Graviner Limited

David N Ball

Robert L Farquhar

A fire or explosion detection system for discriminating between radiation produced by a source of fire or explosion to be detected (e.g. a hydrocarbon fire) and radiation produced by a source not to be detected (e.g. an incendiary ammunition and or pyrophoric reaction between an aircraft skin and an inert round) is disclosed. The radiation detectors are respectively responsive to the intensity of radiation in narrow wavelength bands at 0.96 and 4.4 microns. Two threshold units produce respective electrical signals only when the outputs of the detectors exceed respective predetermined values. In addition, a rate of rise unit produces an electrical signal only when the rate of rise of the output of one of the detectors exceeds a predetermined value. An output gate receives these three electrical signals and produces an output to a delay unit which in turn produces a fire or explosion indicating output only when the output of the gate continuously exists for at least a predetermined period of time. It is found that only fires or explosions to be detected will cause the detectors to produce outputs which will maintain the output of the gate for the length of the delay period.

Fire or explosion detection

The invention is for discriminating between the fire or explosion of an ammunition round and the fire or explosion which may then take place in the object struck by the round, and for initiating suppression of the latter fire or explosion only. Short wavelength radiation detectors feed a ratio detector which produces a logical output dependent on whether or not the color temperature of an event being monitored is above or below a fixed value. If the event is an exploding round then this will take the color temperature above this fixed value. A threshold unit and a rate of rise unit produce logical outputs dependent on whether the magnitude and rate of rise of the output of one of these two detectors are above or below fixed values. An infra-red detector detects radiation at a wavelength characteristic of a fire in the object; its output rises relatively slowly. If this detector detects a fire at this wavelength, it enables an AND gate but the gate does not initiate fire suppression if the ratio unit indicates that the color temperature is above the fixed value, because this signifies that the event is an exploding round. Fire suppression cannot take place until after the color temperature has fallen (and after a fixed delay produced by a monostable). The threshold unit and the rate of rise unit provide protection against incorrect initiation of fire suppression in conditions when the exploding round does not produce a color temperature clearly in excess of the fixed value.

Fire and explosion detection and suppression

Photoelectric type detector responds to radiation in a narrow wavelength band characteristic of a fire or explosion, and a slow-response detector, such as a thermopile, is sensitive to radiation in a different narrow wavelength band centered at, for example, 4.4 microns, again characteristic of the same fire or explosion. The electrical outputs of the detectors are fed into a ratio unit which causes an AND gate to produce a fire or explosion indicating output only when the ratio of the output of the thermopile detector to the output of the other detector exceeds a predetermined value.

Two channel comparison-type fire or explosion detecting system

A system for discriminating between radiation produced by a source of fire or explosion to be detected and that produced by a source not to be detected, comprises two radiation detectors 10, 12 respectively responsive to the intensity of radiation in different and spaced apart narrow wavelength bands. A rate of rise unit 22 and a threshold unit 24 responsive to detector 12 produce signals of a first binary type when the rate of, and the value of, the radiation intensity exceed predetermined values. A ratio unit 16 measures the ratio of the intensities of the radiation received by the two detectors and produces a signal of the opposite binary type when the ratio indicates that the source of radiation is a fire or explosion to which the system is not to respond. An AND gate 36 produces a fire and explosion indicating output only when the signals of the first type exist in the absence of the signal of the opposite type.

Fire and explosion detection

A system for discriminating between radiation produced by a source of fire or explosion to be detected and radiation produced by a source not to be detected comprises two radiation detectors respectively responsive to the intensity of radiation in different wavelength bands to product respective electrical outputs, one band being relatively broad and including the other which is relatively narrow. A rate of rise unit and a threshold unit responsive to the broad band detector produce signals of one binary type when the rate of rise of, and the value of, the intensity of the radiation received by that detector exceed predetermined values. A ratio unit measures the ratio of the intensities of the radiation respectively received by both detectors and produces a signal of the opposite binary type when the ratio indicates that the source of the radiation is a fire or explosion to which the system is not to respond. An AND gate produces a fire and explosion indicating output only when the signals of the first binary type exist in the absence of the signal of the opposite binary type.

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Slough, United Kingdom

David N Ball