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WO2023156767A1 - Gas sensor reference - Google Patents

Gas sensor reference Download PDF

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Publication number
WO2023156767A1
WO2023156767A1 PCT/GB2023/050338 GB2023050338W WO2023156767A1 WO 2023156767 A1 WO2023156767 A1 WO 2023156767A1 GB 2023050338 W GB2023050338 W GB 2023050338W WO 2023156767 A1 WO2023156767 A1 WO 2023156767A1
Authority
WO
WIPO (PCT)
Prior art keywords
measurement
radiation
detector
gas sensor
radiation source
Prior art date
Application number
PCT/GB2023/050338
Other languages
French (fr)
Inventor
John Fuller
Johnny Chu
Michael KELLET
Original Assignee
Gas Sensing Solutions Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Gas Sensing Solutions Ltd filed Critical Gas Sensing Solutions Ltd
Publication of WO2023156767A1 publication Critical patent/WO2023156767A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3504—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0031—General constructional details of gas analysers, e.g. portable test equipment concerning the detector comprising two or more sensors, e.g. a sensor array
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
    • G01N33/0037—NOx
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
    • G01N33/0039—O3
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
    • G01N33/004—CO or CO2
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
    • G01N33/0047—Organic compounds
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
    • G01N33/0054—Ammonia
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
    • G01N33/0059—Avoiding interference of a gas with the gas to be measured
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
    • G01N33/0059—Avoiding interference of a gas with the gas to be measured
    • G01N33/006—Avoiding interference of water vapour with the gas to be measured
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3504—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis
    • G01N2021/3545—Disposition for compensating effect of interfering gases
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/06—Illumination; Optics
    • G01N2201/062—LED's
    • G01N2201/0624—Compensating variation in output of LED source
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/12—Circuits of general importance; Signal processing
    • G01N2201/121—Correction signals
    • G01N2201/1215—Correction signals for interfering gases

Definitions

  • the present invention relates to gas sensors and methods of operation thereof, and particularly, but not exclusively, to gas sensors that can mitigate the influence of interference fluid(s) on the measurement of the gas to be detected.
  • the present invention relates to, but not exclusively, methane gas sensors that can mitigate the influence of water vapour on the measurement of methane.
  • Gas sensors are often configured to be sensitive to one or more analyte gases, such as methane (CPU), carbon dioxide (CO2), ammonia (NH3), nitrogen dioxide (NO2), carbon monoxide (CO), nitric oxide (NO), and/or ozone (O3).
  • analyte gases such as methane (CPU), carbon dioxide (CO2), ammonia (NH3), nitrogen dioxide (NO2), carbon monoxide (CO), nitric oxide (NO), and/or ozone (O3).
  • Such gas sensors are used in a wide variety of applications, such as atmospheric or ambient air quality monitoring.
  • a typical gas sensor may include a radiation source, such as a light emitting diode (LED), one or more detectors, such as photodiodes (PDs), arranged in a manner such that the analyte gas can flow into light path(s) between the LEDs and PDs.
  • a radiation source such as a light emitting diode (LED)
  • detectors such as photodiodes (PDs)
  • the light from the LED is partially absorbed by the analyte gas in the light path(s), and a measurement of the presence or concentration of the gas can be made using PD data.
  • a gas sensor comprising: a radiation source; a measurement detector; and a reference detector; wherein the radiation source and the measurement detector are arranged to define a measurement radiation path, wherein the radiation source and the reference detector are arranged to define a reference radiation path, wherein the reference detector is configured to be responsive to the presence of at least one interference fluid in the reference radiation path, wherein the measurement detector is configured to be responsive to the presence of at least one interference fluid in the measurement radiation path, and wherein the gas sensor is configured to detect at least one analyte gas in the measurement radiation path using measurement data from the measurement detector and reference data from the reference detector, and wherein the gas sensor is configured to compensate for the presence of the at least one interference fluid in the measurement radiation path using the reference data.
  • the gas sensor may be configured to detect the presence of, or measure the concentration of, the at least one analyte gas in the measurement radiation path.
  • the gas sensor may be configured to detect the presence of the at least one analyte gas when the at least one analyte gas is above a threshold value.
  • the gas sensor may be configured to detect the at least one analyte gas by way of absorption, as is known in the field of gas sensors.
  • the reference detector may be located adjacent to the radiation source.
  • the reference detector may comprise at least one radiation detection area.
  • the measurement detector may comprise at least one radiation detection area.
  • the radiation source may comprise at least one radiation emitting area.
  • At least one radiation detection area of the reference detector may be arranged adjacent to a radiation emitting area of the radiation source. At least one radiation detection area of the reference detector may be arranged adjacent to a radiation emitting area of the radiation source.
  • At least one radiation detection area of the reference detector may be arranged to face at least one radiation emitting area of the radiation source.
  • the radiation detector may be arranged in proximity to the radiation source. At least one radiation detection area of the reference detector may be arranged to be in proximity to at least one radiation emitting area of the radiation source.
  • the measurement detector may be arranged to be remote from the radiation source.
  • the radiation detector may be arranged in proximity to the radiation source and the measurement detector may be arranged to be remote from the radiation source.
  • the measurement detector may be arranged to be remote from the radiation source along the measurement radiation path. It will be understood that in this arrangement, the measurement detector and the radiation source could be arranged in the gas sensor to be physically close to each other, but are considered to be remote from each other due to the length of the measurement radiation path.
  • At least one radiation detection area of the measurement detector may be arranged to be remote from at least one radiation emitting area of the radiation source.
  • At least one radiation detection area of the reference detector may be arranged in proximity to at least one radiation emitting area of the radiation source and at least one radiation detection area of the measurement detector may be arranged to be remote from at least one radiation emitting area of the radiation source.
  • the reference detector and the radiation source may be spaced apart.
  • the reference detector and the radiation source may be spaced apart along the reference radiation path. At least one radiation detection area of the reference detector may be spaced apart from at least one radiation emitting area of the radiation source.
  • the reference detector and the radiation source may be spaced apart a sufficient distance to enable the reference detector to be responsive to the at least one interference fluid.
  • the reference detector and the radiation source may be sufficiently close to minimise or remove the sensitivity of the reference detector to the at least one analyte gas.
  • the measurement detector and the radiation source may be spaced apart.
  • the measurement detector and the radiation source may be spaced apart along the measurement radiation path.
  • the measurement detector and the reference detector may be spaced apart.
  • At least a portion of the reference detector and at least a portion of the radiation source may be located on the same substrate.
  • the reference detector and the radiation source may be integrally formed.
  • the reference detector and the radiation source may be integrally formed on the same substrate.
  • the radiation source and the measurement detector may be separately formed.
  • the reference detector and the radiation source may be integrally formed on the same substrate, or the reference detector and the radiation source may be separately formed, or the reference detector and the radiation source may be separately formed on the same substrate.
  • the substrate may be any suitable substrate, such as a semiconductor substrate, a semiconductor die, a printed circuit board, or the like.
  • the reference detector and the radiation source may be fixed relative to each other.
  • the measurement detector and the radiation source may be fixed relative to each other.
  • a radiation emitting area of the radiation source may be located at one or more wall portions thereof.
  • a radiation detection area of the reference detector may be located at one or more wall portions thereof.
  • the reference detector may be configured to detect side radiation emissions from the radiation source.
  • At least one radiation emitting area of the radiation source may be located at one or more side-walls thereof.
  • At least one radiation detection area of the reference detector may be located at one or more side-walls thereof.
  • the at least one radiation emitting area located on the one or more sidewalls of the radiation source may be arranged to face the at least one radiation detection area on the one or more side-walls of the reference detector.
  • One or more side-walls of the radiation source may be arranged adjacent to one or more side-walls of the reference detector.
  • At least one radiation emitting area of the radiation source may be located at a top region, a top wall, or a top surface, thereof. At least one radiation emitting area of the radiation source may be located at a top region, top wall, or top surface thereof and at one or more side-walls thereof.
  • the reference detector may comprise one or more radiation shields.
  • the one or more radiation shields may be configured to substantially block radiation from the radiation source.
  • the one or more radiation shields may be located at at least a portion of a top region, a top wall or a top surface of the reference detector and/or at at least a portion of one or more side-walls of the reference detector.
  • the gas sensor may comprise a compensator element.
  • the compensator element may be operable to compensate for the presence of the at least one interference fluid in the measurement radiation path.
  • the gas sensor may be configured to reduce, mitigate or substantially eliminate the influence of the at least one interference fluid on the measurement of the at least one analyte gas.
  • the measurement detector has a measurement detector output
  • the reference detector has an reference detector output, each of which may take any suitable form, such as a current, a voltage, analog or digital data, or the like.
  • the gas sensor may be configured to compensate for the presence of the at least one interference fluid in the measurement radiation path by obtaining a ratio of the measurement detector output to the reference detector output or a ratio of the reference detector output to the measurement detector output.
  • the compensator element may be operable to obtain the ratio of the measurement detector output to the reference detector output.
  • the gas sensor may be configured to compensate for the presence of the at least one interference fluid in the measurement radiation path by rejecting or minimising signals common to the measurement detector output and the reference detector output.
  • the gas sensor may be configured to improve the signal to noise ratio of the measurement data.
  • the gas sensor may be configured to improve the signal to noise ratio of the measurement data by using reference data from the reference detector.
  • the gas sensor may be configured to improve the signal to noise ratio of the measurement data by obtaining a ratio of the measurement data to the reference data.
  • the measurement detector may be arranged to be responsive to a threshold concentration of the at least one interference fluid.
  • the reference detector may be arranged to be responsive to a threshold concentration of the at least one interference fluid.
  • the at least one analyte gas may include one or more greenhouse gas.
  • the at least one analyte gas may include one or more gaseous alkanes.
  • the at least one analyte gas may include one or more nitrogen-based gases.
  • the at least one analyte gas may include one or more carbonbased gases.
  • the at least one analyte gas may include one or more oxygen-based gases.
  • the at least one analyte gas may include one or more hydrogen-based gases.
  • the at least one analyte gas may include methane (CH4), carbon dioxide (CO2), ammonia (NH3), nitrogen dioxide (NO2), carbon monoxide (CO), nitric oxide (NO), and/or ozone (O3).
  • the at least one analyte gas may be methane (CH4), carbon dioxide (CO2), ammonia (NH3), nitrogen dioxide (NO2), carbon monoxide (CO), nitric oxide (NO), and/or ozone (O3).
  • the gas sensor may be a methane gas sensor, a carbon dioxide gas sensor, an ammonia gas sensor, a nitrogen dioxide gas sensor, a carbon monoxide gas sensor, a nitric oxide gas sensor, and/or an ozone gas sensor.
  • the gas sensor may be configured to detect a single analyte gas.
  • the single analyte gas may be methane, carbon dioxide, ammonia, nitrogen dioxide, carbon monoxide, nitric oxide, or ozone.
  • the measurement detector may be configured to detect methane, carbon dioxide, ammonia, nitrogen dioxide, carbon monoxide, nitric oxide, and/or ozone.
  • the reference detector may be configured to be non-responsive to methane, carbon dioxide, ammonia, nitrogen dioxide, carbon monoxide, nitric oxide, and/or ozone.
  • the reference detector may be configured to be less responsive to the presence of carbon dioxide, ammonia, nitrogen dioxide, carbon monoxide, nitric oxide, and/or ozone in the reference radiation path than the responsiveness of the measurement detector to the presence of methane, carbon dioxide, ammonia, nitrogen dioxide, carbon monoxide, nitric oxide, and/or ozone in the measurement radiation path.
  • the interference fluid may have at least one different property to the at least one analyte gas.
  • the interference fluid may have a different absorption profile to the analyte gas.
  • the interference fluid may be different to the at least one analyte gas.
  • the interference fluid may be a fluid that is not methane.
  • the interference fluid may be a fluid that is not carbon dioxide.
  • the interference fluid may be a fluid that is not ammonia.
  • the interference fluid may be a fluid that is not nitrogen dioxide.
  • the interference fluid may be a fluid that is not carbon monoxide.
  • the interference fluid may be a fluid that is not nitric oxide.
  • the interference fluid may be a fluid that is not ozone.
  • the interference fluid may be a fluid that is not methane, carbon dioxide, ammonia, nitrogen dioxide, carbon monoxide, nitric oxide or ozone.
  • the interference fluid may not include methane.
  • the interference fluid may not include carbon dioxide.
  • the interference fluid may not include ammonia.
  • the interference fluid may not include nitrogen dioxide.
  • the interference fluid may not include carbon monoxide.
  • the interference fluid may not include nitric oxide.
  • the interference fluid may not include ozone.
  • the interference fluid may not include methane, carbon dioxide, ammonia, nitrogen dioxide, carbon monoxide, nitric oxide and/or ozone.
  • the reference detector and the measurement detector may be configured to be responsive to the same interference fluid, or the same interference fluids.
  • the reference detector may be configured to be responsive to a single interference fluid.
  • the measurement detector may be configured to be responsive to a single interference fluid.
  • the at least one interference fluid may include one or more gases, one or more liquids and/or one or more solids.
  • the measurement detector and/or the reference detector may be responsive to at least one interference fluid that may include one or more gases, one or more liquids, and/or one or more solids.
  • the measurement detector and/or the reference detector may be responsive to at least one interference fluid that may include water vapour, and/or liquid water.
  • the gas sensor may be configured such that the at least one analyte gas can move between the measurement radiation path and the reference radiation path.
  • the gas sensor may be configured such that the at least one interference fluid can move between the measurement radiation path and the reference radiation path.
  • the gas sensor may be configured such that a fluid flow path exists between the measurement radiation path and the reference radiation path.
  • the gas sensor may be configured such that a fluid flow path exists between the measurement radiation path and the reference radiation path, such that the at least one analyte gas and the at least one interference fluid can move between the measurement radiation path and the reference radiation path.
  • the gas sensor may comprise one or more gas detection chambers. At least a portion of the measurement radiation path may be located in one or more gas detection chambers. At least a portion of the reference radiation path may be located in one or more gas detection chambers.
  • the one or more gas detection chambers may be configured to receive the at least one analyte gas from a source of analyte gas or gases.
  • the one or more gas detection chambers may be configured to receive the at least one interference fluid from a source of interference fluid or fluids.
  • the source of analyte gas may be from the atmosphere, or ambient environment.
  • the source of interference fluid may be from the atmosphere, or ambient environment.
  • the one or more gas detection chambers may comprise a gas inlet for allowing the at least one analyte gas into the chamber and/or at least one gas outlet for allowing the at least one analyte gas to exit the chamber.
  • the one or more gas detection chambers may comprise a fluid inlet for allowing the at least one interference fluid into the chamber and/or at least one fluid outlet for allowing the at least one interference fluid to exit the chamber.
  • the measurement radiation path may be arranged to pass through at least a region of the one or more gas detection chambers.
  • the reference radiation path may be arranged to pass through at least a region of the one or more gas detection chambers.
  • the measurement radiation path and the reference radiation path may pass through at least a portion of the same gas detection chamber.
  • the gas detection chamber may take any suitable shape or form.
  • the gas sensor may comprise one or more radiation guides.
  • the one or more radiation guides may be arranged to guide radiation from the radiation source to the measurement detector and/or to guide radiation from the radiation source to the reference detector.
  • the radiation guide(s) may take any suitable shape or form.
  • the reference radiation path may be arranged such that radiation from the radiation source can directly reach the reference detector.
  • the reference radiation path may be a straight path between the radiation source and the reference detector.
  • the reference radiation path and the measurement radiation path may be configured to be separate radiation paths, such that radiation from one path cannot reach the other path.
  • the measurement radiation path may be arranged such that radiation from the radiation source can directly reach the measurement detector.
  • the measurement radiation path may be longer than the reference radiation path.
  • the measurement radiation path may be longer than the reference radiation path by a ratio of at least about 5:1 , optionally at least about 10:1 , optionally at least about 20: 1 , optionally at least about 40: 1 , optionally at least about 45:1 , optionally at least about 47:1 , optionally at least about 100:1 , optionally at least about 150:1 , optionally at least about 166: 1 , optionally about 47: 1 , optionally about 166: 1 , optionally about 167:1.
  • the measurement radiation path may be longer than the reference radiation path by a ratio of between about 5:1 and about 500:1 , optionally between about 5:1 and about 250:1 , optionally between about 100:1 and about 200:1 , optionally between about 125:1 and about 175:1 , optionally about 166:1 or about 167:1 , optionally between about 5:1 and about 100:1 , optionally between about 10:1 and about 80:1 , optionally between about 20:1 and about 60:1 , optionally between about 30:1 and about 50:1 , optionally between about 40:1 and about 50:1 .
  • the measurement radiation path may be between approximately 10 mm and 200 mm long, optionally between approximately 50 mm and approximately 180 mm long, optionally between approximately 100 mm and approximately 170 mm long, optionally between approximately 160 mm and approximately 170 mm long, optionally approximately 166 mm or approximately 167 mm long, optionally between approximately 30 mm and approximately 70 mm long, optionally between approximately 40 mm and 60 mm long, optionally approximately 47 mm long, optionally approximately 50 mm long.
  • the measurement radiation path may be at least approximately 10 mm long, optionally at least approximately 20 mm long, optionally at least approximately 40 mm long, optionally at least approximately 50 mm long.
  • the reference radiation path may be between approximately 0.1 mm and 10 mm long, optionally between approximately 0.1 mm and 5 mm long, optionally between approximately 0.1 mm and approximately 2 mm long, optionally between approximately 0.2 mm and approximately 1.5 mm long, optionally between approximately 0.2 mm and approximately 1 mm long, optionally approximately 0.3 mm long, optionally between approximately 0.75 mm and approximately 1.25 mm long, optionally approximately 1 mm long.
  • the reference radiation path may be less than approximately 50 mm long, optionally less than approximately 10 mm long, optionally less than approximately 5 mm long, optionally less than approximately 2 mm long.
  • the measurement radiation path may be arranged to be the major path and the reference radiation path may be arranged to be the minor path. In this arrangement, more radiation from the radiation source travels along the major path than the minor path.
  • the ratio of the radiation in the major path to the minor path may be at least 1 :1 , optionally at least 10:1 , optionally at least 20: 1 , optionally at least 50: 1 , optionally at least 100: 1 .
  • the radiation source may be configured to provide more radiation to the measurement radiation path than the reference radiation path.
  • the radiation source may be configured to provide at least 50 % of its radiation to the measurement radiation path, optionally at least 60 %, optionally at least 70 %, optionally at least 80 %, optionally at least 90 %.
  • the reference detector may be arranged to detect only a portion of the radiation emitted from the radiation source.
  • the measurement detector may be arranged to detect only a portion of the radiation emitted from the radiation source.
  • a part of the radiation from the radiation source may be directed to the measurement radiation path and a part of the radiation from the radiation source may be directed to the reference radiation path.
  • the radiation source may be a common radiation source, common to the measurement radiation path and the reference radiation path.
  • the radiation source may be a broadband radiation source.
  • the radiation source may be one or more light sources.
  • the radiation source may be configured to emit radiation that at least partially corresponds to at least a portion of the absorption feature(s) of the at least one analyte gas.
  • the radiation source may be configured to emit radiation in the UV, visible, infrared (I R), near IR, mid IR, far IR, or any combination thereof.
  • the radiation source may be configured to emit radiation within a wavelength range of between 700 nm to 11 ,000 nm, optionally between 2,000 to 5,000 nm, optionally between 7,000 nm to 11 ,000 nm, optionally between 700 nm to 2,000 nm.
  • the one or more light sources may be light emitting diodes (LEDs).
  • the radiation source may include one or more flashlamps, thermal emitters, LEDs, and/or lasers, or the like.
  • the gas sensor may comprise one or more, or a plurality of radiation sources.
  • the gas sensor may comprise a single radiation source.
  • the single radiation source may be a flashlamp, thermal emitter, LED, or laser, or the like.
  • the gas sensor may comprise one or more, or a plurality of measurement detectors.
  • the gas sensor may comprise a single measurement detector.
  • the measurement data may be one or more output signals from the measurement detector, or may be based on one or more output signals from the measurement detector.
  • the measurement detector may comprise one or more light detectors.
  • the one or more light detectors may be photodiodes (PDs).
  • the measurement detector may include one or more thermopiles, one or more pyroelectric detectors, and/or one or more photodiodes, or the like.
  • the reference data may be one or more output signals from the reference detector, or may be based on one or more output signals from the reference detector.
  • the reference detector may comprise one or more light detectors.
  • the one or more light detectors may be photodiodes (PDs).
  • the reference detector may include one or more thermopiles, one or more pyroelectric detectors, and/or one or more photodiodes, or the like.
  • the reference detector may be arranged to be less sensitive to the presence of the at least one analyte gas in the reference radiation path relative to the sensitivity of the measurement detector to the at least one analyte gas.
  • the reference detector may be arranged to be substantially non-responsive to the presence of the at least one analyte gas in the reference radiation path.
  • the reference detector may be configured to be less responsive to the presence of the at least one analyte gas in the reference radiation path than the responsiveness of the measurement detector to the presence of the at least one analyte gas in the measurement radiation path.
  • the reference detector may be arranged to be more responsive to the presence of the at least one interference fluid in the reference radiation path than the presence of the at least one analyte gas in the reference radiation path.
  • the reference detector may be arranged to be more responsive to the presence of the at least one interference fluid in the reference radiation path than the presence of the at least one analyte gas in the reference radiation path by a factor of at least 50 %, optionally at least 100 %, optionally at least 200 %, optionally at least 500 %.
  • the response of the reference detector to the at least one interference fluid and the response of the measurement detector to the at least one interference fluid may be configured to be substantially proportional, or equally proportional to each other.
  • the change in output of the reference detector and measurement detector is substantially proportional, or may be equally proportional.
  • the reference detector may be configured to obtain a measurement indicative of the output power of the radiation source.
  • the reference detector may be located sufficiently close to the radiation source such that the reference detector output is indicative of the output power of the radiation source.
  • the reference detector may be configured to be substantially less responsive to the presence of the at least one analyte gas in the reference radiation path than the responsiveness of the measurement detector to the presence of the at least one analyte gas in the measurement radiation path, and the reference detector may be configured to obtain a measurement indicative of the output power of the radiation source.
  • the reference detector may be arranged to be substantially non-responsive to the presence of the at least one analyte gas in the reference radiation path and the reference detector may be configured to obtain a measurement indicative of the output power of the radiation source.
  • the gas sensor may be configured to compensate the measurement of the at least one analyte gas by mitigating or minimising the influence of variation(s) in output power of the radiation source.
  • the gas sensor may comprise any suitable signal processing element(s).
  • the gas sensor may comprise one or more, or a plurality of reference detectors. Each reference detector may be arranged to define a reference radiation path between the respective reference detector and the radiation source. The gas sensor may be configured to compensate for the presence of the at least one interference fluid in the measurement radiation path using reference data from the, or each, reference detector.
  • the gas sensor may comprise a single reference detector.
  • the gas sensor may be a lightweight sensor, a portable sensor, a wall- mountable sensor, or the like.
  • the radiation source and the reference detector may be thin-film electronic components.
  • the gas sensor may be configured to measure, or infer, the temperature of the radiation source.
  • the gas sensor may be configured to measure the forward voltage of an LED of the radiation source in order to measure or infer the temperature of the radiation source.
  • the reference detector may be arranged to be close enough to the radiation source such that a measurement of the temperature of the radiation source provides a measurement of, or a suitable approximation of, the temperature of the reference detector.
  • the radiation source and the reference detector may be thermally connected.
  • the radiation source and the reference detector may be thermally connected by way of one or more thermal connection members.
  • the one or more thermal connection members may be, or may include, at least a portion of a substrate on which the radiation source and the reference detector are located.
  • the gas sensor may comprise one or more filters.
  • the one or more filters may be arranged in the measurement light path and/or the reference light path to filter radiation, as is known in the field of gas sensing.
  • the gas sensor may comprise a housing.
  • One or more, or all, of the components of the gas sensor may be located in, or on, the housing.
  • the housing may take any suitable size and shape to house one or more components of the gas sensor.
  • the gas sensor may comprise a power supply and/or may be connectable to a source of power.
  • the power supply may be a battery, or the like.
  • a gas sensor comprising: a radiation source; a measurement detector; and a reference detector; wherein the radiation source and the measurement detector are arranged to define a measurement radiation path, wherein the radiation source and the reference detector are arranged to define a reference radiation path, wherein the gas sensor is configured to detect at least one analyte gas in the measurement radiation path using measurement data from the measurement detector, and wherein the gas sensor is configured to compensate the measurement of the at least one analyte gas using reference data from the reference detector.
  • the gas sensor may comprise a compensator element.
  • the compensator element may be operable to compensate the measurement of the at least one analyte gas by obtaining a ratio of the measurement detector output to the reference detector output or a ratio of the reference detector output to the measurement detector output.
  • the compensator element may be operable to obtain the ratio of the measurement detector output to the reference detector output.
  • the compensator element may be operable to compensate for the presence of at least one interference fluid in the measurement radiation path.
  • the gas sensor may be configured to reduce or mitigate the influence of the at least one interference fluid on the measurement of the at least one analyte gas.
  • the gas sensor may be configured to substantially eliminate the influence of the at least one interference fluid on the measurement of the at least one analyte gas.
  • the gas sensor may be configured to compensate for the presence of the at least one interference fluid in the measurement radiation path by obtaining a ratio of the measurement detector output to the reference detector output.
  • the gas sensor may be configured to compensate the measurement of the at least one analyte gas in the measurement radiation path by rejecting or minimising signals common to the measurement detector output and the reference detector output.
  • the gas sensor may be configured to compensate for the presence of the at least one interference fluid in the measurement radiation path by rejecting or minimising signals common to the measurement detector output and the reference detector output.
  • the gas sensor may be configured to improve the signal to noise ratio of the measurement data.
  • the gas sensor may be configured to improve the signal to noise ratio of the measurement data by using reference data from the reference detector.
  • the gas sensor may be configured to improve the signal to noise ratio of the measurement data by obtaining a ratio of the measurement data to the reference data.
  • the reference detector may be configured to obtain a measurement indicative of the output power of the radiation source.
  • the reference detector may be configured to be substantially less responsive to the presence of the at least one analyte gas in the reference radiation path than the responsiveness of the measurement detector to the presence of the at least one analyte gas in the measurement radiation path, and the reference detector may be configured to obtain a measurement indicative of the output power of the radiation source.
  • the reference detector may be arranged to be substantially non-responsive to the presence of the at least one analyte gas in the reference radiation path and the reference detector may be configured to obtain a measurement indicative of the output power of the radiation source.
  • the gas sensor may be configured to compensate the measurement of the at least one analyte gas by mitigating or minimising the influence of variation(s) in output power of the radiation source.
  • Embodiments of the second aspect of the present invention may include one or more features of the first aspect of the present invention or its embodiments.
  • embodiments of the first aspect of the present invention may include one or more features of the second aspect of the present invention or its embodiments.
  • a method of operating a gas sensor comprising the steps of: (i) providing a gas sensor comprising: a radiation source; a measurement detector; and a reference detector; wherein the radiation source and the measurement detector are arranged to define a measurement radiation path, wherein the radiation source and the reference detector are arranged to define a reference radiation path, wherein the reference detector is configured to be responsive to the presence of at least one interference fluid in the reference radiation path, wherein the measurement detector is configured to be responsive to the presence of at least one interference fluid in the measurement radiation path, and wherein the gas sensor is configured to detect at least one analyte gas in the measurement radiation path using measurement data from the measurement detector and reference data from the reference detector, and wherein the gas sensor is configured to compensate for the presence of the at least one interference fluid in the measurement radiation path using the reference data; and
  • Embodiments of the third aspect of the present invention may include one or more features of the first and/or second aspects of the present invention or their embodiments. Similarly, embodiments of the first and/or second aspects of the present invention may include one or more features of the third aspect of the present invention or its embodiments.
  • a method of operating a gas sensor comprising the steps of:
  • a gas sensor comprising: a radiation source; a measurement detector; and a reference detector; wherein the radiation source and the measurement detector are arranged to define a measurement radiation path, wherein the radiation source and the reference detector are arranged to define a reference radiation path, wherein the gas sensor is configured to detect at least one analyte gas in the measurement radiation path using measurement data from the measurement detector, and wherein the gas sensor is configured to compensate the measurement of the at least one analyte gas using reference data from the reference detector; (ii) activating the radiation source;
  • Embodiments of the fourth aspect of the present invention may include one or more features of the first, second and/or third aspects of the present invention or their embodiments. Similarly, embodiments of the first, second, and/or third aspects of the present invention may include one or more features of the fourth aspect of the present invention or its embodiments.
  • Fig. 1 shows a top view of the reference detector and radiation source of a gas sensor in accordance with an embodiment of the invention
  • Fig. 2 shows a simplified schematic of the gas sensor of Fig. 1 ;
  • Fig. 3 shows graphs of relative humidity, measurement and reference detector outputs, and the compensated output signal
  • Fig. 4 shows a graph of gas measurement versus relative humidity over time
  • Fig. 5 shows a graph of the gas sensor output for different temperatures
  • Fig. 6 shows the performance of the gas sensor across gas concentration, temperature and output power of the radiation source.
  • a gas sensor 1 in accordance with an embodiment of the invention is illustrated and described herein.
  • the gas sensor 1 comprises a radiation source 2, a measurement detector 4, and a reference detector 6.
  • the radiation source 2 and the measurement detector 4 are arranged to define a measurement radiation path 8.
  • the radiation source 2 and the reference detector 6 are arranged to define a reference radiation path 10.
  • the gas sensor 1 is configured to detect at least one analyte gas 12 in the measurement radiation path 8 using measurement data from the measurement detector 4.
  • the gas sensor 1 is configured to compensate the measurement of the at least one analyte gas 12 using reference data from the reference detector 6.
  • the reference detector 6 is configured to be responsive to the presence of at least one interference fluid 14 in the reference radiation path 10
  • the measurement detector 4 is configured to be responsive to the presence of at least one interference fluid 14 in the measurement radiation path 8.
  • the gas sensor 1 is configured to compensate for the presence of the at least one interference fluid 14 in the measurement radiation path 8 using the reference data. It will be understood that in other embodiments, the gas sensor 1 can compensate the measurement of the analyte gas 12 in other ways, some of which will be described below.
  • the gas sensor 1 when the interference fluid 14 is not present, or is below a threshold value, the gas sensor 1 still compensates the measurement of the at least one analyte gas 12.
  • the gas sensor 1 is configured to measure the concentration of the at least one analyte gas 12 in the measurement radiation path 4. However, in other embodiments the gas sensor 1 could detect the presence of the at least one analyte gas 12, which could be when the at least one analyte gas 12 is above a threshold value.
  • the gas sensor 1 detects the at least one analyte gas 12 by way of absorption, as is known in the field of gas sensors. In the embodiments described here, this occurs by radiation in the measurement radiation path 8 being absorbed by the analyte gas 12, which can be detected at the measurement detector 4 as a change in measurement data.
  • the reference detector 6 is located adjacent to the radiation source 2.
  • the reference detector 6 comprises at least one radiation detection area 6a
  • the measurement detector 4 comprises at least one radiation detection area 4a
  • the radiation source 2 comprises at least one radiation emitting area 2a.
  • At least one radiation detection area 6a of the reference detector 6 is arranged adjacent to, and arranged to face, a radiation emitting area 2a of the radiation source 2.
  • the radiation detector 6 is arranged in proximity to the radiation source 2 and the measurement detector 4 is arranged to be remote from the radiation source 2. At least one radiation detection area 6a of the reference detector 6 is arranged to be in proximity to at least one radiation emitting area 2a of the radiation source 2, and at least one radiation detection area 4a of the measurement detector 4 is arranged to be remote from at least one radiation emitting area 2a of the radiation source 2.
  • the reference detector 6 and the radiation source 2 are spaced apart along the reference radiation path 10. At least one radiation detection area 6a of the reference detector 6 is spaced apart from at least one radiation emitting area 2a of the radiation source 2. The reference detector 6 and the radiation source 2 are spaced apart a sufficient distance to enable the reference detector 6 to be responsive to the at least one interference fluid 14. The reference detector 6 and the radiation source 2 are sufficiently close to minimise or remove the sensitivity of the reference detector 6 to the at least one analyte gas 12.
  • the measurement detector 4 and the radiation source 2 are spaced apart along the measurement radiation path 8.
  • the measurement detector 4 and the radiation source 2 are spaced apart a sufficient distance to enable the gas sensor 1 to detect the at least one analyte gas 12.
  • At least one radiation detection area 4a of the measurement detector 4 is spaced apart from at least one radiation emitting area 2a of the radiation source 2.
  • the measurement detector 4 and the reference detector 6 are spaced apart.
  • the reference detector 6 and the radiation source 2 are located on the same substrate 16 and are integrally formed.
  • the substrate 16 can be any suitable substrate, such as a semiconductor die.
  • the radiation source 2 and the measurement detector 4 are separately formed.
  • the reference detector 6, the measurement detector 4 and the radiation source 2 are all fixed relative to each other.
  • the radiation emitting area 2a of the radiation source 2 is located at a top region 2b thereof and at one or more side-walls thereof 2d.
  • the top region 2b includes a top surface 2c which forms a top wall.
  • At least one radiation detection area 6a of the reference detector 6 is located at a side-wall 6d thereof.
  • the at least one radiation emitting area 2a located on the one or more side-walls 2d of the radiation source 2 is arranged to face the at least one radiation detection area 6a on the one or more side-walls 6d of the reference detector 6.
  • a side-wall 2d of the radiation source 2 is arranged adjacent to a side-wall 6d of the reference detector 6.
  • the reference detector 6 comprises a plurality of radiation shields 6e configured to substantially block radiation from the radiation source 2.
  • the radiation shields 6e are located at at least a portion of a top region 6b of the reference detector and at at least a portion of one or more side-walls 6d of the reference detector 6.
  • the top region 6b includes a top surface 6c, which is a top wall.
  • the reference detector 6 is configured to detect side radiation emissions from the radiation source 2.
  • the gas sensor 1 comprises a compensator element 18, which may be any suitable element, such as an amplifier circuit, a computing device, or the like, operable to carry out the required compensation.
  • the compensator element 18 is operable to compensate the measurement of the analyte gas 12 by obtaining a ratio of the measurement detector 4 output to the reference detector 6 output, which mitigates or eliminates the effect of signals common to both reference and measurement.
  • the compensator element 18 is operable to compensate for the presence of the at least one interference fluid 14 in the measurement radiation path 8, using the ratio of signals, because the reference detector 6 is arranged to be sensitive to the interference fluid(s) 14 but insensitive, or substantially less sensitive to the analyte gas 12.
  • the measurement detector 4 and the reference detector 6 will both be responsive to the interference fluid 14, which will be mitigated through a ratio measurement, and changes in analyte gas 12 will result in changes in the overall, compensated, output. Likewise, any degradation in radiation source 2 performance, or variation due to temperature, can be mitigated because the variations will be common to both the reference and measurement detectors 4, 6.
  • the gas sensor 1 is configured to reduce or mitigate the influence of the at least one interference fluid 14 on the measurement of the at least one analyte gas 12. In other embodiments, the gas sensor 1 may be configured to substantially eliminate the influence of the at least one interference fluid 14 on the measurement of the at least one analyte gas 12.
  • the gas sensor 1 is configured to compensate for the presence of the at least one interference fluid 14 in the measurement radiation path 8 by obtaining a ratio of the measurement detector 4 output to the reference detector 6 output (or vice versa).
  • the output of the detectors 4, 6, can take any suitable form, such as output current, output voltage, or the like, depending on the type of detectors 4, 6, and compensator element 18 used.
  • the compensator element 18 is operable to obtain the ratio of the measurement detector 4 output to the reference detector 6 output. However, in other embodiments a different compensation technique could be used.
  • the gas sensor 1 is configured to compensate for the presence of the at least one interference fluid 14 in the measurement radiation path 8 by rejecting or minimising signals common to the measurement detector 4 output and the reference detector 6 output, in the resultant compensated output signal. So, for example, if there is no interference fluid 14 present (or a negligible amount), the compensator element 18 is still able to minimise the influence of common-mode signals, such as changes in radiation source 2 performance, or electrical noise common to the reference and measurement detectors 4, 6.
  • common-mode signals such as changes in radiation source 2 performance, or electrical noise common to the reference and measurement detectors 4, 6.
  • the measurement detector 4 is arranged to be responsive to a threshold concentration of the at least one interference fluid 14.
  • the reference detector 6 may be arranged to be responsive to a threshold concentration of the at least one interference fluid 14.
  • the at least one analyte gas 12 is methane (CH4).
  • the analyte gas 12 may include methane, carbon dioxide (CO2), ammonia (NH3), nitrogen dioxide (NO2), carbon monoxide (CO), nitric oxide (NO), and/or ozone (O3), or may include one or more other gases.
  • the gas sensor 1 can detect a single analyte gas 12. In other embodiments, the gas sensor 1 could be configured to detect or measure the concentration of one or more analyte gases.
  • the measurement detector 4 is configured to detect methane. This can be achieved in any suitable manner. For example, filters at the measurement detector 4 and/or the radiation source 2 can be used as is known in the art of gas sensing.
  • the reference detector 6 is configured to be less responsive to methane than the responsiveness of the measurement detector 4 to methane, at least below an upper threshold value. It will be understood that the distance between the reference detector 6 and the radiation source 2, and the properties of the reference detector 6 and the radiation source 2, can be designed such that the reference detector 6 is less sensitive, or not sensitive, to methane.
  • the interference fluid 14 is water vapour.
  • the reference detector 6 is configured to be responsive to a single interference fluid 14 and the measurement detector 4 is configured to be responsive to a single interference fluid 14.
  • the interference fluid 14 may be one or more fluids that have at least one different property to the at least one analyte gas 12.
  • the interference fluid 14 is different to the at least one analyte gas 12.
  • the interference fluid 14 is not methane, in other embodiments methane could be an interference fluid, and a different analyte gas 12 could be detected.
  • the reference detector 6 and the measurement detector 4 are configured to be responsive to the same interference fluid 14. This can be achieved in numerous ways, such as the use of filters, the design of the spacing between the detectors 4, 6 and the radiation source 2, and in the type of components used.
  • the gas sensor 1 is configured such that a fluid flow path exists between the measurement radiation path 8 and the reference radiation path 10, such that the at least one analyte gas 12 and the at least one interference fluid 14 can move between the measurement radiation path 8 and the reference radiation path 10.
  • the gas sensor 1 comprises a gas detection chamber 20, which encloses the measurement radiation path 8 and the reference radiation path 10.
  • the gas detection chamber 20 is configured to receive the at least one analyte gas 12 from the outside of the gas sensor 1 , although in other embodiments the gas detection chamber 20 could receive the at least one analyte gas 12 from a source of analyte gas or gases.
  • the gas detection chamber 20 is also configured to receive the at least one interference fluid 14 from the outside of the gas sensor 1 , but in other embodiments the at least one interference fluid 14 could be received from a source of interference fluid 14 or interference fluids 14. In this embodiment, both the at least one analyte gas 12 and the at least one interference fluid 14 enter the gas detection chamber 20 from the atmosphere, or ambient environment.
  • the gas detection chamber 20 comprises a fluid inlet and a fluid outlet (not shown) for allowing the at least one analyte gas 12 and the at least one interference fluid 14 into/out of the chamber 20. Any suitable fluid in let/outlet can be used, and the gas detection chamber 20 may take any suitable shape or form.
  • the gas sensor 1 can comprise one or more radiation guides for guiding radiation from the radiation source 2 to the measurement detector 4 and/or to guide radiation from the radiation source 2 to the reference detector 6.
  • the radiation guide(s) may take any suitable shape or form.
  • the reference radiation path 10 is arranged such that radiation from the radiation source 2 can directly reach the reference detector 6.
  • the reference radiation path 10 is a straight path between the radiation source 2 and the reference detector 6.
  • the reference radiation path 10 and the measurement radiation path 8 are configured to be separate radiation paths, such that radiation from one path cannot reach the other path.
  • the measurement radiation path 8 is arranged such that radiation from the radiation source 2 can directly reach the measurement detector 4.
  • the measurement radiation path 8 is longer than the reference radiation path 10 by a ratio of about 47:1 .
  • the measurement radiation path 8 is approximately 47 mm long and the reference radiation path 10 is approximately 1 mm long.
  • the measurement radiation path 8 is arranged to be the major path and the reference radiation path 10 is arranged to be the minor path. In this arrangement, more radiation from the radiation source 2 travels along the major path than the minor path.
  • the ratio of the radiation in the major path to the minor path is at least 5:1 , and can be at least 10:1 , optionally at least 20: 1 , optionally at least 50: 1 , optionally at least 100: 1 , optionally at least 500:1.
  • the radiation source 2 is configured to provide more radiation to the measurement radiation path 8 than the reference radiation path 10.
  • the radiation source 2 is configured to provide at least 90 % of its radiation to the measurement radiation path 8.
  • the reference detector 6 is arranged to detect only a portion of the radiation emitted from the radiation source 2.
  • the radiation source 2 is a common radiation source 2, common to the measurement radiation path 8 and the reference radiation path 10.
  • the radiation source 2 is a broadband radiation source, which in this embodiment is a single light emitting diode (LED) configured to emit light that corresponds to at least a portion of the absorption features of the at least one analyte gas 12.
  • the gas sensor could comprise one or more, or a plurality of radiation sources 2, which could be one or more flashlamps, thermal emitters, LEDs, and/or lasers, or the like.
  • the gas sensor 1 comprises a single measurement detector 4 and a single reference detector 6, which are both photodiodes.
  • the gas sensor 1 could comprise one or more, or a plurality of measurement detectors 4 and one or more, or a plurality of reference detectors 6.
  • the detectors 4, 6, could include one or more thermopiles, one or more pyroelectric detectors, and/or one or more photodiodes, or the like.
  • the measurement data is based on one or more output signals from the measurement detector 4.
  • the reference data is based on one or more output signals from the reference detector 6.
  • the reference detector 6 is arranged to be less responsive to the presence of the at least one analyte gas 12 in the reference radiation path 10 than the responsiveness of the measurement detector 4 to the presence of the at least one analyte gas 12 in the measurement radiation path 8, at least below an upper threshold value.
  • the reference detector 6 is arranged to be more responsive to the presence of the at least one interference fluid 14 in the reference radiation path 10 than the presence of the at least one analyte gas 12 in the reference radiation path 10. In other embodiments it may be sufficient that the reference detector 6 is arranged to be less responsive to the analyte gas 12 than the interference fluid 14.
  • the reference detector 6 is arranged to be more responsive to the presence of the at least one interference fluid 14 in the reference radiation path 10 than the presence of the at least one analyte gas 12 in the reference radiation 10 path by a factor of at least 50 %. In other embodiments this factor could be at least 100 %, optionally at least 200 %, optionally at least 500 %.
  • the response of the reference detector 6 to the at least one interference fluid 14 and the response of the measurement detector 4 to the at least one interference fluid 14 are configured to be substantially proportional, or equally proportional to each other.
  • the change in output of the reference detector 6 and measurement detector 4 is substantially proportional, or may be equally proportional.
  • the reference detector 6 is configured to obtain a measurement indicative of the output power of the radiation source 2.
  • the reference detector 6 functions as a power reference, and the ratio of the measurement data to the reference data helps to mitigate variations in radiation source 2 output power. It will be apparent that if there is no interference fluid 14 present, the reference detector 6 can obtain a measure of the output power of the radiation source 2, which can be used to compensate the measurement detector 4 output.
  • the gas sensor 1 is configured to compensate the measurement of the at least one analyte gas 12 by mitigating or minimising the influence of variation(s) in output power of the radiation source 2.
  • the gas sensor 1 includes amplification and signal processing elements to amplify and process the output from the measurement and reference detectors 4, 6.
  • the gas sensor 1 can include any suitable signal processing elements.
  • the gas sensor 1 is a lightweight, portable and wall- mountable sensor, but in other embodiments the gas sensor 1 may be designed differently.
  • the radiation source 2 and the reference detector 6 are thin-film electronic components.
  • the gas sensor 1 is configured to measure or infer the temperature of the radiation source 2 by measuring the forward voltage of the LED.
  • the reference detector 6 is arranged to be close enough to the radiation source 2 such that a measurement of the temperature of the radiation source 2 provides a measurement of, or a suitable approximation of, the temperature of the reference detector 6.
  • the radiation source 2 and the reference detector 6 are thermally connected by way of the common substate 16 on which they are mounted.
  • the substrate 16 acts as a thermal connection member. It will be understood that the radiation source 2 and the reference detector 6 could be separately formed on different substrates, and in some embodiments they could be thermally connected using any suitable thermal connection member.
  • the gas sensor 1 comprises a filter 22 arranged in the measurement light path 8 to filter radiation, as is known in the field of gas sensing.
  • the reference radiation path 10 does not include filters, but it will be understood that in other embodiments, one or more filters may be included therein.
  • the gas sensor 1 comprises a battery, but in other embodiments the gas sensor 1 could be connectable to a source of power.
  • the components of the gas sensor 1 are located in, or on, a housing (not shown) of the gas sensor 1 .
  • the housing may take any suitable size and shape to house the components of the gas sensor 1 .
  • Figs. 3 to 6 highlight the performance of the gas sensor 1 .
  • Fig. 3 shows (i) the relative humidity over time, (ii) the output from the measurement detector 4, (iii) the output from the reference detector 6 and (iv) the compensated output data obtained after taking a ratio of (ii) and (iii), all for a fixed concentration of analyte gas.
  • Fig. 3 demonstrates for variable relative humidity the compensated output signal is not substantially affected, and thus the presence of water vapour in the reference and measurement radiation paths 10, 8, has been mitigated.
  • Fig. 4 plots the compensated output signal as a gas measurement (in parts per million) of the gas sensor 1 , against the relative humidity over time, which demonstrates the gas sensor’s 1 ability to compensate for an interference fluid 14 (water vapour).
  • Fig. 5 shows the compensated output signal as a gas measurement, for a gas concentration of 50,000 ppm, at various temperatures, showing both the raw output and with averaging applied.
  • the upper and lower boundaries on the graph of Fig. 5 highlight a target performance level to meet.
  • Fig. 6 shows the gas sensor 1 performance across gas concentration (of methane), temperature and the optical power of the radiation source 2.
  • a gas sensor 1 as described above is provided in a location for gas sensing or monitoring.
  • the radiation source 2 is activated, which may include pulsing the radiation source 2 or any suitable way of activating the radiation source 2. Radiation will then travel along the measurement radiation path 8 and the reference radiation path 10. Some of the radiation will be absorbed by the at least one analyte gas 12 (if present) and the at least one interference fluid 14 (if present), and the resultant variations in received radiation at the reference detector 6 and the measurement detector 4 result in variations in their output. A change in analyte gas 12 concentration will predominantly affect the output of the measurement detector 4, and will have no substantial effect, or minimal effect, on the reference detector 6. A change in the concentration of interference fluid 14 will affect both the measurement detector 4 and the reference detector 6.
  • measurement data is obtained from the measurement detector 4.
  • the measurement data is obtained via the measurement photodiode current and subsequent amplification, as is known in the art.
  • the reference data is also obtained from the reference detector 6, using the reference photodiode current and amplification as is known in the art.
  • the measurement data is compensated by obtaining a ratio of the measurement data to the reference data. In this embodiment, this means dividing an amplified measure of the measurement photodiode current by an amplified version of the reference photodiode current.
  • the concentration of analyte gas can be stored or processed in any desirable manner.
  • the compensated measurement signal may be stored as a value, may be transmitted to a computing device, or may be amplified or used for processing by another circuit element or the like.
  • the gas sensor 1 will be configured to then periodically activate and deactivate the radiation source 2 and to obtain periodic measurements of the gas concentration.
  • the at least one interference fluid could include one or more gases, one or more liquids, and/or one or more solids.
  • the interference fluid is water vapour, it will be understood that the interference fluid could include liquid water, or other types of fluid.
  • the measurement radiation path 8 could be arranged to pass through at least a region of the one or more gas detection chambers 20.
  • the reference radiation path 10 could be arranged to pass through at least a region of the one or more gas detection chambers 20.
  • the gas sensor 1 could comprise a plurality of reference detectors 6, each reference detector 6 being arranged to define a reference radiation path 10 between the respective reference detector 6 and the radiation source 2.
  • the gas sensor 1 could be configured to compensate for the presence of the at least one interference fluid 14 in the measurement radiation path 8 using reference data from the, or each, reference detector 6.
  • gas sensor 1 could comprise a plurality of radiation sources 2.
  • an interference fluid 14 water vapour
  • an interference fluid 14 water vapour
  • the analyte gas is methane.
  • the gas sensor could be configured to detect any suitable analyte gas or gases, which may include methane, carbon dioxide (CO2), ammonia (NH3), nitrogen dioxide (NO2), carbon monoxide (CO), nitric oxide (NO), and/or ozone (O3), or the like.

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Abstract

A gas sensor comprising a radiation source, a measurement detector and a reference detector. The radiation source and the measurement detector are arranged to define a measurement radiation path. The radiation source and the reference detector are arranged to define a reference radiation path. The reference detector is configured to be responsive to the presence of at least one interference fluid in the reference radiation path. The measurement detector is configured to be responsive to the presence of at least one interference fluid in the measurement radiation path. The gas sensor is configured to detect at least one analyte gas in the measurement radiation path using measurement data from the measurement detector and reference data from the reference detector. The gas sensor is configured to compensate for the presence of the at least one interference fluid in the measurement radiation path using the reference data.

Description

Gas Sensor Reference
Field of the invention
The present invention relates to gas sensors and methods of operation thereof, and particularly, but not exclusively, to gas sensors that can mitigate the influence of interference fluid(s) on the measurement of the gas to be detected. For example, the present invention relates to, but not exclusively, methane gas sensors that can mitigate the influence of water vapour on the measurement of methane.
Background to the invention
Gas sensors are often configured to be sensitive to one or more analyte gases, such as methane (CPU), carbon dioxide (CO2), ammonia (NH3), nitrogen dioxide (NO2), carbon monoxide (CO), nitric oxide (NO), and/or ozone (O3). Such gas sensors are used in a wide variety of applications, such as atmospheric or ambient air quality monitoring.
A typical gas sensor may include a radiation source, such as a light emitting diode (LED), one or more detectors, such as photodiodes (PDs), arranged in a manner such that the analyte gas can flow into light path(s) between the LEDs and PDs. The light from the LED is partially absorbed by the analyte gas in the light path(s), and a measurement of the presence or concentration of the gas can be made using PD data.
For some gas sensor arrangements, it can be difficult to compensate the gas measurement for variations in LED power, which can occur due to LED degradation, temperature, or other effects. Furthermore, it is thought not to be possible to compensate some types of gas sensor arrangements for the presence of interference fluid(s) in the light path. For example, water vapour is known to interfere with measurements of some types of analyte gas, particularly methane.
The inventors have appreciated the shortcomings in known gas sensors.
Statements of Invention
According to a first aspect of the present invention there is provided a gas sensor comprising: a radiation source; a measurement detector; and a reference detector; wherein the radiation source and the measurement detector are arranged to define a measurement radiation path, wherein the radiation source and the reference detector are arranged to define a reference radiation path, wherein the reference detector is configured to be responsive to the presence of at least one interference fluid in the reference radiation path, wherein the measurement detector is configured to be responsive to the presence of at least one interference fluid in the measurement radiation path, and wherein the gas sensor is configured to detect at least one analyte gas in the measurement radiation path using measurement data from the measurement detector and reference data from the reference detector, and wherein the gas sensor is configured to compensate for the presence of the at least one interference fluid in the measurement radiation path using the reference data.
The gas sensor may be configured to detect the presence of, or measure the concentration of, the at least one analyte gas in the measurement radiation path. The gas sensor may be configured to detect the presence of the at least one analyte gas when the at least one analyte gas is above a threshold value.
The gas sensor may be configured to detect the at least one analyte gas by way of absorption, as is known in the field of gas sensors.
The reference detector may be located adjacent to the radiation source.
The reference detector may comprise at least one radiation detection area. The measurement detector may comprise at least one radiation detection area. The radiation source may comprise at least one radiation emitting area.
At least one radiation detection area of the reference detector may be arranged adjacent to a radiation emitting area of the radiation source. At least one radiation detection area of the reference detector may be arranged adjacent to a radiation emitting area of the radiation source.
At least one radiation detection area of the reference detector may be arranged to face at least one radiation emitting area of the radiation source.
The radiation detector may be arranged in proximity to the radiation source. At least one radiation detection area of the reference detector may be arranged to be in proximity to at least one radiation emitting area of the radiation source.
The measurement detector may be arranged to be remote from the radiation source. The radiation detector may be arranged in proximity to the radiation source and the measurement detector may be arranged to be remote from the radiation source.
The measurement detector may be arranged to be remote from the radiation source along the measurement radiation path. It will be understood that in this arrangement, the measurement detector and the radiation source could be arranged in the gas sensor to be physically close to each other, but are considered to be remote from each other due to the length of the measurement radiation path.
At least one radiation detection area of the measurement detector may be arranged to be remote from at least one radiation emitting area of the radiation source. At least one radiation detection area of the reference detector may be arranged in proximity to at least one radiation emitting area of the radiation source and at least one radiation detection area of the measurement detector may be arranged to be remote from at least one radiation emitting area of the radiation source.
The reference detector and the radiation source may be spaced apart. The reference detector and the radiation source may be spaced apart along the reference radiation path. At least one radiation detection area of the reference detector may be spaced apart from at least one radiation emitting area of the radiation source. The reference detector and the radiation source may be spaced apart a sufficient distance to enable the reference detector to be responsive to the at least one interference fluid. The reference detector and the radiation source may be sufficiently close to minimise or remove the sensitivity of the reference detector to the at least one analyte gas. The measurement detector and the radiation source may be spaced apart. The measurement detector and the radiation source may be spaced apart along the measurement radiation path. The measurement detector and the radiation source may be spaced apart a sufficient distance to enable the gas sensor to detect the at least one analyte gas. At least one radiation detection area of the measurement detector may be spaced apart from at least one radiation emitting area of the radiation source.
The measurement detector and the reference detector may be spaced apart.
At least a portion of the reference detector and at least a portion of the radiation source may be located on the same substrate. The reference detector and the radiation source may be integrally formed. The reference detector and the radiation source may be integrally formed on the same substrate. The radiation source and the measurement detector may be separately formed. The reference detector and the radiation source may be integrally formed on the same substrate, or the reference detector and the radiation source may be separately formed, or the reference detector and the radiation source may be separately formed on the same substrate. The substrate may be any suitable substrate, such as a semiconductor substrate, a semiconductor die, a printed circuit board, or the like.
The reference detector and the radiation source may be fixed relative to each other. The measurement detector and the radiation source may be fixed relative to each other. A radiation emitting area of the radiation source may be located at one or more wall portions thereof. A radiation detection area of the reference detector may be located at one or more wall portions thereof.
The reference detector may be configured to detect side radiation emissions from the radiation source.
At least one radiation emitting area of the radiation source may be located at one or more side-walls thereof. At least one radiation detection area of the reference detector may be located at one or more side-walls thereof. The at least one radiation emitting area located on the one or more sidewalls of the radiation source may be arranged to face the at least one radiation detection area on the one or more side-walls of the reference detector. One or more side-walls of the radiation source may be arranged adjacent to one or more side-walls of the reference detector.
At least one radiation emitting area of the radiation source may be located at a top region, a top wall, or a top surface, thereof. At least one radiation emitting area of the radiation source may be located at a top region, top wall, or top surface thereof and at one or more side-walls thereof.
The reference detector may comprise one or more radiation shields. The one or more radiation shields may be configured to substantially block radiation from the radiation source. The one or more radiation shields may be located at at least a portion of a top region, a top wall or a top surface of the reference detector and/or at at least a portion of one or more side-walls of the reference detector. The gas sensor may comprise a compensator element. The compensator element may be operable to compensate for the presence of the at least one interference fluid in the measurement radiation path.
The gas sensor may be configured to reduce, mitigate or substantially eliminate the influence of the at least one interference fluid on the measurement of the at least one analyte gas.
The measurement detector has a measurement detector output, and the reference detector has an reference detector output, each of which may take any suitable form, such as a current, a voltage, analog or digital data, or the like.
The gas sensor may be configured to compensate for the presence of the at least one interference fluid in the measurement radiation path by obtaining a ratio of the measurement detector output to the reference detector output or a ratio of the reference detector output to the measurement detector output. The compensator element may be operable to obtain the ratio of the measurement detector output to the reference detector output.
The gas sensor may be configured to compensate for the presence of the at least one interference fluid in the measurement radiation path by rejecting or minimising signals common to the measurement detector output and the reference detector output.
The gas sensor may be configured to improve the signal to noise ratio of the measurement data. The gas sensor may be configured to improve the signal to noise ratio of the measurement data by using reference data from the reference detector. The gas sensor may be configured to improve the signal to noise ratio of the measurement data by obtaining a ratio of the measurement data to the reference data.
The measurement detector may be arranged to be responsive to a threshold concentration of the at least one interference fluid.
The reference detector may be arranged to be responsive to a threshold concentration of the at least one interference fluid.
The at least one analyte gas may include one or more greenhouse gas. The at least one analyte gas may include one or more gaseous alkanes. The at least one analyte gas may include one or more nitrogen-based gases. The at least one analyte gas may include one or more carbonbased gases. The at least one analyte gas may include one or more oxygen-based gases. The at least one analyte gas may include one or more hydrogen-based gases.
The at least one analyte gas may include methane (CH4), carbon dioxide (CO2), ammonia (NH3), nitrogen dioxide (NO2), carbon monoxide (CO), nitric oxide (NO), and/or ozone (O3). The at least one analyte gas may be methane (CH4), carbon dioxide (CO2), ammonia (NH3), nitrogen dioxide (NO2), carbon monoxide (CO), nitric oxide (NO), and/or ozone (O3). The gas sensor may be a methane gas sensor, a carbon dioxide gas sensor, an ammonia gas sensor, a nitrogen dioxide gas sensor, a carbon monoxide gas sensor, a nitric oxide gas sensor, and/or an ozone gas sensor.
The gas sensor may be configured to detect a single analyte gas. The single analyte gas may be methane, carbon dioxide, ammonia, nitrogen dioxide, carbon monoxide, nitric oxide, or ozone. The measurement detector may be configured to detect methane, carbon dioxide, ammonia, nitrogen dioxide, carbon monoxide, nitric oxide, and/or ozone. The reference detector may be configured to be non-responsive to methane, carbon dioxide, ammonia, nitrogen dioxide, carbon monoxide, nitric oxide, and/or ozone.
The reference detector may be configured to be less responsive to the presence of carbon dioxide, ammonia, nitrogen dioxide, carbon monoxide, nitric oxide, and/or ozone in the reference radiation path than the responsiveness of the measurement detector to the presence of methane, carbon dioxide, ammonia, nitrogen dioxide, carbon monoxide, nitric oxide, and/or ozone in the measurement radiation path.
The interference fluid may have at least one different property to the at least one analyte gas. The interference fluid may have a different absorption profile to the analyte gas. The interference fluid may be different to the at least one analyte gas. The interference fluid may be a fluid that is not methane. The interference fluid may be a fluid that is not carbon dioxide. The interference fluid may be a fluid that is not ammonia. The interference fluid may be a fluid that is not nitrogen dioxide. The interference fluid may be a fluid that is not carbon monoxide. The interference fluid may be a fluid that is not nitric oxide. The interference fluid may be a fluid that is not ozone. The interference fluid may be a fluid that is not methane, carbon dioxide, ammonia, nitrogen dioxide, carbon monoxide, nitric oxide or ozone. The interference fluid may not include methane. The interference fluid may not include carbon dioxide. The interference fluid may not include ammonia. The interference fluid may not include nitrogen dioxide. The interference fluid may not include carbon monoxide. The interference fluid may not include nitric oxide. The interference fluid may not include ozone. The interference fluid may not include methane, carbon dioxide, ammonia, nitrogen dioxide, carbon monoxide, nitric oxide and/or ozone.
The reference detector and the measurement detector may be configured to be responsive to the same interference fluid, or the same interference fluids.
The reference detector may be configured to be responsive to a single interference fluid. The measurement detector may be configured to be responsive to a single interference fluid.
The at least one interference fluid may include one or more gases, one or more liquids and/or one or more solids. The measurement detector and/or the reference detector may be responsive to at least one interference fluid that may include one or more gases, one or more liquids, and/or one or more solids. The measurement detector and/or the reference detector may be responsive to at least one interference fluid that may include water vapour, and/or liquid water.
The gas sensor may be configured such that the at least one analyte gas can move between the measurement radiation path and the reference radiation path. The gas sensor may be configured such that the at least one interference fluid can move between the measurement radiation path and the reference radiation path. The gas sensor may be configured such that a fluid flow path exists between the measurement radiation path and the reference radiation path. The gas sensor may be configured such that a fluid flow path exists between the measurement radiation path and the reference radiation path, such that the at least one analyte gas and the at least one interference fluid can move between the measurement radiation path and the reference radiation path.
The gas sensor may comprise one or more gas detection chambers. At least a portion of the measurement radiation path may be located in one or more gas detection chambers. At least a portion of the reference radiation path may be located in one or more gas detection chambers.
The one or more gas detection chambers may be configured to receive the at least one analyte gas from a source of analyte gas or gases. The one or more gas detection chambers may be configured to receive the at least one interference fluid from a source of interference fluid or fluids.
The source of analyte gas may be from the atmosphere, or ambient environment. The source of interference fluid may be from the atmosphere, or ambient environment.
The one or more gas detection chambers may comprise a gas inlet for allowing the at least one analyte gas into the chamber and/or at least one gas outlet for allowing the at least one analyte gas to exit the chamber.
The one or more gas detection chambers may comprise a fluid inlet for allowing the at least one interference fluid into the chamber and/or at least one fluid outlet for allowing the at least one interference fluid to exit the chamber.
The measurement radiation path may be arranged to pass through at least a region of the one or more gas detection chambers. The reference radiation path may be arranged to pass through at least a region of the one or more gas detection chambers. The measurement radiation path and the reference radiation path may pass through at least a portion of the same gas detection chamber.
The gas detection chamber may take any suitable shape or form.
The gas sensor may comprise one or more radiation guides. The one or more radiation guides may be arranged to guide radiation from the radiation source to the measurement detector and/or to guide radiation from the radiation source to the reference detector. The radiation guide(s) may take any suitable shape or form.
The reference radiation path may be arranged such that radiation from the radiation source can directly reach the reference detector.
The reference radiation path may be a straight path between the radiation source and the reference detector.
The reference radiation path and the measurement radiation path may be configured to be separate radiation paths, such that radiation from one path cannot reach the other path.
The measurement radiation path may be arranged such that radiation from the radiation source can directly reach the measurement detector.
The measurement radiation path may be longer than the reference radiation path. The measurement radiation path may be longer than the reference radiation path by a ratio of at least about 5:1 , optionally at least about 10:1 , optionally at least about 20: 1 , optionally at least about 40: 1 , optionally at least about 45:1 , optionally at least about 47:1 , optionally at least about 100:1 , optionally at least about 150:1 , optionally at least about 166: 1 , optionally about 47: 1 , optionally about 166: 1 , optionally about 167:1.
The measurement radiation path may be longer than the reference radiation path by a ratio of between about 5:1 and about 500:1 , optionally between about 5:1 and about 250:1 , optionally between about 100:1 and about 200:1 , optionally between about 125:1 and about 175:1 , optionally about 166:1 or about 167:1 , optionally between about 5:1 and about 100:1 , optionally between about 10:1 and about 80:1 , optionally between about 20:1 and about 60:1 , optionally between about 30:1 and about 50:1 , optionally between about 40:1 and about 50:1 .
The measurement radiation path may be between approximately 10 mm and 200 mm long, optionally between approximately 50 mm and approximately 180 mm long, optionally between approximately 100 mm and approximately 170 mm long, optionally between approximately 160 mm and approximately 170 mm long, optionally approximately 166 mm or approximately 167 mm long, optionally between approximately 30 mm and approximately 70 mm long, optionally between approximately 40 mm and 60 mm long, optionally approximately 47 mm long, optionally approximately 50 mm long. The measurement radiation path may be at least approximately 10 mm long, optionally at least approximately 20 mm long, optionally at least approximately 40 mm long, optionally at least approximately 50 mm long.
The reference radiation path may be between approximately 0.1 mm and 10 mm long, optionally between approximately 0.1 mm and 5 mm long, optionally between approximately 0.1 mm and approximately 2 mm long, optionally between approximately 0.2 mm and approximately 1.5 mm long, optionally between approximately 0.2 mm and approximately 1 mm long, optionally approximately 0.3 mm long, optionally between approximately 0.75 mm and approximately 1.25 mm long, optionally approximately 1 mm long. The reference radiation path may be less than approximately 50 mm long, optionally less than approximately 10 mm long, optionally less than approximately 5 mm long, optionally less than approximately 2 mm long.
The measurement radiation path may be arranged to be the major path and the reference radiation path may be arranged to be the minor path. In this arrangement, more radiation from the radiation source travels along the major path than the minor path. The ratio of the radiation in the major path to the minor path may be at least 1 :1 , optionally at least 10:1 , optionally at least 20: 1 , optionally at least 50: 1 , optionally at least 100: 1 .
The radiation source may be configured to provide more radiation to the measurement radiation path than the reference radiation path. The radiation source may be configured to provide at least 50 % of its radiation to the measurement radiation path, optionally at least 60 %, optionally at least 70 %, optionally at least 80 %, optionally at least 90 %.
The reference detector may be arranged to detect only a portion of the radiation emitted from the radiation source. The measurement detector may be arranged to detect only a portion of the radiation emitted from the radiation source.
A part of the radiation from the radiation source may be directed to the measurement radiation path and a part of the radiation from the radiation source may be directed to the reference radiation path. The radiation source may be a common radiation source, common to the measurement radiation path and the reference radiation path. The radiation source may be a broadband radiation source. The radiation source may be one or more light sources. The radiation source may be configured to emit radiation that at least partially corresponds to at least a portion of the absorption feature(s) of the at least one analyte gas. The radiation source may be configured to emit radiation in the UV, visible, infrared (I R), near IR, mid IR, far IR, or any combination thereof. The radiation source may be configured to emit radiation within a wavelength range of between 700 nm to 11 ,000 nm, optionally between 2,000 to 5,000 nm, optionally between 7,000 nm to 11 ,000 nm, optionally between 700 nm to 2,000 nm.
The one or more light sources may be light emitting diodes (LEDs).
The radiation source may include one or more flashlamps, thermal emitters, LEDs, and/or lasers, or the like.
The gas sensor may comprise one or more, or a plurality of radiation sources.
The gas sensor may comprise a single radiation source. The single radiation source may be a flashlamp, thermal emitter, LED, or laser, or the like.
The gas sensor may comprise one or more, or a plurality of measurement detectors. The gas sensor may comprise a single measurement detector.
The measurement data may be one or more output signals from the measurement detector, or may be based on one or more output signals from the measurement detector. The measurement detector may comprise one or more light detectors.
The one or more light detectors may be photodiodes (PDs). The measurement detector may include one or more thermopiles, one or more pyroelectric detectors, and/or one or more photodiodes, or the like.
The reference data may be one or more output signals from the reference detector, or may be based on one or more output signals from the reference detector.
The reference detector may comprise one or more light detectors. The one or more light detectors may be photodiodes (PDs). The reference detector may include one or more thermopiles, one or more pyroelectric detectors, and/or one or more photodiodes, or the like.
The reference detector may be arranged to be less sensitive to the presence of the at least one analyte gas in the reference radiation path relative to the sensitivity of the measurement detector to the at least one analyte gas. The reference detector may be arranged to be substantially non-responsive to the presence of the at least one analyte gas in the reference radiation path. The reference detector may be configured to be less responsive to the presence of the at least one analyte gas in the reference radiation path than the responsiveness of the measurement detector to the presence of the at least one analyte gas in the measurement radiation path. The reference detector may be arranged to be more responsive to the presence of the at least one interference fluid in the reference radiation path than the presence of the at least one analyte gas in the reference radiation path.
The reference detector may be arranged to be more responsive to the presence of the at least one interference fluid in the reference radiation path than the presence of the at least one analyte gas in the reference radiation path by a factor of at least 50 %, optionally at least 100 %, optionally at least 200 %, optionally at least 500 %.
The response of the reference detector to the at least one interference fluid and the response of the measurement detector to the at least one interference fluid may be configured to be substantially proportional, or equally proportional to each other. In this arrangement, as the concentration of the at least one interference fluid changes, the change in output of the reference detector and measurement detector is substantially proportional, or may be equally proportional.
The reference detector may be configured to obtain a measurement indicative of the output power of the radiation source. The reference detector may be located sufficiently close to the radiation source such that the reference detector output is indicative of the output power of the radiation source.
The reference detector may be configured to be substantially less responsive to the presence of the at least one analyte gas in the reference radiation path than the responsiveness of the measurement detector to the presence of the at least one analyte gas in the measurement radiation path, and the reference detector may be configured to obtain a measurement indicative of the output power of the radiation source.
The reference detector may be arranged to be substantially non- responsive to the presence of the at least one analyte gas in the reference radiation path and the reference detector may be configured to obtain a measurement indicative of the output power of the radiation source. The gas sensor may be configured to compensate the measurement of the at least one analyte gas by mitigating or minimising the influence of variation(s) in output power of the radiation source.
The gas sensor may comprise any suitable signal processing element(s).
The gas sensor may comprise one or more, or a plurality of reference detectors. Each reference detector may be arranged to define a reference radiation path between the respective reference detector and the radiation source. The gas sensor may be configured to compensate for the presence of the at least one interference fluid in the measurement radiation path using reference data from the, or each, reference detector.
The gas sensor may comprise a single reference detector.
The gas sensor may be a lightweight sensor, a portable sensor, a wall- mountable sensor, or the like.
The radiation source and the reference detector may be thin-film electronic components.
The gas sensor may be configured to measure, or infer, the temperature of the radiation source. The gas sensor may be configured to measure the forward voltage of an LED of the radiation source in order to measure or infer the temperature of the radiation source.
The reference detector may be arranged to be close enough to the radiation source such that a measurement of the temperature of the radiation source provides a measurement of, or a suitable approximation of, the temperature of the reference detector. The radiation source and the reference detector may be thermally connected. The radiation source and the reference detector may be thermally connected by way of one or more thermal connection members. The one or more thermal connection members may be, or may include, at least a portion of a substrate on which the radiation source and the reference detector are located.
The gas sensor may comprise one or more filters. The one or more filters may be arranged in the measurement light path and/or the reference light path to filter radiation, as is known in the field of gas sensing.
The gas sensor may comprise a housing. One or more, or all, of the components of the gas sensor may be located in, or on, the housing. The housing may take any suitable size and shape to house one or more components of the gas sensor.
The gas sensor may comprise a power supply and/or may be connectable to a source of power. The power supply may be a battery, or the like.
According to a second aspect of the present invention there is provided a gas sensor comprising: a radiation source; a measurement detector; and a reference detector; wherein the radiation source and the measurement detector are arranged to define a measurement radiation path, wherein the radiation source and the reference detector are arranged to define a reference radiation path, wherein the gas sensor is configured to detect at least one analyte gas in the measurement radiation path using measurement data from the measurement detector, and wherein the gas sensor is configured to compensate the measurement of the at least one analyte gas using reference data from the reference detector.
The gas sensor may comprise a compensator element.
The compensator element may be operable to compensate the measurement of the at least one analyte gas by obtaining a ratio of the measurement detector output to the reference detector output or a ratio of the reference detector output to the measurement detector output. The compensator element may be operable to obtain the ratio of the measurement detector output to the reference detector output.
The compensator element may be operable to compensate for the presence of at least one interference fluid in the measurement radiation path.
The gas sensor may be configured to reduce or mitigate the influence of the at least one interference fluid on the measurement of the at least one analyte gas. The gas sensor may be configured to substantially eliminate the influence of the at least one interference fluid on the measurement of the at least one analyte gas.
The gas sensor may be configured to compensate for the presence of the at least one interference fluid in the measurement radiation path by obtaining a ratio of the measurement detector output to the reference detector output. The gas sensor may be configured to compensate the measurement of the at least one analyte gas in the measurement radiation path by rejecting or minimising signals common to the measurement detector output and the reference detector output.
The gas sensor may be configured to compensate for the presence of the at least one interference fluid in the measurement radiation path by rejecting or minimising signals common to the measurement detector output and the reference detector output.
The gas sensor may be configured to improve the signal to noise ratio of the measurement data. The gas sensor may be configured to improve the signal to noise ratio of the measurement data by using reference data from the reference detector. The gas sensor may be configured to improve the signal to noise ratio of the measurement data by obtaining a ratio of the measurement data to the reference data.
The reference detector may be configured to obtain a measurement indicative of the output power of the radiation source.
The reference detector may be configured to be substantially less responsive to the presence of the at least one analyte gas in the reference radiation path than the responsiveness of the measurement detector to the presence of the at least one analyte gas in the measurement radiation path, and the reference detector may be configured to obtain a measurement indicative of the output power of the radiation source.
The reference detector may be arranged to be substantially non- responsive to the presence of the at least one analyte gas in the reference radiation path and the reference detector may be configured to obtain a measurement indicative of the output power of the radiation source.
The gas sensor may be configured to compensate the measurement of the at least one analyte gas by mitigating or minimising the influence of variation(s) in output power of the radiation source.
Embodiments of the second aspect of the present invention may include one or more features of the first aspect of the present invention or its embodiments. Similarly, embodiments of the first aspect of the present invention may include one or more features of the second aspect of the present invention or its embodiments.
According to a third aspect of the present invention there is provided a method of operating a gas sensor, the method comprising the steps of: (i) providing a gas sensor comprising: a radiation source; a measurement detector; and a reference detector; wherein the radiation source and the measurement detector are arranged to define a measurement radiation path, wherein the radiation source and the reference detector are arranged to define a reference radiation path, wherein the reference detector is configured to be responsive to the presence of at least one interference fluid in the reference radiation path, wherein the measurement detector is configured to be responsive to the presence of at least one interference fluid in the measurement radiation path, and wherein the gas sensor is configured to detect at least one analyte gas in the measurement radiation path using measurement data from the measurement detector and reference data from the reference detector, and wherein the gas sensor is configured to compensate for the presence of the at least one interference fluid in the measurement radiation path using the reference data; and
(ii) activating the radiation source;
(iii) obtaining measurement data from the measurement detector;
(iv) obtaining reference data from the reference detector; and
(v) compensating the measurement data using the reference data.
Embodiments of the third aspect of the present invention may include one or more features of the first and/or second aspects of the present invention or their embodiments. Similarly, embodiments of the first and/or second aspects of the present invention may include one or more features of the third aspect of the present invention or its embodiments.
According to a fourth aspect of the present invention there is provided a method of operating a gas sensor, the method comprising the steps of:
(i) providing a gas sensor comprising: a radiation source; a measurement detector; and a reference detector; wherein the radiation source and the measurement detector are arranged to define a measurement radiation path, wherein the radiation source and the reference detector are arranged to define a reference radiation path, wherein the gas sensor is configured to detect at least one analyte gas in the measurement radiation path using measurement data from the measurement detector, and wherein the gas sensor is configured to compensate the measurement of the at least one analyte gas using reference data from the reference detector; (ii) activating the radiation source;
(iii) obtaining measurement data from the measurement detector;
(iv) obtaining reference data from the reference detector; and
(v) compensating the measurement data using the reference data.
Embodiments of the fourth aspect of the present invention may include one or more features of the first, second and/or third aspects of the present invention or their embodiments. Similarly, embodiments of the first, second, and/or third aspects of the present invention may include one or more features of the fourth aspect of the present invention or its embodiments.
It should be appreciated that the order that the steps are recited and any numbering given to those steps in any of the methods described herein is only exemplary, and that the steps may be carried out in any order except where it is clear that a specific order is meant and/or a specific order is required or essential for the proper functioning of the method.
Brief description of the drawings
Embodiments of the invention will now be described, by way of example, with reference to the drawings, in which:
Fig. 1 shows a top view of the reference detector and radiation source of a gas sensor in accordance with an embodiment of the invention;
Fig. 2 shows a simplified schematic of the gas sensor of Fig. 1 ;
Fig. 3 shows graphs of relative humidity, measurement and reference detector outputs, and the compensated output signal;
Fig. 4 shows a graph of gas measurement versus relative humidity over time; Fig. 5 shows a graph of the gas sensor output for different temperatures; and
Fig. 6 shows the performance of the gas sensor across gas concentration, temperature and output power of the radiation source.
Description of preferred embodiments
With reference to Figs. 1 to 6, a gas sensor 1 in accordance with an embodiment of the invention is illustrated and described herein.
The gas sensor 1 comprises a radiation source 2, a measurement detector 4, and a reference detector 6.
As shown in the simplified schematic of Fig. 2, the radiation source 2 and the measurement detector 4 are arranged to define a measurement radiation path 8. The radiation source 2 and the reference detector 6 are arranged to define a reference radiation path 10.
The gas sensor 1 is configured to detect at least one analyte gas 12 in the measurement radiation path 8 using measurement data from the measurement detector 4. The gas sensor 1 is configured to compensate the measurement of the at least one analyte gas 12 using reference data from the reference detector 6.
In the embodiments illustrated and described here, the reference detector 6 is configured to be responsive to the presence of at least one interference fluid 14 in the reference radiation path 10, and the measurement detector 4 is configured to be responsive to the presence of at least one interference fluid 14 in the measurement radiation path 8. In this embodiment, the gas sensor 1 is configured to compensate for the presence of the at least one interference fluid 14 in the measurement radiation path 8 using the reference data. It will be understood that in other embodiments, the gas sensor 1 can compensate the measurement of the analyte gas 12 in other ways, some of which will be described below.
In the embodiment illustrated and described here, when the interference fluid 14 is not present, or is below a threshold value, the gas sensor 1 still compensates the measurement of the at least one analyte gas 12.
The gas sensor 1 is configured to measure the concentration of the at least one analyte gas 12 in the measurement radiation path 4. However, in other embodiments the gas sensor 1 could detect the presence of the at least one analyte gas 12, which could be when the at least one analyte gas 12 is above a threshold value.
The gas sensor 1 detects the at least one analyte gas 12 by way of absorption, as is known in the field of gas sensors. In the embodiments described here, this occurs by radiation in the measurement radiation path 8 being absorbed by the analyte gas 12, which can be detected at the measurement detector 4 as a change in measurement data.
As best shown in Fig. 1 , the reference detector 6 is located adjacent to the radiation source 2.
The reference detector 6 comprises at least one radiation detection area 6a, the measurement detector 4 comprises at least one radiation detection area 4a, and the radiation source 2 comprises at least one radiation emitting area 2a. At least one radiation detection area 6a of the reference detector 6 is arranged adjacent to, and arranged to face, a radiation emitting area 2a of the radiation source 2.
The radiation detector 6 is arranged in proximity to the radiation source 2 and the measurement detector 4 is arranged to be remote from the radiation source 2. At least one radiation detection area 6a of the reference detector 6 is arranged to be in proximity to at least one radiation emitting area 2a of the radiation source 2, and at least one radiation detection area 4a of the measurement detector 4 is arranged to be remote from at least one radiation emitting area 2a of the radiation source 2.
The reference detector 6 and the radiation source 2 are spaced apart along the reference radiation path 10. At least one radiation detection area 6a of the reference detector 6 is spaced apart from at least one radiation emitting area 2a of the radiation source 2. The reference detector 6 and the radiation source 2 are spaced apart a sufficient distance to enable the reference detector 6 to be responsive to the at least one interference fluid 14. The reference detector 6 and the radiation source 2 are sufficiently close to minimise or remove the sensitivity of the reference detector 6 to the at least one analyte gas 12.
The measurement detector 4 and the radiation source 2 are spaced apart along the measurement radiation path 8. The measurement detector 4 and the radiation source 2 are spaced apart a sufficient distance to enable the gas sensor 1 to detect the at least one analyte gas 12. At least one radiation detection area 4a of the measurement detector 4 is spaced apart from at least one radiation emitting area 2a of the radiation source 2. The measurement detector 4 and the reference detector 6 are spaced apart.
The reference detector 6 and the radiation source 2 are located on the same substrate 16 and are integrally formed. The substrate 16 can be any suitable substrate, such as a semiconductor die. The radiation source 2 and the measurement detector 4 are separately formed.
In this embodiment, the reference detector 6, the measurement detector 4 and the radiation source 2 are all fixed relative to each other.
The radiation emitting area 2a of the radiation source 2 is located at a top region 2b thereof and at one or more side-walls thereof 2d. The top region 2b includes a top surface 2c which forms a top wall.
At least one radiation detection area 6a of the reference detector 6 is located at a side-wall 6d thereof.
The at least one radiation emitting area 2a located on the one or more side-walls 2d of the radiation source 2 is arranged to face the at least one radiation detection area 6a on the one or more side-walls 6d of the reference detector 6. A side-wall 2d of the radiation source 2 is arranged adjacent to a side-wall 6d of the reference detector 6.
The reference detector 6 comprises a plurality of radiation shields 6e configured to substantially block radiation from the radiation source 2. The radiation shields 6e are located at at least a portion of a top region 6b of the reference detector and at at least a portion of one or more side-walls 6d of the reference detector 6. The top region 6b includes a top surface 6c, which is a top wall. In this embodiment, the reference detector 6 is configured to detect side radiation emissions from the radiation source 2.
The gas sensor 1 comprises a compensator element 18, which may be any suitable element, such as an amplifier circuit, a computing device, or the like, operable to carry out the required compensation. In this embodiment, the compensator element 18 is operable to compensate the measurement of the analyte gas 12 by obtaining a ratio of the measurement detector 4 output to the reference detector 6 output, which mitigates or eliminates the effect of signals common to both reference and measurement. In this embodiment, the compensator element 18 is operable to compensate for the presence of the at least one interference fluid 14 in the measurement radiation path 8, using the ratio of signals, because the reference detector 6 is arranged to be sensitive to the interference fluid(s) 14 but insensitive, or substantially less sensitive to the analyte gas 12. Therefore, the measurement detector 4 and the reference detector 6 will both be responsive to the interference fluid 14, which will be mitigated through a ratio measurement, and changes in analyte gas 12 will result in changes in the overall, compensated, output. Likewise, any degradation in radiation source 2 performance, or variation due to temperature, can be mitigated because the variations will be common to both the reference and measurement detectors 4, 6.
The gas sensor 1 is configured to reduce or mitigate the influence of the at least one interference fluid 14 on the measurement of the at least one analyte gas 12. In other embodiments, the gas sensor 1 may be configured to substantially eliminate the influence of the at least one interference fluid 14 on the measurement of the at least one analyte gas 12. The gas sensor 1 is configured to compensate for the presence of the at least one interference fluid 14 in the measurement radiation path 8 by obtaining a ratio of the measurement detector 4 output to the reference detector 6 output (or vice versa). The output of the detectors 4, 6, can take any suitable form, such as output current, output voltage, or the like, depending on the type of detectors 4, 6, and compensator element 18 used.
The compensator element 18 is operable to obtain the ratio of the measurement detector 4 output to the reference detector 6 output. However, in other embodiments a different compensation technique could be used.
As discussed above, the gas sensor 1 is configured to compensate for the presence of the at least one interference fluid 14 in the measurement radiation path 8 by rejecting or minimising signals common to the measurement detector 4 output and the reference detector 6 output, in the resultant compensated output signal. So, for example, if there is no interference fluid 14 present (or a negligible amount), the compensator element 18 is still able to minimise the influence of common-mode signals, such as changes in radiation source 2 performance, or electrical noise common to the reference and measurement detectors 4, 6. Without wishing to be bound by theory, the arrangement of the gas sensor 1 and the compensation technique allows for increased signal to noise ratio of the measurement data, increased rejection of common mode signals, whilst resulting in a simpler calibration of the gas sensor 1 .
The measurement detector 4 is arranged to be responsive to a threshold concentration of the at least one interference fluid 14. The reference detector 6 may be arranged to be responsive to a threshold concentration of the at least one interference fluid 14.
The at least one analyte gas 12 is methane (CH4). In other embodiments, the analyte gas 12 may include methane, carbon dioxide (CO2), ammonia (NH3), nitrogen dioxide (NO2), carbon monoxide (CO), nitric oxide (NO), and/or ozone (O3), or may include one or more other gases.
In this embodiment, the gas sensor 1 can detect a single analyte gas 12. In other embodiments, the gas sensor 1 could be configured to detect or measure the concentration of one or more analyte gases.
The measurement detector 4 is configured to detect methane. This can be achieved in any suitable manner. For example, filters at the measurement detector 4 and/or the radiation source 2 can be used as is known in the art of gas sensing.
In this embodiment, the reference detector 6 is configured to be less responsive to methane than the responsiveness of the measurement detector 4 to methane, at least below an upper threshold value. It will be understood that the distance between the reference detector 6 and the radiation source 2, and the properties of the reference detector 6 and the radiation source 2, can be designed such that the reference detector 6 is less sensitive, or not sensitive, to methane.
In the embodiments described here, the interference fluid 14 is water vapour. The reference detector 6 is configured to be responsive to a single interference fluid 14 and the measurement detector 4 is configured to be responsive to a single interference fluid 14. In other embodiments, the interference fluid 14 may be one or more fluids that have at least one different property to the at least one analyte gas 12.
In this embodiment, the interference fluid 14 is different to the at least one analyte gas 12.
It will be understood that, whilst in this embodiment the interference fluid 14 is not methane, in other embodiments methane could be an interference fluid, and a different analyte gas 12 could be detected.
In this embodiment, the reference detector 6 and the measurement detector 4 are configured to be responsive to the same interference fluid 14. This can be achieved in numerous ways, such as the use of filters, the design of the spacing between the detectors 4, 6 and the radiation source 2, and in the type of components used.
The gas sensor 1 is configured such that a fluid flow path exists between the measurement radiation path 8 and the reference radiation path 10, such that the at least one analyte gas 12 and the at least one interference fluid 14 can move between the measurement radiation path 8 and the reference radiation path 10.
The gas sensor 1 comprises a gas detection chamber 20, which encloses the measurement radiation path 8 and the reference radiation path 10.
The gas detection chamber 20 is configured to receive the at least one analyte gas 12 from the outside of the gas sensor 1 , although in other embodiments the gas detection chamber 20 could receive the at least one analyte gas 12 from a source of analyte gas or gases. The gas detection chamber 20 is also configured to receive the at least one interference fluid 14 from the outside of the gas sensor 1 , but in other embodiments the at least one interference fluid 14 could be received from a source of interference fluid 14 or interference fluids 14. In this embodiment, both the at least one analyte gas 12 and the at least one interference fluid 14 enter the gas detection chamber 20 from the atmosphere, or ambient environment.
The gas detection chamber 20 comprises a fluid inlet and a fluid outlet (not shown) for allowing the at least one analyte gas 12 and the at least one interference fluid 14 into/out of the chamber 20. Any suitable fluid in let/outlet can be used, and the gas detection chamber 20 may take any suitable shape or form.
The gas sensor 1 can comprise one or more radiation guides for guiding radiation from the radiation source 2 to the measurement detector 4 and/or to guide radiation from the radiation source 2 to the reference detector 6. The radiation guide(s) may take any suitable shape or form.
The reference radiation path 10 is arranged such that radiation from the radiation source 2 can directly reach the reference detector 6.
The reference radiation path 10 is a straight path between the radiation source 2 and the reference detector 6.
The reference radiation path 10 and the measurement radiation path 8 are configured to be separate radiation paths, such that radiation from one path cannot reach the other path.
The measurement radiation path 8 is arranged such that radiation from the radiation source 2 can directly reach the measurement detector 4. In this embodiment, the measurement radiation path 8 is longer than the reference radiation path 10 by a ratio of about 47:1 . The measurement radiation path 8 is approximately 47 mm long and the reference radiation path 10 is approximately 1 mm long.
The measurement radiation path 8 is arranged to be the major path and the reference radiation path 10 is arranged to be the minor path. In this arrangement, more radiation from the radiation source 2 travels along the major path than the minor path. The ratio of the radiation in the major path to the minor path is at least 5:1 , and can be at least 10:1 , optionally at least 20: 1 , optionally at least 50: 1 , optionally at least 100: 1 , optionally at least 500:1.
The radiation source 2 is configured to provide more radiation to the measurement radiation path 8 than the reference radiation path 10. The radiation source 2 is configured to provide at least 90 % of its radiation to the measurement radiation path 8.
The reference detector 6 is arranged to detect only a portion of the radiation emitted from the radiation source 2.
The radiation source 2 is a common radiation source 2, common to the measurement radiation path 8 and the reference radiation path 10.
The radiation source 2 is a broadband radiation source, which in this embodiment is a single light emitting diode (LED) configured to emit light that corresponds to at least a portion of the absorption features of the at least one analyte gas 12. In other embodiments, the gas sensor could comprise one or more, or a plurality of radiation sources 2, which could be one or more flashlamps, thermal emitters, LEDs, and/or lasers, or the like.
In this embodiment, the gas sensor 1 comprises a single measurement detector 4 and a single reference detector 6, which are both photodiodes. In other embodiments, the gas sensor 1 could comprise one or more, or a plurality of measurement detectors 4 and one or more, or a plurality of reference detectors 6. The detectors 4, 6, could include one or more thermopiles, one or more pyroelectric detectors, and/or one or more photodiodes, or the like.
The measurement data is based on one or more output signals from the measurement detector 4.
The reference data is based on one or more output signals from the reference detector 6.
The reference detector 6 is arranged to be less responsive to the presence of the at least one analyte gas 12 in the reference radiation path 10 than the responsiveness of the measurement detector 4 to the presence of the at least one analyte gas 12 in the measurement radiation path 8, at least below an upper threshold value. The reference detector 6 is arranged to be more responsive to the presence of the at least one interference fluid 14 in the reference radiation path 10 than the presence of the at least one analyte gas 12 in the reference radiation path 10. In other embodiments it may be sufficient that the reference detector 6 is arranged to be less responsive to the analyte gas 12 than the interference fluid 14. Without wishing to be bound by theory, the reference detector 6 is arranged to be more responsive to the presence of the at least one interference fluid 14 in the reference radiation path 10 than the presence of the at least one analyte gas 12 in the reference radiation 10 path by a factor of at least 50 %. In other embodiments this factor could be at least 100 %, optionally at least 200 %, optionally at least 500 %.
The response of the reference detector 6 to the at least one interference fluid 14 and the response of the measurement detector 4 to the at least one interference fluid 14 are configured to be substantially proportional, or equally proportional to each other. In this embodiment, as the concentration of the at least one interference fluid 14 changes, the change in output of the reference detector 6 and measurement detector 4 is substantially proportional, or may be equally proportional.
The reference detector 6 is configured to obtain a measurement indicative of the output power of the radiation source 2. In this embodiment, the reference detector 6 functions as a power reference, and the ratio of the measurement data to the reference data helps to mitigate variations in radiation source 2 output power. It will be apparent that if there is no interference fluid 14 present, the reference detector 6 can obtain a measure of the output power of the radiation source 2, which can be used to compensate the measurement detector 4 output. In this embodiment, the gas sensor 1 is configured to compensate the measurement of the at least one analyte gas 12 by mitigating or minimising the influence of variation(s) in output power of the radiation source 2.
In this embodiment, the gas sensor 1 includes amplification and signal processing elements to amplify and process the output from the measurement and reference detectors 4, 6. The gas sensor 1 can include any suitable signal processing elements.
In this embodiment, the gas sensor 1 is a lightweight, portable and wall- mountable sensor, but in other embodiments the gas sensor 1 may be designed differently.
The radiation source 2 and the reference detector 6 are thin-film electronic components.
In this embodiment, the gas sensor 1 is configured to measure or infer the temperature of the radiation source 2 by measuring the forward voltage of the LED.
The reference detector 6 is arranged to be close enough to the radiation source 2 such that a measurement of the temperature of the radiation source 2 provides a measurement of, or a suitable approximation of, the temperature of the reference detector 6.
The radiation source 2 and the reference detector 6 are thermally connected by way of the common substate 16 on which they are mounted. The substrate 16 acts as a thermal connection member. It will be understood that the radiation source 2 and the reference detector 6 could be separately formed on different substrates, and in some embodiments they could be thermally connected using any suitable thermal connection member.
The gas sensor 1 comprises a filter 22 arranged in the measurement light path 8 to filter radiation, as is known in the field of gas sensing. In this embodiment, the reference radiation path 10 does not include filters, but it will be understood that in other embodiments, one or more filters may be included therein.
The gas sensor 1 comprises a battery, but in other embodiments the gas sensor 1 could be connectable to a source of power.
The components of the gas sensor 1 are located in, or on, a housing (not shown) of the gas sensor 1 . The housing may take any suitable size and shape to house the components of the gas sensor 1 .
Figs. 3 to 6 highlight the performance of the gas sensor 1 .
Fig. 3 shows (i) the relative humidity over time, (ii) the output from the measurement detector 4, (iii) the output from the reference detector 6 and (iv) the compensated output data obtained after taking a ratio of (ii) and (iii), all for a fixed concentration of analyte gas. Fig. 3 demonstrates for variable relative humidity the compensated output signal is not substantially affected, and thus the presence of water vapour in the reference and measurement radiation paths 10, 8, has been mitigated.
Fig. 4 plots the compensated output signal as a gas measurement (in parts per million) of the gas sensor 1 , against the relative humidity over time, which demonstrates the gas sensor’s 1 ability to compensate for an interference fluid 14 (water vapour).
Fig. 5 shows the compensated output signal as a gas measurement, for a gas concentration of 50,000 ppm, at various temperatures, showing both the raw output and with averaging applied. The upper and lower boundaries on the graph of Fig. 5 highlight a target performance level to meet. Fig. 6 shows the gas sensor 1 performance across gas concentration (of methane), temperature and the optical power of the radiation source 2.
An example of how the gas sensor 1 can be used will now be provided.
First, a gas sensor 1 as described above is provided in a location for gas sensing or monitoring.
Next, the radiation source 2 is activated, which may include pulsing the radiation source 2 or any suitable way of activating the radiation source 2. Radiation will then travel along the measurement radiation path 8 and the reference radiation path 10. Some of the radiation will be absorbed by the at least one analyte gas 12 (if present) and the at least one interference fluid 14 (if present), and the resultant variations in received radiation at the reference detector 6 and the measurement detector 4 result in variations in their output. A change in analyte gas 12 concentration will predominantly affect the output of the measurement detector 4, and will have no substantial effect, or minimal effect, on the reference detector 6. A change in the concentration of interference fluid 14 will affect both the measurement detector 4 and the reference detector 6.
Next, measurement data is obtained from the measurement detector 4. In this embodiment, the measurement data is obtained via the measurement photodiode current and subsequent amplification, as is known in the art.
The reference data is also obtained from the reference detector 6, using the reference photodiode current and amplification as is known in the art. To obtain a measurement of the concentration of the analyte gas 12, the measurement data is compensated by obtaining a ratio of the measurement data to the reference data. In this embodiment, this means dividing an amplified measure of the measurement photodiode current by an amplified version of the reference photodiode current. As described above, there are other ways in which the measurement data can be compensated, and the example here is provided for illustrative purposes.
With a compensated measurement obtained, the concentration of analyte gas can be stored or processed in any desirable manner. For example, the compensated measurement signal may be stored as a value, may be transmitted to a computing device, or may be amplified or used for processing by another circuit element or the like.
Typically, the gas sensor 1 will be configured to then periodically activate and deactivate the radiation source 2 and to obtain periodic measurements of the gas concentration.
Modifications and improvements may be made to the foregoing embodiments without departing from the scope of the present invention.
For example, the at least one interference fluid could include one or more gases, one or more liquids, and/or one or more solids. Whilst in the embodiments described above the interference fluid is water vapour, it will be understood that the interference fluid could include liquid water, or other types of fluid.
In other embodiments, the measurement radiation path 8 could be arranged to pass through at least a region of the one or more gas detection chambers 20. The reference radiation path 10 could be arranged to pass through at least a region of the one or more gas detection chambers 20.
The gas sensor 1 could comprise a plurality of reference detectors 6, each reference detector 6 being arranged to define a reference radiation path 10 between the respective reference detector 6 and the radiation source 2. The gas sensor 1 could be configured to compensate for the presence of the at least one interference fluid 14 in the measurement radiation path 8 using reference data from the, or each, reference detector 6.
It will be understood that the gas sensor 1 could comprise a plurality of radiation sources 2.
Whilst in the embodiments illustrated and described here, an interference fluid 14 (water vapour) has been used to explain the concept of reducing or mitigating the effect thereof on the analyte gas measurement, it will be understood that the gas sensor 1 still has effective compensation of the gas measurement even when there is no interference fluid present.
In the embodiments illustrated and described above, the analyte gas is methane. In other embodiments, the gas sensor could be configured to detect any suitable analyte gas or gases, which may include methane, carbon dioxide (CO2), ammonia (NH3), nitrogen dioxide (NO2), carbon monoxide (CO), nitric oxide (NO), and/or ozone (O3), or the like.

Claims

Claims
1. A gas sensor comprising: a radiation source; a measurement detector; and a reference detector; wherein the radiation source and the measurement detector are arranged to define a measurement radiation path, wherein the radiation source and the reference detector are arranged to define a reference radiation path, wherein the reference detector is configured to be responsive to the presence of at least one interference fluid in the reference radiation path, wherein the measurement detector is configured to be responsive to the presence of at least one interference fluid in the measurement radiation path, and wherein the gas sensor is configured to detect at least one analyte gas in the measurement radiation path using measurement data from the measurement detector and reference data from the reference detector, and wherein the gas sensor is configured to compensate for the presence of the at least one interference fluid in the measurement radiation path using the reference data.
2. The gas sensor of claim 1 , wherein at least one radiation detection area of the reference detector is arranged adjacent to a radiation emitting area of the radiation source.
3. The gas sensor of claim 1 or claim 2, wherein at least one radiation detection area of the reference detector is arranged to face at least one radiation emitting area of the radiation source.
4. The gas sensor of any preceding claim, wherein at least one radiation detection area of the reference detector is arranged in proximity to at least one radiation emitting area of the radiation source and at least one radiation detection area of the measurement detector is arranged to be remote from at least one radiation emitting area of the radiation source along the measurement radiation path.
5. The gas sensor of any preceding claim, wherein at least one radiation emitting area of the radiation source is located at one or more side-walls thereof, and wherein at least one radiation detection area of the reference detector is located at one or more side-walls thereof.
6. The gas sensor of claim 5, wherein the at least one radiation emitting area located on the one or more side-walls of the radiation source is arranged to face the at least one radiation detection area on the one or more side-walls of the reference detector.
7. The gas sensor of any preceding claim, wherein the gas sensor is configured to reduce, mitigate or substantially eliminate the influence of the at least one interference fluid on the measurement of the at least one analyte gas.
8. The gas sensor of any preceding claim, wherein the gas sensor is configured to compensate for the presence of the at least one interference fluid in the measurement radiation path by rejecting or minimising signals common to the measurement detector output and the reference detector output.
9. The gas sensor of any preceding claim, wherein the gas sensor is configured to compensate for the presence of the at least one interference fluid in the measurement radiation path by obtaining a ratio of the measurement detector output to the reference detector output or a ratio of the reference detector output to the measurement detector output.
10. The gas sensor of any preceding claim, wherein the at least one analyte gas includes one or more greenhouse gas, one or more gaseous alkanes, one or more nitrogen-based gases, one or more carbon-based gases, one or more oxygen-based gases, one or more hydrogen-based gases, methane (CH4), carbon dioxide (CO2), ammonia (NH3), nitrogen dioxide (NO2), carbon monoxide (CO), nitric oxide (NO), and/or ozone (O3).
11 . The gas sensor of any preceding claim, wherein the at least one interference fluid includes water vapour and/or liquid water.
12. The gas sensor of any preceding claim, wherein the gas sensor is configured such that a fluid flow path exists between the measurement radiation path and the reference radiation path, such that the at least one analyte gas and the at least one interference fluid can move between the measurement radiation path and the reference radiation path.
13. The gas sensor of any preceding claim, wherein the measurement radiation path is longer than the reference radiation path by a ratio of at least about 5:1 , optionally at least about 10:1 , optionally at least about 20:1 , optionally at least about 40:1 , optionally at least about 45:1 , optionally at least about 47:1 , optionally at least about 100:1 , optionally at least about 150:1 , optionally at least about 166:1 , optionally about 47:1 , optionally about 166: 1 , optionally about 167: 1 .
14. The gas sensor of any preceding claim, wherein the measurement radiation path is longer than the reference radiation path by a ratio of between about 5:1 and about 500:1 , optionally between about 5:1 and about 250:1 , optionally between about 100:1 and about 200:1 , optionally between about 125:1 and about 175:1 , optionally about 166:1 or about 167:1 , optionally between about 5:1 and about 100:1 , optionally between about 10: 1 and about 80: 1 , optionally between about 20: 1 and about 60: 1 , optionally between about 30:1 and about 50:1 , optionally between about 40:1 and about 50:1 .
15. The gas sensor of any preceding claim, wherein the radiation source is a common radiation source, common to the measurement radiation path and the reference radiation path.
16. The gas sensor of any preceding claim, wherein the reference detector is arranged to be substantially non-responsive to the presence of the at least one analyte gas in the reference radiation path, or wherein the reference detector is configured to be less responsive to the presence of the at least one analyte gas in the reference radiation path than the responsiveness of the measurement detector to the presence of the at least one analyte gas in the measurement radiation path.
17. The gas sensor of any preceding claim, wherein the reference detector is configured to obtain a measurement indicative of the output power of the radiation source.
18. The gas sensor of any preceding claim, wherein the gas sensor is configured to compensate the measurement of the at least one analyte gas by mitigating or minimising the influence of variation(s) in output power of the radiation source.
19. The gas sensor of any preceding claim, wherein the radiation source and the reference detector are thermally connected by way of one or more thermal connection members.
20. The gas sensor of claim 19, wherein the one or more thermal connection members are at least a portion of substrate on which the radiation source and the reference detector are located.
21 . The gas sensor of any preceding claim, wherein the reference detector and the radiation source are integrally formed on the same substrate, or wherein the reference detector and the radiation source are separately formed, or wherein the reference detector and the radiation source are separately formed on the same substrate.
22. The gas sensor of any preceding claim, wherein the radiation source includes one or more flashlamps, thermal emitters, light emitting diodes (LEDs), and/or lasers and wherein the reference detector includes one or more thermopiles, one or more pyroelectric detectors, and/or one or more photodiodes.
23. A gas sensor comprising: a radiation source; a measurement detector; and a reference detector; wherein the radiation source and the measurement detector are arranged to define a measurement radiation path, wherein the radiation source and the reference detector are arranged to define a reference radiation path, wherein the gas sensor is configured to detect at least one analyte gas in the measurement radiation path using measurement data from the measurement detector, and wherein the gas sensor is configured to compensate the measurement of the at least one analyte gas using reference data from the reference detector.
24. A method of operating a gas sensor, the method comprising the steps of:
(i) providing a gas sensor comprising: a radiation source; a measurement detector; and a reference detector; wherein the radiation source and the measurement detector are arranged to define a measurement radiation path, wherein the radiation source and the reference detector are arranged to define a reference radiation path, wherein the gas sensor is configured to detect at least one analyte gas in the measurement radiation path using measurement data from the measurement detector, and wherein the gas sensor is configured to compensate the measurement of the at least one analyte gas using reference data from the reference detector;
(ii) activating the radiation source;
(iii) obtaining measurement data from the measurement detector;
(iv) obtaining reference data from the reference detector; and
(v) compensating the measurement data using the reference data.
25. A method of operating a gas sensor, the method comprising the steps of:
(i) providing a gas sensor comprising: a radiation source; a measurement detector; and a reference detector; wherein the radiation source and the measurement detector are arranged to define a measurement radiation path, wherein the radiation source and the reference detector are arranged to define a reference radiation path, wherein the reference detector is configured to be responsive to the presence of at least one interference fluid in the reference radiation path, wherein the measurement detector is configured to be responsive to the presence of at least one interference fluid in the measurement radiation path, and wherein the gas sensor is configured to detect at least one analyte gas in the measurement radiation path using measurement data from the measurement detector and reference data from the reference detector, and wherein the gas sensor is configured to compensate for the presence of the at least one interference fluid in the measurement radiation path using the reference data; and
(ii) activating the radiation source;
(iii) obtaining measurement data from the measurement detector;
(iv) obtaining reference data from the reference detector; and
(v) compensating the measurement data using the reference data.
PCT/GB2023/050338 2022-02-15 2023-02-15 Gas sensor reference WO2023156767A1 (en)

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GB2615600A (en) 2023-08-16

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