Gas Sensor

Abstract

To provide a gas sensor with which, even when an interference gas exists in addition to a measurement object gas, it is possible to measure a gas concentration with high accuracy.SOLUTION: A gas sensor (1000) comprises: a first and a second light emitting part (101, 201) for outputting an infrared ray; a first and a second light receiving unit (102, 202) for outputting an output signal that corresponds to the incident infrared ray; a first optical path region (10) which light emitted from the first light emitting unit passes through until entering the first light receiving unit; and a second optical path region (20) which light emitted from the second light emitting unit passes through until entering the second light receiving unit. The optical path regions include a common region (30), the optical path length of the first optical path region being longer than the optical path length of the second optical path region, a change rate of the output signal of the first light receiving unit against the measurement object gas being larger than the second light receiving unit, a change rate of the output signal of the second light receiving unit against an interference gas being larger than the first light receiving unit, the sensitivity peak wavelength of the second light receiving unit overlapping the absorption wavelength of water vapor.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas sensor. [Background technology]

[0002] NDIR (Non Dispersive InfraRed) gas sensors are commonly used in high-precision gas concentration measurement devices due to their high reliability and long-term measurement reproducibility.

[0003] For example, Patent Document 1 discloses a gas sensor that uses one light source and two photodetectors. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-138499 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional gas sensors such as that disclosed in Patent Document 1 have difficulty in measuring gas concentrations with high accuracy when there is absorption by other gases (hereinafter sometimes referred to as interference gases) near the absorption wavelength of the gas to be measured.

[0006] For example, if the gas being measured is methane, the absorption wavelength of methane is between 3.1 and 3.5 μm. Furthermore, the absorption wavelength of water vapor, which is present in considerable amounts in typical environments, is around 2.7 to 3.3 μm. This causes interference between the absorption wavelengths of the gas being measured (methane) and water vapor, making it difficult to measure the concentration of methane gas with high accuracy.

[0007] An object of the present invention is to provide a gas sensor that can measure gas concentration with high accuracy even when an interfering gas is present in addition to the gas to be measured. [Means for solving the problem]

[0008] A gas sensor according to a first aspect of the present invention comprises: a first light-emitting unit and a second light-emitting unit each outputting infrared light; a first light receiving unit and a second light receiving unit that output an output signal corresponding to the incident infrared light; a first optical path region through which light emitted from the first light-emitting unit passes before entering the first light-receiving unit; a second optical path region through which the light emitted from the second light-emitting unit passes before entering the second light-receiving unit, the first optical path region and the second optical path region have at least a partial common region; an optical path length of the first optical path region is longer than an optical path length of the second optical path region; a rate of change in an output signal of the first light receiving unit with respect to a change in concentration of a predetermined amount of the target gas to be measured is greater than a rate of change in an output signal of the second light receiving unit with respect to a change in concentration of the predetermined amount of the target gas to be measured; a rate of change in the output signal of the second light receiving unit with respect to a change in concentration of the predetermined amount of interference gas is greater than a rate of change in the output signal of the first light receiving unit with respect to a change in concentration of the predetermined amount of interference gas; The peak sensitivity wavelength of the second light receiving section overlaps with the absorption wavelength of water vapor. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a gas sensor capable of measuring gas concentration with high accuracy even when an interference gas is present in addition to the measurement target gas. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram illustrating a gas sensor according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram illustrating a gas sensor according to one embodiment of the present invention. [Figure 3]FIG. 3 is a graph showing the correlation between the output signal level of the first light receiving unit and the output signal level of the second light receiving unit at each relative humidity when the ambient temperature is 60° C. and the methane gas concentration is 0 ppm. [Figure 4] FIG. 4 is a graph showing output fluctuation values ​​when humidity correction based on the signal from the second light receiving unit is not applied. [Figure 5] FIG. 5 is a graph showing output fluctuation values ​​when humidity correction is applied using the signal from the second light receiving unit. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described below through embodiments of the invention, but the following embodiments do not limit the scope of the invention according to the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention.

[0012] <Gas sensor> The gas sensor of this embodiment includes a first light-emitting element and a second light-emitting element, each of which outputs infrared light; a first light-receiving element and a second light-receiving element, each of which outputs an output signal corresponding to the incident infrared light; a first optical path region through which light emitted from the first light-emitting element passes before entering the first light-receiving element; and a second optical path region through which light emitted from the second light-emitting element passes before entering the second light-receiving element.

[0013] The optical path length of the first optical path region is longer than the optical path length of the second optical path region. Here, the optical path length means the length of the path where the density of light passing through the optical path region is highest (or the optically shortest distance from the light emitting unit to the light receiving unit).

[0014] The rate of change of the output signal of the first light receiving unit with respect to a change in concentration of a predetermined amount of the target gas to be measured is greater than the rate of change of the output signal of the second light receiving unit with respect to a change in concentration of a predetermined amount of the target gas to be measured. Furthermore, the rate of change of the output signal of the second light receiving unit with respect to a change in concentration of a predetermined amount of the interference gas is greater than the rate of change of the output signal of the first light receiving unit with respect to a change in concentration of a predetermined amount of the interference gas. Furthermore, the peak sensitivity wavelength of the second light receiving unit overlaps with the absorption wavelength of water vapor. Here, "the peak sensitivity wavelength of the second light receiving unit overlaps with the absorption wavelength of water vapor" means that the peak sensitivity wavelength of the second light receiving unit is included in at least a portion of the absorption wavelength of water vapor.

[0015] Although details will be described later, by providing the above-mentioned configuration requirements, it is possible to optimize the detection performance (e.g., SNR: signal to noise ratio) of the interfering gas and the target gas to the desired performance, and by using the output signals of each light receiving element, it is possible to reduce the influence of the interfering gas, determine the presence or absence of the target gas, and measure its concentration with high accuracy. Furthermore, the sensitivity peak wavelength of the second light receiving element overlaps with the absorption wavelength of water vapor, which reduces the influence of water vapor, which has a large influence among interfering gases, and therefore it is possible to determine the presence or absence of the target gas and measure its concentration with high accuracy.

[0016] <Light receiving section> The first light receiving unit and the second light receiving unit in the gas sensor of this embodiment each output an output signal corresponding to the intensity of the incident infrared ray. When a gas that absorbs the infrared ray output from the light emitting unit is present in the first optical path region and the second optical path region, the infrared ray is attenuated and enters the first light receiving unit and the second light receiving unit, respectively. Examples of the light receiving unit include a pyroelectric sensor, a thermopile, a phototransistor, and a photodiode. From the viewpoint of achieving high responsiveness, the light receiving unit is preferably a quantum infrared sensor represented by a phototransistor or a photodiode, and in some cases a photodiode is more preferable.

[0017] In order to ensure that the magnitude relationship between the change rates of the output signals of the first and second light receiving units in response to changes in the concentrations of the target gas and interference gas satisfies the above-mentioned conditions, it may be preferable that the spectral sensitivity characteristics of the first and second light receiving units be different.

[0018] Here, the spectral sensitivity characteristic means the sensitivity characteristic for each wavelength of incident light.

[0019] There are no particular limitations on the method for achieving the desired spectral sensitivity characteristics. For example, when the light receiving section is a photodiode, examples include a method for achieving the desired band gap by adjusting the material and composition ratio of the active layer, and a method for providing an optical filter in the optical path region.

[0020] An optical filter can be used so that the magnitude relationship between the change rates of the output signals of the first light receiving unit and the second light receiving unit relative to changes in the concentrations of the measurement target gas and the interference gas satisfies the above-mentioned condition. When an optical filter is used, the optical filter may be provided in either the first optical path region or the second optical path region, or optical filters with different wavelength transmission characteristics may be provided in each of the first optical path region and the second optical path region.

[0021] Furthermore, as a method for improving long-term reliability while maintaining the accuracy of the gas sensor, it may be preferable to achieve low power consumption by differentiating the response speeds of the first and second light-receiving elements. In particular, when the target gas is a combustible gas, such as methane, and the interference gas is water vapor, which is commonly present in the environment, changes in the concentration of methane gas or combustible gas, which is not commonly present in the environment, are sudden changes due to leakage from storage locations, etc. In contrast, changes in the concentration of water vapor, which is commonly present in the environment, are very gradual. Therefore, by differentiating the response speeds of the first and second light-receiving elements, low power consumption and sufficient accuracy can be ensured, and long-term reliability can be improved.

[0022] When the gas being measured is a combustible gas, such as methane, it absorbs infrared light with wavelengths of 3-4 μm and 7-8.5 μm, and particularly exhibits high absorption for infrared light around 3.3 μm.Water vapor, which is commonly present in the environment as an interference gas, absorbs infrared light with wavelengths of 2-3 μm and 5-8 μm, and exhibits high absorption for infrared light around 2.7-3.3 μm.

[0023] Therefore, the peak sensitivity wavelength of the second light-receiving unit should overlap with the absorption wavelength of water vapor, and is preferably 2 to 3 μm or 5 to 8 μm. Furthermore, to reduce the influence of flammable gases, the peak sensitivity wavelength of the second light-receiving unit should preferably be 2 to 3 μm or 5 to 7 μm, which does not overlap with the absorption wavelength of flammable gases. On the other hand, the peak sensitivity wavelength of the first light-receiving unit should preferably overlap with the absorption wavelength of the gas to be measured, and is preferably 3 to 4 μm or 7 to 8.5 μm.

[0024] Here, by making the sensitivity peak wavelength of the first light receiving element closer to 3.3 μm than the sensitivity peak wavelength of the second light receiving element, it is possible to make the rate of change of the output signal of the first light receiving element greater than the rate of change of the output signal of the second light receiving element in response to a predetermined change in concentration of the gas to be measured.

[0025] Furthermore, by making the sensitivity peak wavelength of the second light receiving element closer to 2.7 μm than that of the first light receiving element, it is possible to make the rate of change of the output signal of the second light receiving element greater than the rate of change of the output signal of the first light receiving element in response to a change in concentration of a predetermined amount of interference gas.

[0026] <Light-emitting part> The first and second light-emitting units in the gas sensor of this embodiment are not particularly limited as long as they are light sources capable of outputting infrared light at the absorption wavelength of the target gas. Examples include thermal light sources such as light bulbs and MEMS heaters, and quantum light sources such as laser light sources and LEDs. Infrared LEDs may be preferable from the viewpoint of response speed. Furthermore, if the target gas or interference gas is flammable, quantum light sources may be preferable because they generate less heat and are safer.

[0027] In order to ensure that the magnitude relationship between the change rates of the output signals of the first light receiving unit and the second light receiving unit in response to changes in the concentrations of the target gas and interference gas satisfies the above-mentioned conditions, it may be preferable that the emission spectra of the first light emitting unit and the second light emitting unit are different.

[0028] Here, the emission spectrum means the light intensity distribution for each wavelength of emitted light.

[0029] In the case of an infrared LED, it is sometimes preferable to adjust the material and composition ratio of the light-emitting layer, since the emission spectrum (central emission wavelength, wavelength band, etc.) can be made as desired.

[0030] <Optical path area> In the present invention, the optical path region refers to the space from the light-emitting unit to the light-receiving unit. That is, the first optical path region refers to the space through which light emitted from the first light-emitting unit passes before entering the first light-receiving unit. The second optical path region refers to the space through which light emitted from the second light-emitting unit passes before entering the second light-receiving unit. The first optical path region and the second optical path region may be collectively referred to as the "optical path region."

[0031] When the target gas and interference gas enter this optical path region, light is absorbed by the target gas and interference gas, changing the amount of light received by the light-receiving unit, and an output signal corresponding to the concentrations of the target gas and interference gas is obtained. In Fig. 1, a light beam L1 (a light path, sometimes referred to as the "first optical path") emitted from the first light-emitting unit 101 is schematically shown by a dashed-dotted line. In Fig. 1, a light beam L2 (a light path, sometimes referred to as the "second optical path") emitted from the second light-emitting unit 201 is also schematically shown by another dashed-dotted line.

[0032] Furthermore, the first optical path and the second optical path may intersect as shown in Fig. 2. From the viewpoint of space saving, it may be preferable for the first optical path and the second optical path to intersect.

[0033] Furthermore, crossing the first and second optical paths may be preferable because it reduces the effect on the measurement results of differences in concentration distribution between the measurement target gas and the interference gas in the optical path space compared to separating the first and second optical paths.

[0034] Typically, the optical path region is formed by arranging a highly reflective member (also called a mirror) so that light emitted from the light-emitting unit reaches the light-receiving unit, or by arranging the light-emitting surface of the light-emitting unit and the light-receiving surface of the light-receiving unit so that they face each other.

[0035] <Example of a specific configuration of the gas sensor according to this embodiment> FIG. 1 is a schematic diagram of a gas sensor 1000 according to one embodiment of the present invention.

[0036] The gas sensor shown in FIG. 1 includes a first light-emitting element 101 and a second light-emitting element 201, each of which outputs infrared light; a first light-receiving element 102 and a second light-receiving element 202, each of which outputs an output signal corresponding to the incident infrared light; a first optical path region 10 through which light emitted from the first light-emitting element 101 passes before entering the first light-receiving element 102; and a second optical path region 20 through which light emitted from the second light-emitting element 201 passes before entering the second light-receiving element 202.

[0037] The first optical path region 10 and the second optical path region 20 have a common region 30 where a part of one is spatially shared with a part of the other.

[0038] The first light receiving unit 102 and the second light receiving unit 202 are designed so that the rate of change of the output signal in response to a change in concentration of a predetermined amount of the target gas at the first light receiving unit is greater than the rate of change of the output signal in response to a change in concentration of a predetermined amount of the target gas at the second light receiving unit, and so that the rate of change of the output signal in response to a change in concentration of a predetermined amount of the interference gas at the second light receiving unit is greater than the rate of change of the output signal in response to a change in concentration of a predetermined amount of the interference gas at the first light receiving unit.

[0039] In addition, the optical path length of the first optical path region (the optical path length indicated by the light ray L1 from the first light-emitting unit 101 until it enters the first light-receiving unit 102) is longer than the optical path length of the second optical path region (the optical path length indicated by the light ray L2 from the light emitted from the second light-emitting unit 201 until it enters the second light-receiving unit 202).

[0040] The light emitting driver 400 is provided to drive the first light emitting unit 101 and the second light emitting unit 201. The light emitting driver 400 may supply a constant current pulse or a constant voltage pulse to the first light emitting unit 101 and the second light emitting unit 201.

[0041] The concentration calculation unit 500 may calculate the concentration of the gas to be measured using the output signals from the first light receiving unit 102 and the second light receiving unit 202 and the output signal from the temperature sensor 300. From the viewpoint of highly accurate measurement, it may be preferable to perform temperature correction using the output from the temperature sensor.

[0042] Alternatively, the light-emitting driver 400 and the concentration calculator 500 may be synchronized to detect the output signals of the first light-receiving unit 102 and the second light-receiving unit 202. The frequency at which the first light-emitting unit 101 emits light and the frequency at which the second light-emitting unit 201 emits light and the second light-receiving unit 202 detects a signal may be different to avoid simultaneous light emission and signal detection. Alternatively, the light-emitting units may emit light at the same frequency and the timing at which the signals are detected may be shifted in time to eliminate crosstalk between the two light-receiving units. This crosstalk elimination can be performed efficiently by using quantum light-emitting and light-receiving units, which may be preferable. Furthermore, if the light-emitting unit is a thermal light source and the light-receiving unit is affected by thermal radiation from the light source, the effect of thermal radiation on the light-receiving unit at the signal detection timing can be individually detected. This allows the effect of thermal radiation to be accurately detected and suppressed by signal processing.

[0043] Furthermore, the first optical filter 103 and the second optical filter 203 may be bandpass filters that transmit light in the absorption wavelength bands of the interference gas and the measurement target gas, respectively.

[0044] When it is desired to save space and lengthen the first and second optical path regions, they may have the configuration shown in Fig. 2. Furthermore, as shown in Fig. 2, by providing a common region for the first and second optical path regions, the influence of differences in the concentration distributions of the measurement target gas and the interference gas in the first and second optical paths can be suppressed, and the influence of the interference gas can be removed with high precision, which may be preferable in some cases.

[0045] Furthermore, the light emission driver 400 and the concentration calculator 500 may be provided within the optical path area, which allows further miniaturization.

[0046] <Example> As shown in Figure 2, the gas sensor was fabricated by arranging the first light-emitting unit, the first light-receiving unit, the second light-emitting unit, the second light-receiving unit, and multiple mirrors to form the first optical path region and the second region so that the light beam from the first light-emitting unit and the light beam from the second light-emitting unit were approximately perpendicular to each other.

[0047] <First light-emitting unit, light-receiving unit, and first optical path region> The first light-emitting section and the first light-receiving section are an LED and a photodiode with a chip size of 0.7 x 0.7 μm2, consisting of a P layer / active layer / N layer stacked structure formed on a GaAs substrate. The active layer uses AlInSb with a thickness of 1.34 μm, and the Al composition is 8.9%.

[0048] The LEDs were divided into seven rows and the photodiodes into 73 rows using an etching process, and finally a metal wiring layer was provided so that they were electrically connected in series.

[0049] The light input and output ports were located on the side of the GaAs substrate where the laminated structure was not formed, and were sealed with resin using SMT (Surface-mount Technology). An optical filter with a central transmission wavelength of 3.3 μm was installed on top of the photodiode package, and a PCB (Printed Circuit Board) was used to connect the LED and photodiode to the respective circuits. To achieve a high SNR, the signal processing circuit was installed near the photodiode.

[0050] The light from the first light-emitting element (LED) is reflected multiple times by 17 concave mirrors with thin aluminum reflective surfaces before reaching the first light-receiving element (photodiode). The optical path length is 1m, and it is designed so that more than 15% of the light emitted from the light-emitting element reaches the light-receiving element.

[0051] The LED was driven intermittently at a current value of 100 mA, and a resolution of several ppm in terms of methane concentration was achieved.

[0052] <Second light-emitting unit, light-receiving unit, and optical path area> The second light-emitting section, the second light-receiving section, and the second optical path region were configured to differ from the above-described first light-emitting section, the first light-receiving section, and the first optical path region in the following points. Active layer thickness: 1 μm Al composition in the active layer: 14% Number of photodiode stages: 41 Number of LED levels: 6 Optical filter central wavelength: 2.7 μm Concave mirror: 5 pieces Optical path length: 80mm The LED was driven intermittently at a current value of 100mA, achieving a resolution of approximately 500 ppm in terms of water vapor concentration.

[0053] <Correction to remove the effects of water vapor> If the correlation function between the output S2 from the second light receiving unit and the output S1 from the first light receiving unit obtained above is f, then the following equation (1) is obtained under the condition that the methane concentration is 0 ppm.

[0054] S1 = f(S2) | 0ppm … (1)

[0055] The output fluctuation rate S1 is calculated by correcting for the influence of water vapor and extracting only the signal change due to methane from the first light receiving unit. adj can be calculated as shown in equation (2).

[0056] S1 adj =(S1−f(S2)| 0ppm ) / f(S2)| 0ppm … (2)

[0057] Here, in equations (1) and (2), "| 0ppm " indicates that the correlation function f was obtained under the condition that the measurement target gas (methane gas) was 0 ppm.

[0058] In equation (2), when methane is 0 ppm, even if the concentration of water vapor is 0 ppm or more, the output fluctuation rate S1 adj In other words, even if the concentration of water vapor changes, if the methane concentration does not change, the output fluctuation rate S1 adj In equation (2), the output fluctuation rate S1 adj changes depending on the methane concentration.

[0059] FIG. 3 shows the measurement results used in this example to derive the correlation function f(S2) shown in equation (1) above. Measurement results for the output S1 from the first light receiving unit and the output S2 from the second light receiving unit were plotted when the relative humidity was changed to 0%, 40%, 60%, and 80% in an environment with a methane concentration of 0 ppm and a temperature of 60°C, and the correlation function f(S2) was derived. Furthermore, to derive the correlation function f(S2), the output S1 from the first light receiving unit and the output S2 from the second light receiving unit may be temperature-corrected using temperature information from a temperature sensor. This allows the correlation function f(S2) to be derived with a temperature correction function.

[0060] Figure 4 shows the output fluctuation rate (S1 - S1(0)) / S1(0) from the first light-receiving element in response to changes in methane concentration without water vapor correction (using only the output S1 from the first light-receiving element) under conditions where the water vapor is equivalent to a temperature of 60°C and relative humidity levels of 40%, 60%, and 80%. The output fluctuation rate is based on the output signal S1(0) from the first light-receiving element when the methane and water vapor levels are 0 ppm, and the signal attenuation S1 - S1(0) is expressed as the output fluctuation rate S1 - S1(0) / S1(0). As is clear from Figure 4, when the relative humidity changes, the output signal changes even for the same methane concentration, making it impossible to accurately determine the methane concentration from the output signal.

[0061] On the other hand, Figure 5 shows the output fluctuation rate S1 obtained by correcting the influence of water vapor from the function shown in the above equations (1) and (2) using the output signal S2 from the second light receiving unit in addition to the output signal from the first light receiving unit, and extracting only the signal change due to methane. adj Shows.

[0062] As shown in Figure 5, even when the relative humidity RH changes, the output signal fluctuation rate corrected for each methane concentration is approximately consistent, and it can be seen that the methane concentration can be determined with high accuracy from the corrected output signal.

[0063] Here, the output fluctuation rate S1 adj The concentration of the target gas can be calculated by applying a concentration calculation table or exponential function fitting to the target gas. For example, the output fluctuation rate S1 when the target gas concentration C is changed under a constant water vapor concentration is adj When the function showing the correlation with is g, the concentration C of the gas to be measured is obtained by the following equation (3).

[0064] C=g(S1 adj ) … (3)

[0065] Here, it is preferable that the formulas (2) and (3) used to calculate the concentration of the gas to be measured are polynomials.

[0066] Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the claims that such modifications and improvements can also be included within the technical scope of the present invention.

[0067] In particular, although the present embodiment has been described with a focus on eliminating the effects of humidity (water vapor), it is also possible to eliminate the effects of other accuracy error factors. For example, it is possible to eliminate the effects of temperature characteristics (output changes due to temperature during measurement). [Explanation of symbols]

[0068] 10 First optical path region 20 Second optical path region 30 Common areas 101 First light-emitting part 102 first light receiving unit 201 Second light-emitting part 202 Second light receiving unit 103 First Optical Filter 203 Second Optical Filter 300 Temperature Sensor 400 Light Emitting Driver 500 Concentration calculation section 1000 Gas Sensor L1 Light ray from the first light emitting part L2 Light ray from the second light emitting part

Claims

1. a first light-emitting unit and a second light-emitting unit each outputting infrared light; a first light receiving section and a second light receiving section each outputting an output signal in response to incident infrared light; a first optical path region through which light emitted from the first light-emitting unit passes before being reflected by a first mirror and incident on the first light-receiving unit; a second optical path region through which the light emitted from the second light-emitting unit passes before being reflected by a second mirror different from the first mirror and being incident on the second light-receiving unit, the first optical path region and the second optical path region have at least a portion of a common region; an optical path length of the first optical path region is longer than an optical path length of the second optical path region; a rate of change in an output signal of the first light receiving unit with respect to a change in concentration of a predetermined amount of the target gas to be measured is greater than a rate of change in an output signal of the second light receiving unit with respect to a change in concentration of the predetermined amount of the target gas to be measured; a rate of change in the output signal of the second light receiving unit with respect to a change in concentration of the predetermined amount of interference gas is greater than a rate of change in the output signal of the first light receiving unit with respect to a change in concentration of the predetermined amount of interference gas; A gas sensor in which the peak sensitivity wavelength of the second light receiving portion overlaps with the absorption wavelength of water vapor.

2. 2. The gas sensor according to claim 1, wherein the first light receiving portion and the second light receiving portion have different spectral sensitivity characteristics.

3. 3. The gas sensor according to claim 1, wherein the first light receiving portion and the second light receiving portion have different response speeds.

4. 4. The gas sensor according to claim 1, wherein the first light receiving portion and the second light receiving portion are quantum infrared sensors.

5. 5. The gas sensor according to claim 1, further comprising an optical filter in either the first optical path region or the second optical path region.

6. 5. The gas sensor according to claim 1, further comprising optical filters in the first optical path region and the second optical path region, the optical filters having different wavelength transmission characteristics.

7. 7. The gas sensor according to claim 1, wherein the first light-emitting portion and the second light-emitting portion have different emission spectra.

8. 8. The gas sensor according to claim 1, wherein the first light-emitting element and the second light-emitting element are infrared LEDs.

9. 9. The gas sensor according to claim 1, wherein the sensitivity peak wavelength of the second light receiving portion overlaps with 2 to 3 μm or 5 to 8 μm.

10. 10. The gas sensor according to claim 1, wherein the peak sensitivity wavelength of the first light receiving portion is closer to 3.3 [mu]m than the peak sensitivity wavelength of the second light receiving portion.

11. 10. The gas sensor according to claim 1, wherein the peak sensitivity wavelength of the second light receiving portion is closer to 2.7 [mu]m than the peak sensitivity wavelength of the first light receiving portion.

12. 12. The gas sensor according to claim 1, further comprising: calculating an equation that removes the influence of the interference gas from the output signal of the first light receiving element and the output signal of the second light receiving element; and calculating the concentration of the measurement target gas using the equation.

13. 13. The gas sensor according to claim 12, wherein the equation is a polynomial.

14. A gas sensor described in any one of claims 1 to 13, wherein a first optical path, which is a light ray emitted from the first light-emitting element, and a second optical path, which is a light ray emitted from the second light-emitting element, intersect.

15. A gas sensor as described in claim 14, wherein at least a portion of the light rays of the first optical path and at least a portion of the light rays of the second optical path intersect at an angle that is approximately perpendicular.

16. A gas sensor described in any one of claims 1 to 15, wherein the first light-emitting portion and the second light-emitting portion are arranged at different positions.

17. A gas sensor described in any one of claims 1 to 16, wherein the first light receiving unit and the second light receiving unit are arranged at different positions.

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