Detecting the presence of a fire

Details Detecting the presence of a fire Detecting the presence of a fire

1994-09-01

1997-03-18

Hannaher, Constantine

Radiant energy

Invisible radiant energy responsive electric signalling

Infrared responsive

G08B 1712

Patent

active

056125372

ABSTRACT:
Apparatus for detecting the presence of a fire includes a pair of detectors for radiation characteristic of a fire, e.g. at 4.3 microns, and a further detector for radiation characteristic of a black body, e.g. at 3.8 microns. Filters select the detector output components at flame flicker frequencies. The filtered outputs of the detector pair are cross-correlated to produce a relatively noise-free signal. This signal is divided by a factor obtained by cross-correlating the further detector filtered output with the average of the detector pair filtered outputs. The result of the division is applied to a threshold-responsive circuit. Thus the relatively noise-free signal is effectively subjected to a threshold which is proportional to the degree of similarity between the variations with time of the output signal of the further detector and the output signals of the detector pair.

REFERENCES:
patent: 4553031 (1985-11-01), Cholin et al.
patent: 5373159 (1994-12-01), Goldenberg et al.

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