an exclusive-OR gate and wherein said counting means comprises a resettable counter.
Claim 5
Dependent Claim
46 words
A fire detection system according to claim 3 wherein said reset means further comprises a delay circuit connected to the output of said exclusive-OR gate for absorbing an output of said exclusive-OR gate due to small time differences between said oscillating pulses and said detection pulses.
Claim 6
Dependent Claim
45 words
A fire detection system according to claim 3 wherein said resettable counter comprises a fixed voltage source and a shift register having a data terminal connected to said fixed voltage source and a clock input terminal connected to the output of said fire detection means.