Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Patent
1996-04-04
1998-02-17
Fields, Carolyn E.
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
G01M 2159
Patent
active
057193975
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an improved method and device for detecting the presence of a target material, e.g. gas, in a fluent composition typically comprising a mixture of gases. The invention is expected to have particular relevance to a monitor for carbon monoxide but the principles to be described will readily be seen to be usable with a wide range of target gases or even for the detection of smoke.
BACKGROUND ART
There is currently a need for a low-cost carbon monoxide detector which may be used in the home, motor car and/or work environments. In U.S. Pat. No. 5,070,244 there is disclosed a method of and apparatus for detecting the presence of a gas within an atmosphere containing the gas. The invention has particular application in the detection of a combustible gas in air but discloses broader applications for the detection of the presence of any gas, e.g. an explosive or toxic gas, in an atmosphere containing the gas. This known invention involves beaming infra-red radiation e.g. from a conventional incandescent lamp, through a chamber containing the atmosphere and detecting, e.g. in a pyroelectric dectector, the level of radiation that impinges on an infra-red detector within the chamber.
An aim of the present is to provide an improved method of detecting a substance in fluent material, preferably comprising a mixture of gases, which makes use of established low-cost electronic and optical components.
DISCLOSURE OF THE INVENTION
According to one aspect of the present invention apparatus for detecting the presence of a target material, e.g. gas, in a fluent composition, preferably comprising a mixture of gases, comprising a source of electromagnetic radiation, detector means for detecting said electromagnetic radiation from said source after passage through said fluent composition and processing means for detecting changes in the output of said detector means occasioned by partial absorption of the electromagnetic radiation from said source by the target material, is characterised in that the detector means comprises at least two spaced apart opto-electric transducers for respectively detecting selected frequency bands for which the target material has different specific absorbtivities, and in that the apparatus further comprises dispersive means for presenting the electromagnetic radiation at each of said different frequency bands to a respective one of said opto-electric transducers.
Apparatus in accordance with this invention works by detecting a relative change in electromagnetic radiation emitted by the source due to absorption of that radiation by the target material or gas. In the case of a carbon monoxide detector infra-red radiation is employed since carbon monoxide absorbs strongly between 4.5 and 5 microns. The presence of a strong absorption band at this frequency can be used as a reliable signature for the presence of CO. Carbon dioxide also has an absorption band between 4 and 4.5 microns and a carbon monoxide detector must be able to discriminate between the two. Other exotic and poisonous gases also have absorption bands in this range and the principle described here can also be extended to other gases (e.g. NO). The apparatus can also be used as a smoke detector, e.g. for detecting the presence or otherwise of smoke by itself, or the detection simultaneously of the presence of smoke and one or more other gaseous means, in a mixture of gases, e.g. the atmosphere. The apparatus could possibly also be used for detection of a target material in a liquid medium (the fluent composition).
According to another aspect of the present invention a method of detecting the presence of a target material (e.g. a target gas) in a fluent composition (preferably comprising a mixture of gases, e.g. the atmosphere) comprising detecting in detector means electromagnetic radiation emitted from a source after it has passed through said fluent composition, is characterised in that the emitted electromagnetic radiation is dispersed prior to the detector means into bands of different f
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Hallett William A.
Silver Joshua D.
Fields Carolyn E.
Spectrasense Limited
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