Co2 gas sensor

Abstract

To provide a CO2 gas sensor capable of measuring the concentration of a CO2 gas at a concentration higher than before.SOLUTION: The CO2 gas sensor 1 includes a tubular measuring cell 2 of a predetermined length into and from which a gas containing a CO2 gas to be detected is introduced and discharged, an optical source 11 for irradiating an atmosphere of the gas containing the CO2 gas to be detected in the measuring cell 2 with light including wavelengths absorbed by the CO2 gas, a detection filter 16 including a first detection filter 16a having a center frequency set to 3.9 μm so as to transmit light of wavelengths not absorbed by the CO2 gas among the light irradiated from the optical source 11 and a second detection filter 16b having a center frequency set to 4.4 to 4.5 μm so as to transmit light of wavelengths absorbed by the CO2 gas among the light irradiated from the optical source 11, and a first light receiving device 16a for receiving light transmitted through the first detection filter. 18a, and a second light receiving device 16b for receiving the light transmitted through the second detection filter 18b.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a CO2 gas sensor that detects the concentration of CO2 (carbon dioxide) in the atmosphere, and more particularly to an NDIR (Non Dispersive InfraRed) type CO2 gas sensor. [Background technology]

[0002] NDIR gas sensors, as disclosed in Patent Documents 1 and 2 below, have been known for some time as sensors that detect gases by utilizing the phenomenon in which radiated infrared rays cause molecular vibrations in the gas to be detected, resulting in the absorption of infrared rays of a specific wavelength.

[0003] To explain further, as shown in FIG. 5, a CO2 gas sensor 31 as an NDIR gas sensor is housed in a cylindrical measurement cell 32 having a gas inlet 32a through which a gas to be detected is introduced and a gas outlet 32b through which the gas to be detected is discharged, with a light source 33 that irradiates light (e.g., infrared light) having a wavelength that is absorbed by the gas to be detected and a gas detector 34 facing each other in the longitudinal direction of the measurement cell 32.

[0004] The gas detector 34 is configured such that two light receiving elements 35a and 35b are arranged side by side on a metal stem with leads (not shown), and the metal stem with leads is covered with a cap with a transmission window (not shown) in which optical filters 36a and 36b with different transmission wavelength ranges are attached at positions facing the light receiving elements 35a and 35b, respectively. This gas detector 34 compares the amount of transmission of infrared light from the light source 33 in an absorption wavelength range where the target gas absorbs the infrared light and a comparison wavelength range where the target gas does not absorb the infrared light, and converts the amount of transmission into a gas concentration.

[0005] FIG. 6 shows the relationship between the concentration of CO2 gas and the output when the concentration of CO2 gas is measured using a conventional NDIR type CO2 gas sensor 31. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2023-137725 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-074629 Summary of the Invention [Problem to be solved by the invention]

[0007] 6, a steep change in output is observed when the CO2 gas concentration in the measurement cell 32 is between 0 and 5%, but when the concentration exceeds 5%, the output does not change much and remains almost constant. Therefore, when the CO2 gas concentration in the measurement cell 32 is 5% or higher, the output remains almost constant, making it impossible to accurately measure the CO2 gas concentration in the measurement cell 32.

[0008] In recent years, as the movement toward achieving carbon neutrality by 2050 has been spreading internationally, CCUS (Carbon dioxide Capture, Utilization, and Storage) has attracted attention as an essential technology for achieving this goal. CCUS is a technology that not only separates and collects CO2 emitted from power plants, chemical plants, and other sources, and stores and injects it deep underground, but also aims to utilize and reuse the separated and stored CO2. CCUS handles CO2 at concentrations higher than the CO2 concentration (4% or 40,000 ppm) that poses a risk to humans, so there is a need to measure CO2 gas concentrations at higher concentrations than before.

[0009] The present invention has been made in view of the above problems, and has as its object to provide a CO2 gas sensor capable of measuring the concentration of CO2 gas at a higher concentration than conventional sensors. [Means for solving the problem]

[0010] In order to achieve the above object, a CO2 gas sensor according to claim 1 of the present invention comprises a cylindrical measurement cell of a predetermined length into which a gas containing CO2 gas as a detection target gas is introduced and discharged; a light source that irradiates a gas atmosphere containing the CO gas to be detected in the measurement cell with light having a wavelength that is absorbed by the CO gas; detection filters including a first detection filter having a center wavelength set to 3.9 μm so as to transmit light of a wavelength that is not absorbed by the CO2 gas among the light irradiated from the light source, and a second detection filter having a center wavelength set to 4.4 to 4.5 μm so as to transmit light of a wavelength that is absorbed by the CO2 gas among the light irradiated from the light source; The light receiving element includes a first light receiving element that receives light that has passed through the first detection filter, and a second light receiving element that receives light that has passed through the second detection filter.

[0011] The CO2 gas sensor according to claim 2 of the present invention is the CO2 gas sensor according to claim 1, the detection filter further includes a third detection filter having a center wavelength set to 4.2 to 4.3 μm so as to transmit light of a wavelength absorbed by the CO gas among the light irradiated from the light source; The light receiving element further includes a third light receiving element that receives light that has passed through the third detection filter.

[0012] A CO2 gas sensor according to claim 3 of the present invention is the CO2 gas sensor according to claim 1, a first aperture provided between the first detection filter and the first light receiving element, which reduces the amount of light transmitted through the first detection filter and inputs the reduced amount of light to the first light receiving element; The optical system is characterized by comprising a second aperture provided between the second detection filter and the second light receiving element, which reduces the amount of light that has passed through the second detection filter and inputs it to the second light receiving element.

[0013] A CO2 gas sensor according to claim 4 of the present invention is the CO2 gas sensor according to claim 2, The optical system further comprises a third aperture provided between the third detection filter and the third light receiving element, which reduces the amount of light that has passed through the third detection filter and inputs it to the third light receiving element. [Effects of the Invention]

[0014] According to the present invention, it is possible to measure CO2 gas concentrations at higher concentrations than before, and it is possible to measure CO2 gas concentrations from 0 to 100%. In addition, it is possible to suppress interference between outputs of adjacent light receiving elements and prevent a decrease in correction accuracy. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram showing the overall configuration of a CO2 gas sensor according to the present invention. [Figure 2] 2A and 2B are diagrams illustrating the CO2 gas sensor of FIG. 1 before and after a diaphragm is attached to the optical filter of the detection unit mounting member. [Figure 3] This figure shows the relationship between wavelength and spectrum when the concentration of CO2 gas is 0%, 1%, 5%, 10%, 50%, and 100% with N2 gas as the base. [Figure 4] FIG. 1 is a diagram showing an example of a calibration curve used in a CO2 gas sensor according to the present invention, illustrating the relationship between the CO2 gas concentration and the standard value when measurements are performed in a measurement environment of 25°C, atmospheric pressure, and N2 gas base with CO2 gas concentrations of 0%, 1%, 5%, 10%, 50%, and 100%. [Figure 5] FIG. 1 is a diagram showing the overall configuration of a conventional CO2 gas sensor. [Figure 6] FIG. 10 is a diagram showing the relationship between the concentration of CO2 gas and the A / D count value in a conventional CO2 gas sensor. DETAILED DESCRIPTION OF THE INVENTION

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0017] In order to develop a CO2 gas sensor capable of measuring higher concentrations of CO2 gas than conventional ones, the present inventors conducted a measurement experiment using a conventionally known CO2 gas sensor 31 having the configuration shown in Figure 5, setting the light source output to 2 W and the optical path length d to 90 mm, and reducing the CO2 gas concentration in the measurement cell from 100%. As a result, the measurement results of the absorption spectrum of CO2 gas shown in Figure 3 were obtained.

[0018] In FIG. 3, the absorption spectrum is present even when the CO2 concentration is 0% because CO2 gas remains in the measurement cell.

[0019] Looking at the measurement results of the CO2 gas absorption spectrum in Figure 3, it can be seen that at a wavelength of around 4.26 μm, which is used in filters for conventional CO2 gas sensors, the absorption spectra overlap when the CO2 concentration is 10%, 50%, and 100%, whereas at a wavelength of around 4.45 μm, the absorption spectra do not overlap when the CO2 concentration is 0%, 1%, 5%, 10%, 50%, and 100%, and there is a gradual sensitivity.The results of this measurement experiment showed that by using a filter with a center wavelength of around 4.45 μm, it is possible to measure CO2 gas concentrations higher than conventional methods.

[0020] As shown in FIG. 1, the CO2 gas sensor 1 of this embodiment has a light source unit 3 and a gas detection unit 4 arranged opposite to each other in the longitudinal direction of a measurement cell 2 into which a gas G containing CO2 gas as a detection target gas is introduced and discharged. The CO2 gas sensor 1 is an NDIR type gas sensor that utilizes the property of CO2 gas molecules absorbing infrared light of a specific wavelength, and enables the measurement of higher concentrations of CO2 gas than conventional gas sensors.

[0021] As shown in FIG. 1, the measurement cell 2 has a main body made of a metal such as aluminum or copper, and is formed in a cylindrical shape with a predetermined optical path length d.

[0022] The measurement cell 2 is provided with a gas inlet 2a for introducing gas G containing CO gas as a detection target gas into the measurement cell 2, and a gas outlet 2b for discharging a portion of the gas G introduced into the measurement cell 2 from the gas inlet 2a to the outside of the measurement cell 2, in parallel at the center of the longitudinal direction.

[0023] The positions of the gas inlet 2a and the gas outlet 2b are not limited to those shown in Fig. 1. Furthermore, the inner surface of the measurement cell 2 may be made mirror-finished or glossy by surface treatment (plating, vapor deposition, sputtering, etc.) with a metal such as gold, silver, nickel, or aluminum to more efficiently reflect light.

[0024] Furthermore, the measuring cell 2 is not limited to a cylindrical shape with a constant width (constant diameter) as shown in FIG. 1, and may have an optical path with an elliptical inner diameter in order to increase the optical path length of the light source unit 3 .

[0025] The light source unit 3 has a light source 11 that emits light (for example, infrared light) having a wavelength that is absorbed by CO2 gas as the gas to be detected, and is attached to a light source unit attachment member 12 that serves as a first attachment member.

[0026] The light source unit mounting member 12 has an opening 13 that is opened with the same dimensions as the inner diameter of the measurement cell 2, and a reflective surface 13a with a predetermined curvature is formed in the opening 13, and a first transmission window 14 made of, for example, calcium fluoride or sapphire is fixed to the opening 13. With the light source 11 fixed to the center of the base end side of the opening 13, the light source unit mounting member 12 is detachably fixed and attached to one end of the measurement cell 2 by screwing via an O-ring 15 as a sealing member so that the inside of the measurement cell 2 is kept airtight.

[0027] In order to detect CO2 gas as the target gas contained in the gas G in the atmosphere within the measurement cell 2, the gas detection unit 4 has a detection filter 16, an aperture 17, and a light receiving element 18 attached to a detection unit attachment member 19 as a second attachment member.

[0028] The detection unit mounting member 19 has a rectangular opening 20 with the same dimensions as the inner diameter of the measurement cell 2, and a second transmission window 21 made of, for example, calcium fluoride or sapphire is fixed to the opening 20, and the detection filter 16, diaphragm 17, and light-receiving element 18 are fixed to the base end of the opening 20. The detection unit mounting member 19 is detachably fixed to the other end of the measurement cell 2 by screwing via an O-ring 22 as a sealing member so that the inside of the measurement cell 2 is kept airtight.

[0029] The detection filter 16 is a filter that transmits only light of a predetermined wavelength from the light that has passed through the second transmission window 21, and is composed of a first detection filter 16a, a second detection filter 16b, and a third detection filter 16c that are attached to the detection unit mounting member 19 facing the second transmission window 21.

[0030] The first detection filter 16a has a center wavelength set to 3.9 μm, and transmits light of a wavelength that is not absorbed by CO2 gas, among the light irradiated from the light source 11, passed through the atmosphere in the measurement cell 2, and transmitted through the second transmission window 21.

[0031] The second detection filter 16b has a central wavelength set to 4.4 to 4.5 μm, and transmits light of a wavelength that is absorbed by CO2 gas out of the light that is irradiated from the light source 11, passes through the atmosphere in the measurement cell 2, and is transmitted through the second transmission window 21.

[0032] The third detection filter 16c has a central wavelength set to 4.2 to 4.3 μm, and transmits light of a wavelength that is absorbed by CO2 gas among the light that is irradiated from the light source 11, passes through the atmosphere in the measurement cell 2, and is transmitted through the second transmission window 21.

[0033] The aperture 17 reduces the amount of light that passes through the detection filter 16, and is located between the detection filter 16 and the light receiving element 18 and attached to the detection unit mounting member 19. It is composed of a first aperture 17a, a second aperture 17b, and a third aperture 17c.

[0034] The first aperture 17a is provided between the first detection filter 16a and a first light receiving element 18a (described later), and reduces the amount of light that has passed through the first detection filter 16a and inputs it to the first light receiving element 18a.

[0035] The second aperture 17b is provided between the second detection filter 16b and a second light receiving element 18b described later, and reduces the amount of light transmitted through the second detection filter 16b and inputs it to the second light receiving element 18b.

[0036] The third aperture 17c is provided between the third detection filter 16c and a third light receiving element 18c described later, and reduces the amount of light transmitted through the third detection filter 16c and inputs it to the third light receiving element 18c.

[0037] The light receiving element 18 is made of, for example, an InSb element, and is attached to the detection unit mounting member 19 facing the diaphragm 17, and is made up of a first light receiving element 18a, a second light receiving element 18b, and a third light receiving element 18c.

[0038] The first light receiving element 18a receives light that has passed through the first detection filter 16a and whose amount has been reduced by the first aperture 17a.

[0039] The second light receiving element 18b receives light that has passed through the second detection filter 16b and whose amount has been reduced by the second diaphragm 17b.

[0040] The third light receiving element 18c receives light that has passed through the third detection filter 16c and whose amount has been reduced by the third diaphragm 17c.

[0041] Next, a method for measuring the concentration of CO2 gas as a detection target gas using the CO2 gas sensor 1 configured as above will be described.

[0042] When measuring the concentration of CO2 gas, which is a gas to be detected, a calibration curve such as that shown in Fig. 4 is prepared in advance. Fig. 4 shows an example of a calibration curve used in the CO2 gas sensor 1. The calibration curve in Fig. 4 shows the relationship between the CO2 gas concentration and the standard value when measurements are performed in a measurement environment of 25°C, atmospheric pressure, and N2 gas base with CO2 gas concentrations of 0%, 1%, 5%, 10%, 50%, and 100%. The calibration curve is a graph prepared using values ​​obtained by integrating the spectral intensity only in a specific wavelength range based on spectral data from 2 to 12 µm measured with a spectrometer.

[0043] The vertical axis in Figure 4 (standard value) is a value normalized by the following formula (1) so that the maximum value (CO2 gas concentration: 0%) is 100 and the minimum value (CO2 gas concentration: 100%) is 0. In formula (1), y is the standard value and x is the output at each concentration.

[0044]

number

[0045] To create the calibration curve shown in Figure 4, in a measurement environment of 25°C and atmospheric pressure, the concentration of CO2 gas in the atmosphere in the measurement cell 2 is sequentially changed from 100%, 75%, 10%, 5%, 1%, and 0%, and light (e.g., infrared light) containing a wavelength that is absorbed by the CO2 gas to be detected is irradiated from the light source 11 into the atmosphere in the measurement cell 2.

[0046] As a result, the light irradiated from the light source 11 to the atmosphere in the measurement cell 2 is received by the corresponding light receiving elements 18 (first to third light receiving elements 18a, 18b, 18c) via each detection filter 16 (first to third detection filters 16a, 16b, 16c) with center wavelengths of 3.9 μm, 4.2 to 4.3 μm (e.g., 4.26 μm), and 4.4 to 4.5 μm (e.g., 4.45 μm).

[0047] Then, an output ratio of each standard gas concentration is calculated from the measurement data of each wavelength received by each light receiving element 18 (first to third light receiving elements 18a, 18b, 18c). Specifically, the output ratio of the third light receiving element 18c when the light passes through the third detection filter 16c with a center wavelength of 4.26 μm / the output ratio of the first light receiving element 18a when the light passes through the first detection filter 16a with a center wavelength of 3.9 μm is calculated. Also, the output ratio of the second light receiving element 18b when the light passes through the second detection filter 16b with a center wavelength of 4.45 μm / the output ratio of the first light receiving element 18a when the light passes through the first detection filter 16a with a center wavelength of 3.9 μm is calculated.

[0048] Then, the output ratio data of each standard gas concentration obtained by the above calculation is substituted into the Lambert-Beer equation in the following equation (2) to create the calibration curve shown in Figure 4. In equation (2), I d : output ratio at each concentration of CO2 gas, I0: output ratio of 0% CO2 gas (zero point), c: standard gas concentration, d: optical path length (constant), ε: absorption coefficient (fitting parameter).

[0049]

number

[0050] When measuring the concentration of CO2 gas as the target gas, the CO2 gas sensor 1 is placed in an atmosphere of gas G containing the CO2 gas as the target gas, and the gas G containing the CO2 gas as the target gas is introduced into the measurement cell 2 through the gas inlet 2a of the measurement cell 2. A portion of the introduced gas G is discharged to the outside of the measurement cell 2 through the gas outlet 2b, causing natural convection of the gas G within the measurement cell 2.

[0051] Thereafter, light (e.g., infrared light) including a wavelength that is absorbed by CO2 gas, the gas to be detected, is emitted from the light source 11 attached to the light source unit mounting member 12. The light emitted from the light source 11 is irradiated into the atmosphere of gas G in the measurement cell 2 through a first transmission window 14 attached to the light source unit mounting member 12. When the light from the light source 11 is irradiated into the atmosphere of gas G in the measurement cell 2 through the first transmission window 14, the light is received by the light receiving element 18 from the atmosphere of gas G in the measurement cell 2 through a second transmission window 21, a detection filter 16, and an aperture 17 attached to the detection unit mounting member 19 on the opposite side of the measurement cell 2.

[0052] At this time, the first detection filter 16a has a center wavelength set to 3.9 μm, and transmits light of a wavelength that is not absorbed by CO2 gas, among the light that has passed through the second transmission window 21. Then, the amount of light that has passed through the first detection filter 16a is reduced by the first aperture 17b, and the light is received by the first light receiving element 18a.

[0053] The second detection filter 16b has a center wavelength set to 4.4 to 4.5 μm, and transmits light of a wavelength that is absorbed by CO2 gas among the light that has passed through the second transmission window 21. The amount of light that has passed through the second detection filter 16b is then reduced by the second diaphragm 17b, and is then received by the second light receiving element 18b.

[0054] Furthermore, the third detection filter 16c has a central wavelength set to 4.2 to 4.3 μm, and transmits light of a wavelength that is absorbed by CO2 gas among the light that has transmitted through the second transmission window 21. Then, the amount of light that has transmitted through the first detection filter 16a is reduced by the third diaphragm 17c, and is received by the third light receiving element 18c.

[0055] Then, an output ratio of CO2 gas concentration is calculated from the measurement data of each wavelength received by each light receiving element 18 (first to third light receiving elements 18a, 18b, 18c). Specifically, the output ratio of the third light receiving element 18c when the light passes through the third detection filter 16c with a center wavelength of 4.26 μm / the output ratio of the first light receiving element 18a when the light passes through the first detection filter 16a with a center wavelength of 3.9 μm is calculated. In addition, the output ratio of the second light receiving element 18b when the light passes through the second detection filter 16b with a center wavelength of 4.45 μm / the output ratio of the first light receiving element 18a when the light passes through the first detection filter 16a with a center wavelength of 3.9 μm is calculated.

[0056] Thereafter, the CO2 gas concentration c is calculated by substituting the output ratio of the CO2 gas concentration of the measurement data for each wavelength into the calibration curve of FIG. 4 that was created in advance.

[0057] When equation (2) is solved for the gas concentration c, the following equation (3) is obtained. In equation (3), I d : output ratio of measurement data, I0: output ratio of 0% CO2 gas (zero point), c: gas concentration (indicated value), d: optical path length (constant), ε: absorption coefficient (constant).

[0058]

number

[0059] Incidentally, when measuring the concentration of CO2 gas as the target gas using the CO2 gas sensor 1, in order to measure with higher accuracy concentrations up to a CO2 concentration (4%: 40,000 ppm) that poses a danger to humans, it is preferable to use the first detection filter 16a with a center wavelength of 3.9 μm and the third detection filter 16c with a center wavelength of 4.2 to 4.3 μm when measuring the CO2 concentration of the target gas with a CO2 concentration of up to 1%, and to use the first detection filter 16a with a center wavelength of 3.9 μm and the second detection filter 16b with a center wavelength of 4.4 to 4.5 μm when measuring the CO2 concentration of the target gas with a CO2 concentration of 1% to 100%.

[0060] Furthermore, in the above-described embodiment, the configuration has been described as including the first detection filter 16a, the second detection filter 16b, and the third detection filter 16c as three types of detection filters 16 with different center wavelengths, and including apertures 17 (first aperture 17a, second aperture 17b, third aperture 17c) and light receiving elements 18 (first light receiving element 18a, second light receiving element 18b, third light receiving element 18c) corresponding to the detection filters 16a, 16b, and 16c, respectively; however, the configuration may also be such that the conventionally well-known third detection filter 16c, whose center wavelength is set to 4.2 to 4.3 μm, and the third aperture 17c and third light receiving element 18c arranged corresponding to the third detection filter 16c are omitted.

[0061] As described above, according to the embodiment described above, in the measurement result of the absorption spectrum of CO2 gas in FIG. 3, the absorption spectra at a wavelength of around 4.45 μm when the CO2 concentration is 0%, 1%, 5%, 10%, 50%, and 100% have a gradual sensitivity without overlapping with each other. Based on this, the detection filters essential for measuring the concentration of CO2 gas are provided: a first detection filter 16a having a center wavelength set to 3.9 μm so as to transmit light of a wavelength that is not absorbed by CO2 gas among the light irradiated from the light source 11; and a second detection filter 16b having a center wavelength set to 4.4 to 4.5 μm so as to transmit light of a wavelength that is absorbed by CO2 gas among the light irradiated from the light source 11; and a first aperture 17a and a first light receiving element 18a are arranged corresponding to the first detection filter 16a, and a second aperture 17b and a second light receiving element 18b are arranged corresponding to the second detection filter 16b. This makes it possible to measure CO2 gas concentrations at higher concentrations than before, and can handle CO2 gas concentration measurements from 0 to 100%.

[0062] In addition to the above configuration, the device is provided with a third detection filter 16c having a central wavelength set to 4.2 to 4.3 μm so as to transmit light of a wavelength that is absorbed by CO2 gas among the light emitted from the light source 11, and by using a third aperture 17c and a third light receiving element 18c arranged in correspondence with the third detection filter 16c, it is possible to measure CO2 gas concentrations up to 1% with high accuracy, and can handle CO2 concentrations (4%: 40,000 ppm) that pose a danger to people.

[0063] Furthermore, diaphragms 17 (first diaphragm 17a, second diaphragm 17b, third diaphragm 17c) are arranged in front of the first light receiving element 18a, second light receiving element 18b, and third light receiving element 18c, respectively, to limit the amount of light. This makes it possible to suppress interference between outputs of adjacent light receiving elements. As a result, it is possible to prevent a decrease in correction accuracy.

[0064] Although the best mode for carrying out the CO2 gas sensor according to the present invention has been described above, the present invention is not limited to the description and drawings of this mode. In other words, all other modes, embodiments, and operational techniques that can be made by those skilled in the art based on this mode are naturally included in the scope of the present invention. [Explanation of symbols]

[0065] 1 CO2 gas sensor 2. Measuring cell 3 Light source section 4 Gas detection unit 11 Light source 12 Light source unit mounting member (first mounting member) 13 Opening 13a Reflective surface 14 First transparent window 15 O-ring (sealing material) 16 Detection filter 16a First detection filter 16b Second detection filter 16c Third detection filter 17 Aperture 17a First aperture 17b 2nd aperture 17c 3rd aperture 18 Photodetector 18a First light receiving element 18b Second light receiving element 18c Third light receiving element 19. Detector mounting member (second mounting member) 20 Opening 21 Second transparent window 22 O-ring (sealing material) 31 NDIR gas sensor (CO2 gas sensor) 32 measuring cells 32a Gas inlet 32b Gas outlet 33 Light source 34 Gas detector 35a, 35b Light receiving element 36a, 36b Optical filters d Optical path length G Gas containing CO2 (detection target gas)

Claims

1. a cylindrical measurement cell of a predetermined length into which a gas containing CO2 gas as a detection target gas is introduced and discharged; a light source that irradiates a gas atmosphere containing the CO gas to be detected in the measurement cell with light having a wavelength that is absorbed by the CO gas; detection filters including a first detection filter having a center wavelength set to 3.9 μm so as to transmit light of a wavelength that is not absorbed by the CO2 gas among the light irradiated from the light source, and a second detection filter having a center wavelength set to 4.4 to 4.5 μm so as to transmit light of a wavelength that is absorbed by the CO2 gas among the light irradiated from the light source; A CO2 gas sensor characterized by comprising a light-receiving element including a first light-receiving element that receives light that has passed through the first detection filter and a second light-receiving element that receives light that has passed through the second detection filter.

2. the detection filter further includes a third detection filter having a center wavelength set to 4.2 to 4.3 μm so as to transmit light of a wavelength that is absorbed by the CO gas among the light irradiated from the light source; 2. The CO2 gas sensor according to claim 1, wherein the light receiving element further includes a third light receiving element that receives light transmitted through the third detection filter.

3. a first aperture provided between the first detection filter and the first light receiving element, which reduces the amount of light transmitted through the first detection filter and inputs the reduced amount of light to the first light receiving element; 2. The CO2 gas sensor according to claim 1, further comprising a second aperture provided between the second detection filter and the second light receiving element, for reducing the amount of light transmitted through the second detection filter and inputting it to the second light receiving element.

4. 3. The CO2 gas sensor according to claim 2, further comprising a third aperture provided between the third detection filter and the third light receiving element, for reducing the amount of light transmitted through the third detection filter and inputting it to the third light receiving element.

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