Gas sensor enabling the identification of a gaseous species

Abstract

gas sensor (1) comprising a housing (2), the sensor also comprising: a light source (10), configured to emit a light wave (11) propagating in the housing, forming, from the light source, a first cone of light (Ω1); two measurement photodetectors, extending at two different distances from the light source; a processing unit, programmed to identify a gaseous species present in the gas from detection signals resulting from the two measurement photodetectors.

Description

Title of the invention: Gas sensor enabling the identification of a gaseous species Technical field

[0001] The technical field of the invention is an optical gas sensor, and more particularly a non-dispersive infrared sensor. PREVIOUS ART

[0002] The use of optical methods for gas analysis is quite common. Devices make it possible to determine the composition of a gas based on the fact that the species composing a gas have different absorption spectral properties from each other. Thus, knowing an absorption spectral band of a gaseous species, its concentration can be determined by an estimation of the absorption of light passing through the gas, using Beer Lambert's law. This principle allows an estimation of the concentration of a gaseous species present in the medium.

[0003] The light source is usually a source emitting in the infrared, the method used being usually designated by the Anglo-Saxon term "NDIR detection", the acronym NDIR meaning Non Dispersive Infra-Red. Such a principle has been frequently implemented, and is for example described in numerous documents, for example in patent US 11022547 or in US20220214267.

[0004] According to the most common methods, the gas analyzed extends between a light source and a photodetector, called a measuring photodetector, the latter being intended to measure a light wave, emitted by the source, transmitted through the gas to be analyzed, and partially absorbed by the latter. The methods generally comprise a measurement of a light wave, called a reference light wave, emitted by the source, and not absorbed by the gas analyzed.

[0005] The comparison between light background in the presence of gas and light background without gas makes it possible to characterize the gas. This involves, for example, determining a quantity of a gaseous species in the gas, according to the technology designated by the term "NDIR by absorption".

[0006] Thus, the devices currently implemented make it possible to quantify a concentration of a gas.

[0007] Each gaseous species absorbs light according to its own spectral absorption band. However, the spectral absorption bands of two different gaseous species can extend along the same wavelengths. This is the case, for example, of CH4 and C3H8, which absorb light at 3 pm as well as at 3.37 pm. When a detection is carried out around one of these wavelengths, it is not possible to know whether the absorbing gaseous species is CH4 or C3H8, unless there is an a priori assumption about the composition of the gas. However, the absorbances of CH4 or C3H8, at each of these wavelengths, are different, which can lead to an error in the estimation of the concentration of the gaseous species. However, some gases may contain CH4 or C3H8. Without other information, it can be difficult to correctly estimate the concentration of each gaseous species.

[0008] The inventors have designed a configuration allowing, in addition to quantification, the identification of a gaseous species present in a gas. Statement of the invention

[0009] A first object of the invention is a method for identifying at least one gaseous species, present in a gas, the gas extending in an enclosure, the gaseous species being selected from at least two candidate gaseous species, each candidate gaseous species absorbing light in an absorption spectral band, the sensor comprising: - a light source, emitting light at least in the absorption spectral band; - a first measurement photodetector, located at a first distance from the light source, the first measurement photodetector being configured to detect a light wave, emitted by the light source, in a first detection spectral band, the first detection spectral band being located in the respective absorption spectral bands of the two candidate gaseous species; - a second measuring photodetector, located at a second distance from the light source, the second distance being different from the first distance, the second measuring photodetector being configured to detect a light wave, emitted by the light source, in a second detection spectral band, the second detection spectral band being located in the absorption spectral band of at least one of the two candidate gaseous species.

[0010] the method comprising: a. illumination of the gas using the light source; b. measurement of intensities of a light wave, emitted by the light source, and having propagated through the enclosure by the first measuring photodetector and by the second measuring photodetector; c. forming a first detection signal from the intensity measured by the first measuring photodetector and forming a second signal from detection from the intensity measured by the second measuring photodetector; d. from the first and second detection signals, identification of a gaseous species present in the gas, among the candidate gaseous species.

[0011] The method may comprise, following step d), an estimation of a proportion of the or each gaseous species identified during step d).

[0012] According to one possibility, which enclosure comprises: - a first reference photodetector, located at the first distance from the light source, the first reference photodetector being configured to detect the light wave in a first reference spectral band, considered as not absorbed by each candidate gaseous species; - a second reference photodetector, located at the second distance from the light source, the second reference photodetector being configured to detect the light wave in a second reference spectral band, considered as not absorbed by each candidate gaseous species.

[0013] The process can then be such that: - the first detection signal comprises a ratio between the light intensities respectively detected by the first measuring photodetector and the first reference photodetector; - the second detection signal comprises a ratio between the light intensities respectively detected by the second measuring photodetector and the second reference photodetector.

[0014] According to one possibility, the first reference spectral band is identical to the second reference spectral band.

[0015] According to one possibility, the method comprises: - prior to step d), establishing several response functions, each response function allowing an estimation of the second detection signal from the first detection signal, each response function being associated with a candidate gaseous species in the gas, the response functions being stored in a processing unit; - during step d), selection, by the processing unit, of the response function minimizing a difference between: - the second detection signal, resulting from step c); - and an estimate of the second detection signal, obtained by applying the response function to the first detection signal resulting from step c); - identification of the gaseous species as being the gaseous species associated with the selected response function.

[0016] According to one possibility, the method comprises: - prior to step d), establishing several response functions, each response function allowing an estimation of the second detection signal from the first detection signal, each response function being associated with a proportion of at least one candidate gaseous species in the gas, the response functions being stored in a processing unit; - during step d), selection, by the processing unit, of the response function minimizing a difference between: - the second detection signal, resulting from step c); - and an estimate of the second detection signal, obtained by applying the response function to the first detection signal resulting from step c); - determination of the proportion of the gaseous species as being the proportion of the gaseous species associated with the selected response function.

[0017] According to one possibility, the method comprises: - prior to step d), establishing several response functions, each response function allowing an estimation of the second detection signal from the first detection signal, each response function being associated with proportions of at least two candidate gaseous species in the gas, the response functions being stored in a processing unit; - during step d), selection, by the processing unit, of the response function minimizing a difference between: - the second detection signal, resulting from step c); - and an estimate of the second detection signal, obtained by applying the response function to the first detection signal resulting from step c); - determination of the proportions of the two species as being the proportions of said gaseous species associated with the selected response function.

[0018] According to one possibility, the second absorption spectral band is located in the respective absorption spectral bands of the two candidate gaseous species.

[0019] According to one possibility, the second reference spectral band is merged with the first reference spectral band.

[0020] A second object of the invention is a gas sensor comprising an enclosure, configured to receive a gas potentially comprising at least one gaseous species chosen from at least two candidate gaseous species, each candidate gaseous species absorbing light in an absorption spectral band, the sensor also comprising: a light source, configured to emit a light wave spreading within the enclosure; - a first measurement photodetector, located at a first distance from the light source, the first measurement photodetector being configured to detect a light wave, emitted by the light source, in a first detection spectral band, the first detection spectral band being located in the respective absorption spectral bands of the two candidate gaseous species; - a second measuring photodetector, located at a second distance from the light source, the second distance being different from the first distance, the second measuring photodetector being configured to detect a light wave, emitted by the light source, in a second detection spectral band, the second detection spectral band being located in the absorption spectral band of at least one of the two candidate gaseous species. - a processing unit, programmed to implement steps c) and d) of a method according to the first subject of the invention from the intensities respectively measured by the first measurement photodetector and the second measurement photodetector.

[0021] The sensor may comprise: - a first reference photodetector, located at the first distance from the light source, the first reference photodetector being configured to detect the light wave in a first reference spectral band, considered as not absorbed by each candidate gaseous species; - and / or a second reference photodetector, located at the second distance from the light source, the second reference photodetector being configured to detect the light wave in a second reference spectral band, considered as not absorbed by each candidate gaseous species.

[0022] The invention will be better understood upon reading the description of the exemplary embodiments presented in the remainder of the description, in conjunction with the figures listed below. FIGURES

[0023] [Fig. 1] represents an example of a configuration of a gas sensor according to the invention. In this example, the gas sensor comprises two measurement photodetectors and two reference photodetectors.

[0024] [Fig.2] represents a so-called relative absorbance of two gaseous species, as a function of the concentration.

[0025] Figures 3A and 3B show an evolution of a second detection signal, resulting from the second measuring photodetector and the second reference photodetector, as a function of a first detection signal, resulting from the first measuring photodetector and the first reference photodetector.

[0026] In [Fig.3A], different concentrations of CH4 have been taken into account.

[0027] In [Fig.3B], different concentrations of C3H8 have been taken into account.

[0028] [Fig.3C] shows the curves respectively represented in Figures 3A and 3B.

[0029] The curves shown in Figures 3A, 3B and 3C form functions of sensor response.

[0030] [Fig.4] shows schematically the main steps of implementing a method according to the invention. PRESENTATION OF SPECIAL EMBODIMENTS

[0031] [Fig.l] shows a diagram of a gas sensor 1 according to the invention. The gas sensor 1 comprises an enclosure 2 intended to contain a gas G to be analyzed. The gas to be analyzed comprises at least one gaseous species Gx that it is desired to identify, and preferably to determine the concentration Cx or a relative proportion in the gas. of which it is desired to determine a concentration Cx in the gas.

[0032] The gaseous species Gx absorbs light, and in particular infrared light, in one or more spectral absorption bands AXx which are specific to it.

[0033] The gas is likely to contain one or more so-called candidate gaseous species. These are predetermined gaseous species, potentially present in the gas. The candidate gaseous species absorb infrared light in at least one same absorption spectral band.

[0034] The sensor 1 also comprises: • a light source 10, configured to emit, in the enclosure 2, a light wave in an emission spectral band AX. The emission spectral band can extend between the near ultraviolet and the mid-infrared, for example between 200 nm and 20 pm, and most often in the infrared, the emission spectral band AX being for example between 1 pm and 20 pm. • a first measurement photodetector 21, configured to detect a light wave, called a transmitted light wave, in a first detection band AXd4. The transmitted light wave is a light wave emitted by the light source 10, and having propagated through the enclosure, gradually attenuating during its journey through the gas. The first measurement photodetector 21 may be associated with a bandpass filter 31, defining the first spectral detection band AXd b The first measurement photodetector 21 is located at a first distance di from the light source. • possibly a first reference photodetector 21ref, configured for detect a reference light wave. The reference light wave detected by the first reference photodetector 21ref is considered to be unattenuated by the gas G present in the enclosure. In this example, the first reference photodetector 21ref detects reference light background in a first reference spectral band AXref>i, in which the attenuation of the light background emitted by the source is considered to be negligible. The first reference photodetector 21ref may be associated with a first reference bandpass filter 3 lref, defining the first reference spectral band AXref>i. For example, the first reference spectral band AXref>i is centered around the wavelength 3.91 pm.The use of a first reference photodetector is optional but is advantageous. Alternatively, the first reference photodetector 21ref is not arranged in the enclosure 2 containing the gas, in which case the first reference spectral band may be similar to the first detection spectral band.

[0035] The light source 10 may be pulsed, and emit light pulses whose duration is generally between 50 ms and 1 s. It may in particular be an infrared light source of the filament type formed on a suspended membrane, the filament being traversed by an electric current. In this way, the suspended membrane is heated to a temperature between 400°C and 800°C, so as to emit infrared light.

[0036] An important aspect of the invention is that the gas sensor also comprises: • a second measurement photodetector 22, configured to detect a light wave, called a transmitted light wave, in a second detection spectral band AXd>2, which may be different or identical to the first detection spectral band AXd>2. The second measurement photodetector 22 may be associated with a second bandpass filter 32, defining the second detection spectral band AXd>2. The second measurement photodetector 22 is located at a second distance d2 from the light source. The second distance d2 is different from the first distance db. The relative difference between the first distance and the second distance is preferably greater than 10% or 20% so as to increase the difference between the light intensities respectively detected by the first measurement photodetector 21 and the second measurement photodetector 22. • possibly a second reference photodetector 22ref, configured to detect a reference light wave. The reference light wave detected by the first reference photodetector 22ref is considered to be unattenuated by the gas G present in the enclosure. The second reference photodetector 22ref detects the reference light wave in a second reference spectral band AXref>2, in which the background attenuation of light emitted by the source is considered negligible, and which may be identical to the first reference spectral band AXref>i. The second reference photodetector 22ref may be associated with a second reference bandpass filter 32ref, defining the second reference spectral band AXref>2.

[0037] Each measuring photodetector 21, 22 and each reference photodetector 21ref, 22ref may be thermopiles or pyrodetectors or photodiodes. Each photodetector is configured to generate a detection signal, the amplitude of which corresponds to a detected light background intensity.

[0038] According to one possibility, the device comprises a single reference photodetector, for example the first reference photodetector 21ref. The reference intensity, at the second measurement photodetector 22, can be determined by calculation, knowing the reference intensity measured by the first reference photodetector as well as the distance between the first measurement photodetector 21 and the second measurement photodetector 22. Conversely, the device may comprise only the second reference photodetector 22ref. The reference intensity, at the first measurement photodetector 21, can be determined by calculation, knowing the reference intensity measured by the second measurement photodetector 22 as well as the distance between the first measurement photodetector 21 and the second measurement photodetector 22.

[0039] We now consider a gaseous species Gx, chosen from among the candidate gaseous species. The intensity I of the light background detected by each measuring photodetector depends on the concentration Cx of the gaseous species considered Gx according to the Beer Lambert relation: j

[0040] where: - qfCx) is an attenuation coefficient, dependent on the concentration C, re sought; - I is the thickness of gas crossed by the luminous flux in the enclosure; - Io corresponds to the background intensity which is or would be detected by the photo measuring detector in the absence of absorbing gas in the enclosure.

[0041] The comparison between I and Zo> taking the form of a ratio 1 / corresponds to an attenuation att caused by the gaseous species Gx considered. During each pulse of the light source 10, it is thus possible to determine n(Cx), which makes it possible to estimate the quantity Cx knowing that the relationship between Cx and Cx) is known.

[0042] The intensity l0 can be predetermined, for example during a calibration, or measured in the absence of gas in the enclosure 2. When the sensor comprises a photo reference detector, the reference intensity / ^measured by the reference photodetector makes it possible to measure variations in A).

[0043] The sensor comprises a processing unit 40, receiving the signals measured respectively by the measurement photodetectors 21, 22 and the possible reference photodetectors 21ref, 22ref. The processing unit 40 makes it possible to carry out, from the latter, calculations allowing: - to identify at least one gaseous species present in the gas, chosen from a predetermined list of candidate gaseous species; - preferably estimate a concentration of the gaseous species or of each gaseous species identified.

[0044] The processing unit 40 comprises for example a microprocessor or several microprocessors, each microprocessor then implementing specific operations.

[0045] Each detection spectral band is located in an absorption spectral band of at least one candidate gaseous species. Preferably, at least one detection spectral band, or even each detection spectral band, is located in an absorption spectral band of several candidate gaseous species, and preferably of each candidate gaseous species.

[0046] The invention is based on the fact that by comparing the intensities of the signals respectively detected by each measuring photodetector, after the light source has been activated, it is possible to identify at least one gaseous species present in the gas, among the candidate gaseous species.

[0047] A detection of either CH4 or C3H8 was simulated by a sensor as described in patent application US20220214267A1.

[0048] An arrangement of the first measuring photodetector and the first reference photodetector was simulated at a first distance di = 1.71 cm from the light source. An arrangement of the second measuring photodetector and the second reference photodetector was simulated at a second distance d2 = 4.04 cm from the light source.

[0049] Each measuring photodetector included a filter defining a detection spectral band centered around 3.37 pm. For modeling purposes, only the intensity detected at a wavelength of 3.37 pm was taken into account. As indicated in the prior art, the wavelength of 3.37 pm is located in the absorption spectral bands of CH4 and C3H8. According to another possibility, the first filter 31 is centered around 3 pm and the second filter 32 is centered on 3.37 pm, or vice versa. According to another possibility, each filter is centered on the wavelength 3 pm.

[0050] Figure 2 represents the evolution of a quantization signal Sc, expressed in %, comprising a combination of the light intensities measured by each photodetector.

[0051]

[0052]

[0053]

[0054]

[0055]

[0056]

[0057] In Figure 2, the CH4 and C3H8 curves correspond to a situation where only CH4 and C3H8 are respectively present in the gas. The x-axis corresponds to the concentration (unit ppm) and the y-axis corresponds to the quantification signal Sc defined in relation to expression (2). It is observed that for the same quantification signal Sc, as defined in (2), the concentration of the two candidate gaseous species is different. For example, a quantification signal Sc equal to 1% corresponds to concentrations of CH4 or C3H8 respectively close to 10000 ppm or 600 ppm. When there is no a priori on the gaseous species likely to be present in the gas, the same quantification signal 5C. can be generated by very different concentrations of these two gaseous species. When the sensor is used to generate an alarm when a threshold concentration has been exceeded, for example relative to a CH4 concentration equal to 6000 ppm, an alarm can be triggered even though the gas does not contain CH4 and the C3H8 concentration exceeds only a few hundred ppm. This corresponds to a false alarm. To prevent such a situation from occurring, two measuring photodetectors are used, arranged so that the light waves reaching them follow optical paths of different lengths. The invention benefits from: - the difference in optical paths between the light source and each measuring photodetector, respectively; - the difference in absorbance between the candidate gaseous species: in this example, at 3.37 pm, the absorbance of C3H8 is higher than that of CH4. In this example, the candidate gaseous species are CH4 and C3H8. From the intensities detected by each measuring photodetector, we form: - a first detection signal representative of an absorbance of the gas, measured by the first measurement photodetector 21. The first detection signal 5} is formed from the light intensity 7j detected by the first measurement photodetector 21. Preferably, the first detection signal is formed from a ratio between the light intensity and the light intensity Iref,i detected by the first reference photodetector 21ref- So, according to one possibility, S\ = (3). In this example,5. = 1-AM - a second detection signal S2, representative of an absorbance of the gas, measured by the second measurement photodetector 22. The second detection signal S2 is formed from the light intensity / 2 detected by the second measurement photodetector 22. Preferably, the second detection signal is formed from a ratio between the light intensity and the light intensity Jref,2 detected by the second reference photodetector 22ref.

[0058] Thus, according to one possibility, S2 = / 2 (5). In this example, $ — (6)

[0059] An important aspect of the invention is to identify at least one gaseous species, present in the gas, from the first detection signal and the second detection signal.

[0060] Figure 3A shows the first detection signal (x-axis - %) and the second detection signal (y-axis - %) for different methane (CH4) concentrations. This corresponds to a response function f of the sensor for CH4.

[0061] Figure 3B shows the first detection signal (x-axis - %) and the second detection signal (y-axis - %) for different concentrations of propane (C3H8). This corresponds to a response function f of the sensor for C3H8.

[0062] Figures 3A and 3B were obtained by performing modeling taking into account a few discrete concentrations, which correspond to the points materialized in each of these figures. The points of each curve were then interpolated taking into account a second-degree polynomial. In Figures 3A and 3B, the equation of each polynomial and a correlation coefficient R2 are indicated.

[0063] In Figure 3C, the two response functions described in connection with Figures 3A and 3B are represented. A response function f VC3H8' is also represented, which corresponds to a proportion of x% of CH4 and 3'% of C3H8. x and 3' are real numbers strictly between 0 and 1. The response functions are stored in the processing unit.

[0064] An important aspect of the invention is to identify, from the first detection signal and the second detection signal, at least one gaseous species present in the analyzed gas. In this example, if ç _ f (ç Y the identified gaseous species 2 JC H4\ V is CH4. If ç _ f (ç \ the identified gaseous species is C3H8. 2 J y

[0065] Thus the processing unit 40 is programmed to: - calculate the first detection signal S} and the second detection signal S2 from the intensities / jet A respectively measured by the first photodetector and by the second photodetector; - identify at least one gaseous species from the first detection signal Si and the second detection signal S2. In this example, response functions, respectively associated with different gaseous species, have been previously determined. The identified gaseous species corresponds to that associated with the response function giving a minimal difference between: • the measured S2 signal; • and its estimate $ by applying the response function to the first detection signal Sj: 5 J.

[0066] More generally, several response functions corresponding to different compositions can be established, for example response functions associated with a composition of x% CH4 and y% C3H8. In [Fig.3C]: - the function f CH4 corresponds to x% of CH4 and C3H8 with v= 100 and -v = 0; - the function f corresponds to x% of CH4 and y% of C3H8 with x=0 and 3' = 100; - the function f xCff^vC3ff# represented in dotted lines, corresponds to x% of CH4 and y% of C3H8.

[0067] The response functions can be established numerically and / or from measurements carried out with one or more calibration gases of known composition.

[0068] Thus, the invention makes it possible to identify a gaseous species, present in a gas, from among several candidate gaseous species. It also makes it possible to estimate a relative proportion of different candidate gaseous species. This is done by means of predetermined response functions, each response function being associated with a candidate gaseous species or a mixture of candidate gaseous species. The identification of each gaseous species present in the gas and its proportion is carried out by selecting the response function minimizing the difference between S2, resulting from the measurement, and the estimate _ y^

[0069] After a gaseous species has been identified, its concentration in the gas can be determined either from the value of the selected response function, knowing that each value of the response function corresponds to a concentration. The concentration in the gas can also be determined from the first detection signal and / or the second detection signal, for example by implementing a quantification signal as explained in (2).

[0070] [Fig.4] shows schematically the main stages of the invention

[0071] Step 90: sensor calibration: this involves defining sensor response functions by taking into account different concentrations of different species predetermined candidate gases. Each response function allows an estimate of the second detection signal $ from a measurement of the first detection signal S]. Each response function is associated with a determined proportion of each candidate gaseous species.

[0072] Step 100: admission of gas into enclosure 2 and illumination of the gas by the light source

[0073] Step 110: detection of light intensities by the first and second measurement and reference photodetectors.

[0074] Step 120: formation of detection signals, representative of the attenuation of light, by the gas, between the light source and each measurement photodetector.

[0075] Step 130: from the calibration functions, identification of at least one gaseous species present in the gas, from the list of candidate gaseous species, and determination of a proportion of each identified gaseous species. This involves in particular determining the response function minimizing a difference between the second detection signal and its estimation from the response function applied to the first detection signal.

[0076] Step 140: optionally quantification of the concentration of each gaseous species identified during step 130. The quantification can be carried out from the value of the response function, or from at least one detection signal.

[0077] In the example described, the first distance di is less than the second distance d2. The invention also applies to a configuration according to which the second distance d2 is less than the first distance db. However, it is preferable for the difference between the two distances to be greater than 10%, or even 20%.

[0078] According to one possibility, three photodetectors can be implemented, respectively located at three different distances from the light source. This makes it possible to detect one gaseous species among three candidate gaseous species, or to estimate a concentration of three different gaseous species, according to the principles previously explained.

[0079] The invention may be applied for gas detection in environmental monitoring, or in industrial gas control applications, particularly in the food industry, the oil industry, or gas distribution.

Claims

1. Claims Method for identifying at least one gaseous species, present in a gas, the gas extending in an enclosure (2), the gaseous species being selected from at least two candidate gaseous species, each candidate gaseous species absorbing light in a spectral absorption band, the sensor comprising: - a light source, emitting light at least in the absorption spectral band; - a first measuring photodetector (21), located at a first distance (di) from the light source, the first measuring photodetector being configured to detect a light wave, emitted by the light source, in a first detection spectral band, the first detection spectral band being located in the respective absorption spectral bands of the two candidate gaseous species; - a second measuring photodetector (22), located at a second distance (d2) from the light source, the second distance being different from the first distance, the second measuring photodetector being configured to detect a light wave, emitted by the light source, in a second detection spectral band, the second detection spectral band being located in the absorption spectral band of at least one of the two candidate gaseous species. the process comprising: a. illumination of the gas using the light source (10); b. measurement of intensities of a light wave, emitted by the light source, and having propagated through the enclosure (2) by the first measurement photodetector (21) and by the second measurement photodetector (22); c. forming a first detection signal ( $0 from the intensity measured by the first measuring photodetector and forming a second detection signal ( S2) from the intensity measured by the second measuring photodetector;

2.

3.

4. d. from the first and second detection signals, identification of a gaseous species present in the gas, among the candidate gaseous species. Method according to claim 1, comprising, following step d), an estimation of a proportion of the or each gaseous species identified during step d). A method according to claim 1 or claim 2, following step d), an estimation of an amount of the or each gaseous species identified during step d). A method according to any preceding claim, wherein the enclosure comprises: - a first reference photodetector (2 lref), located at the first distance from the light source, the first reference photodetector being configured to detect the light wave in a first reference spectral band, considered as not absorbed by each candidate gaseous species; - a second reference photodetector (22ref), located at the second distance from the light source, the second reference photodetector being configured to detect the light wave in a second reference spectral band, considered as not absorbed by each candidate gaseous species; and in which: - the first detection signal includes a ratio ( h ) between the Aï / ,! light intensities respectively detected by the first measuring photodetector and the first reference photodetector; - the second detection signal has a ratio ( h ) between the light intensities respectively detected by the second measuring photodetector and the second reference photodetector.

5. The method of claim 4, wherein the first reference spectral band is identical to the second reference spectral band.

6. Method according to any one of the preceding claims, comprising: - prior to step d), establishing several response functions (( / c / / 4, fc^ fxCH±yC3HS), each response function allowing an estimation of the second detection signal from the first detection signal, each response function being associated with a candidate gaseous species in the gas, the response functions being stored in a processing unit (40); - during step d), selection, by the processing unit, of the response function minimizing a difference between: - the second detection signal (S2), resulting from step c); - and an estimation of the second detection signal (^2), obtained by applying the response function to the first detection signal (¾ resulting from step c); - identification of the gaseous species as being the gaseous species associated with the selected response function.

7. Method according to any one of claims 1 to 5, comprising: - prior to step d), establishing several response functions (fŒ4, f^, fxCH±yC3HJ, each response function allowing an estimation of the second detection signal from the first detection signal, each response function being associated with a proportion of at least one candidate gaseous species in the gas, the response functions being stored in a processing unit; - during step d), selection, by the processing unit, of the response function minimizing a difference between: - the second detection signal (S2), resulting from step c); - and an estimation of the second detection signal ($2), obtained by applying the response function to the first detection signal (Sj resulting from step c); - determination of the proportion of the gaseous species as being the proportion of the gaseous species associated with the selected response function.

8. Method according to claim 7, comprising: - prior to step d), establishing several response functions ( / c^aclue response function allowing an estimation of the second detection signal from the first detection signal, each response function being associated with proportions of at least two candidate gaseous species in the gas, the response functions being stored in a processing unit; - during step d), selection, by the processing unit, of the response function minimizing a difference between: - the second detection signal, resulting from step c); - and an estimation of the second detection signal, obtained by applying the response function to the first detection signal resulting from step c); - determination of the proportions of the two gaseous species as being the proportions of said gaseous species associated with the selected response function.

9. A method according to any preceding claim, wherein the second absorption spectral band is located within the respective absorption spectral bands of the two candidate gaseous species.

10. Gas sensor (1) comprising an enclosure (2), configured to receive a gas (G) potentially comprising at least one gaseous species chosen from at least two candidate gaseous species, each candidate gaseous species absorbing light in an absorption spectral band, the sensor also comprising: - a light source (10), configured to emit a light wave propagating in the enclosure; - a first measurement photodetector (21), located at a first distance (dj from the light source, the first pho- a measurement detector being configured to detect a light wave, emitted by the light source, in a first detection spectral band, the first detection spectral band being located in the respective absorption spectral bands of the two candidate gaseous species; - a second measuring photodetector (22), located at a second distance (d2) from the light source, the second distance being different from the first distance, the second measuring photodetector being configured to detect a light wave, emitted by the light source, in a second detection spectral band, the second detection spectral band being located in the absorption spectral band of at least one of the two candidate gaseous species. - a processing unit (40), programmed to implement steps c) and d) of a method which is the subject of any one of the preceding claims from the intensities respectively measured by the first measurement photodetector and the second measurement photodetector.

11. Sensor according to claim 10, comprising: - a first reference photodetector (2 lref), located at the first distance from the light source, the first reference photodetector being configured to detect the light wave in a first reference spectral band, considered as not absorbed by each candidate gaseous species; - and / or a second reference photodetector (22ref), located at the second distance from the light source, the second reference photodetector being configured to detect light in a second reference spectral band, considered as not absorbed by each candidate gaseous species.

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