GB2192710A

GB2192710A - Gas sensor

Info

Publication number: GB2192710A
Application number: GB08716542A
Authority: GB
Inventors: Dr Patrick Timothy Moseley; Dr David Edward Williams; Dr John Oliver Wilson Norris
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1986-07-17
Filing date: 1987-07-14
Publication date: 1988-01-20
Anticipated expiration: 2007-07-14
Also published as: GB2192710B; GB8716542D0; GB8617430D0

Abstract

The gas sensor includes an optical device 1 having a coating 2 of a material which is capable of catalysing a reaction involving the gas when the gas is in the presence of the material such that a temperature change is produced. The gas may be, for example, a combustible gas such as H2, CO or H2S. The material may be, for example, one capable of catalysing combustion of a combustible gas. By way of example the optical device may be an integrated optical device (e.g. a microchip having both electronic and optical properties) or an optical fibre. The temperature change may be detected by anti-Stokes Ramon radiation detection. Alternatively, the optical device or coating includes a substance such that temperature dependent colour change, or refractive index change or fluorescence decay lifetime change occurs. Alternatively, the sensor includes an infra-red phosphor. <IMAGE>

Description

SPECIFICATION Sensor The present invention relates to- sensors and more particularly to sensors finding application in the detection of gases (e.g. combustible gases).

According to one aspect of the present invention there is provided a gas sensor four the detection of a gas which sensor includes an optical device having a coating of a material which is capable of catalysing a reaction involving the gas when the gas is in the presence of the material such that a temperature change is produced.

The term optical device as used in this Specification embraces, for example, an integrated optical device (e.g. a microchip having both electronic and optical properties) and an optical fibre.

In accordance with one embodiment of the present invention there is provided a gas sensor for the detection of a combustible gas which sensor includes an optical device having a coating of a material which is capable of catalysing combustion of the combustible gas when the combustible gas is in the presence of the gas such that a temperature change is produced.

In the circumstance where the material catalyses the combustion of a combustible gas, the temperature change produced will generally be a temperature rise.

Temperature change produced in accordance with the present invention may be detected by any suitable means. Thus, for example antistokes raman radiation detection may be employed.

Further, by way of example, a substance may be included in the optical-device or coating such that temperature dependent colour change, or refractive: index change or fluorescence decay lifetime change may occur when the temperature change is produced and the temperature change may thus be detected by measuring colour change, refractive index change or fluorescence decay lifetime change.

By way of further example, an infra-red phosphor may be optionally used in conjunction with the coating. Thus, for example, a temperature rise produced by combustion of a combustible gas mat be used to cause an infra-red phosphor to produce infra-red radiation which may be detected by a suitable detection means.

Further, by way of example, by use of a suitable technique (such as Optical Time Domain Reflectrometry) the temperature distribution along the length of an optical device (such as optical fibre) may be measured.

Thus, a distributed gas sensor may be constructed. In such a sensor, the coating could be applied along the whole length of an optical device (e.g. along the whole length of an optical fibre) or could be applied at appropri ate intervals along the length (e.g. a length of a few centimetres every few metres).

A sensor in accordance wilh the present invention may be used to detect a selected combustible gas at low concentration, for example at low concentration in air.

Examples of gases which may be detected in air in accordance with the present invention are H2, CO and H2S.

Examples of materials capable of catalysing combustion of gases are precious metal catalysts such as platinum and palladium and mixtures thereof.

The material may include a support forth catalyst e.g. tin oxide-and the catalyst may be finely divided.

According to another aspect of the present invention there is provided a method for the detection of a gas which includes contacting the gas with a gas sensor, said gas sensor including an optical device having a coating of a material which is capable of catalysing a reaction involving the gas when the gas is n the presence of the material such that a tem- perature change is produced and measuring the temperature change.

In accordance with one embodiment of the preceding aspect of the present invention there is provided a method for the detection of a combustible gas which includes contacting the gas with a gas sensor, said gas sensor including an optical device having a coating of a material which is capable of catalysing combustion of the combustible gas when the combustible gas is in the presence of the material such that a temperature change is produced and measuring the temperature change.

The combustion of combustible gas may be catalysed by the material at any convenient temperature (e.g. normal room temperature)~.

The catalytic combustion of combustible gas may give rise to a temperature rise of 30 degrees C.

The present invention will now be further described, by way of example only, with reference to the single Figure of the accompanying drawing which shows a sensor in accordance with the present invention.

Referring now to the single Figure of the accompanying drawing there is shown a sensor having an optical fibre 1, a coating 2 of a material which is capable of catalysing combustion of a combustible gas when the combustible gas is in the presence of the material such that a temperature change is produced and means 3 capable of sensing the temperature change.

In operation a gas to be detected is admitted to the presence of the coating 2 and the resulting change in temperature is detected by means 3.

Claims

-1. A gas sensor for the detection of a- gas which sensor includes an optical device having a coating of- a material which is capable of catalysing-a reaction involving the-gas when the gays is in the presence of the material such that a temperature change is produced.
2. A gas sensor as claimed in Claim 1 and -for the detection of a combustible gays which sensor includes an optical device having a coating of a material which is capable of cata lysing combustion of the combustible gas when the combustible gas is in the presence of the- gas such that a temperature change is produced. \
3. A gas-sbnsor as claimed in Claim 1 or Claim 2 wherein the temperature-change is detected by anti-stokes raman rndiationdetec- - tions
4.A gas sensor as claimed in Claim 1 or Claim 2 wherein the optical device or coating includes a substance such that temperature dependent colour change, or refractive index change or fluorescence decay lifetime- change may occur when the temperature change is produced- whereby the temperature change may be detected by measuring colour change, refractive index change or fluorescene decay lifetime change.
5. A gas sensor as claimed in any one of the preceding -Claims wherein the sensor fur ther includes an infra-red phosphor.

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6. A gas sensor as claimed in any one of the preceding Claims wherein means are pro vided for measuring temperature distribution a!ong a length of an optical device.
7. A gas-sensor as claimed in any-one of the preceding Claims wherein the coating is provided along a whole length of the optical device.
8. A gas sensor as claimed in any one of Claims - 1 to 6- wherein the- coating is provided at intervals along a length of an optical de vice.
9. A gas sensor as claimed in any one of the preceding Claims- wherein the material which is capable of catalysing a reaction com prises a precious metal.
10. A gas sensor as claimed'in Claim 9 wherein the material is- platinum or palladium or a mixture thereof.
11. A gas sensor as claimed in any one of the preceding Claims wherein the material which is capable of catalysing a reaction in cludes a support for a catalyst.
12. A gas sensor as claimed in Claim 11 wherein the support comprises tin oxide.
13. A method for the detection of a gas which includes contacting the gas with a gas sensor, said gas sensor including an optical device having a coating of a material which is capable of catalysing a reaction involving the gas when the gas is in the presence of the material such that a temperature change is produced and measuring the temperature change.
14. A method as claimed in Claim 13 and for the detection of a combustible gas which includes contacting the gas with a gas sensor, said gas sensor including an optical device having a coating of a material which is capable of catalysing combustion of the com bustible gas when the combustible gas is in the presence of the material such that a tem perature change is produced and measuring the temperature change.
15. A methods claimed in Claim 13 or Claim 14 wherein- hydrogen, carbon monoxide or hydrogen sulphide is detected in air.
16. A sensor substantially as hereinbefore described with reference to the single Figure of the accompånying Drawing.
17. A method for detecting a gas substantially as hereinbefore described with reference to the single Figure of the accompanying Drawing.