Method of detecting a fire of open uncontrolled flames

• US 4,866,420 A
• Filed: 04/26/1988
• Issued: 09/12/1989
• Est. Priority Date: 04/26/1988
• Status: Expired due to Term

• Current Assignee: Meggitt Safety Systems, Inc. (Meggitt PLC)
• Original Assignee: Systron Donner Corporation
• Inventors: Meyer, Robert H. Jr.
• Primary Examiner(s): Swann, III, Glen R.
• Assistant Examiner(s): Mullen, Jr., Thomas J.
• Application Number:
  US07/186,155
• Time in Patent Office: 504 Days
• Field of Search: 340/578, 340/587, 250/339, 250/554, 250/340
• US Class Current: 340/578
• CPC Class Codes: F23N 2223/08 Microprocessor; Microcomputer
• CPC Class Codes: F23N 2229/08 detecting flame flicker
• CPC Class Codes: F23N 5/082 using electronic means
• CPC Class Codes: G08B 17/12 Actuation by presence of radiation or particles, e.g. of infrared radiation or of ions

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.

Claims

1. 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.

2. 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.

3. A method as in claim 2 where said decibel amount is 7.5.

4. 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?

5. A method as in claim 4 where said number of maximum deviations in step 2 is four.

6. A method as in claim 1 where said time period is no more than 2 seconds.

7. A method as in claim 1 where the radiation detection wavelength of said detector means is centered at 0.95 uM.

8. A method as in claim 1 where the radiation wavelength spectrum of said detector means lies within the infrared spectrum.

9. A method as in claim 1 where said curve is normalized for a maximum at 0 Hz and a minimum at substantially 25 Hz.

10. A method as in claim 1 where said time period is greater than a rise time of said fire.

11. 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.