CN102798609A - Automobile exhaust remote sensing detection system and method based on quantum cascade laser - Google Patents
Automobile exhaust remote sensing detection system and method based on quantum cascade laser Download PDFInfo
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Abstract
The invention discloses an automobile exhaust remote sensing detection system and a method based on a quantum cascade laser. According to the invention, a signal generated by any function generator is input into a laser current pulse driving module; the quantum cascade laser is driven by the laser current pulse driving module to generate intermediate-infrared or far-infrared laser; a modulation signal is obtained through a chopper after the intermediate-infrared or far-infrared laser passes through an automobile exhaust emission area; a pyroelectric sensor module detects the modulated intermediate-infrared or far-infrared laser signal, and then inputs the detected signal into a lock-in amplifier for operation; the lock-in amplifier outputs the data into a computer; and the computer calculates the contents of different emission products in the automobile exhaust through a data processing method analysis method.
Description
Technical Field
The invention belongs to the technical field of automobile exhaust emission detection, and particularly relates to an automobile exhaust remote sensing detection system and method based on a quantum cascade laser.
Background
With the rapid development of economy in China, the automobile holding capacity is continuously increased, and the pollution of harmful waste gas discharged by automobiles becomes one of the main sources of urban air pollution in China. According to the statistics of environmental protection departments, 20 percent of CO in urban air pollution260-70% of CO and 40% of NOxAnd 70% of the HC is from automobile exhaust. For example, in the ratio of pollutants emitted by automobiles in Beijing and Guangzhou cities in ambient air, carbon monoxide (CO) accounts for more than 80%, and Nitrogen Oxides (NO)x) Accounting for more than 40 percent. In order to control the emission of pollutants in the tail gas of automobiles, laws and regulations for limiting the emission of the exhaust gas of the automobiles are set in sequence in various countries and regions in the world. Emission standards of light automobile pollutants emission limit and measurement method (stage III and IV in China), which are equivalent to European regulation III, are implemented in China from 7 months in 2007. However, compared with developed countries, the current situation of automobile exhaust emission in China is still not optimistic: the management of automobile emission pollution starts late; the pollution caused by automobile exhaust in key cities is very serious; emission related components on vehicles are very deficient. In order to improve the air quality of urban environment, the reduction and control of the emission pollution of automobile exhaust are very slow.
The current automobile exhaust monitoring method in China mainly comprises a working condition method and an idling method. At present, the two methods can be mainly tested on an experimental test platform of an automobile production plant or in an annual inspection place of a vehicle, and the real-time monitoring of the tail gas emission process of the automobile in the driving process cannot be realized. In the actual driving process, the exhaust emission of the automobile not only depends on the structure of the automobile, but also depends on various factors such as the composition of the fuel used by the automobile, the load, the driving mode, the degree of traffic congestion and the like. The remote sensing monitoring technology for automobile exhaust is an advanced automobile exhaust monitoring technology, can monitor the instantaneous emission of automobile exhaust under the condition that an automobile normally runs, identifies polluted vehicles with substandard emission, provides an effective means for monitoring and controlling urban automobile exhaust pollution, and has great social demands and receives extensive research and attention.
The traditional remote sensing monitoring method for automobile exhaust mainly aims at CO2Non-spectroscopic infrared methods of CO and HC detection. Most of the detection conditions of the discharged pollutants are that under the idling condition, the characteristics of harmful exhaust emission of the automobile under the driving condition and photochemical reaction possibly formed by the exhaust in the air cannot be reflected. The prior art automobile exhaust gas detection device, such as "a multi-idle motor vehicle exhaust gas detection device" with patent number CN2440208Y, needs to connect a hose to an automobile exhaust pipe orifice to perform detection and analysis of CO and HC in the exhaust gas. The infrared laser detection system and method for detecting the automobile exhaust in real time, which is disclosed in patent No. CN1412541A, uses a non-spectroscopic infrared analyzer, which has no spectral resolution, and the detected exhaust is single in type, and only can detect the concentrations of CO and HC. The detection of single CO and HC concentration is developed into CO and CO2、HC、NOx、NH3And SOxThe detection of various components is the direction of the current remote sensing detection of the automobile exhaust. Currently, remote sensing technology for detecting automobile exhaust is actively developed in many countries such as the united states, canada, australia, sweden, brazil, singapore and india.
The quantum cascade laser is a milestone of semiconductor laser theory and is becoming a leading-edge technology for dispute and tracking of countries in the world. The quantum cascade laser has the advantages of good monochromaticity, high quantum efficiency, good temperature stability, flexible wavelength design, high inherent response speed and the like. The quantum cascade laser has wide application prospect in the aspect of gas detection, particularly in the aspect of low-concentration gas and atmosphere trace gas detection, has incomparable advantages of the traditional semiconductor laser, and can be widely applied to high-sensitivity detection of coal mine gas and detection of automobile tail gas and industrial waste gas.
Disclosure of Invention
The invention aims to provide a system and a method for remotely sensing and detecting automobile exhaust based on a quantum cascade laser aiming at the defects of the prior art, and the system and the method are used for remotely sensing and detecting the automobile exhaust running on a road.
The technical scheme adopted by the invention for solving the technical problems is as follows:
the automobile exhaust remote sensing detection system based on the quantum cascade laser comprises an arbitrary function generator, a current pulse driving module, the quantum cascade laser, a polyethylene collimation focusing lens, a spectroscope, a chopper, a pyroelectric sensor module, a gold-plated right-angle reflector, a lock-in amplifier and a computer;
voltage signals generated by an arbitrary function generator are input into a current pulse driving module, then current pulses generated by the current pulse driving module drive a quantum cascade laser, the quantum cascade laser emits amplitude-modulated middle and far infrared laser under the driving of current pulses, the middle and far infrared laser is collimated and emitted in parallel through a polyethylene collimation focusing lens, the parallel middle and far infrared laser is divided into a reference light path and a detection light path through a spectroscope, the middle and far infrared laser of the reference light path is detected by a pyroelectric sensor module of the reference light path after being modulated by a chopper, the middle and far infrared laser of the detection light path penetrates through an automobile exhaust emission area in driving and is reflected by a gold-plated right-angle reflector, and the reflected middle and far infrared laser is detected by the pyroelectric sensor module of the detection light path after passing through the chopper and the polyethylene collimation focusing lens; sine wave signal components of the pyroelectric sensor module of the detection light path, the pyroelectric sensor module of the reference light path and the arbitrary function generator are respectively input into a phase-locked amplifier for relevant operation, and the phase-locked amplifier outputs the result to a computer; and the computer performs subtraction operation on the correlation operation output value of the pyroelectric sensor module of the reference light path and the correlation operation output value of the pyroelectric sensor module of the detection light path, and performs data processing and spectrum analysis on the calculation result to finally obtain the measurement result of the automobile exhaust.
The spectroscope is arranged right in front of the polyethylene collimating and focusing lens, and the light rays which are collimated and emitted in parallel with the polyethylene collimating and focusing lens form an angle of 45 degrees;
the arbitrary function generator generates three signals which are respectively: the laser comprises a rectangular pulse signal, a sawtooth wave signal and a sine wave signal, wherein the three voltage signals are superposed in an arbitrary function generator and then input into a current pulse driving module, the current pulse driving module outputs a modulated current signal to drive a quantum cascade laser after voltage-current conversion, the arbitrary function generator outputs a superposed signal to the current pulse driving module and simultaneously inputs a sine wave signal component in the superposed signal into a phase-locked amplifier for signal correlation operation, and the phase-locked amplifier is connected to a computer.
The pyroelectric sensor module comprises a pyroelectric sensor, a resistor and a filter capacitor; a pin 1 of the pyroelectric sensor is simultaneously connected with a direct current voltage VCC and one end of a filter capacitor, a pin 2 is connected with one end of a resistor, a pin 3 and the other end of the resistor are simultaneously grounded, and the other end of the filter capacitor is connected with a phase-locked amplifier; the alternating current signal passing through the filter capacitor is input into a phase-locked amplifier, and simultaneously, a sine alternating current signal output by the phase-locked amplifier drives a chopper to rotate at a certain frequency, and the phase-locked amplifier is connected to a computer; the polyethylene collimation focusing lens and the chopper are arranged right in front of the pyroelectric sensor module.
The remote sensing detection method of the automobile exhaust based on the quantum cascade laser comprises the following steps:
step (1), the lock-in amplifier outputs the original spectral data obtained by measurement to a computer;
removing random noise in original spectral data by using an average filtering function according to the frequency of a sawtooth wave in an arbitrary function generator, specifically realizing average filtering by adopting the period of the sawtooth wave signal in a synthetic signal, and obtaining spectral data with different wavelengths under frequency sweeping after filtering;
and (3) fitting the filtered spectral data by using a Voigt linear function, wherein the Voigt linear function adopted by the fitting function is described by a formula (1).
Wherein,，
；
γ D -width of gaussian linear function spectrum;
γ C -Lorentzian linear function spectral width;
meanwhile, the spectral width of the Foster linear function can be obtained：
（2）
Wherein:
is the collision line width of the spectral lines;
is the Doppler line width of the spectral line;
repeating the fitting for n times by using a Voigt linear function to obtain the spectral distribution data of n different spectral lines
Obtaining the most probable absorption spectral line according to the fuzzy function membership degree judgment method for any spectral line data obtained by fitting, and setting the set of the spectral data of the ith spectral line obtained by measurement as U ═ toneu i1，u i2，u i3，…u im At the same time, the set of standard spectral data of the ith spectral line is V ═ fv i1，v i2，v i3，…v imI is a natural number, and i is less than or equal to m; m is a natural number; then calculating similarity coefficients of the set U and the set V
：
If similarity coefficient
≥
Then the corresponding spectrumThe line is judged as an absorption spectral line, so that the ith spectral line is obtained as an effective absorption spectral line, wherein
The level value is calibrated in advance;
and (5) finally, inputting the spectral data of the effective absorption spectrum line into an artificial neural network trained and calibrated in advance for processing, and calculating the concentrations of different gases in the automobile exhaust through the artificial neural network
Wherein
Is the spectral data of the effective absorption line.
The level value in the fuzzy function membership degree discriminant function in the step (4) and the step (5)
And the parameter calibration process of the artificial neural network is as follows:
(a) fixing the angles and the positions of the gold-plated plane reflecting mirror, the quantum cascade laser and the pyroelectric detector; fixing the position of the long optical path gas pool and a heating device; collecting a spectral output value of clean air at room temperature;
(b) the method comprises the following steps of simulating automobile exhaust under different working conditions by mixing pure gases in different proportions, and filling the simulated automobile exhaust into a long-optical-path gas pool as gas to be calibrated in the calibration process;
the pure gas comprises CO and CO2、NO、NO2、NH3And SO2；
(c) Winding heating coils around the long-optical-path gas pool to uniformly heat air in the long-optical-path gas pool, so that the temperature of the air in the long-optical-path gas pool changes along with the change of the setting conditions, and acquiring spectral data output values at different temperatures;
one end of the long optical path gas pool is provided with a gold-plated right-angle reflecting mirror, and the other end is provided with a quantum cascade laser and a pyroelectric sensor module of a detection light path.
(d) Training to obtain a fuzzy function membership level value according to the actual mixing proportion of the spectral data output value and the simulated automobile exhaust
And artificial neural network parameters, and obtaining the membership level value of the fuzzy function according to the average value of N times of different measurement results
Simultaneously training an artificial neural network by using the data sample; if the error of the calibration result is more than 20%, re-calibration is needed; otherwise, ending the calibration process.
The invention has the following beneficial effects:
firstly, the automobile exhaust remote sensing detection system based on the quantum cascade laser drives the quantum cascade laser by using a voltage signal generated by an arbitrary function generator, and the quantum cascade laser emits middle and far infrared lasers with different wavelengths. The spectrum sweep frequency signal with fast sweep speed can be obtained by changing the repetition frequency and the amplitude of the sawtooth wave signal in the voltage signal, so that the spectrum measurement result can be obtained quickly. Because the speed of one-time measurement is high, the automobile exhaust remote sensing detection system based on the quantum cascade laser can obtain automobile exhaust concentration data by adopting a non-contact mode under the condition of not interfering the normal running of the automobile in the running process of the automobile at medium speed and low speed.
Secondly, the quantum cascade laser can emit middle and far infrared laser with the wavelength capable of being adjusted in a large range, and the emitted laser spectrum is wide in coverage range, so that more types of gases can be measured, and CO can be measured in one-time measuring process2、NO、NO2、NH3And SO2And monitoring the concentration of the gases. Because only one quantum cascade laser is needed as a spectrum radiation source, the automobile exhaust remote sensing detection system based on the quantum cascade laser has a very simple and compact structure. Meanwhile, the medium and far infrared laser has very high sensitivity to the components of the automobile exhaust, so that the sensitive detection of the components of the automobile exhaust can be realized.
Thirdly, the automobile exhaust remote sensing detection system based on the quantum cascade laser can be flexibly arranged on two sides of roads with different widths according to actual road conditions. The angle of a gold-plated right-angle reflecting mirror arranged on one side of a road is adjusted, so that middle and far infrared laser emitted by the quantum cascade laser is reflected in parallel and is detected and received by the pyroelectric sensor module. The adopted spectrum original data processing method can realize data processing and analysis under the conditions of complex road conditions and vehicle exhaust emission through fuzzy function membership degree judgment, artificial neural networks and other artificial intelligent algorithms.
Drawings
FIG. 1 is a schematic structural view of the present invention;
FIG. 2 is a schematic diagram of a quantum cascade laser driving circuit;
FIG. 3 is a schematic diagram of a pyroelectric sensor module detection circuit structure;
FIG. 4 is a flowchart of a spectral data processing routine;
FIG. 5 is a graph showing the level of the membership discriminant function of the fuzzy function
And a parameter calibration flow chart of the artificial neural network.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
As shown in fig. 1, the automobile exhaust remote sensing detection system based on the quantum cascade laser comprises an arbitrary function generator 1, a current pulse driving module 2, a quantum cascade laser 3, a polyethylene collimation focusing lens 4, a spectroscope 5, a chopper 6, a pyroelectric sensor module 7, a gold-plated right-angle reflector 8, a lock-in amplifier 9 and a computer 10;
a voltage signal generated by an arbitrary function generator 1 is input into a current pulse driving module 2, then the current pulse driving module 2 generates a current pulse to drive a quantum cascade laser 3, the quantum cascade laser 3 emits middle and far infrared laser with amplitude modulation under the driving of the current pulse, the middle and far infrared laser is collimated and parallelly emitted through a polyethylene collimating and focusing lens 4, the parallel middle and far infrared laser is divided into a reference light path and a detection light path through a spectroscope 5, the middle and far infrared laser of the reference light path is detected by a pyroelectric sensor module 7 of the reference light path after being modulated by a chopper 6, the middle and far infrared laser of the detection light path passes through an automobile exhaust emission region in driving and is reflected by a gold-plated right-angle reflector 8, the reflected middle and far infrared laser passes through the chopper 6, the polyethylene collimation focusing lens 4 is detected by a pyroelectric sensor module 7 of a detection light path. Sine wave signal components of the pyroelectric sensor module 7 of the detection light path, the pyroelectric sensor module 7 of the reference light path and the arbitrary function generator 1 are respectively input into the lock-in amplifier 9 for relevant operation, and the lock-in amplifier 9 outputs the result to the computer 10. The computer 10 performs subtraction operation on the correlation operation output value of the pyroelectric sensor module 7 of the reference light path and the correlation operation output value of the pyroelectric sensor module 7 of the detection light path, and performs data processing and spectrum analysis on the calculation result to finally obtain the measurement result of the automobile exhaust.
The spectroscope 5 is arranged right in front of the polyethylene collimating and focusing lens 4 and forms an angle of 45 degrees with the light rays which are collimated and emitted in parallel by the polyethylene collimating and focusing lens 4;
as shown in fig. 2, the voltage signal generated by the arbitrary function generator 1 is controlled by a computer, and three signals are generated: a rectangular pulse signal, a sawtooth wave signal and a sine wave signal; firstly, the quantum cascade laser works in a pulse state by rectangular pulse, so that the working temperature of the laser cannot be too high; secondly, the output wavelength of the quantum cascade laser is modulated by the sawtooth wave, and the wavelength variation range of the middle and far infrared rays output by the quantum cascade laser is in direct proportion to the amplitude of the rectangular wave; finally, the sine wave carries out sine modulation on the output middle and far infrared laser, so that the laser can detect the light intensity thereof by a related detection method, thereby improving the signal-to-noise ratio and the sensitivity of detection; the three signals are superposed in an arbitrary function generator 1 and then input into a current pulse driving module 2, the current pulse driving module 2 outputs a modulated current signal to drive a quantum cascade laser 3 after voltage and current conversion, the arbitrary function generator 1 outputs a superposed signal to the current pulse driving module 2 and simultaneously inputs a sine wave signal component in the superposed signal into a phase-locked amplifier 9 for signal correlation operation, and the phase-locked amplifier is connected to a computer 10.
As shown in fig. 3, the pyroelectric sensor module 7 includes a pyroelectric sensor 13, a resistor 12, and a filter capacitor 11; a pin 1 of the pyroelectric sensor 13 is simultaneously connected with a direct current voltage VCC and one end of the filter capacitor 11, a pin 2 is connected with one end of the resistor 12, a pin 3 is simultaneously connected with the other end of the resistor 12, and the other end of the filter capacitor 11 is connected with the phase-locked amplifier 9; the alternating current signal passing through the filter capacitor 11 is input into the phase-locked amplifier 9, meanwhile, the sine alternating current signal output by the phase-locked amplifier 9 drives the chopper 6 to rotate at a certain frequency, and the phase-locked amplifier 9 is connected to the computer 10; the polyethylene collimating and focusing lens 4 and the chopper 6 are placed right in front of the pyroelectric sensor module 7.
As shown in FIG. 4, the remote sensing detection method for the automobile exhaust based on the quantum cascade laser comprises steps 410-460, and the steps 410-460 are realized by processing spectral data through mean value filtering, spectral line type fitting, fuzzy algorithm, neural network algorithm and the like. The phase-locked amplifier outputs original spectral data obtained by measurement (step 410), random noise in the original spectral data is removed by using an average filtering function according to the frequency of a sawtooth wave in an arbitrary function generator (step 420), spectral data with different wavelengths under frequency sweeping are obtained after filtering, and the average filtering function adopts the period of the sawtooth wave signal in a synthesized signal to realize average filtering; the filtered spectral data is first fitted with a Forster (Voigt) linear function (step 430), which is described by equation 1 using the Forster (Voigt) linear function.
1
Wherein,
，
；
wherein:
γ D -width of gaussian linear function spectrum;
γ C -Lorentzian linear function spectral width;
meanwhile, the spectral width of the Foster linear function can be obtained
：
Wherein:
is the line width of collision of spectral lines；
Is the Doppler line width of the spectral line;
repeating n times and fitting with Voigt linear function to obtain n spectral distribution data of different spectral lines
(step 440). Obtaining the most probable absorption spectral line according to the fuzzy function membership judgment method for any spectral line data obtained by fitting (step 450), and if the set of the spectral data of the ith spectral line obtained by measurement is assumed to be U ═ toneu i1，u i2，u i3，…u im And if the data set of the standard spectral database of the ith spectral line is V ═ tonev i1，v i2，v i3，…v imI is a natural number, and i is less than or equal to m; m is a natural number; then the similarity coefficients of the set U and the set V are calculated:
if similarity coefficient
≥
The corresponding spectral line is judged as an absorption spectral line, so that the ith spectral line is obtained as an effective absorption spectral line, wherein
Is a level value calibrated in advance. Finally, inputting the spectral data of the effective absorption spectral line into an artificial neural network trained and calibrated in advanceProcessing, calculating the concentration of different gases in the automobile exhaust through an artificial neural network
(step 460) in which
Is the spectral data of the effective absorption line.
As shown in FIG. 5, the level value in the discriminant function of membership of the fuzzy function
And the parameter calibration process of the artificial neural network comprises the following steps:
starting (step 510); fixing the angles and positions of the gold-plated plane mirror, the quantum cascade laser and the pyroelectric detector (step 520); fixing the position of the long-path gas cell and the heating device (step 530); collecting a spectral output value of clean air at room temperature (step 540); the automobile exhaust under different working conditions can be simulated by mixing the pure gases in different proportions, wherein the types of the pure gases comprise CO and CO2、NO、NO2、NH3And SO2Filling automobile exhaust mixed in different proportions into a long-optical-path gas pool as gas to be calibrated in the calibration process (step 550); winding heating coils around the long-optical-path gas pool to uniformly heat the air in the long-optical-path gas pool, so that the temperature of the air in the long-optical-path gas pool changes along with the change of the setting conditions, and acquiring spectral data output values at different temperatures (step 560); the fuzzy function membership level value can be obtained by training according to the spectral data output value and the actual mixed concentration of the automobile exhaust
And artificial neural network parameters (step 570), obtaining fuzzy function membership level values according to the average value of N different measurement results
Simultaneously training an artificial neural network by using the data sample; if the error of the calibration result is more than 20%, re-calibration is needed, and the steps 540 to 570 are continuously executed in a circulating manner; otherwise, the calibration process is ended (step 590).
Claims (2)
1. The automobile exhaust remote sensing detection system based on the quantum cascade laser comprises an arbitrary function generator (1), a current pulse driving module (2), the quantum cascade laser (3), a polyethylene collimation focusing lens (4), a spectroscope (5), a chopper (6), a pyroelectric sensor module (7), a gold-plated right-angle reflector (8), a lock-in amplifier (9) and a computer (10);
voltage signals generated by an arbitrary function generator (1) are input into a current pulse driving module (2), then the current pulse driving module (2) generates current pulses to drive a quantum cascade laser (3), the quantum cascade laser (3) emits middle and far infrared laser with amplitude modulation under the driving of the current pulses, the middle and far infrared laser is collimated and parallelly emitted through a polyethylene collimating and focusing lens (4), the parallel middle and far infrared laser is divided into a reference light path and a detection light path through a spectroscope (5), the middle and far infrared laser of the reference light path is detected by a pyroelectric sensor module (7) of the reference light path after being modulated by a chopper (6), the middle and far infrared laser of the detection light path penetrates through an automobile exhaust emission area in driving and is reflected by a gold-plated right angle reflector (8), the reflected middle and far infrared laser passes through a chopper (6) and a polyethylene collimation focusing lens (4) and then is detected by a pyroelectric sensor module (7) of a detection light path; sine wave signal components of a pyroelectric sensor module (7) of a detection light path, a pyroelectric sensor module (7) of a reference light path and an arbitrary function generator (1) are respectively input into a phase-locked amplifier (9) for relevant operation, and the phase-locked amplifier (9) outputs results to a computer (10); the computer (10) performs subtraction operation on the correlation operation output value of the pyroelectric sensor module (7) of the reference light path and the correlation operation output value of the pyroelectric sensor module (7) of the detection light path, and performs data processing and spectrum analysis on the calculation result to finally obtain the measurement result of the automobile exhaust;
the spectroscope (5) is arranged right in front of the polyethylene collimating and focusing lens (4) and forms an angle of 45 degrees with the light rays which are collimated and emitted in parallel by the polyethylene collimating and focusing lens (4);
the arbitrary function generator (1) generates three signals which are respectively: the pulse laser comprises a rectangular pulse signal, a sawtooth wave signal and a sine wave signal, wherein the three voltage signals are superposed in an arbitrary function generator (1) and then input into a current pulse driving module (2), the current pulse driving module (2) outputs a modulated current signal to drive a quantum cascade laser (3) after voltage-current conversion, the arbitrary function generator (1) outputs a superposed signal to the current pulse driving module (2) and simultaneously inputs a sine wave signal component in the superposed signal into a phase-locked amplifier (9) to perform signal correlation operation, and the phase-locked amplifier is connected to a computer (10);
the pyroelectric sensor module (7) comprises a pyroelectric sensor (13), a resistor (12) and a filter capacitor (11); a pin 1 of the pyroelectric sensor (13) is simultaneously connected with a direct current voltage VCC and one end of a filter capacitor (11), a pin 2 is connected with one end of a resistor (12), the other end of a pin 3 and the other end of the resistor (12) are simultaneously grounded, and the other end of the filter capacitor (11) is connected with a phase-locked amplifier (9); the alternating current signal passing through the filter capacitor (11) is input into a phase-locked amplifier (9), meanwhile, a sine alternating current signal output by the phase-locked amplifier (9) drives a chopper (6) to rotate at a certain frequency, and the phase-locked amplifier (9) is connected to a computer (10); the polyethylene collimation focusing lens (4) and the chopper (6) are arranged right in front of the pyroelectric sensor module (7).
2. The method for using the automobile exhaust remote sensing detection system based on the quantum cascade laser device as claimed in claim 1, specifically comprising the following steps:
the remote sensing detection method of the automobile exhaust based on the quantum cascade laser comprises the following steps:
step (1), the lock-in amplifier outputs the original spectrum data obtained by measurement to a computer (10);
removing random noise in original spectral data by using an average filtering function according to the frequency of a sawtooth wave in an arbitrary function generator, specifically realizing average filtering by adopting the period of the sawtooth wave signal in a synthetic signal, and obtaining spectral data with different wavelengths under frequency sweeping after filtering;
step (3), firstly, fitting the filtered spectral data by using a Voigt linear function, wherein the Voigt linear function adopted by the fitting function is described by a formula (1);
wherein,
，
；
γ D -width of gaussian linear function spectrum;
γ C -Lorentzian linear function spectral width;
meanwhile, the spectral width of the Foster linear function can be obtained：
Wherein:
is the collision line width of the spectral lines;
is the Doppler line width of the spectral line;
repeating the fitting for n times by using a Voigt linear function to obtain the spectral distribution data of n different spectral lines
Obtaining the most probable absorption spectral line according to the fuzzy function membership degree judgment method for any spectral line data obtained by fitting, and setting the set of the spectral data of the ith spectral line obtained by measurement as U ═ toneu i1，u i2，u i3，…u im At the same time, the set of standard spectral data of the ith spectral line is V ═ fv i1，v i2，v i3，…v imI is a natural number, and i is less than or equal to m; m is a natural number; then calculating similarity coefficients of the set U and the set V
：
If similarity coefficient
≥
The corresponding spectral line is judged as an absorption spectral line, so that the ith spectral line is obtained as an effective absorption spectral line, wherein
The level value is calibrated in advance;
and (5) finally, inputting the spectral data of the effective absorption spectrum line into an artificial neural network trained and calibrated in advance for processing, and calculating the concentrations of different gases in the automobile exhaust through the artificial neural network
Wherein
Is the spectral data of the effective absorption line;
the level value in the fuzzy function membership degree discriminant function in the step (4) and the step (5)
And the parameter calibration process of the artificial neural network is as follows:
(a) fixing the angles and the positions of the gold-plated plane reflecting mirror, the quantum cascade laser and the pyroelectric detector; fixing the position of the long optical path gas pool and a heating device; collecting a spectral output value of clean air at room temperature;
(b) the method comprises the following steps of simulating automobile exhaust under different working conditions by mixing pure gases in different proportions, and filling the simulated automobile exhaust into a long-optical-path gas pool as gas to be calibrated in the calibration process;
the pure gas comprises CO and CO2、NO、NO2、NH3And SO2；
(c) Winding heating coils around the long-optical-path gas pool to uniformly heat air in the long-optical-path gas pool, so that the temperature of the air in the long-optical-path gas pool changes along with the change of the setting conditions, and acquiring spectral data output values at different temperatures;
one end of the long optical path gas pool is provided with a gold-plated right-angle reflecting mirror, and the other end of the long optical path gas pool is provided with a quantum cascade laser and a pyroelectric sensor module of a detection light path;
(d) training to obtain a fuzzy function membership level value according to the actual mixing proportion of the spectral data output value and the simulated automobile exhaust
And artificial neural network parameters, and obtaining the membership level value of the fuzzy function according to the average value of N times of different measurement results
Simultaneously training an artificial neural network by using the data sample; if the error of the calibration result is more than 20%, re-calibration is needed; otherwise, ending the calibration process.
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