CN114047136A - High-sensitivity combined light source type photoacoustic spectroscopy multi-component gas detection system and method - Google Patents
High-sensitivity combined light source type photoacoustic spectroscopy multi-component gas detection system and method Download PDFInfo
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Abstract
The invention provides a high-sensitivity combined light source type photoacoustic spectroscopy multi-component gas detection system and method, and belongs to the technical field of gas detection. Laser is incited to the optoacoustic cell from the aperture of trompil concave surface speculum, makes laser produce multiple reflection in order to increase the gas absorption journey between trompil concave surface speculum and the plane reflecting mirror of installing on the light filter switching wheel, and the reflection number of times can exceed 20 times to optoacoustic signal has been strengthened by a wide margin, adopts trompil concave surface speculum to hardly destroy the optical path of infrared thermal radiation light source's axial incident light sum reverberation simultaneously, thereby makes middle infrared thermal radiation light form the double pass in the optoacoustic cell and absorbs in order to strengthen optoacoustic signal. The invention fully utilizes the advantages of the photoacoustic spectrometry and the laser photoacoustic spectrometry based on the mid-infrared thermal radiation light source, which are respectively suitable for measuring multi-component gas and have high detection precision, realizes technical complementation and provides a technical scheme with strong competitiveness for the high-sensitivity detection of multi-component trace gas.
Description
Technical Field
The invention belongs to the technical field of gas detection, and relates to a high-sensitivity combined light source type photoacoustic spectroscopy multi-component gas detection system and method.
Background
The photoacoustic spectrometry gas detection technology has the remarkable advantages of high sensitivity, more measurement components, no gas consumption, small sampling amount and the like, and plays an important role in the analysis of dissolved gas in transformer oil and other applications. Power transformer for connecting different powerThe operation reliability of the core component of the pressure class is directly related to the stable and safe operation of the power system. At present, oil-immersed transformers are generally adopted in large-scale power transformers, insulating oil is a mixture composed of hydrocarbon molecules with different molecular weights, and during long-term operation, faults such as overheating and discharging cause the insulating oil and insulating paper to crack so as to generate various characteristic gases (mainly comprising CH)4、C2H6、C2H4、C2H2CO and CO2) Most of these gases are dissolved in oil. The analysis of the components and the content of the dissolved gas in the oil can judge the type and the severity of the latent insulation fault in the transformer, so that the real-time monitoring of the dissolved gas in the oil has important significance for the reliable operation of a power grid.
Photoacoustic spectroscopy is a spectral calorimetry technique that directly measures the heat generated by a gas due to the absorption of light energy, and is a background-free absorption spectroscopy technique. The photoacoustic spectroscopy is mainly classified into photoacoustic spectroscopy based on a mid-infrared thermal radiation light source and laser photoacoustic spectroscopy according to different photoacoustic excitation light sources. The mid-infrared thermal radiation light source has a wide spectral emission range and covers the characteristic absorption band of most polar gas molecules. The photoacoustic spectrometer based on the mid-infrared thermal radiation light source can detect various gas components by selecting optical filters with different central wavelengths, but has the problems of low detection sensitivity and large cross interference. British Kelman corporation first developed a photoacoustic spectroscopy analysis device for gas dissolved in oil based on a blackbody radiation infrared broad spectrum light source, and can perform online monitoring on various characteristic gases in oil. The laser has the characteristics of narrow line width, large spectral power density and the like, the signal-to-noise ratio of photoacoustic measurement can be greatly improved by adopting a second harmonic detection technology, and meanwhile, the measurement error caused by the overlapping of spectral lines of multi-component gas is reduced. However, laser light sources, particularly mid-infrared lasers, are expensive, and the existing laser photoacoustic spectrometers only have great advantages in detection of trace gases with few components. In the analysis application of the dissolved gas in the transformer oil, the photoacoustic spectrometer based on the mid-infrared thermal radiation light source which is commonly adopted at present has the following problems: acetylene and methane, etc. due to cross-interference and background absorptionThe detection sensitivity of the gas is not high enough. The document Chen K, Gong Z, Yu Q.Fiber-amplified photosynthetic sensor for sub-ppb level acetyl ethylene detection [ J]Sensors and Actuators A: Physical,2018,274:184-4gas detection[J]Optical Express,2021,29(9): 13600-. The patent 'an optoacoustic spectrum multi-component trace gas detection instrument and method' can realize the measurement of multi-component gas by utilizing a mid-infrared thermal radiation light source and a laser light source, but is influenced by factors with short absorption range, and the sensitivity is still required to be improved. Therefore, the high-sensitivity photoacoustic spectroscopy system has important application value in multi-component trace gas detection.
Disclosure of Invention
The invention aims to provide a high-sensitivity combined light source type photoacoustic spectroscopy multi-component gas detection system and method, aims to solve the problems that individual gas detection precision is low and mid-infrared thermal radiation light and laser are difficult to be simultaneously and efficiently coupled to a photoacoustic cell in a photoacoustic spectroscopy based on a mid-infrared thermal radiation light source, and expands a larger space for the application of a photoacoustic spectroscopy multi-component trace gas detection technology in the trace gas detection field.
The technical scheme of the invention is as follows:
a high-sensitivity combined light source type photoacoustic spectroscopy multi-component gas detection system comprises a mid-infrared thermal radiation light source 1, a collimating lens 2, a chopper 3, an optical filter switching wheel 4, a window sheet 5, a photoacoustic cell 6, a laser light source module 7, an optical fiber coupler 8, an optical fiber collimator 9, an open-hole concave reflector 10, an air inlet valve 11, an air outlet valve 12, a microphone 13, a control and signal processing circuit 14 and a computer 15; after wide spectrum light emitted by the intermediate infrared thermal radiation light source 1 is focused by the collimating lens 2, the wide spectrum light is modulated by the chopper 3; the control and signal processing circuit 14 controls the optical filter switching wheel 4, modulated light penetrates through one optical filter in the optical filter switching wheel 4, then enters the photoacoustic cell 6 through the window sheet 5, and is reflected by the perforated concave reflecting mirror 10 to generate double-pass absorption enhancement in the photoacoustic cell; the modulation signal output by the control and signal processing circuit 14 modulates the wavelength of the laser light source module 7; two beams of laser in the laser source module 7 pass through the optical fiber coupler 8 and then pass through the optical fiber collimator 9 to be collimated, and then are incident into the photoacoustic cell 6 from the small hole of the perforated concave reflector 10; the photoacoustic cell 6 is provided with an air inlet valve 11 and an air outlet valve 12 which are used for controlling the inlet and the outlet of the gas to be measured; a microphone 13 is mounted on the photoacoustic cell 6 for detecting photoacoustic signals generated in the photoacoustic cell 6; the signal input end of the control and signal processing circuit 14 is connected with the microphone 13, and digital signal processing is carried out after photoacoustic signals are collected; the computer 15 is connected with the control and signal processing circuit 14 and is used for setting the working parameters of the control and signal processing circuit 14 and displaying the output photoacoustic signal measured value.
A high-sensitivity combined light source type photoacoustic spectroscopy multi-component gas detection method is characterized in that mid-infrared thermal radiation light and laser are efficiently coupled into the same small-volume photoacoustic cell, and high-sensitivity detection of multi-component gas is realized through multiple reflection and absorption enhancement; the method comprises the following specific steps:
firstly, after receiving a control instruction input by a computer 15, a control and signal processing circuit 14 opens an air inlet valve 11 and an air outlet valve 12 to make the gas to be measured fill the photoacoustic cell 6 and set working parameters; after wide spectrum light emitted by the intermediate infrared thermal radiation light source 1 is converged by the collimating lens 2, the light intensity is modulated by the chopper 3; the control and signal processing circuit 14 controls the optical filter switching wheel 4, and the different component gases are respectively measured by switching the optical filters in the optical filter switching wheel 4; modulated light penetrates through one optical filter in the optical filter switching wheel 4, then enters the photoacoustic cell 6 through the window piece 5, is reflected by the perforated concave reflecting mirror 10, and then generates double-pass absorption enhancement in the photoacoustic cell.
Then, the control and signal processing circuit 14 controls the optical filter switching wheel 4, and rotates the plane mirror 16 installed on the optical filter switching wheel 4 to the front of the window piece 5; the output modulation signal of the control and signal processing circuit 14 is formed by superposing a sine signal with fixed frequency and a sawtooth wave signal, and the modulation signal is input into the laser light source module 7 to change the working current of the laser so as to realize the modulation and scanning of the laser wavelength; two bundles of laser in the laser source module 7 pass through the optical fiber coupler 8, and then pass through the optical fiber collimator 9 to carry out beam collimation, and the aperture from the trompil concave surface reflector 10 is incited to the optoacoustic cell 6, and laser light sees through window piece 5 and produces multiple reflection at trompil concave surface reflector 10 and plane mirror 16, and the number of reflection exceeds 20, increases substantially the gas to laser energy's absorption journey.
After the gas molecules to be measured in the photoacoustic cell 6 absorb light energy, part of the molecules are excited to an excited state and return to a ground state after radiationless transition, and the energy of the molecules is converted into periodic temperature change of the gas in the form of translation energy, so that photoacoustic signals are generated in the photoacoustic cell 6; the microphone 13 converts the detected photoacoustic signal into an electrical signal and inputs the electrical signal to the signal input end of the control and signal processing circuit 14, the photoacoustic signal excited by the mid-infrared thermal radiation light source 1 adopts an intensity modulation-fundamental wave detection method, and the photoacoustic signal excited by the laser light source module 7 adopts a wavelength modulation-second harmonic detection method; the control and signal processing circuit 14 respectively processes fundamental wave and second harmonic wave signals, and then displays the measured concentration value of the multi-component gas on the computer 15; finally, the control and signal processing circuit 14 controls the opening of the inlet valve 11 and the outlet valve 12 to discharge the gas.
The wavelength of the emission spectrum of the intermediate infrared thermal radiation light source 1 is 3-12 μm, and the infrared absorption spectrum wave band of ethane, ethylene, carbon monoxide and carbon dioxide gas molecules is covered.
The working frequency of the chopper 3 is 20-200 Hz.
The optical filter switching wheel 4 is provided with 1 plane reflector and 4 band-pass infrared optical filters. The plane mirror is used for enhancing laser photoacoustic signals through multiple reflection when methane and acetylene are measured; the center wavelengths of the 4 bandpass infrared filters correspond to the absorption peaks of ethane, ethylene, carbon monoxide and carbon dioxide, respectively.
The transmission wavelength range of the window sheet 5 is 1.5-12 μm, and both the mid-infrared light and the near-infrared light emitted by the mid-infrared thermal radiation light source 1 and the laser light source module 7 can penetrate through the window sheet 5.
The photoacoustic cell 6 is a non-resonant photoacoustic cell, and the diameter of an internal air chamber is 10mm, and the length of the internal air chamber is 30 mm.
The laser light source module 7 is composed of two near-infrared tunable lasers and is used for measuring acetylene and methane respectively.
The splitting ratio of the optical fiber coupler 8 is 50: 50.
The middle of the perforated concave reflector 10 is provided with a small hole with the aperture of 0.5 mm.
The control and signal processing circuit 14 extracts fundamental and second harmonic photoacoustic signals simultaneously.
The principle of the invention is as follows: the middle infrared thermal radiation light and the laser are simultaneously and efficiently coupled to a specially designed cylindrical photoacoustic cell, wherein the middle infrared thermal radiation light is condensed and then enters the photoacoustic cell from a window sheet through an infrared band-pass filter, and after being reflected by an open-hole concave reflector, the middle infrared thermal radiation light generates double-pass absorption enhancement in the photoacoustic cell, and the photoacoustic signal is measured by adopting an intensity modulation-fundamental wave detection technology, so that the high-sensitivity detection of ethane, ethylene, carbon monoxide and carbon dioxide gas is realized; laser is emitted to the photoacoustic cell from the small hole of the perforated concave reflecting mirror through the optical fiber collimator, multiple reflection is generated between the perforated concave reflecting mirror and the plane reflecting mirror arranged on the optical filter switching wheel by the laser, the photoacoustic signal is measured by adopting a wavelength modulation-second harmonic detection technology, the interference of the fundamental frequency photoacoustic signal generated by the solid photoacoustic effect due to the multiple reflection on the surface of the cell wall is eliminated, background-free detection is realized, and high-sensitivity detection on methane and acetylene gas is realized.
The invention has the advantages that: by adopting the scheme of fusing the intermediate infrared thermal radiation light source and the laser light source, the advantages of high measurement precision and high detection precision of multi-component gas respectively possessed by the photoacoustic spectrometry and the laser photoacoustic spectrometry based on the intermediate infrared thermal radiation light source are fully utilized, and technical complementation is realized. Laser is incited to the optoacoustic cell from the aperture of trompil concave surface speculum, makes laser produce multiple reflection in order to increase the gas absorption journey between trompil concave surface speculum and the plane reflecting mirror of installing on the light filter switching wheel, and the reflection number of times can exceed 20 times to optoacoustic signal has been strengthened by a wide margin, adopts trompil concave surface speculum to hardly destroy the optical path of infrared thermal radiation light source's axial incident light sum reverberation simultaneously, thereby makes middle infrared thermal radiation light form the double pass in the optoacoustic cell and absorbs in order to strengthen optoacoustic signal. The structure can enable two kinds of photoacoustic excitation light to be efficiently coupled at the same time, and compared with a scheme that one photoacoustic cell is matched with one light source, the structure of the system is effectively simplified, and the requirement on the gas sample amount is reduced. The invention provides a very competitive technical scheme for high-sensitivity detection of multi-component trace gas.
Drawings
Fig. 1 is a schematic structural view of the present invention.
Fig. 2 is a schematic structural diagram of the filter switching wheel.
In the figure: 1 a mid-infrared thermal radiation light source; 2 a collimating lens; 3, a chopper; 4 optical filter switching wheel;
5 window sheets; 6, a photoacoustic cell; 7 laser light source module; 8, a fiber coupler; 9 a fiber collimator;
10 opening a concave reflector; 11 an intake valve; 12 an air outlet valve; 13 a microphone;
14 control and signal processing circuitry; 15 a computer; 16 plane mirrors;
17 mid-infrared bandpass filters for ethane measurement;
18 a mid-infrared bandpass filter for measuring ethylene;
19 a mid-infrared band pass filter for measuring carbon monoxide;
20 mid-infrared band pass filters for measuring carbon dioxide.
Detailed Description
The following detailed description of the invention refers to the accompanying drawings.
A high-sensitivity combined light source type photoacoustic spectroscopy multi-component gas detection system mainly comprises a mid-infrared thermal radiation light source 1, a collimating lens 2, a chopper 3, an optical filter switching wheel 4, a window sheet 5, a photoacoustic cell 6, a laser light source module 7, an optical fiber coupler 8, an optical fiber collimator 9, an open-hole concave reflector 10, an air inlet valve 11, an air outlet valve 12, a microphone 13, a control and signal processing circuit 14 and a computer 15. After receiving a control instruction input by the computer 15, the control and signal processing circuit 14 opens the air inlet valve 11 and the air outlet valve 12 to make the gas to be measured fill the photoacoustic cell 6 and set working parameters; after wide spectrum light emitted by the intermediate infrared thermal radiation light source 1 is converged by the collimating lens 2, the light intensity is modulated by the chopper 3; the control and signal processing circuit 14 controls the optical filter switching wheel 4, and the different component gases are respectively measured by switching the optical filters in the optical filter switching wheel 4; modulated light penetrates through one optical filter in the optical filter switching wheel 4, is incident into the photoacoustic cell 6 through the window sheet 5, is reflected by the perforated concave reflecting mirror 10, and then generates double-pass absorption enhancement in the photoacoustic cell; the control and signal processing circuit 14 controls the optical filter switching wheel 4, and rotates the plane mirror 16 arranged on the optical filter switching wheel 4 to the front of the window piece 5; the output modulation signal of the control and signal processing circuit 14 is formed by superposing a sine signal with fixed frequency and a sawtooth wave signal, and the modulation signal is input into the laser light source module 7 to change the working current of the laser so as to realize the modulation and scanning of the laser wavelength; two beams of laser in the laser source module 7 pass through the optical fiber coupler 8 and then pass through the optical fiber collimator 9 to be collimated, the laser beams are incident into the photoacoustic cell 6 from the small hole of the perforated concave reflector 10, and the laser beams are reflected for multiple times on the perforated concave reflector 10 and the plane reflector 16 through the window sheet 5, so that the absorption range of the gas to the laser energy is greatly improved; after the gas molecules to be measured in the photoacoustic cell 6 absorb light energy, part of the molecules are excited to an excited state and return to a ground state after radiationless transition, and the energy of the molecules is converted into periodic temperature change of the gas in the form of translation energy, so that photoacoustic signals are generated in the photoacoustic cell 6; the microphone 13 converts the detected photoacoustic signal into an electrical signal and inputs the electrical signal to the signal input end of the control and signal processing circuit 14, the photoacoustic signal excited by the mid-infrared thermal radiation light source 1 adopts an intensity modulation-fundamental wave detection method, and the photoacoustic signal excited by the laser light source module 7 adopts a wavelength modulation-second harmonic detection method; the control and signal processing circuit 14 respectively processes fundamental wave and second harmonic wave signals, and then displays the measured concentration value of the multi-component gas on the computer 15; the control and signal processing circuit 14 controls the opening of the inlet valve 11 and the outlet valve 12 to discharge the gas.
Wherein, the coverage wavelength range of the mid-infrared heat radiation light source 1 is 3-12 μm. The operating frequency of the chopper 3 is 40 Hz. The filter switching wheel 4 is provided with 1 plane reflector and 4 band-pass infrared filters. The window piece 5 is a film-coated zinc selenide window piece, and the transmission wavelength range is 1.5-12 mu m; the photoacoustic cell 6 is a non-resonant photoacoustic cell, and the diameter of an internal air chamber is 10mm, and the length of the internal air chamber is 30 mm.
The laser light source module 7 consists of two near-infrared narrow linewidth DFB lasers, the central wavelengths of which are 1532nm and 1653nm respectively, and the lasers are used for measuring acetylene and methane gas respectively. The splitting ratio of the fiber coupler 8 is 50: 50. The middle of the open concave reflector 10 is provided with a small hole with the aperture of 0.5 mm. The control and signal processing circuit 14 is a high performance digital lock-in amplifier that can extract both fundamental and second harmonic photoacoustic signals.
Fig. 2 is a schematic structural diagram of the filter switching wheel. The filter switching wheel 4 is provided with a plane mirror 16, a mid-infrared band-pass filter 17 for measuring ethane, a mid-infrared band-pass filter 18 for measuring ethylene, a mid-infrared band-pass filter 19 for measuring carbon monoxide and a mid-infrared band-pass filter 20 for measuring carbon dioxide. The central wavelength of the mid-infrared band-pass filter 17 for ethane measurement was 3.3 μm, the central wavelength of the mid-infrared band-pass filter 18 for ethylene measurement was 10.5 μm, the central wavelength of the mid-infrared band-pass filter 19 for carbon monoxide measurement was 4.6 μm, and the central wavelength of the mid-infrared band-pass filter 20 for carbon dioxide measurement was 4.3 μm.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A high-sensitivity combined light source type photoacoustic spectroscopy multi-component gas detection system is characterized by comprising a mid-infrared thermal radiation light source (1), a collimating lens (2), a chopper (3), a light filter switching wheel (4), a window sheet (5), a photoacoustic cell (6), a laser light source module (7), an optical fiber coupler (8), an optical fiber collimator (9), an open-hole concave reflecting mirror (10), an air inlet valve (11), an air outlet valve (12), a microphone (13), a control and signal processing circuit (14) and a computer (15); wide spectrum light emitted by the intermediate infrared thermal radiation light source (1) is focused by the collimating lens (2) and then is modulated by light through the chopper (3); the control and signal processing circuit (14) controls the optical filter switching wheel (4), modulated light penetrates through one optical filter in the optical filter switching wheel (4), then enters the photoacoustic cell (6) through the window sheet (5) arranged at one end of the photoacoustic cell (6), is reflected by the perforated concave reflecting mirror (10) arranged at the other end of the photoacoustic cell (6), and generates double-pass absorption enhancement in the photoacoustic cell (6); the modulation signal output by the control and signal processing circuit (14) modulates the wavelength of the laser light source module (7); two beams of laser in the laser source module (7) pass through the optical fiber coupler (8), then pass through the optical fiber collimator (9) to be collimated, and enter the photoacoustic cell (6) from the small hole of the perforated concave reflector (10); an air inlet valve (11) and an air outlet valve (12) are arranged on the photoacoustic cell (6) and are used for controlling the gas to be detected to enter and discharge; the microphone (13) is arranged on the photoacoustic cell (6) and is used for detecting photoacoustic signals generated in the photoacoustic cell (6); the signal input end of the control and signal processing circuit (14) is connected with the microphone (13), and digital signal processing is carried out after photoacoustic signals are collected; the computer (15) is connected with the control and signal processing circuit (14) and is used for setting the working parameters of the control and signal processing circuit (14) and displaying the output photoacoustic signal measured value.
2. A high sensitivity combined light source type photoacoustic spectrometry multi-component gas detection system according to claim 1, wherein the aperture of the aperture concave mirror (10) is 0.5 mm.
3. A high sensitivity combined light source type photoacoustic spectroscopy multicomponent gas detection system according to claim 1 or 2, wherein the photoacoustic cell (6) is a non-resonant photoacoustic cell, and has an internal gas cell with a diameter of 10mm and a length of 30 mm.
4. The high-sensitivity combined light source type photoacoustic spectrometry multi-component gas detection system according to claim 1 or 2, wherein 1 plane mirror and 4 bandpass infrared filters are installed on the filter switching wheel (4); the laser light source module (7) consists of two near-infrared tunable lasers which are respectively used for measuring acetylene and methane; the splitting ratio of the optical fiber coupler (8) is 50: 50.
5. A high sensitivity combined light source type photoacoustic spectroscopy multi-component gas detection system according to claim 3, wherein the filter switching wheel (4) is installed with 1 plane mirror and 4 bandpass infrared filters; the laser light source module (7) consists of two near-infrared tunable lasers which are respectively used for measuring acetylene and methane; the splitting ratio of the optical fiber coupler (8) is 50: 50.
6. A high-sensitivity combined light source type photoacoustic spectroscopy multi-component gas detection method is characterized in that mid-infrared thermal radiation light and laser are efficiently coupled into the same small-volume photoacoustic cell, and high-sensitivity detection of multi-component gas is realized through multiple reflection and absorption enhancement; the method is characterized by comprising the following steps:
firstly, after a control and signal processing circuit (14) receives a control instruction input by a computer (15), an air inlet valve (11) and an air outlet valve (12) are opened, so that a photoacoustic cell (6) is filled with gas to be detected, and working parameters are set; after wide spectrum light emitted by the intermediate infrared thermal radiation light source (1) is converged by the collimating lens (2), the light intensity is modulated by the chopper (3); the control and signal processing circuit (14) controls the optical filter switching wheel (4), and different component gases are respectively measured by switching the optical filters in the optical filter switching wheel (4); modulated light penetrates through one optical filter in the optical filter switching wheel (4), enters the photoacoustic cell (6) through the window sheet (5), is reflected by the perforated concave reflecting mirror (10) and then generates double-pass absorption enhancement in the photoacoustic cell;
then, a control and signal processing circuit (14) controls the optical filter switching wheel (4) and rotates a plane mirror (16) arranged on the optical filter switching wheel (4) to the front of the window sheet (5); the output modulation signal of the control and signal processing circuit (14) is formed by superposing a sine signal and a sawtooth wave signal with fixed frequency, and the modulation signal is input into the laser light source module (7) to change the working current of the laser so as to realize the modulation and scanning of the laser wavelength; two beams of laser in the laser source module (7) pass through the optical fiber coupler (8) and then pass through the optical fiber collimator (9) to be collimated, the laser beams are emitted into the photoacoustic cell (6) from the small hole of the perforated concave reflector (10), the laser beams are reflected for more than 20 times on the perforated concave reflector (10) and the plane reflector (16) through the window sheet (5), and the absorption range of gas to laser energy is greatly improved;
after the gas molecules to be measured in the photoacoustic cell (6) absorb light energy, part of the molecules are excited to an excited state and return to a ground state after radiationless transition, and the energy of the molecules is converted into periodic temperature change of the gas in the form of translation energy, so that photoacoustic signals are generated in the photoacoustic cell (6); the microphone (13) converts detected photoacoustic signals into electric signals and then inputs the electric signals into the signal input end of the control and signal processing circuit (14), the photoacoustic signals excited by the intermediate infrared thermal radiation light source (1) adopt an intensity modulation-fundamental wave detection method, and the photoacoustic signals excited by the laser light source module (7) adopt a wavelength modulation-second harmonic detection method; the control and signal processing circuit (14) respectively processes fundamental wave and second harmonic wave signals and then displays the measured concentration values of the multi-component gas on the computer (15); finally, the control and signal processing circuit (14) controls the opening of the air inlet valve (11) and the air outlet valve (12) to discharge the gas.
7. The high-sensitivity combined light source type photoacoustic spectrometry multi-component gas detection method according to claim 6, wherein the mid-infrared thermal radiation light source (1) has an emission spectrum with a wavelength of 3-12 μm covering the infrared absorption spectrum bands of ethane, ethylene, carbon monoxide and carbon dioxide gas molecules.
8. The high-sensitivity combined light source type photoacoustic spectrometry multi-component gas detection method according to claim 6 or 7, wherein the chopper (3) has an operating frequency of 20-200 Hz.
9. The high-sensitivity combined light source type photoacoustic spectrometry multi-component gas detection method according to claim 6 or 7, wherein the window sheet (5) has a transmission wavelength range of 1.5-12 μm, and both the mid-infrared light and the near-infrared light emitted from the mid-infrared thermal radiation light source (1) and the laser light source module (7) can pass through the window sheet (5).
10. The method for detecting the multi-component gas by the combined light source type photoacoustic spectroscopy according to claim 8, wherein the window sheet (5) has a transmission wavelength in the range of 1.5 to 12 μm, and both the mid-infrared light and the near-infrared light emitted from the mid-infrared thermal radiation light source (1) and the laser light source module (7) can pass through the window sheet (5).
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