Anti-interference ndir mixed gas detection method and system based on differential elimination

Abstract

The application provides an anti-interference NDIR mixed gas detection method and system based on differential elimination, which comprises the following steps: performing a standard gas calibration experiment; establishing a quantitative analysis model through differential operation according to the calibration experiment result; obtaining a detector response of a to-be-detected gas under irradiation of two light sources respectively; and substituting the detector response into the quantitative analysis model to obtain the concentration of the to-be-detected gas. The application can eliminate environmental interference factors, realize measurement of concentrations of various gases, and significantly improve the precision of NDIR mixed gas detection.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas detection, in particular to an anti-interference NDIR mixed gas detection method and system based on differential elimination. BACKGROUND

[0002] With the development of industry, a series of problems of ecological environment need to be solved urgently, such as greenhouse effect, acid rain, haze and so on. These problems have seriously affected the normal activities of human beings, and the root cause is closely related to environmental gas. Carbon dioxide and methane in the environment are the main gases causing greenhouse effect. In some specific environments, if the gas concentration exceeds a certain limit, it will also cause poisoning, fire, explosion and other risks. Therefore, multi-gas detection technology is more and more important in the fields of coal mining, fire warning, atmospheric environment detection and so on. Common multi-gas detection technologies include chemical method, tunable diode absorption spectrum (TDLAS) technology and non-dispersive infrared spectrum (NDIR) technology. Chemical methods include electrochemical detection, catalytic combustion detection, photoionization detection and so on, which mainly measure the physical and chemical properties of gas, such as the change of resistance, capacitance or potential caused by chemical reaction, etc. The advantages are simple process, low cost, but their long-term stability and cross-sensitivity to impurity gas are poor. TDLAS technology has the advantages of high sensitivity, short response time and high resolution, but it needs to accurately modulate the light source, the system is complex, the power consumption is high, the cost is high, and it is not easy to realize small size and low power consumption application. Compared with this, NDIR technology has the advantages of high detection precision, large range, good selectivity, fast response speed, long service life and easy maintenance, and is widely used in gas detection field.

[0003] Most of the existing literatures report that the NDIR-based mixed gas technology adopts the following schemes: 1. Filter wheel type multi-gas measurement, in which the light path and signal processing circuit are relatively simple, but the rotation of the filter wheel needs to increase the power module, which greatly prolongs the measurement time and makes the whole measurement system larger; 2. Confocal gas chamber structure multi-gas measurement, which reduces the system volume to a certain extent, but the number of measured multiple gases is limited, the surface roughness of the inner wall of the gas chamber greatly affects the sensitivity of the instrument, and the material of the gas chamber has certain requirements, the processing requirement is high, and the manufacturing difficulty is great. In addition, in these methods, a reference channel is added to reduce part of the noise and baseline drift, but because the measurement channel and the reference channel contain different phase noises, this part of the noise cannot be eliminated by ratio, and the problem of inconsistent response of the detectors used in the two channels exists. In addition, because the concentration of the measured gas is affected by environmental factors (such as temperature, humidity, air pressure, etc.), the wavelengths measured by the measurement channel and the reference channel are inconsistent, and the environmental factor interference cannot be eliminated by the reference channel measurement, therefore, the double-channel measurement method is greatly affected by the environmental factors such as temperature and humidity, and needs to be calibrated regularly or add compensation algorithm. SUMMARY

[0004] In view of the defects in the prior art, the purpose of the present application is to provide a differential elimination-based anti-interference NDIR mixed gas detection method and system.

[0005] According to one aspect of the present application, a differential elimination-based anti-interference NDIR mixed gas detection method is provided, which comprises:

[0006] Performing a standard gas calibration experiment;

[0007] According to the calibration experiment results, a quantitative analysis model is established through differential operation;

[0008] Obtaining the detector response of the measured gas under the irradiation of two light sources respectively;

[0009] Substituting the detector response into the quantitative analysis model, the concentration of the measured gas can be obtained.

[0010] Further, the standard gas calibration experiment comprises: under each different mixed gas concentration, the two light sources work alternately, and the original voltage signal of the known concentration of the mixed gas under different optical paths is measured.

[0011] Further, the quantitative analysis model is established through differential operation according to the calibration experiment results, which comprises:

[0012] The original voltage signal is processed to obtain the voltage peak value corresponding to different optical paths under different concentrations;

[0013] According to the voltage peak-to-peak value, a differential expression based on a detector response The detector response corresponding to different concentrations of different optical paths is determined, and the differential expression is The ratio of the voltage peak-to-peak value U1 of the detector when the light source is working to the voltage peak-to-peak value U m I1, I m are the corresponding exit light intensities;

[0014] A three-dimensional surface model is constructed with the gas concentration as the independent variable and the detector response as the dependent variable, that is, the quantitative analysis model.

[0015] Further, the original voltage signal is processed, wherein: a Goertzel digital filtering method is used for processing.

[0016] Further, the detector response of the gas to be measured under the irradiation of two light sources is obtained, comprising:

[0017] The original signal of the detector output of the gas to be measured under the irradiation of two light sources is measured, and the original signal of the detector output of the gas to be measured under the irradiation of two light sources is measured.

[0018] According to the detector output original signal, the detector response of the gas to be measured corresponding to different detectors is determined.

[0019] According to the second aspect of the present application, an anti-interference NDIR mixed gas detection system based on differential elimination is provided for realizing the anti-interference NDIR mixed gas detection method based on differential elimination, and the system comprises:

[0020] A light source module comprising two infrared light sources and a driving circuit corresponding to the two infrared light sources, the driving circuit being used to realize periodic change of light source intensity;

[0021] A detector module comprising a plurality of pyroelectric detectors, the number of pyroelectric detectors being the same as the number of component types of the gas to be measured, the pyroelectric detectors and the light sources being located in a gas chamber; a plurality of the pyroelectric detectors acquiring original voltage signals of the gas to be measured under different optical paths;

[0022] A main control module for processing the original voltage signal to obtain gas concentration information.

[0023] Further, the infrared light source adopts a broadband light source with a parabolic emission surface type.

[0024] Further, the driving circuit comprises a PWM generation circuit and a light source driving circuit, the PWM generation circuit generates two-channel square wave signals and transmits them to the light source driving circuit to modulate the light source, so that the light source intensity realizes periodic change.

[0025] Further, the structure of the air chamber is straight; the air chamber is provided with a support for fixing the light source and the pyroelectric detector, and the projection of two light sources on each pyroelectric detector is in a cross shape, so as to ensure that the pyroelectric detector is equally irradiated by the light source.

[0026] Further, the main control module comprises:

[0027] The signal biasing and amplifying module is used for pre-processing the original voltage signal;

[0028] The microcontroller is used for collecting the pre-processed data and converting the analog signal into a digital signal;

[0029] The storage module is used for storing the digital signal.

[0030] Compared with the prior art, the present application has at least one of the following beneficial effects:

[0031] 1. The present application obtains a plurality of data containing a plurality of influencing factor parameters (such as humidity, temperature, detector responsivity, etc.) through a plurality of light paths and difference elimination operation, so as to analyze the concentration of the mixed gas. Since the sensor response SR only depends on the light path length L, the gas concentration C and the absorption constant k of the gas to be measured, and is irrelevant to other factors (such as light source drift, environmental temperature and humidity, etc.), the present application can eliminate environmental interference factors (such as light source jitter, environmental temperature and humidity interference, etc.), and realize the measurement of a plurality of gas concentrations.

[0032] 2. Compared with the conventional multi-channel detection system, the measurement system of the present application is smaller in size, lower in cost and higher in stability, and provides a simpler method for the detection of various gases.

[0033] 3. The double light source and multi-detector mixed gas measurement model adopted by the present application is suitable for carbon dioxide, methane and other gases, and the measurement method of the present application can significantly improve the accuracy of NDIR mixed gas detection. BRIEF DESCRIPTION OF DRAWINGS

[0034] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments with reference to the attached drawings:

[0035] Figure 1 Fig. 1 is a schematic diagram of the principle of the anti-interference NDIR mixed gas detection method based on difference elimination of the embodiment of the present application;

[0036] Figure 2 Fig. 2 is a flowchart of the anti-interference NDIR mixed gas detection method based on difference elimination of the embodiment of the present application;

[0037] Figure 3 A three-dimensional surface model of two mixed gases (carbon dioxide concentration range: 0-3000ppm, methane concentration range: 0-1000ppm) in an embodiment of the present application; wherein a is a three-dimensional surface model corresponding to the detector response SR1, and b is a three-dimensional surface model corresponding to the detector response SR2;

[0038] Figure 4 A structural block diagram of an anti-interference NDIR mixed gas detection system based on difference elimination in an embodiment of the present application;

[0039] Figure 5 A flowchart of a measurement process using the system of Figure 4 ;

[0040] Figure 6 A structural diagram of a CO2 and CH4 mixed gas detection system in an embodiment of the present application. DETAILED DESCRIPTION

[0041] The present application will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application. These all belong to the protection scope of the present application.

[0042] In the description of embodiments of the present application, sensor and detector represent the same meaning, and sensor response and detector response represent the same meaning.

[0043] Different gas molecules have unique gas absorption peaks, and the absorption degree is related to the concentration of the gas molecules, and follows the Lambert-Beer law, such as formula 1:

[0044] I t = I0e -kCL Formula 1

[0045] In formula 1, I0 is the incident light intensity, I t is the transmitted light intensity, k is the molar absorption coefficient of the measured gas, C is the gas concentration, and L is the optical path length.

[0046] Based on the above law, referring to Figure 1 , taking the measurement of two gases as an example, an additional light source is added, and the detector response is measured under different optical paths by working the two light sources alternately to obtain the concentration information of the gas to be measured. According to the Lambert-Beer law, formulas 2-5 can be written:

[0047]

[0048]

[0049]

[0050]

[0051] where I 10 , I 20 are the incident light intensities when the two light sources work alone, L1, L2, L3, L4 are the optical path lengths between different detectors and different light sources, I1, I2, I3, I4 are the corresponding exit light intensities, k1, k2 are the molar absorption coefficients of the two gases to be measured, and C1, C2 are the concentrations of the gases to be measured.

[0052] In the four expressions, k1, k2 and L1, L2, L3, L4 are constant terms, I1, I2, I3, I4 can be obtained by measurement, and I 10 , I 20 and C1, C2 are unknown quantities, which can be solved by the equation group to obtain equation 6:

[0053]

[0054] The voltage U output by the detector is proportional to the exit light intensity I, satisfying where K is a constant term. Assuming that the interference of temperature T and humidity R on the concentration of the gas to be measured is represented by a function f(T, R), the transmission light intensity I considering the environmental interference is t as expression 7:

[0055] I t = I0e -kCL+f(T,R) expression 7

[0056] The voltage U' output by the detector considering the environmental interference is defined as U', and equation 8 can be obtained:

[0057]

[0058] In this simplification process, the influences of light source jitter, environmental temperature and humidity and other interference factors can be eliminated by difference operation. The difference expression of the sensor response is further defined as: The concentrations of the two gases to be measured can be obtained, as shown in equation 9:

[0059]

[0060] where M = L2L3 - L1L4.

[0061] This method can be extended to n kinds of gases, and n detectors are required for measuring n kinds of gases. Assuming that when the n kinds of gases are compared with the mth gas, the equation group can be written as equation 10. The sensor response The subscripts of L represent different gas types m, n, such as m representing carbon dioxide and n representing methane, and the superscript i represents the light source 1 or 2 working when the signal is collected. For example, the sensor response represents the ratio of the peak-to-peak voltage of the detector 1 (for measuring gas 1) to the peak-to-peak voltage of the detector m (for measuring gas m) when the light source 1 is working.

[0062]

[0063] Similarly, the differential operation can eliminate environmental interference, and can be simplified to the following matrix form, as shown in equation 11.

[0064]

[0065] In the formula, L 11 , L 12 respectively represent the distance between the detector 1 and the light source 1 and the light source 2, that is, the optical path; L m1 represents the optical path between the mth detector and the light source 1, and L m2 represents the optical path between the mth detector and the light source 2.

[0066] Based on the above analysis, combined with the differential elimination detection method, the concentration of n kinds of gases to be measured can be solved through the measurement system based on the double light source and multiple optical paths.

[0067] Based on the above, the anti-interference NDIR multi-gas measurement method based on differential elimination can avoid the interference of environmental temperature and humidity and other factors. Without considering environmental disturbance, only the detector voltages under two different optical paths need to be measured to obtain the concentration information of multiple gases to be measured.

[0068] Based on the above principle, the anti-interference NDIR mixed gas detection method based on differential elimination provided by the embodiment of the application, with reference to Figure 2 , comprises:

[0069] Step S1, performing a standard gas calibration experiment;

[0070] Step S2, according to the calibration experiment result, performing a differential operation to establish a quantitative analysis model;

[0071] Step S3, obtaining the detector response (that is, the sensor response) of the gas to be measured under the irradiation of two light sources respectively;

[0072] Step S4, substituting the detector response into the quantitative analysis model, so as to obtain the concentration of the gas to be measured.

[0073] In some embodiments, in step S1, the standard gas used in the calibration experiment is a mixed gas formed by mixing a pure gas (such as carbon dioxide) identical to the gas component to be detected with nitrogen, and the concentration thereof is predetermined. The standard gas calibration experiment is performed, including: under each different mixed gas concentration, by alternately working the two light sources, measuring the original voltage signal of the mixed gas with known concentration under different optical paths.

[0074] In some embodiments, in step S2, according to the calibration experiment results, a quantitative analysis model is established through difference operation, including: processing the original voltage signal to obtain the voltage peak-to-peak value corresponding to different optical paths under different concentrations; according to the voltage peak-to-peak value, determining the detector response corresponding to different optical paths under different concentrations through difference operation, that is, according to the ratio of the voltage peak-to-peak values of the two gases, specifically, the difference expression of the detector response The difference expression represents the ratio of the voltage peak-to-peak value U1 of the detector when the light source is working to the voltage peak-to-peak value U m I1, I m are the corresponding exit light intensities; taking the gas concentration of each component in the mixed gas as the independent variable and taking the detector response as the dependent variable, a three-dimensional surface model is constructed, that is, the quantitative analysis model.

[0075] Further, the original voltage signal is processed, wherein: the Goertzel digital filtering method is used for processing.

[0076] In step S3, the detector response of the gas to be detected under the irradiation of the two light sources is obtained, including: measuring the detector output original signal corresponding to different optical paths under the irradiation of the two light sources; according to the detector output original signal, obtaining the voltage peak-to-peak value corresponding to different optical paths of the gas to be detected, and determining the detector response of the gas to be detected corresponding to different detectors.

[0077] In a specific embodiment, taking the mixed gas of carbon dioxide and methane as an example, in step S1, first, a calibration experiment is performed, and before the experiment, a gas washing operation is required, that is, the entire gas sealed tank (including the gas chamber) is flushed with nitrogen (with a purity of 99.99%), and then the container is pumped to vacuum by a vacuum pump, and the above operation is repeated 3-4 times, and then the gas measurement is started. After the gas sealed tank is pumped to vacuum, the gas with known concentration is filled into the gas sealed tank to restore to a standard atmospheric pressure, and the computer displays and records the current voltage change. The gas concentration is selected as carbon dioxide (0, 500, 1000, 2000, 3000 ppm) and methane (0, 500, 1000 ppm) respectively for mixing, and the four optical paths before the two light sources and the two detectors are L1=50mm, L2=20mm, L3=60mm, and L4=30mm, and the original voltage signal is collected.

[0078] In the original signal acquisition process, under the condition of each different mixed gas concentration (a total of 5x3 = 15), two infrared light sources work alternately and independently and repeat acquisition 20 times, a total of (15x2x20 = 600) groups of sinusoidal signal original data are obtained.

[0079] Step S2, then the original data is processed. The data preprocessing of the original signal includes Goertzel digital filtering. Goertzel algorithm has the following key parameters: sampling rate R, target frequency f, detection section sample number N, detection section contains the number of complete cycles of target frequency K, wherein the sampling rate R refers to the number of samples per second of the data to be analyzed, according to the Nyquist sampling law, which is twice higher than the signal frequency, the higher the sampling rate, the more accurate the signal obtained. The target frequency f refers to the frequency value to be detected, and the relationship between the parameters satisfies K = Nf / R. Through these parameters, the frequently occurring coefficient C = 2cos(2πK / N) in Fourier transform can be calculated in advance, and then the following iterative calculation can be performed on N sampling points, that is, the power value P of the frequency f in the signal can be obtained:

[0080] Q0 = CQ1 - Q2 + S

[0081] Q1 = Q0

[0082] Q2 = Q1

[0083] P = Q1 2 + Q2 2 - Q1Q2

[0084] The power value P represents the energy spectrum value of the target frequency. In the initialization, Q1 = 0, Q2 = 0. In the experiment, the sampling point number N is 2000, the target frequency f is 5Hz (which is the working frequency of the light source), the sampling rate R is 1000 (> 2f), and the number of complete cycles containing the target frequency K = 10. 600 groups of sinusoidal signal data are measured, and the signal intensity (i.e. the peak-to-peak voltage value of the original signal) corresponding to different concentrations of different optical paths can be obtained through the Goertzel algorithm, and the SR can be obtained through the sensor response definition calculation in the principle derivation:

[0085]

[0086]

[0087] The final sensor response of all samples and the corresponding sample concentration are used to establish a quantitative analysis model. The mixed gas concentration is used as the independent variable and the sensor response is used as the dependent variable to construct a three-dimensional surface calibration model. In this embodiment, the carbon dioxide gas concentration (0, 496, 1001, 2002, 3000 ppm) is used as the x-axis, the methane gas concentration (0, 500, 1000 ppm) is used as the y-axis, and the corresponding sensor responses SR1 and SR2 are used as the z-axis to construct a three-dimensional surface model and perform three-dimensional surface fitting. The fitting results are shown in FIGS. 6 and 7, and the fitted binary quadratic surface equation is as follows: Figure 3

[0088] f(x,y) = p00 + p10 * x + p01 * y + p20 * x^2 + p11 * x * y + p02 * y^2

[0089] p00 = -0.6351; p10 = -0.0001075; p01 = -0.0001282;

[0090] p20 = 1.024e-07; p11 = -5.18e-08; p02 = 1.816e-08

[0091] The R-square of the C-SR1 fitting surface model is 0.9996 and the RMSE is 0.01013. 2

[0092] f(x,y) = p00 + p10 * x + p01 * y + p20 * x^2 + p11 * x * y + p02 * y^2

[0093] p00 = -0.8229; p10 = -2.941e-05; p01 = -4.048e-05;

[0094] p20 = 3.376e-08; p11 = -1.413e-08; p02 = 3.989e-09

[0095] The R-square of the C-SR2 fitting surface model is 0.9929 and the RMSE is 0.003406. 2

[0096] Step S3, measure the raw signals of the detector output under the irradiation of the two light sources, respectively, and calculate the sensor responses SR1 and SR2.

[0097] Step S4, finally, according to the established calibration model, the sensor response is substituted into the quantitative analysis model established by calibration in advance, and the concentration C to be measured can be obtained.

[0098] ​​​Specifically, the following methods can be used to obtain the final concentration value: (1) formula method. The constant term is obtained by calibration calculation in advance, and after SR1 and SR2 are calculated, they are substituted into formula 9 to obtain the concentration of the two gases to be measured. (2) Substituting the model method. Substitute the values of SR1 and SR2 into the three-dimensional surface model to obtain a curve with different gas concentrations in the horizontal and vertical coordinates, and solve the intersection point of the two curves to obtain the final concentration value.

[0099] In the anti-interference NDIR mixed gas detection method based on difference elimination in the above embodiments of the application, the measurement results under multiple optical paths are subjected to difference operation, so that environmental interference factors (such as light source jitter, environmental temperature and humidity interference, etc.) can be eliminated, and the concentration of multiple gases can be measured.

[0100] Based on the same inventive concept, another embodiment of the application provides an anti-interference NDIR mixed gas detection system based on difference elimination, which is used to implement the anti-interference NDIR mixed gas detection method based on difference elimination described above, and refers to Figure 4 The system includes a light source module, a gas chamber, a detector module, a corresponding modulation circuit module, standard sample gas with different concentrations, a gas sealing tank, and a main control module. The light source module includes two infrared light sources and a driving circuit corresponding to the two infrared light sources, and the driving circuit is used to realize the periodic change of the light source intensity. The detector module includes a plurality of pyroelectric detectors, and the number of pyroelectric detectors is the same as the number of gas components to be measured. The pyroelectric detectors and the light sources are located in the gas chamber. The plurality of pyroelectric detectors obtains the original voltage signals of the gas to be measured under different optical paths. The main control module is used to process the original voltage signals to obtain the concentration information of the gas to be measured.

[0101] In some embodiments, the infrared light source uses a broadband light source with a parabolic emission surface type. Specifically, for example, the selected light source model is IR715EN-PR (PerkinElmer Optoelectronics Company; Germany), and the emission range is 2-5 μm. The driving circuit includes a PWM generation circuit and a light source driving circuit. Because the selected pyroelectric detector only responds to a periodic change type signal, a PWM generation circuit is selected to generate a two-channel fixed frequency duty cycle 50% square wave signal and transmit it to the light source driving circuit to modulate the light source, so that the light source intensity realizes periodic change.

[0102] In some embodiments, taking the measurement of carbon dioxide and methane mixed gas as an example, both probes in the detection module adopt LME-335 series of Infratec Company, respectively carrying wide measurement range carbon dioxide filter (NBP 4.2 μm) and methane filter (NBP 3.4 μm). Since the probe needs ±5V double power supply, a driving circuit (TPS5430) is additionally provided for power supply. The probe signal is output to an amplification filter circuit (AD620). In addition, in order to ensure that the AD collects complete signals, a bias circuit and its voltage conversion circuit (SGM3204) are additionally provided.

[0103] In some embodiments, the gas chamber adopts acrylic material, which can realize customized structure, such as fixing the light source and the detector and adjusting the distance therebetween; the structure of the gas chamber is direct type, which has the advantages of simple structure and stable optical path system; the acrylic support for fixing the light source and the pyroelectric detector is arranged in the gas chamber, and the projection of the two light sources on each pyroelectric detector is in a cross shape, so as to ensure that the pyroelectric detector is equally irradiated by the light source.

[0104] In some embodiments, the main control module includes a signal bias amplification module, a microcontroller and a storage module, wherein: the signal bias amplification module is used for pre-processing the original voltage signal output by the sensor; the detector output voltage is a continuous analog signal, which needs to be converted into a digital signal to be read, and the microcontroller is used for collecting the pre-processed data and converting the analog signal into a digital signal; the microcontroller based on the ATmega382 kernel, Arduino Uno, is selected in the system. In order to reduce the volume and circuit complexity of the prototype, the digital processing circuit adopts the 10-bit analog-digital conversion module of Arduino. The storage module is used for storing the digital signal.

[0105] The main control module further includes a key module, which controls the microcontroller Arduino to collect data, convert the analog signal into a digital signal and store it in the SD card, so as to perform the next step of data processing. At the same time, the microprocessor can perform real-time communication with the PC end through the serial port.

[0106] The detection system in the above embodiment adopts 12V lithium battery power supply mode, in order to meet the voltage requirements of different modules, a multi-channel voltage reduction circuit LM2596 is used for voltage regulation. The process of using the above detection system to detect the mixed gas is as shown in Figure 5 .

[0107] Taking the measurement of carbon dioxide and methane mixed gas as an example, referring to Figure 6The NDIR mixed gas detection system based on differential elimination includes a light source module, a detector module, a gas chamber, and a main control module. The gas chamber has an inlet valve and an outlet valve; the inlet is connected to a vacuum pump, and carbon dioxide and methane are stored separately in gas tanks. The light source module includes two infrared light sources and their driving modules. Figure 6 Mid-infrared drive). The infrared light source is a broadband light source with a parabolic emitting surface (covering the infrared characteristic absorption peak of CO2 at 4.26μm and CH4 at 3.34μm). The light source drive module includes a PWM generator and a power drive module. The PWM generator produces a square wave signal with a fixed duty cycle of 50%, which is transmitted to the power drive module to drive the light intensity of the light source to vary according to a sinusoidal curve. The detector module includes a probe and its conditioning circuit module. A pyroelectric detector is selected, equipped with a wide measurement range carbon dioxide filter (NBP 4.2μm) and a methane filter (NBP 3.4μm), respectively. This probe has low temperature drift and a structure to suppress mechanical vibration interference. Since the probe requires a ±5V dual power supply, a drive circuit is added to provide power. The detector signal output is sent to the amplification and filtering circuit (…). Figure 6 (Medium-amplification and filtering module). In addition, to ensure the AD acquires a complete signal, a bias circuit and its voltage conversion circuit are added, such as... Figure 6 Medium voltage conversion module. Preferably, the gas chamber material is acrylic, and the structure is direct-projection. Simultaneously, the gas chamber fixes the position of the light source and the probe, with the projection forming a cross shape to ensure that the detector is evenly illuminated by the light source. The main control module includes a microcontroller, a button module, and a storage module. Figure 6 The system includes an SD card module and a signal bias amplification module. Preferably, an Arduino Uno microcontroller based on the ATmega382 core is used. To reduce the prototype's size and circuit complexity, the digital processing circuit uses the Arduino's built-in 10-bit analog-to-digital converter module. The raw voltage signal output from the sensor is transmitted to the signal bias amplification module for data preprocessing. The Arduino microcontroller is controlled by a button module to acquire data, converting the analog signal into a digital signal and storing it in the SD card for further data processing. Simultaneously, the microcontroller can communicate with a PC in real time via a serial port.

[0108] The anti-interference NDIR mixed gas detection method and system based on differential elimination in the above embodiments have smaller measurement system size, lower cost and higher stability compared with the prior art. They can easily obtain the concentration information of various gases to be measured, and eliminate the interference of ambient temperature and humidity. They can significantly expand the measurement range and measurement accuracy of mixed gases using nondispersive infrared technology.

[0109] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the specific embodiments described above, and various modifications or changes can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application. The above preferred features can be combined in any manner without conflict, and used.

Claims

1. A differential elimination based anti-interference NDIR mixed gas detection method, characterized in that, The method comprises the following steps: A standard gas calibration experiment is carried out, including: under each different mixed gas concentration, the original voltage signal of the known concentration of the mixed gas under different optical paths is measured by taking turns to work of two light sources; According to the calibration experiment results, a quantitative analysis model is established through difference operation, including: The original voltage signal is processed to obtain the voltage peak-to-peak value corresponding to different concentrations under different optical paths; According to the voltage peak-to-peak value, a differential expression based on a detector response is determined , the detector response corresponding to different concentrations and different optical paths, the sensor response The subscripts of the differential expression represent different gas species m, n in turn, and the superscript i represents the light source 1 or 2 that is working when the signal is collected. The differential expression represents the ratio of the voltage peak-to-peak value measured by detector 1 for gas 1 when light source 1 is working to the voltage peak-to-peak value measured by detector m for gas m , , is the corresponding exit light intensity. A three-dimensional surface model is constructed by taking the gas concentration of each component in the mixed gas as the independent variable and the detector response as the dependent variable, which is the quantitative analysis model; The detector response of the to-be-measured gas under the irradiation of two light sources is obtained; The to-be-measured gas concentration can be obtained by substituting the detector response into the quantitative analysis model. The method eliminates environmental interference factors by performing difference operation on the measurement results under multiple optical paths.

2. The differential elimination based anti-interference NDIR mixed gas detection method according to claim 1, characterized in that, The original voltage signal is processed, wherein: the Goertzel digital filtering method is used for processing.

3. The differential elimination based interference-resistant NDIR mixed gas detection method according to claim 1, wherein, The detector response of the to-be-measured gas under the irradiation of two light sources is obtained, including: The original signal of the detector output corresponding to different optical paths of the to-be-measured gas under the irradiation of two light sources is measured; The detector response of the to-be-measured gas corresponding to different detectors is determined according to the original signal of the detector output.

4. A differential elimination based anti-interference NDIR mixed gas detection system for implementing the differential elimination based anti-interference NDIR mixed gas detection method of any one of claims 1-3, characterized in that, The method comprises the following steps: The light source module comprises two infrared light sources and a driving circuit corresponding to the two infrared light sources, and the driving circuit is used to realize the periodic change of the light source intensity; The detector module comprises a plurality of pyroelectric detectors, the number of the pyroelectric detectors is the same as the number of to-be-measured gas component types, and the pyroelectric detectors and the light sources are located in the gas chamber; a plurality of pyroelectric detectors obtain the original voltage signal of the to-be-measured gas under different optical paths; The main control module is used to process the original voltage signal to obtain the to-be-measured gas concentration information.

5. The differential elimination based anti-interference NDIR mixed gas detection system according to claim 4, wherein, The infrared light source adopts a broadband light source with a parabolic emission surface type.

6. The differential elimination based anti-interference NDIR mixed gas detection system according to claim 4, wherein, The driving circuit comprises a PWM generation circuit and a light source driving circuit, the PWM generation circuit generates two-channel square wave signals and transmits them to the light source driving circuit to modulate the light source, so that the light source intensity realizes periodic change.

7. The differential elimination based anti-interference NDIR mixed gas detection system according to claim 4, wherein, The structure of the gas chamber is straight; the gas chamber is provided with a support for fixing the light source and the pyroelectric detector, and the projection of the two light sources on each pyroelectric detector is in a cross shape, so as to ensure that the pyroelectric detector is equally irradiated by the light source.

8. The differential elimination based anti-interference NDIR mixed gas detection system according to claim 4, wherein, The main control module comprises: The signal bias amplification module is used to pretreat the original voltage signal; The microcontroller is used to collect the pretreated data and convert the analog signal into a digital signal; The storage module is used to store the digital signal.

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