Laser photoacoustic spectrum detection device for measuring multi-component gas by adopting single photoacoustic cell
Technical Field
The invention belongs to the technical field of photoacoustic spectroscopy gas detection, and particularly relates to an on-line monitoring or off-line detection device for characteristic gas components in the industries of electric power, nuclear energy and petrochemical industry.
Background
Various gases capable of reflecting fault properties and insulating aging properties can be decomposed and generated inside equipment such as a power transformer, a GIS and the like in the power/nuclear energy industry; the method has the advantages that fault and aging characteristic gas is accurately detected, and the method is the key for realizing the diagnosis of the operation state of important power transformation equipment; the raw materials of basic chemical materials such as ethanol and fine chemical products are mainly natural gas, and the accurate real-time monitoring of the raw materials and the gas components and content in the production process is the core for ensuring the quality of the chemical products. Real-time accurate detection of CO and CO2、CH4(methane), C2H4(ethylene) C2H6(ethane), C2H2(acetylene), H2、SO2F2(sulfuryl difluoride), CF4(carbon tetrafluoride), SO2、H2S, COS (hydroxyl sulfur) and other gases have important significance for ensuring the operation safety of equipment or the product quality in the industries of electric power, nuclear energy, petrochemical industry and the like. The traditional detection methods include a chromatographic method, an electrochemical sensor method, a nano sensor method, an absorption spectrum method and the like. The chromatographic column needs to be replaced regularly, so that the detection cost and the labor consumption are increased, and the long-term online monitoring of equipment cannot be realized; the types and sensitivity of gases detected by an electrochemical sensor method are limited; the poor repeatability of the nanosensor method has not been effectively solved. Spectroscopy detectionGas is a popular novel detection method in recent years, wherein an absorption spectrum method is easily influenced by light scattering and refraction, an absorption cell with a long optical path is required, and the cost is high; the Fourier infrared spectroscopy has a complex structure, and the accuracy of quantitative analysis needs to be improved; the detection sensitivity of the Raman spectroscopy is low, and the trace gas cannot be detected. The photoacoustic spectrometry is a background-free measurement method, is not influenced by light scattering, and has wide application market in the field of gas detection. The core components of the device mainly comprise a light source, a photoacoustic conversion cell, an acoustoelectric converter, a background noise deduction module and the like. However, the conventional photoacoustic spectroscopy is easily interfered by vibration, noise and temperature change of the surrounding environment, and the resonant frequency of the resonant photoacoustic cell drifts due to the change of the gas components inside the photoacoustic cell. When the gas is measured for a long time, impurities and corrosive gas in the gas to be measured can pollute the corrosion microphone and influence the acoustic characteristics of the corrosion microphone.
The differential photoacoustic cell can effectively weaken the interference caused by the vibration, noise and temperature change of the surrounding environment, and the gas to be detected is not in contact with the acoustic-electric converter, so that the corrosion to the acoustic-electric converter can be effectively avoided. The resonant photoacoustic cell can form standing wave amplification on photoacoustic signals in the photoacoustic cell, so that the detection sensitivity of the system is further improved, the cylindrical resonant photoacoustic cell can be divided into three resonant modes, namely a longitudinal resonant mode, an angular resonant mode and a radial resonant mode according to different standing wave distribution modes, wherein the resonant photoacoustic cell working in the longitudinal resonant mode has the highest constant, and the standing wave amplification effect on the photoacoustic signals is most obvious. However, most of the traditional differential photoacoustic cells adopt a mode of matching a single photoacoustic cell with a single laser, the differential photoacoustic cell is only filled with one standard gas of a component to be detected, only the detection of a single gas can be met, and the system structure becomes very complicated when the types of the detected gases are more.
Disclosure of Invention
The invention aims to solve the technical problem of providing a device for on-line monitoring or off-line detection of characteristic gas components in the industries of electric power, nuclear energy and petrochemical industry, which can carry out real-time on-line monitoring or off-line detection on the content of the characteristic gas components in the industries of electric power, nuclear energy and petrochemical industry, and has the characteristics of simultaneous monitoring of various components, no consumption of carrier gas, no pollution, strong anti-interference capability, simple device, high detection sensitivity, no maintenance and the like. The invention adopts a mode of quantum cascade laser array, couples a plurality of laser beams into a beam path, and realizes the function of measuring the multi-component gas by a single-differential resonance type photoacoustic cell in a mode of pre-charging the multi-component gas with specific concentration in the photoacoustic cell according to the gas absorption ratio.
The technical scheme of the invention is as follows: the system is characterized by comprising an on-line monitoring or off-line detection system for characteristic gas components in the industries of electric power, nuclear energy and petrochemical industry, wherein the system is connected to a characteristic gas intake of equipment to be monitored or used for extracting process gas in the production process of products during detection, a particulate matter filtering device, a gas drying device, a first electromagnetic switch valve, a pressure sensor, a reference gas chamber to be detected, a second electromagnetic switch valve, a sonic nozzle and a vacuum pump are sequentially connected to a stop valve, and the characteristic gas to be detected is sequentially passed through the modules and finally discharged through the vacuum pump; the detection device comprises a quantum cascade laser array module, a spectroscope module, a reference gas chamber to be detected, a differential resonance photoacoustic cell, an acoustoelectric conversion module, a thermostat, an optical power detector, a light extinction cell, a phase-locked amplification circuit and an industrial personal computer.
The quantum cascade laser array module comprises a laser driving and temperature control module, a quantum cascade laser array, light path calibration lasers, a full-wavelength full-reflection mirror and a specific-wavelength full-reflection mirror, wherein each quantum cascade laser can excite ultra-narrow line width lasers aiming at single or multiple characteristic gas component absorption peaks, the ultra-narrow line width lasers are focused by a focusing lens and then converged to the same light path through the full-reflection mirror and the full-wavelength full-reflection mirror to be emitted into a spectroscope module, and the concentration of each component gas can be reflected by detecting photoacoustic signals generated by lasers with different wavelengths. The light path calibration laser is laser with visible wavelength, is converged by a total reflection mirror with specific wavelength and then is emitted into the spectroscope module, is used for calibrating the light path of the quantum cascade laser array module and is not used for exciting gas to be detected to generate photoacoustic signals, and is visible light with the wavelength of 0.38-0.78 mu m. The laser driving and temperature control module can freely adjust the current according to the actual situation, the output voltage range is 0-20V, the output current is 0-1A, the current stability is superior to 0.1mA, the kHz modulation output can be realized according to the requirement, the chip temperature control is realized by combining a semiconductor cooler (TEC), and the wavelength of the chip is accurately adjusted. And the lasers in the laser driving and temperature control module are switched in an analog switch mode, so that different wavelength outputs are realized.
The quantum cascade laser array can realize the function of detecting multiple gas components by a single laser, wherein:
1) when the device is used for detecting the power and nuclear transformer:
the wavelength tunable range of the first configured quantum cascade laser is 7.10-7.38 mu m, and the wavelength covers C2H4、 CH4、C2H2Characteristic absorption peaks of the three gases, selected C2H4、CH4、C2H2The characteristic absorption peak wavelengths of the gas are respectively positioned at 7.10 μm, 7.38 μm and 7.37 μm;
the wavelength tunable range of the second configured quantum cascade laser is 4.34-4.54 μm, and the wavelength covers CO and CO2Characteristic absorption peaks of two gases, selected from CO and CO2The characteristic absorption peak wavelengths of the gas are respectively positioned at 4.54 μm and 4.34 μm;
the third arranged quantum cascade laser has a wavelength of 3.35 μm and covers C2H6Characteristic absorption peak of gas, selected C2H6The characteristic absorption peak wavelength of the gas lies at 3.35 μm.
2) SF (sulfur hexafluoride) equipment for detecting electric power GIS (gas insulated switchgear)6When the gas is decomposed:
the wavelength of the quantum cascade laser I is 7.07 mu m, and the wavelength covers H2Characteristic absorption peak of S gas, selected H2The characteristic absorption peak wavelength of S gas is 7.07 μm;
the wavelength tunable range of the second configured quantum cascade laser is 4.34-4.54 μm, and the wavelength covers CO and CO2Characteristic absorption peaks of two gases, selected from CO and CO2The characteristic absorption peak wavelengths of the gas are respectively positioned at 4.54 μm and 4.34 μm;
the wavelength tunable range of the configured quantum cascade laser III is 7.43 mu m-7.87μ m, wavelength of SO2、CF4、 SO2F2Characteristic absorption peaks of the three gases, selected SO2、CF4、SO2F2The characteristic absorption peak wavelengths of the gases are respectively 7.43 μm, 7.79 μm and 7.87. mu.m.
3) When the method is used for detecting the gas in the petrochemical natural gas quality control:
the wavelength of the quantum cascade laser I is 7.07-7.43 μm, and the wavelength covers H2S、SO2Characteristic absorption peaks of the two gases, selected H2S、SO2The characteristic absorption peak wavelengths of the gas are respectively positioned at 7.07 mu m and 7.43 mu m;
the wavelength of the second quantum cascade laser is 4.34 μm, and the wavelength covers CO2Characteristic absorption peak of gas, selected CO2The characteristic absorption peak wavelength of the gas is positioned at 4.34 mu m;
the wavelength tunable range of the configured quantum cascade laser III is 4.83 mu m, the wavelength covers the characteristic absorption peak of the COS gas, and the wavelength of the characteristic absorption peak of the selected COS gas is 4.83 mu m.
4) The method is used for detecting the conversion synthesis efficiency monitoring gas of petrochemical methanol production equipment:
the wavelength of the quantum cascade laser I is 7.54 mu m, and the wavelength covers CH4Characteristic absorption peak of gas, selected CH4The characteristic absorption peak wavelength of the gas is 7.54 mu m;
the wavelength tunable range of the second configured quantum cascade laser is 4.34-4.54 μm, and the wavelength covers CO and CO2Characteristic absorption peaks of two gases, selected from CO and CO2The characteristic absorption peak wavelengths of the gas are respectively positioned at 4.54 μm and 4.34 μm;
and a third quantum cascade laser can not be configured when the petrochemical methanol production equipment is used for detecting the conversion synthesis efficiency monitoring gas.
The beam splitter module comprises a semi-transparent semi-reflecting mirror and a total reflecting mirror, and the laser emitted by the quantum cascade laser array module is decomposed into two beams of laser with the same energy. The semi-transparent semi-reflecting mirror in the spectroscope module is a broadband semi-transparent semi-reflecting mirror or is composed of a narrow-band semi-transparent semi-reflecting mirror rotating disc controlled by a driving motor, and the rotating disc converts the semi-transparent semi-reflecting mirror with a specific waveband according to the transmitted laser wavelength. The angle between the semi-transmitting and semi-reflecting mirror and the angle.
The reference gas cell to be measured is two chambers of the same size hollowed out in a square, wherein the gas cell to be measured is the container for the gas to be measured to enter the detection device. And the inner walls of the gas chamber to be measured and the reference gas chamber are plated with gold or nickel, the gas chamber to be measured and the reference gas chamber have the same size, the diameter is 5mm-50mm, and the length is 0.1mm-200 mm. The reference gas chamber is pre-charged with pure N by a capillary tube2He, Ar or air, in the detection of SF6SF which can be pre-purified for decomposition of gas and natural gas components6And the standard natural gas is used for offsetting the interference of the background gas absorption spectrum line on the absorption spectrum line of the gas to be measured.
The differential resonance photoacoustic cell is a first-order longitudinal resonance photoacoustic cell, is a container for generating photoacoustic signals, is made of brass or stainless steel, is an integral piece formed by respectively digging cavities with the same size in two square pieces and then splicing, and a horn-shaped cavity capable of containing an acoustoelectric conversion module is dug at the joint of the two square pieces, the diameter of the joint of the cavity and the photoacoustic cell is 1-2 mm, and the diameter of the part connected with the acoustoelectric conversion module is 10-20 mm. The material is brass or stainless steel, the inner wall of the photoacoustic cell is plated with gold or nickel, the diameter of the photoacoustic cell is 5mm-10mm, the length of the photoacoustic cell is 50mm-200mm, the length-diameter ratio of the photoacoustic cell is greater than or equal to 12:1, and the photoacoustic cell works in a first-order resonance mode. The proportion of the filled standard gas is proportioned according to the difference of the absorption peak absorption intensity selected by different gases, so that the strength of the photoacoustic signals generated by different gases is ensured to be positioned in the flat response curve of the acoustic-electric conversion module, and a wide detection dynamic range is obtained. The photoacoustic spectroscopic signal generated by the system can be expressed as:
where S is the intensity of the generated photoacoustic spectrum signal, P is the optical power of the excitation light, M is the sensitivity of the acousto-electric conversion module, CcellIs cell constant of photoacoustic wave, ηiFor absorbing lightEfficiency of conversion into heat, alphaiMolar absorption coefficient of the absorbing component at the wavelength of the exciting light, ciTo absorb the concentration of the component, AbIs the efficiency of background signal generation. When the modulation frequency is lower than 10kHz, etaiCan be approximated by a constant 1. In a certain system: exciting light optical power P, sensitivity M of acoustoelectric conversion module, and photo-acoustic cell constant CcellAll values are constant, so that the intensity of the photoacoustic signal generated by each gas in the photoacoustic cell is in the flat response curve of the acousto-electric conversion module, and ciAnd alphaiThe product of (d) should be constant. After the differential resonance photoacoustic cell is combined with the theoretical basis and actual test, the standard gas of the corresponding characteristic gas components in the industries of electricity, nuclear energy and petrochemical industry is precharged through the gas charging port II, and the proportionality coefficient is as follows:
1) when the device is used for detecting the power and nuclear transformer: the differential resonance photoacoustic cell is pre-charged through a gas charging port II C2H4、CH4、 C2H2、CO、CO2、C2H6And N2Seven kinds of gases. Wherein C is2H4、CH4、C2H2、CO、CO2、C2H6The ratio of (2) is proportional to the absorption coefficient thereof, and the ratio coefficient of the volume concentration of the six gases to be precharged is 700:70:50:5:5: 1.
2) SF (sulfur hexafluoride) equipment for detecting electric power GIS (gas insulated switchgear)6When the gas is decomposed: the differential resonance photoacoustic cell is pre-charged with H through the inflation inlet2S、 CO、CO2、SO2、CF4、SO2F2And N2Seven kinds of gases. Wherein H2S、CO、CO2、SO2、CF4、SO2F2Proportional to its absorption coefficient, and the pre-charged coefficients of the six gas volume concentrations are 60000:80:80:120:1: 10.
3) When the method is used for detecting the gas in the petrochemical natural gas quality control: the differential resonance photoacoustic cell is pre-charged with H through the inflation inlet2S、 SO2、CO2COS and N2Five kinds of gases. Wherein H2S、SO2、CO2The ratio of COS and the absorption coefficient thereof are in direct proportion, and the ratio coefficient of the volume concentration of the pre-filled four gases is 4000:10:5: 1.
4) When being used for detecting petrochemical industry methanol production equipment conversion synthesis efficiency monitoring gas: the differential resonance photoacoustic cell is pre-charged with CH through the inflation inlet two4CO, CO and N2Four gases. Wherein CH4、CO、CO2The ratio of the three gases is in direct proportion to the absorption coefficient of the gas, and the ratio coefficient of the volume concentration of the three gases to be precharged is 10:1: 1.
The acoustic-electric conversion module is a capacitance microphone for detecting differential photoacoustic signals, and the sensitivity is 30 mV/Pa.
The constant temperature box is a resistance wire heating constant temperature box and is used for maintaining the temperature in the reference air chamber to be measured and the differential resonance photoacoustic cell at 50 ℃.
The optical power detector is used for detecting the power drift of laser, feeding back a laser drift signal to the laser driving and temperature control module in real time, and correcting the output wavelength and energy of the quantum cascade laser array by adjusting the parameters of the laser driving and temperature control module.
The extinction pool is used for absorbing laser energy which is not used for exciting photoacoustic signals, high-concentration gas components which are the same as those of the photoacoustic pool are filled in the extinction pool, and the proportionality coefficient of the extinction pool is the same as that of the photoacoustic pool.
The phase-locked amplifying circuit and the industrial personal computer are used for extracting specific wavelength frequency signals, noise signals beyond 1kHz-4kHz can be filtered, the noise converted to the input end is 50nV, the temperature drift is less than or equal to 10 ppm/DEG C, the adjustable range of the amplification factor of the amplifier is not less than 104。
Drawings
Some specific embodiments of the invention will be described in detail below, by way of example and not by way of limitation, with reference to the accompanying drawings. The same reference numbers in the drawings identify the same or similar elements or components. Those skilled in the art will appreciate that the drawings are not necessarily drawn to scale.
Fig. 1 is a schematic view of the entire structure of the photoacoustic spectroscopy detection apparatus of the present invention.
FIG. 2 is a drawing of a laserOptical device-detection C2H4、CH4、C2H2Schematic diagram of selected wavelengths of three gases.
FIG. 3 is a diagram of the second laser for detecting CO and CO2Schematic diagram of selected wavelengths of two gases.
FIG. 4 is a diagram of laser three detection C2H6Schematic diagram of selected wavelengths of gas.
The reference numerals in the figures have the following meanings:
1-a stop valve, 2-a particulate matter filtering device, 3-a gas drying device, 4-a first electromagnetic switch valve, 5-a pressure sensor, 6-a second electromagnetic switch valve, 7-a sonic nozzle, 8-a vacuum pump, 9-a quantum cascade laser array module, 91-a laser driving and temperature control module, 92-a quantum cascade laser array, 921-a first laser, 922-a second laser, 923-a third laser, 924-a first focusing lens, 925-a second focusing lens, a third focusing lens, 93-a light path calibration laser, 94-a full wavelength total reflection mirror, 95-a first specific wavelength total reflection mirror, 96-a second specific wavelength total reflection mirror, 97-a third specific wavelength total reflection mirror, 98-a fourth specific wavelength total reflection mirror, 10-a spectroscope module, 101-semi-transparent semi-reflective mirror, 102-total reflective mirror, 11-reference gas chamber to be detected, 111-gas inlet, 112-gas outlet, 113-window sheet I, 114-window sheet II, 115-window sheet III, 116-window sheet IV, 117-gas chamber to be detected, 118-reference gas chamber, 119-gas filling port I, 12-differential resonance photoacoustic cell, 121-window sheet V, 122-window sheet VI, 123-window sheet VII, 124-window sheet VIII, 125-window sheet I, 126-photoacoustic cell II, 127-gas filling port II, 13-acoustoelectric conversion module, 131-acoustoelectric conversion module diaphragm, 14-thermostat, 15-optical power detector, 16-extinction cell, 17-phase-locking amplification circuit and 18-industrial personal computer.
Detailed Description
The technical scheme of the invention is further described in detail by combining the drawings and the specific embodiments in the specification.
Fig. 1 shows an embodiment of the photoacoustic spectroscopy detection apparatus of the present invention for measuring multi-component gases using a single photoacoustic cell, which is used to detect the fault signature gas components of a power transformer. As shown in fig. 1, the detection device includes a stop valve 1, a particulate matter filtering device 2, a gas drying device 3, a first electromagnetic switch valve 4, a pressure sensor 5, a second electromagnetic switch valve 6, a sonic nozzle 7, a vacuum pump 8, a quantum cascade laser array module 9, a spectroscope module 10, a reference gas chamber 11 to be detected, a differential resonance photoacoustic cell 12, an acousto-electric conversion module 13, a thermostat 14, a light power detector 15, an extinction cell 16, a phase-locked amplification circuit 17, and an industrial personal computer 18.
In one embodiment, the device for online monitoring of the transformer fault characteristic gas components is connected to a transformer vacuum degassing device through one side of a stop valve 1, then a particulate matter filtering device 2, a gas drying device 3, a first electromagnetic switch valve 4, a pressure sensor 5, a reference gas chamber 11 to be tested, a second electromagnetic switch valve 6, a sonic nozzle 7 and a vacuum pump 8 are sequentially connected to a gas path of the stop valve 1, and the characteristic gas passes through the modules in sequence and is finally discharged through the vacuum pump 8; the detection device comprises a quantum cascade laser array module 9, a spectroscope module 10, a reference gas chamber 11 to be detected, a differential resonance photoacoustic cell 12, an acoustoelectric conversion module 13, a thermostat 14, an optical power detector 15, an extinction cell 16, a phase-locked amplification circuit 17 and an industrial personal computer 18.
The quantum cascade laser array module 9 comprises a laser driving and temperature control module 91, a quantum cascade laser array 92, a light path calibration laser 93, a full-wavelength total reflection mirror 94 and specific-wavelength total reflection mirrors 95-98. The quantum cascade laser array 92 comprises three quantum cascade lasers 921-923, each of the quantum cascade lasers 921-923 can excite ultra-narrow linewidth laser aiming at the absorption peak of the decomposed gas component of one or more transformers, and the ultra-narrow linewidth laser is focused by a focusing lens 924-926 and then converged to the same optical path through a specific wavelength total reflection mirror 95-98 and a total wavelength total reflection mirror 94 to be emitted into the spectroscope module 10. The quantum cascade laser 921 and 923 can excite laser with different wavelengths, and the concentration of each component in the gas to be detected can be inverted by detecting photoacoustic signals generated by the gas to be detected to the laser with different wavelengths. The light path calibration laser 93 is a laser with a visible wavelength, and is converged by the specific wavelength total reflection mirror 95-98 and the total wavelength total reflection mirror 94 and then enters the spectroscope module 10, so as to calibrate the light path of the quantum cascade laser array module 9, and is not used for exciting the gas to be measured to generate a photoacoustic signal. The laser driving and temperature control module 91 in the quantum cascade laser array module 9 can freely adjust the current according to the actual situation, the output voltage range is 0-20V, the output current is 0-1A, the current stability is 0.1mA, the kHz modulation output can be realized according to the requirement, the chip temperature control is realized by combining a semiconductor cooler (TEC), and the chip wavelength is accurately adjusted. The laser driving and temperature control module 91 in the quantum cascade laser array module 9 switches the quantum cascade lasers 921 and 923 in an analog switch mode, so as to realize different wavelength outputs. Specifically, the optical path calibration laser 93 in the qc laser array module 9 is visible light with a wavelength of 0.55 μm. The angles of the full-wavelength total reflection mirror 94 and the specific-wavelength total reflection mirrors 95-98 can be manually adjusted through the base.
The quantum cascade laser array 92 in the quantum cascade laser array module 9 can realize the function of detecting multiple gas components by a single laser, wherein the wavelength tunable range of the first quantum cascade laser 921 is 7.10-7.38 μm, and the wavelength covers C2H4、CH4、C2H2Characteristic absorption peaks of the three gases, as shown in FIG. 2, C selected2H4、CH4、C2H2The characteristic absorption peak wavelengths are respectively positioned at 7.10 mu m, 7.38 mu m and 7.37 mu m; the tunable range of the wavelength of the second quantum cascade laser 922 is 4.34-4.54 μm, and the wavelength covers CO and CO2Characteristic absorption peaks of the two gases, shown in FIG. 3, for selected CO, CO2The characteristic absorption peak wavelengths are respectively positioned at 4.54 μm and 4.34 μm; the wavelength of the quantum cascade laser III 923 is 3.35 mu m and covers C2H6Characteristic absorption peaks of the gas, shown in FIG. 4, selected C2H6The characteristic absorption peak wavelength was located at 3.35 μm.
The beam splitter module 10 includes a half mirror 101 and a full mirror 102, and splits the laser beam emitted from the quantum cascade laser array module 9 into two laser beams with the same energy, and the half mirror 101 in the beam splitter module 10 is a broadband half mirror. The angle between the half mirror 101 and the full mirror 102 can be manually adjusted by the base.
The reference gas chamber 11 to be measured is arranged atTwo cylindrical chambers of the same size are hollowed out in a square, respectively a gas cell 117 to be measured and a reference gas cell 118. The material of the reference gas chamber 11 to be measured is brass, the inner walls of the gas chamber 117 to be measured and the reference gas chamber 118 are plated with gold, and the gas chamber 117 to be measured and the reference gas chamber 118 have the same size, the diameter is 20mm, and the length is 100 mm. The air inlet 111 is located the air chamber that awaits measuring apart from advancing light side 10mm department, and the diameter is 3mm, and is long 4mm, and the gas outlet 112 is located the air chamber that awaits measuring apart from light-emitting side 10mm department, and the diameter is 3mm, and is long 4 mm. The first window sheet 113 and the second window sheet 114 are respectively attached to the incoming light of the gas chamber 117 to be measured and the reference gas chamber 118 by using corrosion-resistant sealant for measurement, so as to ensure that laser in the quantum cascade laser array module 9 can be emitted into the gas chamber 117 to be measured and the reference gas chamber 118 through the window sheets, the third window sheet 115 and the fourth window sheet 116 are respectively attached to the outgoing light of the gas chamber 117 to be measured and the reference gas chamber 118 by using corrosion-resistant sealant for measurement, so as to ensure that the laser passing through the gas chamber 117 to be measured and the reference gas chamber 118 can be emitted into the photoacoustic cells 125 and 126, and the material of the window sheets is made of quartz material with light transmittance being more than. The reference cell 118 is pre-charged with pure N via charge port one 1192。
The differential resonance photoacoustic cell 12 is an integral member formed by respectively digging cylindrical chambers with the same size in two square members and then assembling, and the two chambers form a first photoacoustic cell 125 and a second photoacoustic cell 126. The connecting part of the two square pieces is hollowed to form a horn-shaped cavity for placing the acoustic-electric conversion module 13, the diameter of the connecting part of the horn-shaped cavity, the first photoacoustic cell 125 and the second photoacoustic cell 126 is 2mm, and the diameter of the connecting part of the horn-shaped cavity and the acoustic-electric conversion module 13 is 7 mm. The material of the differential resonance photoacoustic cell 12 is brass, the inner walls of the first photoacoustic cell 125 and the second photoacoustic cell 126 are plated with gold, the diameters of the first photoacoustic cell 125 and the second photoacoustic cell 126 are 8mm, the lengths of the first photoacoustic cell 125 and the second photoacoustic cell 126 are 100mm, and the length-diameter ratio of the first photoacoustic cell 125 to the second photoacoustic cell is 25: 2. The five window sheets 121 and the six window sheets 122 are respectively attached to the incoming light of the first photoacoustic cell 125 and the second photoacoustic cell 126 by using corrosion-resistant sealant to ensure that the laser passing through the gas cell 117 to be measured and the reference gas cell 118 can be emitted into the first photoacoustic cell 125 and the second photoacoustic cell 126 through the window sheets, and the seven window sheets 123 and the eight window sheets 124 are respectively attached to the outgoing light of the first photoacoustic cell 125 and the second photoacoustic cell 126 by using corrosion-resistant sealant to ensure that the laser passing through the first photoacoustic cell 125 and the second photoacoustic cell 126 is detectedLight can be emitted into the optical power detector 15 and the extinction pool 16, and the window sheet is made of quartz material with light transmittance being more than or equal to 99%. The differential resonance photoacoustic cell 12 is pre-charged with C through the second inflation inlet 1272H4、CH4、C2H2、CO、CO2、C2H6And N2Seven gases with volume ratios of 7%, 0.7%, 0.5%, 0.05%, 0.01% and 91.69% respectively.
The acoustoelectric conversion module 13 is used for detecting differential photoacoustic signals, the acoustoelectric conversion module is a capacitance type sensor adopting a titanium film, the acoustoelectric conversion module 13 is arranged at the central axis of the differential resonance photoacoustic cell 12 and is connected to the middle opening of the photoacoustic cell I125 and the photoacoustic cell II 126, the connection part is in a horn mouth shape, the diameter of the wide mouth is 7mm, and the diameter of the narrow mouth is 2 mm. The diameter of the sound-electricity conversion module 13 is 14mm, and the sound-electricity conversion module membrane 131 is made of a titanium metal material membrane, the diameter is 12mm, and the thickness is 10 micrometers. The sound-electricity conversion module 13 is used for detecting differential photoacoustic signals generated by the gas to be detected in the two groups of metal tubes to obtain acoustic signals linearly proportional to the concentration of the gas to be detected, and the sensitivity of the acoustic signals is 10 mV/Pa-50 mV/Pa.
The constant temperature box 14 is a resistance wire heating constant temperature box, and the reference gas chamber 11 to be measured and the differential resonance photoacoustic cell 12 are placed in the constant temperature box, so as to ensure that the temperature in the reference gas chamber 11 to be measured and the temperature in the differential resonance photoacoustic cell 12 are maintained at 50 ℃.
The optical power detector 15 is configured to detect power drift of the laser, feed back a laser drift signal to the laser driving and temperature control module 91 in real time, and adjust parameters of the laser driving and temperature control module 91 to modify the output wavelength and energy of the quantum cascade laser array 92.
The extinction pool 16 is used for absorbing laser energy which is not used for exciting the photoacoustic signal, and the extinction pool 16 is filled with high-concentration C2H4、CH4、C2H2、CO、CO2、C2H6Six gases, and the volume proportion coefficients are 85%, 7%, 3%, 2% and 1%, respectively.
The phase-locked amplifying circuit 17 and the industrial controlThe phase-locked amplifier 18 is used for extracting specific wavelength frequency signals, the phase-locked amplifying circuit 17 and the industrial personal computer 18 can filter noise signals beyond 1kHz-4kHz, the noise converted to the input end is 50nV, the temperature drift is less than or equal to 10 ppm/DEG C, the adjustable range of the amplification factor of the amplifier is not less than 104。
The present applicant has described and illustrated embodiments of the present invention in detail with reference to the accompanying drawings, but it should be understood by those skilled in the art that the above embodiments are merely preferred embodiments of the present invention, and the detailed description is only for the purpose of helping the reader to better understand the spirit of the present invention, and not for limiting the scope of the present invention, and on the contrary, any improvement or modification made based on the spirit of the present invention should fall within the scope of the present invention.