US4866420A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method of detecting a fire of open uncontrolled flames
Assignee: Meggitt Safety Systems Inc
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Filing: 1988-04-26
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Granted: 1989-09-12
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Expires: 2008-04-26
Abstract
Abstract A method of detecting fires utilizing its flicker frequency spectrum provides a standard theoretical flicker frequency spectrum which is compared to the real time spectrum over a 2 second time period. The comparison includes whether or not the real time fire spectrum deviates from the idealized fire spectrum by a minimum amount and has further discrimination against false fire signals, including the extent of time of the real time spectrum is outside a predetermined window and a limit on maximum deviations.
Inventors
- 👤 Robert H. Meyer, Jr.
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 23:52
CPC Classifications
G; G08; G08B; G08B17/00; G08B17/12; F; F23; F23N; F23N5/00; F23N5/02; F23N5/08; F23N5/082; F23N2223/00; F23N2223/08; F23N2229/00; F23N2229/08
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
163 words
A method of detecting a fire of open uncontrolled flames having a spectrum of flicker frequencies, which are the modulations of radiation of particular wavelengths of said fire, said flicker frequencies being in the range of substantially D.C. to 7 Hz where a photodiode detector is responsive to said flicker spectrum to produce an output signal, comprising the following steps: determining a theoretical said spectrum in the form of a double exponential curve of frequencies and related amplitudes, said curve representing an idealized theoretical said fire; sampling said detector signal over a sufficient time period to provide flicker frequency data from substantially one Hz, which satisfies a minimum Nyquist rate and with a sampling rate to provide higher flicker frequencies to provide a real time spectrum of said fire; and selecting criteria referenced to said curve which consist of at least (a) a limit of deviation of said real time fire from said idealized fire and (b) a discrimination against false fire signals.
Claim 2
Independent Claim
163 words
A method of detecting a fire of open uncontrolled flames having a spectrum of flicker frequencies, which are the modulations of radiation of particular wavelengths of said fire, said flicker frequencies being in the range of substantially D.C. to 7 Hz where a photodiode detector is responsive to said flicker spectrum to produce an output signal, comprising the following steps: determining a theoretical said spectrum in the form of a double exponential curve of frequencies and related amplitudes, said curve representing an idealized theoretical said fire; sampling said detector signal over a sufficient time period to provide flicker frequency data from substantially one Hz, which satisfies a minimum Nyquist rate and with a sampling rate to provide higher flicker frequencies to provide a real time spectrum of said fire; and selecting criteria referenced to said curve which consist of at least (a) a limit of deviation of said real time fire from said idealized fire and (b) a discrimination against false fire signals.
Claim 3
Dependent Claim
29 words
A method as in claim 1 where said criterion "a)" is a standard deviation from said curve by said real time spectrum of less than a predetermined decibel amount.
Claim 4
Dependent Claim
12 words
A method as in claim 2 where said decibel amount is 7.5.
Claim 5
Dependent Claim
49 words
A method as in claim 1 where said curve has a predetermined bandwidth and said criterion "b)" includes (1) is the real time spectrum outside of a 20 dB window less than substantially 19% of said bandwidth? (2) are at least two maximum deviations each less than 25 dB?
Claim 6
Dependent Claim
17 words
A method as in claim 4 where said number of maximum deviations in step 2 is four.
Claim 7
Dependent Claim
16 words
A method as in claim 1 where said time period is no more than 2 seconds.
Claim 8
Dependent Claim
20 words
A method as in claim 1 where the radiation detection wavelength of said detector means is centered at 0.95 uM.
Claim 9
Dependent Claim
20 words
A method as in claim 1 where the radiation wavelength spectrum of said detector means lies within the infrared spectrum.
Claim 10
Dependent Claim
24 words
A method as in claim 1 where said curve is normalized for a maximum at 0 Hz and a minimum at substantially 25 Hz.
Claim 11
Dependent Claim
19 words
A method as in claim 1 where said time period is greater than a rise time of said fire.
Claim 12
Independent Claim
170 words
A method of detecting a fire of open uncontrolled flames having a spectrum of flicker frequencies, which are the modulations of radiation of particular wavelengths of said fire, said flicker frequencies being in the range of substantially D.C. to 7 Hz where a photodiode detector is responsive to said flicker spectrum to produce an output signal, comprising the following steps: determining a theoretical said spectrum in the form of a curve of frequencies and related amplitudes, said curve representing an idealized theoretical said fire; sampling said detector signal over a sufficient time period to provide flicker frequency data from substantially one Hz, which satisfies a minimum Nyquist rate and with a sampling rate to provide higher flicker frequencies to provide a real time spectrum of said fire; and selecting criteria referenced to said curve which consist of at least (a) a limit of deviation of said real time fire from said idealized fire of a standard deviation of less than 7.5 decibels and (b) a discrimination against false fire signals.
Claim 13
Independent Claim
170 words
A method of detecting a fire of open uncontrolled flames having a spectrum of flicker frequencies, which are the modulations of radiation of particular wavelengths of said fire, said flicker frequencies being in the range of substantially D.C. to 7 Hz where a photodiode detector is responsive to said flicker spectrum to produce an output signal, comprising the following steps: determining a theoretical said spectrum in the form of a curve of frequencies and related amplitudes, said curve representing an idealized theoretical said fire; sampling said detector signal over a sufficient time period to provide flicker frequency data from substantially one Hz, which satisfies a minimum Nyquist rate and with a sampling rate to provide higher flicker frequencies to provide a real time spectrum of said fire; and selecting criteria referenced to said curve which consist of at least (a) a limit of deviation of said real time fire from said idealized fire of a standard deviation of less than 7.5 decibels and (b) a discrimination against false fire signals.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1992-09-11 | 1993-03-13 | 1993-09-12 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-09-11 | 1997-03-13 | 1997-09-12 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-09-11 | 2001-03-13 | 2001-09-12 | $7700.00 | Window Closed / Lapsed |