Gas concentration measurement method and low-power infrared gas sensor

Abstract

The present application relates to a gas concentration measurement method and a low-power infrared gas sensor. The method comprises: collecting the signal intensities of infrared light emitted from the same low-power infrared light source that reaches two infrared detectors; and calculating, by means of the inversion of the ratio of the signal intensities of the two infrared detectors, the concentration of a gas to be measured. A detection optical path of said gas of a gas sensor comprises a low-power infrared light source, a light-splitting structure, and the two infrared detectors, and light emitted from the light source is split by the light-splitting structure and is then directed to both the two infrared detectors.

Description

Gas concentration detection methods and low-power infrared gas sensors

[0001] This application claims priority to Chinese Patent Application No. 202411427541.2, filed on October 14, 2024, entitled "Gas Concentration Detection Method and Low-Power Infrared Gas Sensor for Implementing the Method", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of gas concentration detection technology, specifically to a gas concentration detection method and a low-power infrared gas sensor for implementing the method. Background Technology

[0003] Infrared gas sensors possess advantages such as fast response speed, high measurement accuracy, strong anti-interference capability, normal operation in oxygen-free environments, and long service life, making them a promising candidate for market applications in the gas sensor field. The working principle of infrared gas sensors utilizes the inherent vibrational and rotational frequencies of gas molecules to absorb infrared light signals of specific wavelengths, and the relationship between light absorption intensity and gas molecule concentration follows the Lambert-Beer Law. Therefore, by detecting the change in the absorption intensity of a specific wavelength of light after the interaction between infrared light and gas molecules, the concentration of a specific gas can be detected.

[0004] A common problem with infrared gas sensors is installation. For example, installation often requires laying cables beforehand, sometimes necessitates road construction, and in extreme environments, there may be no power supply. Therefore, the industry desires infrared gas sensors that can be installed and used anytime, anywhere without any external cables. However, traditional infrared gas sensors are limited by their high power consumption, making battery power unsuitable. Thus, low-power infrared gas sensors have emerged as a solution.

[0005] While low-power infrared gas sensors can solve a range of installation problems through battery power, their low power consumption is due to the use of low-power infrared light sources (LEDs). Low-power LEDs are particularly sensitive to temperature; higher temperatures result in lower luminous efficiency and intensity. Especially in the industrial operating temperature range of -40°C to +70°C, the maximum luminous intensity of an LED can reach more than seven times its minimum under temperature variations. This demonstrates the significant temperature-dependent changes in LED luminous intensity (see Figure 7).

[0006] Low-power infrared gas sensors detect gas concentration by calculating it based on measured light intensity. Generally, gas absorption causes a change in the detected light intensity of 0.5 to 1 times. In contrast, temperature changes cause a much larger change in the sensor signal value than gas absorption. Without appropriate compensation, the gas concentration measurement error will be extremely large, and the low-power sensor will not function properly.

[0007] Several light intensity compensation methods exist, such as Chinese Patent Publication No. CN108444935A and CN112925363A, which compensate light intensity through pulse width modulation (PWM) to ensure the stability of low-power infrared light intensity at any temperature. However, the PWM method for compensating light intensity has the following problems:

[0008] 1. Light intensity compensation is a complex operation that requires collecting a large amount of data on the variation of light source intensity with ambient temperature and the variation of light source intensity with light source pulse width. Then, these two sets of data are integrated to obtain the curve relationship between light source pulse width and ambient temperature, and light intensity compensation is performed.

[0009] 2. It cannot compensate for light source aging. As the light emission time increases, the brightness of the light source will gradually decrease. The pulse width modulation method cannot compensate for light intensity aging.

[0010] 3. Different sensors use different light sources. Due to individual differences in the temperature characteristics of the light sources, the compensation amount for each light source is different. Each sensor needs to be compensated individually, which is not conducive to the mass production of sensors.

[0011] The above problems urgently need to be addressed. Summary of the Invention

[0012] To overcome the shortcomings of existing technologies, this application provides a gas concentration detection method and a low-power infrared gas sensor for implementing the method.

[0013] The technical solution of this application is as follows:

[0014] A method for detecting gas concentration involves introducing a gas to be measured, collecting the signal intensities of infrared light emitted from the same low-power infrared light source at two infrared detectors with the same filter band, and calculating the concentration of the gas to be measured by inverting the ratio of the signal intensities from the two infrared detectors. Specifically, the method includes the following steps:

[0015] Step 1: Introduce the gas to be measured with a known concentration gradient into the low-power infrared gas sensor;

[0016] Step 2: Obtain the fitting calculation formula for concentration and normalized detection signal intensity;

[0017] Record the normalized detection signal intensity measured by the low-power infrared gas sensor at different concentrations; obtain the calculation formula by fitting a nonlinear curve and write it into the chip;

[0018] Step 3: Detect the normalized detection signal intensity of the unknown concentration of the gas to be measured using a low-power infrared gas sensor.

[0019] Step 4: Calculate the concentration of the gas to be tested using the formula.

[0020] This application also provides a low-power infrared gas sensor for implementing the gas concentration detection method described above. The low-power infrared gas sensor has a gas chamber for introducing gas. The gas chamber is provided with a gas detection optical path, which includes a first low-power infrared light source, a first beam splitting structure, a first infrared detector, and a second infrared detector. The emitted light from the first low-power infrared light source is split into two beams with the same center wavelength by the first beam splitting structure, and directed to the first infrared detector and the second infrared detector, which have the same filter band, respectively. The distance from the first infrared detector to the first beam splitting structure and the distance from the second infrared detector to the first beam splitting structure are different, so that the optical path length from the first low-power infrared light source to the first infrared detector is not equal to the optical path length from the first low-power infrared light source to the second infrared detector, and the difference is defined as the length of the equivalent optical path of the gas detection optical path.

[0021] In some embodiments of this application, the optical path for detecting the gas to be tested further includes a first off-axis parabolic reflector, an outer ring reflector, and a second off-axis parabolic reflector. The first off-axis parabolic reflector is used to collimate the emitted light from the first low-power infrared light source and reflect it onto the outer ring reflector. The outer ring reflector is used to reflect the light four times to form a rectangular optical path. The outer ring reflector reflects the light once, twice, or three times and then directs it toward the first beam splitter. The light transmitted through the first beam splitter is directed toward the next reflection point of the outer ring reflector. The light reflected by the first beam splitter is directed toward the first infrared detector. The outer ring reflector reflects the light four times and then directs it toward the second off-axis parabolic reflector. The light is reflected by the second off-axis parabolic reflector and converges to the second infrared detector.

[0022] In some embodiments of this application, the air chamber has a first mounting surface and a second mounting surface facing each other and parallel to each other. The outer ring reflective surface is located between the first mounting surface and the second mounting surface, and the plane containing the rectangular optical path of the outer ring reflective surface is parallel to the two mounting surfaces. The first low-power infrared light source, the first infrared detector, and the second infrared detector are disposed on the first mounting surface, and the first beam splitting structure, the first off-axis parabolic reflective surface, and the second off-axis parabolic reflective surface are located on the second mounting surface. The optical paths from the first low-power infrared light source to the first off-axis parabolic reflective surface, the first beam splitting structure to the first infrared detector, and the second off-axis parabolic reflective surface to the second infrared detector are all perpendicular to the plane containing the rectangular optical path.

[0023] In some embodiments of this application, the gas chamber is provided with an interfering gas detection optical path, which includes a second low-power infrared light source, a second beam splitting structure, a third infrared detector, and a fourth infrared detector. The emitted light from the second low-power infrared light source is split into two beams with the same center wavelength by the second beam splitting structure, and directed to the third infrared detector and the fourth infrared detector, which have the same filter band, respectively. The distance from the third infrared detector to the second beam splitting structure and the distance from the fourth infrared detector to the second beam splitting structure are different, so that the optical path length from the second low-power infrared light source to the third infrared detector is not equal to the optical path length from the second low-power infrared light source to the fourth infrared detector, and the difference is defined as the length of the equivalent optical path of the interfering gas detection optical path.

[0024] In some embodiments of this application, the interfering gas detection optical path further includes a third off-axis parabolic reflector, an inner ring reflector, and a fourth off-axis parabolic reflector. The third off-axis parabolic reflector is used to collimate the emitted light of the second low-power infrared light source and reflect it to the second beam splitter. The second beam splitter reflects part of the light to the third infrared detector, and the light transmitted through the second beam splitter is directed to the inner ring reflector. The inner ring reflector reflects the light to the fourth off-axis parabolic reflector, and the light is reflected by the fourth off-axis parabolic reflector and converged to the fourth infrared detector.

[0025] In some embodiments of this application, both the first beam-splitting structure and the second beam-splitting structure have a metal reflector. The metal reflector has a plurality of light-transmitting holes. The ratio of the area of ​​all the light-transmitting holes to the area of ​​the metal reflector is the light transmittance of the metal reflector. The ratio of the area of ​​the metal reflector after removing all the light-transmitting holes to the area of ​​the metal reflector is the reflectance of the metal reflector. The number of light-transmitting holes in the metal reflector is fixed or adjustable.

[0026] In some embodiments of this application, the middle interlayer of the metal reflector is provided with a deflector plate, and the surfaces of both the metal reflector plate and the deflector plate are coated with a reflective film. The number of light-transmitting holes blocked by the deflector plate can be adjusted by adjusting the relative position of the deflector plate and the metal reflector plate.

[0027] In some embodiments of this application, the top plate of the air chamber is provided with a plate movable groove at the position corresponding to the beam splitting structure, and the actuating plate can slide within the corresponding plate movable groove.

[0028] In some embodiments of this application, the air chamber has a first mounting surface and a second mounting surface facing each other and parallel to each other, and the inner ring reflective surface is located between the first mounting surface and the second mounting surface; the second low-power infrared light source, the third infrared detector and the fourth infrared detector are disposed on the first mounting surface, and the second beam splitting structure, the third off-axis parabolic reflective surface and the fourth off-axis parabolic reflective surface are located on the second mounting surface; the optical paths from the second low-power infrared light source to the third off-axis parabolic reflective surface, the second beam splitting structure to the third infrared detector, and the fourth off-axis parabolic reflective surface to the fourth infrared detector are all perpendicular to the plane where the rectangular optical path is located.

[0029] In some embodiments of this application, the distance from the straight line containing the optical path from the first off-axis parabolic reflector to the outer ring reflector to the center point of the outer ring reflector is equal to the square root of the radius of the outer ring reflector, so that the rectangular optical path is a square optical path.

[0030] In some embodiments of this application, the air chamber is composed of a bottom plate, a perforated plate, and a top plate. The upper surface of the bottom plate forms the first mounting surface of the air chamber, and the lower surface of the top plate forms the second mounting surface of the air chamber. The upper surface of the perforated plate is provided with an outer peripheral plate and an inner peripheral plate in a concentric circular structure. The inner sidewall of the outer peripheral plate is coated with a reflective surface to form an outer ring reflective surface, and the inner sidewall of the inner peripheral plate is coated with a reflective surface to form an inner ring reflective surface. The perforated plate is provided with a plurality of perforations, which are used to transmit the emitted light from the low-power infrared light source on the bottom plate, the received light from the infrared detector, or the reflected light from the beam-splitting structure on the top plate.

[0031] In some embodiments of this application, the top plate is provided with a plurality of vent holes, which are used to introduce gas into the optical path for detecting the gas to be tested and the optical path for detecting the interfering gas.

[0032] In some embodiments of this application, the top plate is provided with a limiting boss or a limiting groove, and the outer plate of the hollow plate is provided with a matching limiting groove or a limiting boss.

[0033] In some embodiments of this application, a low-power circuit board is also provided at the bottom of the air chamber, and the pins of the low-power infrared light source and infrared detector in the air chamber extend out of the bottom of the air chamber and are soldered to the low-power circuit board.

[0034] In some embodiments of this application, a housing is also included, the housing comprising an outer protective cover and a bottom shell, the top of the outer protective cover having an air inlet, and a plurality of sensor pins extending from the bottom shell.

[0035] According to the above-described scheme, the beneficial effects of this application are as follows:

[0036] This application simultaneously collects the signal intensity of infrared light emitted from the same low-power infrared light source from a low-power infrared gas sensor reaching two infrared detectors. The concentration of the gas to be measured is calculated by inverting the ratio of the signal intensity detected by the two infrared detectors, ensuring that the low-power sensor is not affected by external environmental temperature, light source aging, or other factors during operation, thus achieving the stability and accuracy of the low-power infrared gas sensor in detecting gas concentration.

[0037] By implementing a high-stability, low-power infrared gas sensor, the individual differences between different sensors and different light source temperature characteristics can be eliminated, eliminating the need for individual compensation for each sensor, which is beneficial for the mass production of low-power infrared gas sensors.

[0038] Furthermore, the optical path structure of the low-power infrared gas sensor can be divided into two optical paths: an external optical path for detecting the gas to be measured, used to measure the concentration of the gas to be measured; and an internal optical path for detecting interfering gases, used to measure the concentration of specific interfering gases. Through data processing algorithms, the low-power infrared gas sensor can achieve the function of detecting the concentration of specific interfering gases. Moreover, whether it is the detection of the concentration of the gas to be measured or the detection of the concentration of interfering gases, the concentration detection results can be ensured to be unaffected by factors such as external ambient temperature and light source aging, thus ensuring the stability and accuracy of the detected gas concentration. Attached Figure Description

[0039] Figure 1 is a flowchart of the method of this application;

[0040] Figure 2 is an exploded view of the structure of this application;

[0041] Figure 3 is a schematic diagram of the structure of the perforated plate of this application;

[0042] Figure 4 is a structural schematic diagram of the top plate of this application;

[0043] Figure 5 is a schematic diagram of the optical path of this application;

[0044] Figure 6 is a graph showing the change of the detector light intensity ratio as a function of temperature in this application;

[0045] Figure 7 shows the curve of the light intensity detected by an existing low-power infrared gas sensor as a function of temperature.

[0046] In the diagram: 1. Hollow plate; 11. Outer ring reflective surface; 12. Inner ring reflective surface; 13. Hollow opening; 14. Limiting groove; 20. Base plate; 2. First low-power infrared light source; 3. First infrared detector; 4. Second infrared detector; 5. Second low-power infrared light source; 6. Third infrared detector; 7. Fourth infrared detector; 8. Top plate; 81. First off-axis parabolic reflective surface; 82. Second off-axis parabolic reflective surface; 83. Third off-axis parabolic reflective surface; 84. Fourth off-axis parabolic reflective surface; 85. First beam splitting structure; 86. Second beam splitting structure; 87. Vent hole; 88. Limiting boss; 9. Low-power circuit board; 10. Outer protective cover; 101. Air inlet. Detailed Implementation

[0047] To better understand the purpose, technical solution, and technical effects of this application, the following description, in conjunction with the accompanying drawings and embodiments, will provide further explanation. It should be noted that similar reference numerals and letters in the following drawings indicate similar items; therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. It is also stated that the embodiments described below are only for explaining this application and are not intended to limit this application.

[0048] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be directly on the other component or there may be an intermediate component. When a component is referred to as "connected to" another component, it can be directly connected to the other component or there may be an intermediate component.

[0049] The indicated orientation or positional relationship is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product is usually placed when in use, or the orientation or positional relationship in which a person skilled in the art would normally understand it, or the orientation or positional relationship in which the product is usually placed when in use. It is only for the purpose of facilitating the description of this application and simplifying the description, and is not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0050] The terms “first,” “second,” “third,” and “fourth” are used for descriptive purposes only and should not be construed as indicating or implying relative importance or specifying the number of technical features. “Several” means two or more, unless otherwise expressly and specifically defined.

[0051] As shown in Figures 1 to 6, a method for detecting gas concentration involves introducing a gas to be measured and collecting the signal intensities of infrared light emitted from the same low-power infrared light source at two infrared detectors with the same filter band. The concentration of the gas to be measured is calculated by inverting the ratio of the signal intensities of the two infrared detectors. The filter band of the internal filter of the infrared detector determines its detection band; therefore, the detection bands of the two infrared detectors are the same and both fall within the absorption band of the gas to be measured. After the gas to be measured is introduced, the gas molecules absorb the emitted infrared light, and both identical infrared detectors can detect the change in light intensity. When the ambient temperature changes, the light intensity changes of the two infrared detectors with the same filter band follow the same pattern. Therefore, the ratio of the signal intensities of the two infrared detectors is not affected by temperature. Thus, calculating the concentration of the gas to be measured by inverting the ratio of the signal intensities of the two infrared detectors can eliminate the influence of temperature changes on the gas concentration calculation.

[0052] The following example illustrates the principle of this method:

[0053] Let the optical path length from the low-power infrared light source to infrared detector A be L1, and the optical path length from the low-power infrared light source to infrared detector B be L2;

[0054] When the ambient temperature is T1 and there is no gas to be measured, the light intensity detected by infrared detector A is I. O1 The light intensity detected by infrared detector B is I. O2 When the gas to be measured is present, the light intensity detected by infrared detector A is I. 11 The light intensity detected by infrared detector B is I. 12 According to Beer-Lambert Law:

[0055] When the ambient temperature is T2 and there is no gas to be measured, the light intensity detected by infrared detector A is I. O3 The light intensity detected by infrared detector B is I. O4 When the gas to be measured is present, the light intensity detected by infrared detector A is I. 13 The light intensity detected by infrared detector B is I. 14 According to Beer-Lambert Law:

[0056] In the formula, α(υ) is the absorption coefficient of the gas to be measured, C is the concentration of the gas to be measured, and e is a constant;

[0057] Dividing equation (2) by equation (1) yields:

[0058] Equation (4) divided by Equation (3), and since the light source brightness at ambient temperature T2 is k times that at ambient temperature T1, i.e., I O3 =k·I O1I O4 =k·I O2 Therefore, we can conclude that:

[0059] In equation (6), since I O1 I O2 These are values ​​measured without the target gas. It is a constant.

[0060] As can be seen from equations (5) and (6), even though low-power infrared light sources have different luminous intensity at different ambient temperatures, for the same concentration of the gas to be measured, there is... That is, the normalized detection signal strength remains constant and does not change with the brightness of the light source, and is therefore unaffected by temperature factors.

[0061] As shown in Figure 6, the intensity of the light signal received by infrared detector A is divided by the intensity of the light signal received by infrared detector B and multiplied by 10000 to obtain the normalized detection signal intensity. It can be seen that the normalized detection signal intensity is not affected by changes in the external ambient temperature. When the external ambient temperature changes from -40 degrees to 70 degrees, the normalized detection signal intensity remains basically constant.

[0062] Similarly, for the reduced brightness of the light source caused by the aging of the light source in low-power infrared gas sensors, and for the inconsistent brightness changes with temperature due to individual differences in the temperature characteristics of the light source among different sensors, since the measured normalized detection signal intensity remains constant, the gas concentration obtained by inversion calculation is not affected by factors such as external ambient temperature and light source aging, thus ensuring the stability and accuracy of the detected gas concentration. It can also eliminate individual differences between different sensors and different light source temperature characteristics, eliminating the need for individual compensation for each sensor, which is beneficial for the mass production of low-power infrared gas sensors.

[0063] In one specific embodiment, a method for detecting gas concentration includes the following steps:

[0064] Step 1: Introduce the gas to be measured with a known concentration gradient into the low-power infrared gas sensor;

[0065] For the analyte gas of different concentrations, the formula is used. It can be seen that low-power infrared gas sensors can obtain different normalized detection signal intensities.

[0066] Step 2: Obtain the fitting calculation formula for concentration and normalized detection signal intensity;

[0067] Record the normalized detection signal intensity corresponding to each gas concentration at different concentrations; by fitting a nonlinear curve, the exponential function f(x) = e^(-x / x) can be obtained. xThe calculation formula is then written into the chip of the low-power infrared gas sensor.

[0068] Step 3: Detect the normalized detection signal intensity of the gas to be tested at an unknown concentration;

[0069] A low-power infrared gas sensor can be placed in an environment with an unknown concentration of the gas to be measured and can measure a normalized detection signal intensity.

[0070] Step 4: Calculate the concentration of the gas to be measured using the formula.

[0071] The chip of the low-power infrared gas sensor automatically calculates the concentration value corresponding to the normalized detection signal intensity measured in step 3, which is the concentration of the unknown gas to be measured.

[0072] Example 1

[0073] As shown in Figures 2 to 6, a low-power infrared gas sensor is used to implement the gas concentration detection method described above. The low-power infrared gas sensor has a gas chamber for introducing gas. The gas chamber is equipped with a detection optical path for the gas to be measured. The detection optical path includes a first low-power infrared light source 2, a first beam splitting structure 85, a first infrared detector 3, and a second infrared detector 4. The emitted light from the first low-power infrared light source 2 is split into two beams with the same center wavelength by the first beam splitting structure 85, and these beams are respectively directed to the first infrared detector 3 and the second infrared detector 4. The first infrared detector 3 and the second infrared detector 4 have the same filter band, ensuring that the detection bands of both detectors are within the absorption band of the gas to be measured. The distance from the first infrared detector 3 to the first beam splitting structure 85 and the distance from the second infrared detector 4 to the first beam splitting structure 85 are different, so that the optical path length from the first low-power infrared light source 2 to the first infrared detector 3 is unequal to the optical path length from the first low-power infrared light source 2 to the second infrared detector 4. The difference between the two optical path lengths is defined as the equivalent optical path length of the detection optical path for the gas to be measured.

[0074] Using the low-power infrared gas sensor of this embodiment, after gas is introduced, the ratio of the detection light intensity signals of the first infrared detector 3 and the second infrared detector 4 is: This is the normalized detection signal intensity obtained by measuring the gas under test in the gas detection optical path.

[0075] As shown in Figure 5, in this embodiment, the optical path for detecting the gas to be tested also includes a first off-axis parabolic reflector 81, an outer ring reflector 11, and a second off-axis parabolic reflector 82. Infrared light emitted from the first low-power infrared light source 2 first strikes the first off-axis parabolic reflector 81, which collimates the infrared light, making the divergent infrared light collimated or nearly collimated, forming parallel reflected light. The first off-axis parabolic reflector 81 reflects the light to the outer ring reflector 11. Since the outer ring reflector 11 forms a closed ring reflection, the light entering the space of the outer ring reflector 11 will be reflected multiple times, achieving a longer optical path in a narrow or effective space. After being reflected four times by the outer ring reflector 11, the light is guided out of the space of the outer ring reflector 11 by the second off-axis parabolic reflector 82, thus achieving four reflections of the light by the outer ring reflector 11 to form a rectangular optical path.

[0076] The first beam-splitting structure 85 can be positioned after the first reflection point, the second reflection point, or the third reflection point of the outer ring reflector 11. The first infrared detector 3 is positioned directly below the first beam-splitting structure 85 to ensure reception of reflected light from it. Changing the position of the first beam-splitting structure 85 changes the optical path length L1 from the first low-power infrared light source 2 to the first infrared detector 3.

[0077] If the first beam splitting structure 85 is located after the first reflection point of the outer ring reflector 11, the optical path length L1 from the first low-power infrared light source 2 to the first infrared detector 3 can be determined by the light propagation path. The optical path is: first low-power infrared light source 2 - first off-axis parabolic reflector 81 - first reflection point of outer ring reflector 11 - first beam splitting structure 85 - first infrared detector 3.

[0078] If the first beam splitting structure 85 is located after the second reflection point of the outer ring reflector 11, the optical path from the first low-power infrared light source 2 to the first infrared detector 3 is: first low-power infrared light source 2 - first off-axis parabolic reflector 81 - first reflection point of outer ring reflector 11 - second reflection point of outer ring reflector 11 - first beam splitting structure 85 - first infrared detector 3.

[0079] If the first beam splitting structure 85 is located after the third reflection point of the outer ring reflector 11, the optical path from the first low-power infrared light source 2 to the first infrared detector 3 is as follows: first low-power infrared light source 2 - first off-axis parabolic reflector 81 - first reflection point of outer ring reflector 11 - second reflection point of outer ring reflector 11 - third reflection point of outer ring reflector 11 - first beam splitting structure 85 - first infrared detector 3.

[0080] In addition to its reflection function, the first beam splitting structure 85 also has a light transmission function. A portion of the light transmitted through the first beam splitting structure 85 is directed to the next reflection point of the outer ring reflector 11. Therefore, regardless of where the first beam splitting structure 85 is located in the rectangular optical path, the outer ring reflector 11 reflects the light four times before directing it to the second off-axis parabolic reflector 82. After being reflected by the second off-axis parabolic reflector 82, the light converges to the second infrared detector 4. Thus, the light propagation path from the first low-power infrared light source 2 to the second infrared detector 4 remains unchanged, and the optical path length L2 is a fixed value. The optical path is as follows: first low-power infrared light source 2 - first off-axis parabolic reflector 81 - first reflection point of outer ring reflector 11 - second reflection point of outer ring reflector 11 - third reflection point of outer ring reflector 11 - fourth reflection point of outer ring reflector 11 - second off-axis parabolic reflector 82 - second infrared detector 4.

[0081] As can be seen, different settings of the first beam splitting structure 85 can adjust the distance difference between the two infrared detectors and the first low-power infrared light source 2, i.e. (L2-L1), thereby changing the equivalent optical path of the gas detection optical path. Since the longer the equivalent optical path is, the higher the detection accuracy of the sensor, and the shorter the equivalent optical path is, the larger the range of the sensor, the position of the first beam splitting structure 85 can be adjusted according to the requirements to select higher detection accuracy or a larger range when manufacturing low-power infrared gas sensors.

[0082] The first beam splitting structure 85 has a metal reflector plate. The surface of the metal reflector plate is coated with a reflective film, and the metal reflector plate is provided with several light-transmitting holes. When light is incident on the non-light-transmitting holes of the metal reflector plate, it will be reflected. When it is incident on the light-transmitting holes, it will pass through the first beam splitting structure 85. It can be seen that the ratio of the area of ​​all the light-transmitting holes to the area of ​​the metal reflector plate is the light transmittance of the metal reflector plate, which is also the light transmittance of the first beam splitting structure 85. The ratio of the area of ​​the metal reflector plate after removing all the light-transmitting holes to the area of ​​the metal reflector plate is the reflectance of the metal reflector plate, which is also the reflectance of the first beam splitting structure 85.

[0083] In some embodiments of this application, the number of light-transmitting holes in the metal reflector is adjustable. Specifically, a toggle plate is provided in the middle layer of the metal reflector, and both the surface of the metal reflector and the toggle plate are coated with a reflective film. By adjusting the relative position of the toggle plate and the metal reflector, the number of light-transmitting holes blocked by the toggle plate can be changed, thereby making the number of light-transmitting holes in the metal reflector adjustable. Alternatively, the number of light-transmitting holes in the metal reflector can be fixed at the factory of the low-power infrared gas sensor.

[0084] As shown in Figures 2 and 3, in this embodiment, the low-power infrared gas sensor includes a housing and a gas chamber. The housing serves as the sensor casing, protecting the internal gas chamber and its electrical components. The gas chamber consists of a base plate 20, a perforated plate 1, and a top plate 8, with the perforated plate 1 located between the base plate 20 and the top plate 8. The top plate 8 has several vent holes 87, through which gas can enter the gas chamber and thus enter the optical path for gas detection.

[0085] The upper surface of the base plate 20 forms the first mounting surface of the air chamber, and the lower surface of the top plate 8 forms the second mounting surface of the air chamber. The first mounting surface and the second mounting surface face each other and are parallel. The first low-power infrared light source 2, the first infrared detector 3, and the second infrared detector 4 are disposed on the first mounting surface. The first beam splitting structure 85, the first off-axis parabolic reflector 81, and the second off-axis parabolic reflector 82 are located on the second mounting surface. Specifically, the first beam splitting structure 85, the first off-axis parabolic reflector 81, and the second off-axis parabolic reflector 82 are directly machined onto the second mounting surface by machining.

[0086] The upper surface of the perforated plate 1 has an outer perimeter plate, and the inner sidewall of the outer perimeter plate is coated with a reflective surface to form an outer ring reflective surface 11. Therefore, the outer ring reflective surface 11 is located between the first mounting surface and the second mounting surface, and the rectangular light path of the outer ring reflective surface 11 is parallel to the two mounting surfaces. The perforated plate 1 has a plurality of perforations 13, which correspond to the first low-power infrared light source 2, the first infrared detector 3 and the second infrared detector 4, respectively, so that the emitted light of the first low-power infrared light source 2 passes through the corresponding perforation and enters the space of the outer ring reflective surface 11, and the reflected light after passing through the first beam splitting structure 85 passes through the corresponding perforation and enters the first infrared detector 3, and the reflected light after passing through the second off-axis parabolic reflective surface 82 passes through the corresponding perforation and enters the second infrared detector 4. As can be seen, the first low-power infrared light source 2 is correspondingly set with the first off-axis parabolic reflector 81, the first beam splitting structure 85 is correspondingly set with the first infrared detector 3, and the second off-axis parabolic reflector 82 is correspondingly set with the second infrared detector 4; the optical paths of the first off-axis parabolic reflector 81 of the first low-power infrared light source 2, the optical paths from the first beam splitting structure 85 to the first infrared detector 3, and the optical paths from the second off-axis parabolic reflector 82 to the second infrared detector 4 are all perpendicular to the plane where the rectangular optical path is located.

[0087] The top plate 8 is provided with a limiting boss 88, and the outer plate of the hollow plate 1 is provided with a matching limiting groove 14. Through the cooperation of the limiting boss 88 and the limiting groove 14, the hollow plate 1 and the top plate 8 can be quickly positioned and installed. The hollow plate 1 and the bottom plate 20 can be quickly positioned and installed through the hollow opening 13. Therefore, the low-power infrared gas sensor can be quickly positioned and installed. In other optional embodiments, the top plate is provided with a limiting groove, and the outer plate of the hollow plate 1 is provided with a matching limiting boss.

[0088] Example 2

[0089] As shown in Figures 2 to 5, a low-power infrared gas sensor, similar to Embodiment 1, has a gas detection optical path inside its gas chamber. The difference lies in that the gas chamber also includes an interfering gas detection optical path, comprising a second low-power infrared light source 5, a second beam splitting structure 86, a third infrared detector 6, and a fourth infrared detector 7. The infrared light emitted by the second low-power infrared light source 5 is split into two beams with the same center wavelength by the second beam splitting structure 86, and directed towards the third infrared detector 6 and the fourth infrared detector 7, which have the same filter band, respectively. The distances from the third infrared detector 6 to the second beam splitting structure 86 and from the fourth infrared detector 7 to the second beam splitting structure 86 are different, resulting in an unequal optical path length between the second low-power infrared light source 5 and the third infrared detector 6, and the difference is defined as the equivalent optical path length of the interfering gas detection optical path.

[0090] The working principle of the interfering gas detection optical path is the same as that of the gas to be tested detection optical path. The only difference is that the interfering gas detection optical path is used to detect the normalized detection signal intensity of the interfering gas in order to calculate the concentration of the interfering gas.

[0091] As shown in Figures 4 and 5, in this embodiment, the interfering gas detection optical path further includes a third off-axis parabolic reflector 83, an inner ring reflector 12, and a fourth off-axis parabolic reflector 84. The infrared light emitted by the second low-power infrared light source 5 first reaches the third off-axis parabolic reflector 83, and after being collimated by the third off-axis parabolic reflector 83, it becomes parallel reflected light and is directed towards the second beam-splitting structure 86. The second beam-splitting structure 86 uses its reflection function to reflect part of the light to the third infrared detector 6, and the remaining light passes through the second beam-splitting structure 86 and is directed towards the inner ring reflector 12. The light is reflected only once by the inner ring reflector 12, and after reflection, it is directed towards the fourth off-axis parabolic reflector 84. The light is reflected by the fourth off-axis parabolic reflector 84 and converges to the fourth infrared detector 7. The inner ring reflector 12 is located inside the outer ring reflector 11, and its size should be small to avoid affecting the detection optical path of the gas to be measured. The second low-power infrared light source 5, the third infrared detector 6, the fourth infrared detector 7, the second beam splitting structure 86, the third off-axis parabolic reflector 83, and the fourth off-axis parabolic reflector 84 are all located within the projected circular area of ​​the inner ring reflector 12.

[0092] The second beam splitting structure 86 is set in the optical path between the reflection point of the inner ring reflector 12 and the third off-axis parabolic reflector 83, ensuring that the optical path length L3 from the second low-power infrared light source 5 to the third infrared detector 6 and the optical path length L4 from the second low-power infrared light source 5 to the fourth infrared detector 7 are not equal. Therefore, the equivalent optical path of the interfering gas detection optical path is (L4-L3).

[0093] The second beam-splitting structure 86 has a metal reflector plate with a reflective film coated on its surface. The metal reflector plate has several light-transmitting holes. Light rays incident on the non-light-transmitting holes of the metal reflector plate are reflected, while light rays incident on the light-transmitting holes pass through the second beam-splitting structure 86. Similar to the first beam-splitting structure 85, the transmittance and reflectance of the second beam-splitting structure 86 depend on the number of light-transmitting holes on its metal reflector plate. In some embodiments of this application, the number of light-transmitting holes in the metal reflector plate is adjustable or fixed. Similarly, the top plate 8 has a movable groove corresponding to the position of the second beam-splitting structure 86. The movable plate of the metal reflector plate of the second beam-splitting structure 86 can slide within the corresponding movable groove, thereby adjusting the number of light-transmitting holes in the metal reflector plate of the second beam-splitting structure 86, thus changing the reflectance and transmittance of the second beam-splitting structure 86.

[0094] Compared to Embodiment 1, the top plate 8 has a greater number of vent holes 87. The additional vent holes 87 are used to correspond to the interfering gas detection optical path so that gas can enter the interfering gas detection optical path.

[0095] The second low-power infrared light source 5, the third infrared detector 6, and the fourth infrared detector 7 are disposed on the first mounting surface (i.e., the upper surface of the base plate 20), and the second beam-splitting structure 86, the third off-axis parabolic reflector 83, and the fourth off-axis parabolic reflector 84 are located on the second mounting surface (i.e., the lower surface of the top plate 8). Specifically, the second beam-splitting structure 86, the third off-axis parabolic reflector 83, and the fourth off-axis parabolic reflector 84 are directly machined onto the second mounting surface by means of machining.

[0096] As shown in Figure 3, compared to Embodiment 1, the upper surface of the perforated plate 1 is provided with an outer plate and an inner plate in a concentric circle structure. The structural features and functions of the outer plate are the same as in Embodiment 1, and will not be repeated here. The inner sidewall of the inner plate is coated with a reflective surface to form an inner ring reflective surface 12. The surface on which the light path is reflected by the inner ring reflective surface 12 is parallel to the first mounting surface and the second mounting surface.

[0097] Compared to Embodiment 1, the perforated plate 1 has a greater number of perforations 13. These additional perforations correspond to the second low-power infrared light source 5, the third infrared detector 6, and the fourth infrared detector 7, respectively. This allows the emitted light from the second low-power infrared light source 5 to pass through the corresponding perforations into the space of the inner ring reflective surface 12. It also allows the reflected light from the second beam splitting structure 86 to pass through the corresponding perforations into the third infrared detector 6, and the reflected light from the fourth off-axis parabolic reflective surface 84 to pass through the corresponding perforations into the fourth infrared detector 7. It is evident that the second low-power infrared light source 5 is correspondingly positioned to the third off-axis parabolic reflective surface 83, the second beam splitting structure 86 to the third infrared detector 6, and the fourth off-axis parabolic reflective surface 84 to the fourth infrared detector 7. The optical paths from the second low-power infrared light source 5 to the third off-axis parabolic reflective surface 83, from the second beam splitting structure 86 to the third infrared detector 6, and from the fourth off-axis parabolic reflective surface 84 to the fourth infrared detector 7 are all perpendicular to the plane containing the reflected light path of the inner ring reflective surface 12, and also perpendicular to the plane containing the rectangular optical path.

[0098] As shown in Figure 5, in some embodiments of this application, the distance from the straight line of the light path from the first off-axis parabolic reflector 81 to the center point of the outer ring reflector 11 is equal to the square root of the radius of the outer ring reflector 11, so that the rectangular light path of the outer ring reflector 11 is a square light path. Geometrically, a rectangle has the largest area when it is a square within a circle. Therefore, the internal space of the square light path is the largest, providing ample space for the inner enclosure plate and preventing the inner enclosure plate from obstructing the light from the outer light path of the gas to be detected.

[0099] The low-power infrared gas sensor in this embodiment is suitable for application scenarios where there are interfering gases in the gas detection environment. The detection band of the infrared detector in the gas detection optical path is within the absorption band of the gas to be measured, and the detection band of the infrared detector in the interfering gas detection optical path is within the absorption band of the interfering gas.

[0100] The detection results of the optical path for detecting the gas to be tested and the optical path for detecting interfering gases can vary in the following ways:

[0101] Case 1--

[0102] The optical path for detecting the gas under test only responds to the gas under test; that is, the center wavelength of the first low-power infrared light source and the detection bands of the first and second infrared detectors are all within the absorption band of the gas under test, and not within the absorption band of the interfering gas. The optical path for detecting the interfering gas only responds to the interfering gas; that is, the center wavelength of the second low-power infrared light source and the detection bands of the third and fourth infrared detectors are all within the absorption band of the interfering gas, and not within the absorption band of the gas under test.

[0103] In this case, interfering gases will not affect the concentration results of the gas being measured.

[0104] Case 2--

[0105] The optical path for detecting the gas under test responds to both the gas under test and the interfering gas. Specifically, the center wavelength of the first low-power infrared light source and the detection bands of the first and second infrared detectors are both within the absorption bands of the gas under test and the interfering gas. The optical path for detecting the interfering gas responds only to the interfering gas. Specifically, the center wavelength of the second low-power infrared light source and the detection bands of the third and fourth infrared detectors are both within the absorption bands of the interfering gas, but not within the absorption band of the gas under test.

[0106] In this case, in the optical path for detecting the gas to be tested, the relationship between the concentration of the gas to be tested and the absorptivity is f1, and the relationship between the concentration of the interfering gas and the absorptivity is f2; in the optical path for detecting the interfering gas, the relationship between the concentration of the interfering gas and the absorptivity is f3; then, f1, f2, and f3 can be obtained through theoretical calculations or experimental data. Assuming that the gas concentration of the gas to be tested A is C1, the gas concentration of the interfering gas B is C2, the absorptivity of the optical path for detecting the gas to be tested is D1, and the absorptivity of the optical path for detecting the interfering gas is D2, D1 and D2 can be calculated by the ratio of the currently detected light intensity to the zero-point detected light intensity. Therefore, the following relationships can be obtained: f1(C1) + f2(C2) = D1 (7), f3(C2) = D2 (8);

[0107] In equations (7) and (8), f1, f2, f3, D1, and D2 are known. The concentrations of the gas to be measured, C1, and the concentrations of the interfering gas, C2, can be calculated through mathematical calculation or the least squares method. To facilitate understanding, an example of a linear relationship is given below. If the absorption rates of the gas to be measured and the interfering gas are low, and the optical path lengths of the optical paths for detecting the gas to be measured and the interfering gas are short, the relationship between the concentrations of the gas to be measured and the interfering gas and the absorption rate can be regarded as a linear relationship. Then we have: k1×C1+k2×C2=D1 (71), k3×C2=D2 (81);

[0108] In equations (71) and (81), k1, k2, k3, D1, and D2 are all known, and the values ​​of the concentration of the gas to be measured, C1, and the concentration of the interfering gas, C2, can be easily calculated through mathematical calculation.

[0109] Case 3--

[0110] The optical path for detecting the gas under test responds to both the gas under test and the interfering gas. Specifically, the center wavelength of the first low-power infrared light source and the detection bands of the first and second infrared detectors are both within the absorption bands of the gas under test and the interfering gas. Similarly, the optical path for detecting the interfering gas responds to both the gas under test and the interfering gas. This means that the center wavelength of the second low-power infrared light source and the detection bands of the third and fourth infrared detectors are both within the absorption bands of the gas under test and the interfering gas.

[0111] In this case, in the optical path for detecting the gas to be tested, the relationship between the concentration of the gas to be tested and the absorptivity is f1, and the relationship between the concentration of the interfering gas and the absorptivity is f2; in the optical path for detecting the interfering gas, the relationship between the concentration of the gas to be tested and the absorptivity is f3, and the relationship between the concentration of the interfering gas and the absorptivity is f4; then, f1, f2, f3, and f4 can be obtained through theoretical calculations or experimental data. Assuming that the gas concentration of the gas to be tested A is C1, the gas concentration of the interfering gas B is C2, the absorptivity of the optical path for detecting the gas to be tested is D1, and the absorptivity of the optical path for detecting the interfering gas is D2, D1 and D2 can be calculated by the ratio of the currently detected light intensity to the zero-point detected light intensity. Therefore, the following relationships can be obtained: f1(C1)+f2(C2)=D1 (9), f3(C1)+f4(C2)=D2 (10);

[0112] In equations (9) and (10), f1, f2, f3, f4, D1, and D2 are known. The concentrations of the gas to be measured, C1, and the concentrations of the interfering gas, C2, can be calculated through mathematical calculations or the least squares method. Similarly, for example of a linear relationship, we have: k1×C1+k2×C2=D1 (91), k3×C1+k4×C2=D2 (101);

[0113] In equations (91) and (101), k1, k2, k3, k4, D1, and D2 are all known, and the values ​​of the concentration of the gas to be measured, C1, and the concentration of the interfering gas, C2, can be easily calculated through mathematical calculation.

[0114] In summary, in cases 2 and 3, if the interfering gas affects the calculation of the concentration of the gas to be measured, the actual concentration of the gas to be measured and the concentration of the interfering gas can be calculated separately by adding an interfering gas detection optical path, thereby eliminating the influence of the interfering gas on the calculation result of the concentration of the gas to be measured.

[0115] In this application, the first off-axis parabolic reflector 81 is used to collimate and reflect the first low-power infrared light source 2, and the third off-axis parabolic reflector 83 is used to collimate and reflect the second low-power infrared light source 5. In order to ensure that the off-axis parabolic reflector can efficiently reflect the light emitted by the corresponding low-power infrared light source, the center of the emitting surface of the low-power infrared light source is vertically positioned directly above the focal point of the off-axis parabolic reflector. The distance between the center of the emitting surface and the focal point of the off-axis parabolic reflector depends on the size of the emitting surface and the divergence angle. The backward extension of the light emitted from the edge of the emitting surface at the maximum divergence angle coincides with the focal point of the off-axis parabolic reflector.

[0116] As shown in Figure 2, the low-power infrared gas sensor uses a low-power circuit board 9, which is located at the bottom of the gas chamber, specifically below the bottom plate 20 of the gas chamber. The pins of the first low-power infrared light source, the second low-power infrared light source, and the four infrared detectors inside the gas chamber extend out of the bottom plate 20 of the gas chamber and are then soldered to the low-power circuit board 9.

[0117] The housing includes an outer protective cover 10 and a bottom shell. The top of the outer protective cover 10 is provided with an air inlet 101, allowing gas from the external environment to enter the sensor and then enter the gas chamber through the vent 87. Several sensor pins are provided on the bottom shell for connecting and fixing the low-power infrared gas sensor.

[0118] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0119] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for detecting gas concentration, the method comprising: The gas to be tested is introduced, and the signal intensities of infrared light emitted from the same low-power infrared light source reaching two infrared detectors with the same filter band are collected. The concentration of the gas to be tested is calculated by inverting the ratio of the signal intensities of the two infrared detectors. The specific steps include: A gas of known concentration gradient is introduced into a low-power infrared gas sensor; Obtain the fitting calculation formula for concentration and normalized detection signal intensity, wherein the normalized detection signal intensity is the ratio of the signal intensities of two infrared detectors with the same filter band; Record the normalized detection signal intensity measured by the low-power infrared gas sensor at different concentrations; obtain the calculation formula by fitting a nonlinear curve and write it into the chip; The normalized detection signal intensity of a gas of unknown concentration is detected by a low-power infrared gas sensor. The concentration of the gas to be measured is obtained based on the calculation formula; The low-power infrared gas sensor has a gas chamber for introducing gas. The gas chamber is equipped with a detection optical path for the gas to be tested and a detection optical path for interfering gas. The working principle of the detection optical path for interfering gas is the same as that of the detection optical path for the gas to be tested. The detection optical path for interfering gas is used to detect the normalized detection signal intensity of the interfering gas in order to calculate the concentration of the interfering gas.

2. The gas concentration detection method according to claim 1, wherein The optical path for detecting the gas to be tested includes a first low-power infrared light source, a first beam splitting structure, a first infrared detector, and a second infrared detector. The emitted light from the first low-power infrared light source is split into two beams with the same center wavelength by the first beam splitting structure, and then directed to the first infrared detector and the second infrared detector, which have the same filter band, respectively. The distance from the first infrared detector to the first beam splitting structure and the distance from the second infrared detector to the first beam splitting structure are different, so that the optical path length from the first low-power infrared light source to the first infrared detector is not equal to the optical path length from the first low-power infrared light source to the second infrared detector, and the difference is defined as the length of the equivalent optical path of the gas detection optical path.

3. The method of detecting a concentration of a gas according to claim 2, wherein The detection optical path for the gas under test further includes a first off-axis parabolic reflector, an outer ring reflector, and a second off-axis parabolic reflector. The first off-axis parabolic reflector is used to collimate the emitted light from the first low-power infrared light source and reflect it onto the outer ring reflector. The outer ring reflector is used to reflect the light four times to form a rectangular optical path. The outer ring reflector reflects light once, twice, or three times before directing it toward the first beam splitter. The light transmitted through the first beam splitter is directed toward the next reflection point of the outer ring reflector, and the light reflected by the first beam splitter is directed toward the first infrared detector. The outer ring reflector reflects the light four times before directing it toward the second off-axis parabolic reflector, where it is reflected and converged to the second infrared detector.

4. The gas concentration detection method according to claim 3, wherein The air chamber has a first mounting surface and a second mounting surface that face each other and are parallel. The outer ring reflective surface is located between the first mounting surface and the second mounting surface, and the rectangular optical path of the outer ring reflective surface is parallel to the two mounting surfaces. The first low-power infrared light source, the first infrared detector, and the second infrared detector are disposed on the first mounting surface, and the first beam splitting structure, the first off-axis parabolic reflector, and the second off-axis parabolic reflector are located on the second mounting surface; The optical paths from the first low-power infrared light source to the first off-axis parabolic reflector, the first beam splitting structure to the first infrared detector, and the second off-axis parabolic reflector to the second infrared detector are all perpendicular to the plane containing the rectangular optical path.

5. The gas concentration detection method according to claim 3, wherein The interfering gas detection optical path includes a second low-power infrared light source, a second beam splitting structure, a third infrared detector, and a fourth infrared detector. The emitted light from the second low-power infrared light source is split into two beams with the same center wavelength by the second beam splitting structure, and then directed to the third infrared detector and the fourth infrared detector, which have the same filter band, respectively. The distance from the third infrared detector to the second beam splitter is different from the distance from the fourth infrared detector to the second beam splitter, so that the optical path length from the second low-power infrared light source to the third infrared detector is not equal to the optical path length from the second low-power infrared light source to the fourth infrared detector, and the difference is defined as the length of the equivalent optical path of the interfering gas detection optical path.

6. The gas concentration detection method according to claim 5, wherein The interfering gas detection optical path further includes a third off-axis parabolic reflector, an inner ring reflector, and a fourth off-axis parabolic reflector. The third off-axis parabolic reflector is used to collimate the emitted light of the second low-power infrared light source and reflect it to the second beam splitter. The second beam splitter reflects part of the light to the third infrared detector, and the light transmitted through the second beam splitter is directed to the inner ring reflector. The inner ring reflector reflects the light to the fourth off-axis parabolic reflector, and the light is reflected by the fourth off-axis parabolic reflector and converged to the fourth infrared detector.

7. The gas concentration detection method according to claim 6, wherein The air chamber has a first mounting surface and a second mounting surface facing each other and parallel to each other, and the inner ring reflective surface is located between the first mounting surface and the second mounting surface; the second low-power infrared light source, the third infrared detector and the fourth infrared detector are disposed on the first mounting surface, and the second beam splitting structure, the third off-axis parabolic reflective surface and the fourth off-axis parabolic reflective surface are located on the second mounting surface; The optical paths from the second low-power infrared light source to the third off-axis parabolic reflector, the second beam splitting structure to the third infrared detector, and the fourth off-axis parabolic reflector to the fourth infrared detector are all perpendicular to the plane containing the rectangular optical path.

8. The gas concentration detection method according to claim 6, wherein The air chamber is composed of a bottom plate, a perforated plate, and a top plate. The upper surface of the bottom plate forms the first mounting surface of the air chamber, and the lower surface of the top plate forms the second mounting surface of the air chamber. The upper surface of the perforated plate is provided with an outer plate and an inner plate in a concentric circle structure. The inner sidewall of the outer plate is coated with a reflective surface to form the outer ring reflective surface, and the inner sidewall of the inner plate is coated with a reflective surface to form the inner ring reflective surface.

9. The gas concentration detection method according to claim 8, wherein The perforated plate has several perforations, which are used to transmit the emitted light from the low-power infrared light source on the bottom plate, the received light from the infrared detector, and the reflected light from the beam-splitting structure on the top plate. The inner ring reflector is located within the outer ring reflector. The second low-power infrared light source, the third infrared detector, the fourth infrared detector, the second beam splitting structure, the third off-axis parabolic reflector, and the fourth off-axis parabolic reflector are all located within the projected circular area of ​​the inner ring reflector.

10. The gas concentration detection method according to claim 5, wherein Both the first beam-splitting structure and the second beam-splitting structure have a metal reflector. The metal reflector has a plurality of light-transmitting holes. The ratio of the area of ​​all the light-transmitting holes to the area of ​​the metal reflector is the light transmittance of the metal reflector. The ratio of the area of ​​the metal reflector after removing all the light-transmitting holes to the area of ​​the metal reflector is the reflectance of the metal reflector. The number of light-transmitting holes in the metal reflector is fixed or adjustable.

11. The method of detecting a concentration of a gas according to claim 3, wherein, The rectangular optical path is a square optical path.

12. A low-power infrared gas sensor having a gas chamber for introducing gas; The gas chamber is provided with a gas detection optical path, which includes a first low-power infrared light source, a first beam splitting structure, a first infrared detector and a second infrared detector. The emitted light from the first low-power infrared light source is split into two beams with the same center wavelength by the first beam splitting structure and directed to the first infrared detector and the second infrared detector with the same filter band, respectively. The distance from the first infrared detector to the first beam splitting structure and the distance from the second infrared detector to the first beam splitting structure are different, so that the optical path length from the first low-power infrared light source to the first infrared detector is not equal to the optical path length from the first low-power infrared light source to the second infrared detector, and the difference is defined as the length of the equivalent optical path of the gas detection optical path. The detection optical path for the gas under test further includes a first off-axis parabolic reflector, an outer ring reflector, and a second off-axis parabolic reflector. The first off-axis parabolic reflector is used to collimate the emitted light from the first low-power infrared light source and reflect it onto the outer ring reflector. The outer ring reflector is used to reflect the light four times to form a rectangular optical path. The outer ring reflector reflects light once, twice, or three times before directing it toward the first beam splitter. The light transmitted through the first beam splitter is directed toward the next reflection point of the outer ring reflector, and the light reflected by the first beam splitter is directed toward the first infrared detector. The outer ring reflector reflects the light four times before it is directed toward the second off-axis parabolic reflector, where it is reflected and converged to the second infrared detector. The air chamber has a first mounting surface and a second mounting surface that face each other and are parallel. The outer ring reflective surface is located between the first mounting surface and the second mounting surface, and the rectangular optical path of the outer ring reflective surface is parallel to the two mounting surfaces. The first low-power infrared light source, the first infrared detector, and the second infrared detector are disposed on the first mounting surface, and the first beam splitting structure, the first off-axis parabolic reflector, and the second off-axis parabolic reflector are located on the second mounting surface; The optical paths from the first low-power infrared light source to the first off-axis parabolic reflector, the first beam splitting structure to the first infrared detector, and the second off-axis parabolic reflector to the second infrared detector are all perpendicular to the plane containing the rectangular optical path. The gas chamber is provided with an interfering gas detection optical path, which includes a second low-power infrared light source, a second beam splitting structure, a third infrared detector and a fourth infrared detector. The emitted light from the second low-power infrared light source is split into two beams with the same center wavelength by the second beam splitting structure, and then directed to the third infrared detector and the fourth infrared detector with the same filter band, respectively. The distance from the third infrared detector to the second beam splitter and the distance from the fourth infrared detector to the second beam splitter are different, so that the optical path length from the second low-power infrared light source to the third infrared detector is not equal to the optical path length from the second low-power infrared light source to the fourth infrared detector, and the difference is defined as the length of the equivalent optical path of the interfering gas detection optical path. The interfering gas detection optical path further includes a third off-axis parabolic reflector, an inner ring reflector, and a fourth off-axis parabolic reflector. The third off-axis parabolic reflector is used to collimate the emitted light of the second low-power infrared light source and reflect it to the second beam splitting structure. The second beam splitting structure reflects part of the light to the third infrared detector, and the light transmitted through the second beam splitting structure is directed to the inner ring reflector. The inner ring reflector reflects the light to the fourth off-axis parabolic reflector, and the light is reflected by the fourth off-axis parabolic reflector and converged to the fourth infrared detector. The inner ring reflective surface is located between the first mounting surface and the second mounting surface; the second low-power infrared light source, the third infrared detector, and the fourth infrared detector are disposed on the first mounting surface, and the second beam splitting structure, the third off-axis parabolic reflective surface, and the fourth off-axis parabolic reflective surface are located on the second mounting surface; The optical paths from the second low-power infrared light source to the third off-axis parabolic reflector, the second beam splitter to the third infrared detector, and the fourth off-axis parabolic reflector to the fourth infrared detector are all perpendicular to the plane containing the rectangular optical path.

13. The low power infrared gas sensor of claim 12, wherein, The air chamber is composed of a base plate, a perforated plate, and a top plate. The upper surface of the base plate forms the first mounting surface of the air chamber, and the lower surface of the top plate forms the second mounting surface of the air chamber. The upper surface of the perforated plate is provided with an outer perimeter plate and an inner perimeter plate in a concentric circular structure. The inner sidewall of the outer perimeter plate is coated with a reflective surface to form the outer ring reflective surface, and the inner sidewall of the inner perimeter plate is coated with a reflective surface to form the inner ring reflective surface. The perforated plate has several perforations, which are used to transmit the emitted light from the low-power infrared light source on the base plate, the received light from the infrared detector, or the reflected light from the beam-splitting structure on the top plate. The inner ring reflective surface is located inside the outer ring reflective surface. The second low-power infrared light source, the third infrared detector, the fourth infrared detector, the second beam-splitting structure, the third off-axis parabolic reflective surface, and the fourth off-axis parabolic reflective surface are all located within the projected circular area of ​​the inner ring reflective surface.

14. The low power infrared gas sensor of claim 12, wherein, Both the first beam-splitting structure and the second beam-splitting structure have a metal reflector. The metal reflector has a plurality of light-transmitting holes. The ratio of the area of ​​all the light-transmitting holes to the area of ​​the metal reflector is the light transmittance of the metal reflector. The ratio of the area of ​​the metal reflector after removing all the light-transmitting holes to the area of ​​the metal reflector is the reflectance of the metal reflector. The number of light-transmitting holes in the metal reflector is fixed or adjustable.

15. The low power infrared gas sensor of claim 12, wherein, The rectangular optical path is a square optical path.

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