GB1329430A - Apparatus for detecting fire or flames - Google Patents

Abstract

1329430 Fire alarms CERBERUS AG 3 Dec 1970 [3 Dec 1969] 57473/70 Heading G4N [Also in Divisions G1 and H1] A fire alarm is generated by the outputs from two photo electric devices of differing spectral sensitivities differing in at least one polarity from a predetermined value by not less than a predetermined amount. The devices may be photo-voltaic or photo-conductive and may be connected in series, parallel, or parallel relationship in circuits including ballast resistors. The alarm signal may be generated only in response to flicker frequencies. Flicker frequencies in the difference of the outputs from red and blue responsive photo cells 2, 3 are applied to an amplitude discriminator 7 to operate an alarm and/or optical indicator. In Fig. 2 blue and red photoconductive elements are connected to ballast resistor 14 and an analyser 10. In further embodiments two reflection filters with different spectral reflection characteristics (29, 30, Fig. 9, not shown) or a dichroic filter (31, Fig. 10, not shown) are employed and arranged so that each detector receives light from a different'part of the spectrum. Alternatively the photo-electric elements may be in the form of photoresistances on a common base material (21, Fig. 7, not shown) and covered by red or blue optical filters. The effect of unwanted light, such as sunlight, may be eliminated by employing a mechanically movable screening device (26, Fig. 8, not shown) in such a way that one or both of the photoelectric devices may be partially screened. In both cases the effect of the unwanted light is eliminated by making the outputs of the photoelectric devices equal. Thus light from any other source will create an unequal signal. In a further embodiment (Fig. 12, not shown) a number of pairs of photoelectric devices of differing spectral sensitivities are connected in series and arranged so that each pair receives light from a different direction. In another embodiment an integrator is used to eliminate short duration disturbances since the alarm will then only be set off when a predetermined value is exceeded for a specified length of time. Furthermore a locking or latching circuit is included so that once the alarm is set off it is automatically held in an "on" condition and can be re-set from a central station. The apparatus can be tested by emitting a signal from the central station to produce alarm stimulation in the device so that the device is enabled to emit an alarm signal that can be registered in the central station.