Long-short dual optical path measurement system and method based on non-spectroscopic infrared principle

Abstract

The application relates to a long-short double-light-path measurement system and method based on a non-spectroscopic infrared principle, and belongs to the field of gas concentration detection. The application aims to solve the problem of inaccurate measurement caused by drift in the prior art, and provides a long-short double-light-path measurement system and method based on a non-spectroscopic infrared principle. The method discloses a long-short double-light-path measurement system and a specific design method of the system on the basis of a non-spectroscopic infrared absorption type gas sensor. The system adopts two gas chamber channels with different optical path lengths to perform measurement, can compensate for the sensor error caused by the spectral drift of an infrared light source, improves the precision of the sensor, and simultaneously discloses a unique calibration method of the system, compared with a traditional calibration method, the calibration method is more scientific and reasonable, and can reduce the error introduced by the sensor due to calibration.

Description

TECHNICAL FIELD

[0001] The application relates to a long-short dual optical path measurement system and method based on a non-spectroscopic infrared principle, and belongs to the field of gas concentration detection. BACKGROUND

[0002] In the field of environmental monitoring, gas detection has a wide demand. At present, a sensor based on a non-spectroscopic infrared absorption principle is widely applied to the field of gas measurement due to its simple structure, small size and low power consumption. The non-spectroscopic infrared absorption sensor is mainly based on the Lambert-Beer law, that is, when a light beam is shot into a gas chamber filled with an absorption gas, the light intensity of the light beam will be reduced due to the absorption effect of the gas, and the relationship between the outgoing light intensity I and the incident light intensity I0 is as follows:

[0003]

[0004] In the formula, k υ represents the absorption coefficient of the gas, C represents the concentration of the gas, and L represents the optical path length of the light beam in the gas chamber. When the structure of the system is determined and the to-be-detected gas fills the entire gas chamber to reach equilibrium, the absorption coefficient k υ of the gas, the propagation optical path L and the incident light intensity I0 are determined and known, and the outgoing light intensity I is only related to the concentration C of the to-be-detected gas. Therefore, the concentration of the to-be-detected gas can be calculated by measuring the outgoing light intensity I.

[0005] Based on the Lambert-Beer law, researchers designed a non-spectroscopic gas sensor. The non-spectroscopic sensor no longer needs to perform spectroscopic processing on the light source, but filters the light beam through a filter after the light beam passes through the to-be-detected gas to obtain the light beam in the wave number range in which the to-be-detected gas can have an absorption effect. For example, carbon dioxide gas measurement generally selects a wavelength range of 2350 cm -1 around. Then, the light intensity of the light beam is measured by a detector to calculate the concentration of carbon dioxide. Considering that the light intensity of the light source is difficult to measure directly, the non-spectroscopic sensor generally adopts a double-channel structure, selects different wavelength range filters for the measurement channel and the reference channel, reduces the influence of the detector itself caused by the environment, and realizes the measurement of the gas concentration.

[0006] The technical reasons for determining and generating these shortcomings of the existing non-spectroscopic sensor technology are roughly described as follows: when error compensation is performed, the compensation is performed only through the double-channel measurement scheme of the reference channel and the measurement channel, and the individual differences of the detector itself caused by the manufacturing process and the drift caused by the environmental factors have good compensation effect, but due to the different light ranges of the filters used by the two channels of the detector, the output result of the detector is highly related to the light intensity of the light source in the corresponding spectral range, and if the light spectrum of the light source changes, the light intensity measured by the two channels will also fluctuate, thereby causing the sensor reading to drift. And the drift of the light spectrum of the light source is very common in actual use, and the aging of the light source and the voltage fluctuation of the light source will cause the drift of the light spectrum of the light source. Through actual analysis, 1% voltage fluctuation of the light source will cause 40ppm reading drift of the sensor due to the spectral drift, which is unacceptable in the measurement environment requiring high precision such as carbon emission. SUMMARY

[0007] The purpose of the present application is to solve the problem of inaccurate measurement caused by drift in the prior art, and to provide a long-short double optical path measurement system and method based on non-spectroscopic infrared principle. The method discloses a long-short double optical path measurement system and a specific design method of the system based on a non-spectroscopic infrared absorption type gas sensor. The system uses two gas chamber channels with different optical path lengths for measurement, which can compensate for the sensor error caused by the spectral drift of the infrared light source and improve the precision of the sensor. At the same time, the system discloses a unique calibration method, which is more scientific and reasonable than the traditional calibration method, and can reduce the error introduced by the sensor due to calibration.

[0008] The purpose of the present application is achieved by the following technical solutions:

[0009] The long-short double optical path measurement system based on non-spectroscopic infrared principle comprises a light source, a measurement gas chamber, a spherical mirror, a filter and a detector. The measurement gas chamber is composed of a first gas chamber, a second gas chamber and a partition layer. The optical path of the first gas chamber is longer than that of the second gas chamber. The light emitted by the light source is irradiated to the end of the partition layer, and the reflected light is focused by the spherical mirrors of the first gas chamber and the second gas chamber and then enters the detector with the filter.

[0010] The long-short double optical path measurement method based on non-spectroscopic infrared principle comprises the following steps:

[0011] Step one, calculate the optical path length of the first gas chamber according to the light spectrum of the light source;

[0012] The actual measured light intensity I of the detector is represented as follows

[0013] I = ∫S(v)F(v)T(v)dυ (2)

[0014] In the formula, the spectral density function S(υ) is a constant s; F(υ) represents the transmission coefficient of the filter with respect to the light wave number, and T(υ) represents the absorption coefficient spectrum of the measured gas;

[0015] The transmission function of the filter is

[0016]

[0017] In the formula, υ L represents the minimum light wave number of the filter, υ H represents the maximum light wave number of the filter, i.e., [υ L ,υ H ] represents the light wave range of the filter;

[0018] According to the Lambert-Beer law, T(υ) is represented as

[0019] T(υ) = e -k(υ)CL (4)

[0020] In the formula, k(υ) represents the gas absorption coefficient corresponding to the wave number, C represents the concentration of the measured gas, and L represents the optical path length of the light path;

[0021] According to the formula (1), (2) and (3), the transmittance of the light beam in the light wave range of the filter is calculated, as shown in the following formula

[0022]

[0023] According to the measurement accuracy required by the measurement system, the value of the transmittance can be determined, and the optical path length of the first gas chamber is calculated;

[0024] Step two, determine the optical path length difference of the first gas chamber and the second gas chamber, and then obtain the optical path length of the second gas chamber;

[0025] The measurement result of the measurement system is represented as the ratio of the intensities of the two detectors, and according to the formula (3), we have

[0026]

[0027] In the formula, T L (υ) and T S (υ) represent the absorption coefficient spectra of the first gas chamber channel and the second gas chamber channel, respectively, t L and t S represent the transmittances of the first gas chamber channel and the second gas chamber channel, respectively, and ΔL is the length difference between the first gas chamber and the second gas chamber; according to the required measurement accuracy of the measurement system, the required ratio of the detector intensities is determined, the length difference ΔL of the gas chamber is calculated, and the optical path length of the second gas chamber is calculated;

[0028] Step three, the light emitted by the light source is reflected and converged to the detector, and the gas concentration is obtained according to the Lambert-Beer law.

[0029] The optical path length of the first gas chamber is L L , the optical path length of the second gas chamber is L S , the signal intensity measured by the first gas chamber is I L , and the signal intensity measured by the second gas chamber is I S , then according to the Lambert-Beer law, we have

[0030]

[0031]

[0032] In the formula, k L represents the proportional coefficient of the first gas chamber channel, k S represents the proportional coefficient of the second gas chamber channel, I0 represents the light intensity of the light source, and C represents the concentration of the measured gas; dividing the two equations, we have

[0033]

[0034] The concentration C of the measured gas is calculated from the formula, and the quantities that do not change during the measurement process are denoted as constants a and b, and we have

[0035]

[0036] Through prior calibration, the values of constants a and b can be determined, and the concentration of the measured gas can be calculated.

[0037] The calibration method of step three is:

[0038] The Lambert-Beer law will have an additional constant term d' in actual calibration, that is;

[0039] f=a'e b ' C +d' (11)

[0040] In the formula, f represents the sensor reading, that is, the ratio of the light intensity of the first gas chamber to the light intensity of the second gas chamber, a', b', and d' are all constants to be calibrated, and because the concentration needs to be calculated according to the sensor reading after calibration, the independent variable and dependent variable in the conversion formula are changed, and the sensor reading is taken as the independent variable, and the formula is obtained

[0041]

[0042] For convenience of calibration, the constants in the formula are redefined, and we have

[0043] C=a"ln(f-b")+d" (13)

[0044] According to the formula, the sensor reading needs to be subtracted by an offset before taking the logarithm. Therefore, the calibration formula changes to:

[0045]

[0046] In the formula, f long For the output of the first air chamber channel, f short For the output of the second air chamber channel, b long The value of b in the calibration curve of the first air chamber channel, b short For the b value in the calibration curve of the second air chamber channel, a double b double and d double All are constants;

[0047] The calibration process is as follows: First, calibrate according to the formula to obtain the calibration curves of the first and second air chamber detectors, and then obtain b. long and b short The value of a is then obtained by further calibration and calculation using the formula. double and d double Once the value is obtained, the calibration of the measurement system is complete.

[0048] When the partition layer has a structure that is symmetrical about the endpoints of the tilt angle, the method for determining the thickness and tilt angle of the middle partition layer is as follows:

[0049] For the sake of symmetry, only the diaphragm located in the first air chamber is considered, and the first air chamber is abstracted as... Figure 3 The polygon is formed by six points ABCDEF; EG represents the inclined reflective surface of the air chamber partition, on which a plane mirror can be installed. The inclination angle of the reflective surface is denoted as α. The dimension of EF can be determined as a constant x based on the dimension of the plane mirror; the light source is placed at point A, which is abstracted as a point light source and its luminous cone angle is denoted as β; according to geometric optics, construct the point J that is symmetric to A about EG. Then the light rays emitted from A and reflected by the plane EG can be regarded as light rays emitted from point J; connect JG and extend it to intersect AB at H; construct ∠HJI intersecting AB at I, satisfying ∠HJI=β; for the convenience of subsequent calculations, extend BA to K, so that KJ is parallel to AF;

[0050] The design of the partition layer needs to meet the following two conditions: 1. Light source cone angle condition: The light source generally has a certain collimation characteristic, so the light beam emitted by it can reach the spherical mirror after being reflected by the partition layer; 2. Detection surface angle condition: The light reflected by the spherical mirror can reach the detection surface and is not blocked by the partition layer.

[0051] The spherical mirror is a square with a side length of D. The above constraints are converted into geometric constraints.

[0052] The region of the gas chamber wall reached by the light beam from the light source after reflection by the spacer EG is the region of the HI midpoint Figure 3 The light source cone angle condition can be written as: the length of HI is less than or equal to the side length D of the spherical mirror, i.e. HI≤D, where x is the length of EF and y is the length of AF, then we have:

[0053] KJ=AG×[1+tan(2α)]=[y-x·tan(α)][1+tan(2α)] (15)

[0054] HI=KI-KH=KJ×[tan(2α)-tan(2α+β)] (16)

[0055] Therefore, the light source cone angle condition can be expressed as

[0056] [y-x·tan(α)][1+tan(2α)][tan(2α)-tan(2α+β)]≤D (17)

[0057] The detection surface angle condition requires calculating the position of the light beam reaching the detection surface, i.e. the position of the image of the light source on the detector surface. According to the imaging principle of the spherical mirror, we have

[0058]

[0059] In the formula, l 物 and l 像 represent the horizontal distance of the object plane or image plane from the center of the mirror, r 物 and r 像 represent the vertical distance of the object plane or image plane from the optical axis of the mirror. The spherical mirror is installed on AB, and the center is taken as the midpoint of HI for maximum utilization of the mirror surface, so we have l 物 =KJ, r 物 =(KH+KI) / 2; for the first gas chamber, we have l 物 =L L ; for the second gas chamber, we have l 物 =L S , so the height r 像 of the image from the center of the spherical mirror can be calculated according to the formula ;

[0060] The detection surface angle condition is geometrically considered as the connecting line between H point and image point not passing through the line segment EG, so we have

[0061]

[0062] In the formula, the expression of HI is shown in formula (2.29), and the expression of AH is as follows

[0063] AH=AG×tan(2α)=[y-xtan(α)]tan(2α) (20)

[0064] The feasible region of the light source cone angle condition and the detection surface opening angle condition is solved, and finally the interval and the inclination angle of the barrier layer are determined according to the result.

[0065] The focal length of the spherical mirror is determined;

[0066] According to the imaging law of the spherical mirror,

[0067]

[0068] In the formula, r 球 represents the focal length of the spherical mirror, and according to the geometric calculation when the barrier layer parameters are determined, there are

[0069]

[0070] The focal length of the spherical mirror is solved and calculated.

[0071] Beneficial effects:

[0072] 1. The long-short double optical path measurement method based on the non-spectroscopic infrared principle disclosed in the application adopts two gas chambers with different optical path lengths to perform measurement, and can eliminate the influence of light source spectral drift on the system measurement result, and has higher measurement precision compared with the prior art;

[0073] 2. The calibration method of the long-short double optical path measurement system based on the non-spectroscopic infrared principle disclosed in the application can obtain higher calibration precision compared with the prior calibration scheme, and reduces the measurement error introduced due to calibration curve fitting;

[0074] 3. The long-short double optical path measurement method based on the non-spectroscopic infrared principle disclosed in the application gives a general system design process, different design indexes can be used according to the required measurement precision and requirements, and the design is performed based on the design scheme given in the measurement method, so that a measurement system meeting different measurement precisions is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0075] Figure 1 The system basic structure schematic diagram of the application;

[0076] Figure 2 The system specific structure schematic diagram of the application;

[0077] Figure 3 The barrier layer design geometry abstract graph of the application;

[0078] Figure 4 The transmittance change curve of the gas chambers with different lengths;

[0079] Figure 5 The change curve of the detector intensity ratio and the gas chamber length difference under different gas concentrations;

[0080] Figure 6 The curve of the difference of the intensity ratio of the detector versus the difference of the lengths of the gas chambers;

[0081] Figure 7 The structural diagram of the embodiment of the scheme with the same length of the gas chambers but different optical paths;

[0082] Figure 8 The structural diagram of the embodiment of the scheme with the same length of the gas chambers but different optical paths;

[0083] Figure 9 The structural diagram of the embodiment of the scheme with the same length of the gas chambers but different optical paths;

[0084] Figure 10 The structural diagram of the embodiment of the scheme with the same length of the gas chambers but different optical paths. DETAILED DESCRIPTION

[0085] In order to better illustrate the purposes and advantages of the present application, the following further illustrates the content of the application in combination with the drawings and examples.

[0086] Example 1:

[0087] The embodiment discloses a long-short double optical path measurement system based on a non-spectroscopic infrared principle, comprising a light source, a measurement gas chamber, a spherical mirror, a filter and a detector; the measurement gas chamber is composed of a first gas chamber, a second gas chamber and a partition layer; the optical path of the first gas chamber is longer than that of the second gas chamber; the light emitted by the light source is irradiated to the end of the partition layer, and the reflected light is focused by the spherical mirror of the first gas chamber and the second gas chamber and then respectively enters the detector with the filter. The system structural diagram is shown in the figure, the light source and the spherical mirror are both installed on the left plane of the gas chamber, the two detectors are respectively installed on the right side of the two gas chamber channels, and the right side of the gas chamber channel is provided with a gas hole for guiding the measured gas to enter and fill the whole gas chamber. Figure 2

[0088] Step one: calculating the optical path length of the first gas chamber according to the spectrum of the light source;

[0089] The actual measured light intensity I of the detector is represented as follows

[0090] I = ∫S(υ)F(υ)T(υ)dυ (23)

[0091] In the formula, the spectral density function S(υ) is a constant s; F(υ) represents the transmission coefficient function of the filter with respect to the light wave number, and T(υ) represents the absorption coefficient spectrum of the measured gas,

[0092] The transmission function of the filter is

[0093]

[0094] In the formula, υ​L represents the minimum pass wave number of the filter, υ H represents the maximum pass wave number of the filter, i.e. [υ L , υ H ] represents the pass wave range of the filter, considering that the central wavelength of the filter pass wave range for carbon dioxide in practical use is near 4.26 μm, the half pass bandwidth is generally taken as 90 nm or 180 nm, and the smaller half pass bandwidth (90 nm) is taken in the calculation to consider the worst case of weak system light intensity. According to the central wavelength and the half pass bandwidth, the pass wave range of the filter is calculated, and υ L = 2300 cm -1 , υ H = 2400 cm -1 ;

[0095] According to the Lambert-Beer law, T(υ) is represented as

[0096] T(υ) = e -k(υ)CL (25)

[0097] In the formula, k(υ) represents the gas absorption coefficient corresponding to the wave number, C represents the concentration of the measured gas, and L represents the optical path length of the light path;

[0098] According to the formula (1), (2) and (3), the transmittance of the light beam in the pass wave range of the filter is calculated, as shown in the following formula

[0099]

[0100] The transmittance corresponding to different lengths of the optical path is calculated according to the formula (4), and the curve of the transmittance changing with the length of the gas chamber is drawn, and the calculation result is as follows Figure 4 , and for the consideration of the miniaturization of the sensor, the length of the gas chamber is only considered to be 20 cm at most, and the volume is too large to be not conducive to the development of the experiment;

[0101] It can be seen from Figure 4 that the transmittance will change obviously with the length of the gas chamber, and when the length of the gas chamber is 10 cm, it is basically the position with the largest slope of the change curve, and the benefit brought by further increasing the length of the gas chamber gradually decreases, and the transmittance of the 10 cm gas chamber is about 0.92, which basically can meet the measurement requirements of the detector, and the volume of the gas chamber will not be too large, so 10 cm is selected as the length of the first gas chamber.

[0102] Step two: determine the difference between the optical path lengths of the first gas chamber and the second gas chamber, and then obtain the optical path length of the second gas chamber;

[0103] The measurement result of the measurement system is the ratio of the intensities of the two detectors, and according to the formula (3), we have

[0104]

[0105] In the formula, T L (υ) and T S (υ) represents the absorption coefficient spectra of the first and second air chamber channels, respectively, t L and t S ΔL represents the transmittance of the first air chamber channel and the second air chamber channel, respectively, and ΔL is the length difference between the first air chamber and the second air chamber.

[0106] As shown in equation (5), the ratio of detector intensities is the same as the ratio of corresponding channel transmittances. Furthermore, this ratio is only related to the optical path difference between the air cells and is independent of the specific length of the air cells. The first air cell is defined as 10 cm. Therefore, by varying the length difference between the air cells, the curve of the detector intensity ratio changing with the air cell length difference can be calculated, as shown below. Figure 5 As shown, to determine whether the system can distinguish gas concentrations differing by 40 ppm, the figure presents two transmittance ratio curves for carbon dioxide concentrations differing by 40 ppm. For a more intuitive demonstration, the absolute value of the difference between the two curves is used as the ordinate to plot the transmittance ratio difference as a function of the chamber length difference, as shown below. Figure 6 As shown, the difference in detector intensity gradually increases with the increase in the difference in cell length, but the rate of increase gradually slows down after 4 cm. That is, the first derivative of the curve first increases and then decreases, reaching its maximum value at around 4 cm. At this point, the benefit of further increasing the cell length difference gradually diminishes. Furthermore, considering that the length of the first cell is already determined to be 10 cm, an excessively large cell length difference would result in an excessively small length for the second cell, leading to a less significant carbon dioxide absorption effect and making the sensor signal more sensitive to external noise, which would be counterproductive. Therefore, the cell length difference ΔL is chosen to be 4 cm, meaning the length of the second cell is chosen to be 4 cm.

[0107] Step 3: Confirm Figure 2 The thickness and tilt angle of the intermediate septum.

[0108] For the sake of symmetry, only the diaphragm located in the first air chamber is considered, and the first air chamber is abstracted as... Figure 3 The polygon is formed by six points ABCDEF; EG represents the inclined reflective surface of the air chamber partition, on which a plane mirror can be installed. The inclination angle of the reflective surface is denoted as α. The dimension of EF can be determined as a constant x based on the dimension of the plane mirror; the light source is placed at point A, which is abstracted as a point light source and its luminous cone angle is denoted as β; according to geometric optics, construct the point J that is symmetric to A about EG. Then the light rays emitted from A and reflected by the plane EG can be regarded as light rays emitted from point J; connect JG and extend it to intersect AB at H; construct ∠HJI intersecting AB at I, satisfying ∠HJI=β; for the convenience of subsequent calculations, extend BA to K, so that KJ is parallel to AF;

[0109] The design of the partition layer needs to meet the following two conditions: 1. Light source cone angle condition: The light source generally has a certain collimation characteristic, so the light beam emitted by it can reach the spherical mirror after being reflected by the partition layer; 2. Detection surface angle condition: The light reflected by the spherical mirror can reach the detection surface and is not blocked by the partition layer.

[0110] Before determining the specific constraints, the dimensions of the spherical mirror must first be determined. A square mirror is also chosen to ensure complete reflection of the beam; otherwise, the reflection ratio at the upper and lower boundaries of the mirror would be very small or even nonexistent. Considering that the size of the air chamber should not be too large, and the size of the interlayer mirror is 12.5 × 12.5 mm, an EF of 12.5 mm is chosen to facilitate mirror installation. The spherical mirror size is selected as 25.00 × 25.00 mm, and the width of the air chamber is chosen as 30 mm to ensure the installation of the spherical mirror. After determining the dimensions of the spherical mirror, the above constraints can be converted into geometric constraints. According to the previous analysis of geometric optics, the area where the beam reaches the air chamber wall after being reflected by the plane mirror from the light source is the... Figure 3 In the region HI, the light source cone angle condition is equivalent to the length of HI being less than or equal to the size of the spherical mirror, i.e., HI ≤ 25mm. Since EF is already determined to be 12.5mm, for convenience, we can denote it as a constant x. Then, according to geometric relationships, we have...

[0111] KJ=AG×[1+tan(2α)]=[yx·tan(α)][1+tan(2α)] (28)

[0112] HI=KI-KH=KJ×[tan(2α)-tan(2α+β)] (29)

[0113] Therefore, the light source cone angle condition is expressed as:

[0114] [yx·tan(α)][1+tan(2α)][tan(2α)-tan(2α+β)]≤D (30)

[0115] The angular condition of the detector surface requires calculating the position of the light beam reaching the detector surface, i.e., the position of the image of the light source on the detector surface. According to the imaging principle of a spherical mirror, we have...

[0116]

[0117] In the formula, l 物 and l 像 r represents the horizontal distance from the object plane or image plane to the center of the mirror, respectively. 物 and r 像 This represents the perpendicular distance from the object plane or image plane to the optical axis of the mirror. The spherical mirror is mounted on AB, and its center can be considered the midpoint of HI to maximize the use of the mirror surface; therefore, l物 = KJ, r 物 = (KH + KJ) / 2; for the first gas chamber, l 物 = L L ; for the second gas chamber, l 物 = L S , so the image distance r 像 from the center of the spherical mirror can be calculated according to the formula

[0118] The condition of the detection surface opening angle is that the connecting line between the H point and the image point does not pass through the line segment EG, so

[0119]

[0120] In the formula, the expression of HI is shown in formula (2.29), and the expression of AH is as follows

[0121] AH = AG x tan(2a) = [y - xtan(a)]tan(2a) (33)

[0122] The feasible region determined by the light source cone angle condition and the detection surface opening angle condition is solved; finally, the interval and the inclination angle of the spacer layer are determined as 15 mm and 8°, respectively.

[0123] Step four: determine the optical parameters of the spherical mirror:

[0124] Further determine the optical parameters of the spherical mirror, and only the focal length is involved in this topic. According to the imaging law of the spherical mirror,

[0125]

[0126] In the formula, r represents the focal length of the spherical mirror, so according to the geometric calculation when determining the spacer layer parameters, we have

[0127]

[0128] Solving can get r L = 49.834 mm, r S = 42.736 mm.

[0129] Finally, the height of the gas chamber is adjusted through COMSOL simulation to select the gas chamber height with the best focusing effect of the detector surface. The gas chamber height refers to the farthest vertical distance from the light source to the channel surface, that is, the length of the AB segment in the formula Figure 3 In order to avoid too many times of light reflection on the gas chamber wall, causing the attenuation of light intensity, and also to prevent the sensor volume from being too large, COMSOL simulation can be considered, and finally the height of the first gas chamber channel is selected as 38 mm, and the height of the second gas chamber channel is selected as 44 mm.

[0130] According to the designed scheme, the sensor is processed, and a sensor physical diagram is obtained as shown in the figure Figure 7 According to the method, the sensor is calibrated, and a calibration curve function is obtained as shown in the following

[0131] C = 1239 * ln (f-0.2526) + 3365 (36)

[0132]

[0133] Next, the inhibition effect of the sensor on the light source drift is verified, and the traditional measurement scheme and the double-gas-chamber channel measurement scheme are tested respectively. The drift of the light spectrum of the light source is simulated by changing the voltage at both ends of the light source. The experiment is carried out in a 300ppm standard gas environment, and the test results are shown in the figure Figure 8 As can be seen from the figure, the error of the long-short double optical path measurement scheme is far lower than that of the traditional measurement scheme, and the error reduction rate is more than 50%, which fully proves the effectiveness of the long-short double optical path measurement scheme.

[0134] Embodiment 2:

[0135] The scheme disclosed in the present application does not necessarily require that the two gas chamber channels have a difference in physical length, but only need to have different optical path lengths. For example, a structure diagram as shown in the figure Figure 9 The dotted line represents the propagation path of the light, and the light emitted by the light source reaches the detector after multiple refractions on the gas chamber wall. By processing the gas chamber partition layer, the incidence angle of the light in the first gas chamber and the second gas chamber is limited, so as to control the number of refractions of the light during the propagation in the gas chamber. The number of refractions of the first gas chamber is much larger than that of the second gas chamber, so the optical path of the light in the first gas chamber is also much larger than that of the light in the second gas chamber. According to formula (10), the concentration of the measured gas in the gas chamber can also be calculated, and the measurement effect described in the patent is achieved. At the same time, this embodiment can also be calibrated by using the calibration scheme described in the method, and a calibration curve thereof is obtained.

[0136] Embodiment 3:

[0137] The detector in the gas chamber does not necessarily need to use two, if the light emitted by the light source can be converged to two different signal channels of the same detector, one detector can also be used. The two signal channels of the detector are no longer the reference channel and the measurement channel, but both are measurement channels, and the filters used on the channels are completely the same and the light waves in the light range will all have an absorption effect on the measured gas. At this time, the first gas chamber and the second gas chamber still need to have different optical path lengths, but the specific method of generating the optical path difference can be the method in embodiment 1, can be the method in embodiment 2, or can be other methods, as long as the optical path lengths of the two channels are different, so that the absorption effect occurs differently, the sensitivity to the gas concentration can be realized. Here, a specific embodiment is given according to the scheme of the optical path difference described in embodiment 2, as shown in Figure 9 This scheme can have good miniaturization space, and only one detector is used, further saving the manufacturing cost of the sensor compared to the previous scheme.

[0138] The above specific description further details the purpose, technical scheme and beneficial effects of the application. It should be understood that the above description is only a specific embodiment of the application and is not used to limit the protection scope of the application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A gas concentration measurement method of a long-short dual optical path measurement system based on a non-dispersive infrared principle, characterized in that: The long-short dual optical path measurement system based on the non-spectroscopic infrared principle comprises a light source, a measurement gas chamber, a spherical mirror, a filter and a detector; the measurement gas chamber is composed of a first gas chamber, a second gas chamber and a partition layer; the optical path of the first gas chamber is longer than that of the second gas chamber; the light emitted by the light source is irradiated to the end of the partition layer, and the reflected light is focused by the spherical mirror of the first gas chamber and the second gas chamber and then enters the detector with the filter respectively; The method for measuring the gas concentration by using the system comprises the following steps: Step one: calculating the optical path length of the first gas chamber according to the spectrum of the light source; The actual measured light intensity I of the detector is represented as follows I = ∫S(v)F(v)T(v)dυ (1) In the formula, the spectral density function S(v) is a constant s; v represents the wave number of light, F(v) represents the transmission coefficient of the filter with respect to the function of the wave number of light, and T(v) represents the absorption coefficient spectrum of the measured gas; The transmission function of the filter is wherein υ L represents the minimum pass wave number of the filter, υ H represents the maximum pass wave number of the filter, i.e. [υ L , υ H ] represents the pass wave range of the filter; According to the Lambert-Beer law, T(v) is represented as T(u) = e -k(υ)CL (3) In the formula, k(v) represents the gas absorption coefficient corresponding to the wave number, C represents the concentration of the measured gas, and L represents the optical path length of the light path; According to the formula (1), (2) and (3), the transmittance of the light beam in the light transmission range of the filter is calculated as shown in the following formula According to the measurement accuracy required by the measurement system, the value of the transmittance can be determined, and the optical path length of the first gas chamber is calculated; Step two: determining the difference between the optical path lengths of the first gas chamber and the second gas chamber, and then obtaining the optical path length of the second gas chamber; The measurement result of the measurement system is represented as the ratio of the intensities of the two detectors, and according to the formula (3), the following formula is obtained: where T L (u) and T S (u) represent the absorption coefficient spectra of the first and second gas cell channels, respectively, t L and t S represent the transmittances of the first and second gas cell channels, respectively, and ΔL is the length difference between the first and second gas cells; the required detector intensity ratio is determined according to the required measurement accuracy of the measurement system, the gas cell length difference ΔL is calculated, and the optical path length of the second gas cell is calculated; Step three: the light emitted by the light source is reflected and converged to the detector, and the light intensity is calculated according to the Lambert-Beer law to obtain the concentration of the gas; Let the optical path length of the first gas cell be L L , the optical path length of the second gas cell be L S , the signal intensity measured by the first gas cell be I L , the signal intensity measured by the second gas cell be I S , then according to the Lambert-Beer law, where k L represents the proportionality coefficient of the first gas cell light path, k S represents the proportionality coefficient of the second gas cell light path, I0 represents the light intensity of the light source, and C represents the concentration of the measured gas; dividing the two equations, we obtain The concentration C of the measured gas is calculated from the formula (8), and the quantities that do not change during the measurement process are recorded as constants a and b, and the following formula is obtained Through prior calibration, the values of the constants a and b can be determined, and the concentration of the measured gas is calculated.

2. The gas concentration measuring method according to claim 1, wherein: The calibration method of step three is as follows: The Lambert-Beer law will have an additional constant term d' in the actual calibration, and the following formula is obtained f = a'e b'C + d' (10) In the formula, f represents the sensor reading, that is, the ratio of the light intensity of the first gas chamber to the light intensity of the second gas chamber, a', b' and d' are all constants to be calibrated, and because the sensor reading needs to be used to calculate the concentration after calibration, the independent variable and the dependent variable in the conversion formula (10) are changed, the sensor reading is taken as the independent variable, and the formula (11) is obtained For the convenience of calibration, the constants in the formula (11) are redefined, and the following formula is obtained C = a"ln(f-b") + d" (12) According to the formula (12), it is known that the sensor reading needs to be reduced by an offset before taking the logarithm, and the calibration formula is changed as follows: where f long is the output of the first gas chamber channel, f short is the output of the second gas chamber channel, b long is the value of b in the calibration curve of the first gas chamber channel, b short is the value of b in the calibration curve of the second gas chamber channel, a double , b double , and d double are constants; The calibration procedure is as follows: first, the calibration curves of the first gas chamber detector and the second gas chamber detector are obtained according to formula (12), and the values of b long and b short are obtained; then, the values of a double and d double are obtained by further calibration according to formula (13), and thus the calibration of the measurement system is completed.

Images