Sensing presence of fire

Claim 2

Method to indicate presence of fire by testing an atmospheric sample comprising irradiating the sample with radiation by irradiating the sample by radiation in a spectral range in which the gaseous combustion products have absorption bands; sensing the spectral absorption characteristics of the irradiated sample to test for absorption within said bands and hence gaseous combustion products and deriving a gas analysis signal; sensing dispersion of irradiating radiation to test for dispersed particles in the atmospheric sample and delivering a particle signal; detecting coincidence of the gas analysis signal and the particle signal; and providing an output signal if and only if coincidence is dEtected.

Claim 3

Method according to claim 1, wherein the radiation is in a spectral range between 0.8 and 8.5 Mu .

Claim 4

Method according to claim 2, wherein the spectral range of the radiation includes the absorption bands of at least one of: carbon monoxide, carbon dioxide.

Claim 5

Method according to claim 1, further comprising the step of generating irradiating radiation from a single source; and delivering a portion of said radiation to irradiate the portion of the sample to carry out the dispersion sensing step and further directing another portion of said radiation to a portion of the sample to carry out the spectral absorption sensing step.

Claim 6

Method according to claim 4, wherein the step of generating irradiating radiation comprises the step of generating radiation in the spectral range between 0.8 and 8.5 Mu .

Claim 7

Method according to claim 4, wherein the step of generating irradiating radiation from the single source comprises generating radiation primarily including the spectral range in which at least one of: carbon monoxide; and carbon dioxide, have absorption bands.

Claim 8

Fire sensor comprising means (1) defining a measuring chamber (2, 5, 6): a radiation source (4) directing radiation into the measuring chamber; at least two photo-electric devices (7, 8), one photo-electric device (8) being located in the measuring chamber to receive direct radiation from said source (4) and being primarily sensitive to radiation in a spectral range in which the absorption bands of gaseous combustion products are present whereby, upon introduction of atmosphere containing combustion products, output from said photo-electric device will decrease due to absorption of gaseous combustion products in the spectral range, the other photo-electric device (7) being outside the path of direct radiation from said source, whereby radiation to said other device will increase due to dispersion of light from the source due to presence of particulate matter in the measuring chamber; and an electrical circuit, including a coincidence circuit (11), providing an output signal if and only if the directly irradiated photo-electric device (8) indicates decrease in radiation due to absorption of radiation and, simultaneously, the other photo-electric device (7) indicates an increase in radiation applied thereto due to dispersion of combustion products and hence dispersion of light derived from the source and applied to said second photo-electric device.

Claim 9

Fire sensor comprising means (1) defining a measuring chamber (2, 5, 6): a radiation source (4) directing radiation into the measuring chamber; at least two photo-electric devices (7, 8), one photo-electric device (8) being located in the measuring chamber to receive direct radiation from said source (4) and being primarily sensitive to radiation in a spectral range in which the absorption bands of gaseous combustion products are present whereby, upon introduction of atmosphere containing combustion products, output from said photo-electric device will decrease due to absorption of gaseous combustion products in the spectral range, the other photo-electric device (7) being outside the path of direct radiation from said source, whereby radiation to said other device will increase due to dispersion of light from the source due to presence of particulate matter in the measuring chamber; and an electrical circuit, including a coincidence circuit (11), providing an output signal if and only if the directly irradiated photo-electric device (8) indicates decrease in radiation due to absorption of radiation and, simultaneously, the other photo-electric device (7) indicates an increase in radiation applied thereto due to dispersion of combustion products and hence dispersion of light derived from the source and applied to said second photo-electric device.

Claim 10

Sensor according to claim 7, wherein the source comprises a semiconductor laser diode.

Claim 11

Sensor according to claim 8, wherein a single source (4) is provided, directing radiation into said chamber and directly irradiating said first photo-electric device (8), and providing indirect radiation, upon presence of particulate matter in said chamber, to said second photo-electric device (7).

Claim 12

Sensor according to claim 9, wherein said source comprises a semiconductor laser diode.

Claim 13

Sensor according to claim 10, wherein said semiconductor laser diode is a three-element laser diode.

Claim 14

Sensor according to claim 11, wherein said laser diode comprises Ga As P, Pb Sn Se, Cd Hg Te, Pb Sn Te, Pb Sn Se or Pb S Se.

Claim 15

Sensor according to claim 7, wherein said radiation source comprises a source directing radiation to the first photo-electric device (8) and a source directing radiation towards the second photo-electric device (7).

Claim 16

Sensor according to claim 7, wherein the photo-electric device (8) receiving direct radiation comprises a photo-electric transducer including tryglicinsulfate.

Claim 17

Sensor according to claim 7, wherein the photo-electric device (8) receiving direct radiation comprises a three-element photo diode including Cd, Hg, Te.

Claim 18

Sensor according to claim 7, wherein the electrical circuit comprises an AND-gate (14), the inputs of which are controlled by said photo-electric devices (7, 8).

Claim 19

Sensor according to claim 7, further comprising two threshold detectors (12, 13), one each connected to one of the photo-electric devices (7, 8), the threshold detector connected to the directly irradiated photo-electric device (8) providing an output signal when the output from said photoelectric device (8) indicates a drop below a predetermined irradiation threshold level; and the threshold detector (12) connected to the other photo-electric device (7) responsive to dispersion, providing an output signal when the dispersed light impinging on said second photo-electric device (7) exceeds a predetermined level; and wherein said electrical coincidence circuit comprises an AND-gate (14) controlled from the outputs of said threshold detectors.

Claim 20

Sensor according to claim 7, wherein the electrical circuit further comprises a timing circuit (16), said timing circuit being connected to the coincidence circuit (11) and to an alarm circuit and providing a time-delayed output to control the alarm circuit to provide an alarm signal if and only if a simultaneous increase in signal from said indirectly irradiated photo-electric device (7) and a decrease of irradiation of said directly irradiated photo-electric device (8) exceeds a predetermined time period as determined by said timing circuit (16).