Full-scale carbon dioxide detection device based on photoacoustic spectrum and frequency tracking

Abstract

The utility model discloses a full-scale carbon dioxide detection device based on a photoacoustic spectrum and frequency tracking. The full-scale carbon dioxide detection device comprises a laser light source module, a photoacoustic cell module, a control and receiving module and a computer, the control and receiving module is used for controlling the laser light source module to emit specific laser and locking and demodulating a sound signal from the photoacoustic cell module; the computer is used for receiving and processing the sound signal demodulated by the control and receiving module to obtain the concentration of the carbon dioxide gas to be detected, and transmitting a control signal to the control and receiving module, so that the control and receiving module controls the laser light source module to emit specific laser; based on the photoacoustic spectrum and frequency tracking technology, the full-scale linear detection of the carbon dioxide concentration is realized, and the device has the characteristics of high detection precision and wide detection range.

Description

TECHNICAL FIELD

[0001] The utility model relates to a gas detection technical field especially relates to a full range carbon dioxide detection device based on photoacoustic spectrum and frequency tracking. BACKGROUND

[0002] Most of the existing gas detection technologies are based on gas chromatography, electrochemical method, metal oxide method and catalytic combustion method. Bartle K D et al. (Bartle K D, Myers P. History of gas chromatography[J]. Trac Trends in Analytical Chemistry, 2002, 21(9-10): 547-557. DOI: 10.1016 / S0165-9936(02)00806-3.) can separate the chromatographic column by gas chromatography and analyze the gas components by using specific detectors (such as flame ionization detector). However, the sample pretreatment in this method is relatively complex and has a long analysis period, the instrument maintenance and operation are relatively complex, and the overall cost is relatively high. Ariyaratne R et al. (Ariyaratne R, Elangasinghe MA, Zamora ML, Understanding the effect of temperature and relative humidity on sensor sensitivities in field environments and improving the calibration models of multiple electrochemical carbon monoxide (CO) sensors in a tropical environment, Sensors and Actuators B: Chemical 390 (2023) 133935.) can generate current or voltage by using the chemical reaction of gas on the electrode by electrochemical method, and determine the gas concentration by measuring these electrical signals, but this method may be disturbed by background gas, the measurement result accuracy is low, the sensor service life is short, and the long-term use stability is poor. Dey A (Dey A, Semiconductor metal oxide gas sensors: A review, Materials science and Engineering: B 229 (2018) 206-217.) proposed a review of semiconductor metal oxide gas sensors, which can change the electrical conductivity by the reaction of carbon dioxide gas with the surface of metal oxide by metal oxide method, and calculate the gas concentration by measuring the change of electrical conductivity, but the metal oxide method is sensitive to environmental humidity and temperature changes, the detection sensitivity and selectivity are relatively low, and the power consumption is relatively high.Hosoya A et al. (Hosoya A, Tamura S, Imanaka N, A catalytic combustion-type carbon monoxide gas sensor incorporating an apatite-type oxide, ISIJ International 56(9) (2016) 1634-1637.) by catalytic combustion method by gas combustion on the surface of the catalyst, heat is generated, by measuring the temperature change in the combustion process to determine the concentration of gas. But this method needs to be operated at high temperature, there are certain security risks, and the change of oxygen concentration and other gas components in the environment is sensitive, the detection effect is poor. SUMMARY

[0003] In order to overcome the above-mentioned shortcomings in the prior art, the purpose of the utility model is to provide a kind of full range carbon dioxide detection device based on photoacoustic spectroscopy and frequency tracking, by using QCL laser, DFB laser and helium-neon laser, the advantages of photoacoustic spectroscopy and frequency tracking technology can be realized Linear detection of full range carbon dioxide concentration, with the characteristics of high detection precision and wide detection range.

[0004] In order to realize the above-mentioned purpose, the technical scheme adopted by the utility model is as follows:

[0005] A kind of full range carbon dioxide detection device based on photoacoustic spectroscopy and frequency tracking, comprising:

[0006] Laser light source module: including QCL laser 3, DFB laser 4 and helium-neon laser 5, wherein QCL laser 3 and DFB laser 4 are used to emit infrared light, and helium-neon laser 5 is used to emit visible light;

[0007] Photoacoustic cell module: including differential photoacoustic cell 11, gas control unit and sound signal acquisition unit, wherein differential photoacoustic cell 11 is used to accommodate background gas and to-be-measured carbon dioxide gas, and sound signal is generated after to-be-measured carbon dioxide gas absorbs incident laser energy;Gas control unit is used to control and transport to-be-measured carbon dioxide gas;Sound signal acquisition unit is used to convert the collected sound signal into electrical signal;

[0008] Control and receiving module 2: the electrical signal output end of control and receiving module 2 is connected with the electrical signal input end of QCL laser 3, DFB laser 4 and helium-neon laser 5 respectively, for controlling that laser light source module emits specific laser;The electrical signal output end of sound signal acquisition unit is connected with the electrical signal input end of control and receiving module 2, for locking demodulation sound signal from sound signal acquisition unit;

[0009] The signal output end of the computer 1 is connected with the signal input end of the control and receiving module 2, which is used for receiving and processing the sound signal demodulated from the control and receiving module 2 to obtain the concentration of the carbon dioxide gas to be detected; the signal output end of the computer 1 is connected with the signal input end of the control and receiving module 2, which is used for transmitting the control signal to the control and receiving module 2 to make the control and receiving module 2 control the laser light source module to emit specific laser light.

[0010] The laser output end of the QCL laser 3 is connected with the laser incident end of the differential photoacoustic cell 11, and the incident laser light of the QCL laser 3 directly enters the differential photoacoustic cell 11;

[0011] The laser output end of the DFB laser 4 is connected with the laser input end of the collimator 19, the laser output end of the collimator 19 is connected with the laser incident end of the differential photoacoustic cell 11, and the incident laser light of the DFB laser 4 enters the differential photoacoustic cell 11 after being focused by the collimator 19;

[0012] The laser output end of the helium-neon laser 5 is connected with the laser input end of the chopper 18, the laser output end of the chopper 18 is connected with the laser incident end of the differential photoacoustic cell 11, and the incident laser light of the helium-neon laser 5 enters the differential photoacoustic cell 11 after being frequency-modulated by the chopper 18.

[0013] The differential photoacoustic cell 11 includes a first buffer cavity 20 and a second buffer cavity 21 in a cylindrical shape arranged at both ends along the direction of the gas flow, and a first resonant cavity 22 and a second resonant cavity 23 in a cylindrical shape arranged in parallel between the two buffer cavities; the carbon dioxide gas enters the buffer cavities of the differential photoacoustic cell 11 through the gas inlet 12 of the differential photoacoustic cell 11, and the gas outlet 13 of the differential photoacoustic cell 11 is connected with the buffer cavities of the differential photoacoustic cell 11 and the gas inlet of the air pump 10 to extract the carbon dioxide gas after absorbing the laser energy.

[0014] The laser output end of the differential photoacoustic cell 11 is connected with the laser input end of the optical garbage can 16, which is used for absorbing excess laser light to prevent laser light from diverging.

[0015] The gas control unit includes a gas cylinder 9, a flow rate controller 8, a humidity controller 7 and a pressure controller 6; the gas cylinder 9 is used for storing the carbon dioxide gas to be detected; the flow rate controller 8 is used for controlling the gas to pass through the differential photoacoustic cell 11 at a specified flow rate; the humidity controller 7 is used for controlling the gas to pass through the differential photoacoustic cell 11 at a specified humidity; and the pressure controller 6 is used for controlling the pressure in the differential photoacoustic cell 11 and keeping it stable.

[0016] The sound signal collecting unit comprises a first microphone 14, a second microphone 15 and an adder difference circuit 17 for subtracting two microphone signals, the first microphone 14 and the second microphone 15 are arranged in the middle of the two resonant cavities of the differential photoacoustic cell 11 respectively, the electrical signal output ends of the first microphone 14 and the second microphone 15 are connected with the electrical signal input end of the adder difference circuit 17, and the electrical signal output end of the adder difference circuit 17 is connected with the electrical signal input end of the control and receiving module 2.

[0017] The electrical signal output end of the control and receiving module 2 is connected with the electrical signal input end of the chopping controller, the electrical signal output end of the chopping controller is connected with the electrical signal input end of the chopper 18, and the control and receiving module 2 controls the incident laser emitted by the helium-neon laser 5 to be modulated into pulsed light with a certain period through the chopper 18 through the chopping controller.

[0018] The control and receiving module 2 comprises a laser driving module 27, a signal collecting module 24, a signal modulation and demodulation module 25 and a signal input and output module 26, the signal output end of the computer 1 is connected with the input end of the laser driving module 27 through the signal input and output module 26, the laser driving module 27 is controlled by the computer 1 to supply power to the QCL laser 3, the DFB laser 4 and the helium-neon laser 5, and the temperature and current of the laser are controlled, the output end of the signal collecting module 24 is connected with the input end of the signal modulation and demodulation module 25, the output end of the signal modulation and demodulation module 25 is connected with the signal input end of the computer 1 through the signal input and output module 26, the signal collecting module 24 supplies power to the microphone arranged on the differential photoacoustic cell 11, and the electrical signal collected by the microphone is transmitted to the computer 1 after being analyzed and calculated through the signal modulation and demodulation module 25.

[0019] The signal modulation and demodulation module 25 comprises a signal generator, an adder and a phase-locked amplifier, wherein the signal generator outputs a sine wave for frequency modulation and a sawtooth wave for wavelength scanning, the adder is used for adding the sine wave and the sawtooth wave output by the signal generator into a signal and transmitting the signal to the laser in the laser light source module, and the phase-locked amplifier is used for receiving the sine wave signal output by the signal generator and the electrical signal of the sound signal collecting unit and performing phase-locked amplification.

[0020] Compared with the prior art, the utility model has the advantages of:

[0021] Compared with the existing QCL and DFB based photoacoustic spectrum light source module, the utility model discloses through the introduction helium neon laser, adopts full light source technology, combines the advantage of photoacoustic spectrum and frequency tracking technology, utilize the high accuracy of photoacoustic spectrum technology, safe and lossless and excellent selectivity, also combined the high dynamic range and high linearity of frequency tracking technology, widen the carbon dioxide concentration detection range, realized the full range linear detection of carbon dioxide concentration, the utility model discloses through the adoption integrated technology, signal generator and lock-in amplifier are integrated to signal modulation and demodulation module, reduce the overall volume, simplify the operation process, and help to realize commercial application, with the characteristics of high detection precision, wide detection range, small volume and simple operation. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is the structure schematic diagram of the carbon dioxide detection device based on photoacoustic spectrum and frequency tracking of the utility model.

[0023] Figure 2 It is the structure schematic diagram of the differential photoacoustic cell of the utility model.

[0024] Figure 3 It is the structure schematic diagram of the control and collection module of the utility model.

[0025] Figure 4 It is the carbon dioxide and water vapor spectrum distribution characteristic diagram based on HITRAN database of the utility model, wherein, Figure 4 (a) is near infrared waveband, Figure 4 (b) is mid-infrared waveband.

[0026] Figure 5 It is the photoacoustic signal and resonance frequency variation curve with carbon dioxide concentration of the utility model, wherein, Figure 5 (a) is the photoacoustic signal variation curve with carbon dioxide concentration under QCL mode, and the concentration range is 0-80ppm; Figure 5 (b) is the photoacoustic signal variation curve with carbon dioxide concentration under DFB mode, and the concentration range is 0-100%; Figure 5 (c) is the resonance frequency variation curve with carbon dioxide concentration under He-Ne mode, and the concentration range is 0-100%.

[0027] Figure 6 It is the result of measuring carbon dioxide gas under different concentrations by the utility model, wherein, Figure 6 (a) is 30ppm, Figure 6 (b) is 10%, Figure 6 (c) is 80%.

[0028] In the figure: 1-computer; 2-control and receiving module; 3-QCL laser; 4-DFB laser; 5-helium-neon laser; 6-pressure controller; 7-humidity controller; 8-flow controller; 9-gas cylinder; 10-pump; 11-differential optical sound cell; 12-gas inlet; 13-gas outlet; 14-first microphone; 15-second microphone; 16-optical dustbin; 17-adder differential circuit; 18-chopper; 19-collimator; 20-first buffer cavity; 21-second buffer cavity; 22-first resonant cavity; 23-second resonant cavity; 24-signal acquisition module; 25-signal modulation and demodulation module; 26-signal input and output module; 27-laser drive module. DETAILED DESCRIPTION

[0029] The technical scheme of the utility model will be further described below with reference to the drawings.

[0030] A full-range carbon dioxide detection device based on photoacoustic spectroscopy and frequency tracking, comprising:

[0031] The laser source module comprises a QCL laser 3, a DFB laser 4 and a helium-neon laser 5, wherein the QCL laser 3 and the DFB laser 4 are used for emitting infrared light to the inner wall of the resonant cavity of the differential optical sound cell 11, and the helium-neon laser 5 is used for emitting visible light to the inner wall of the resonant cavity of the differential optical sound cell 11;

[0032] The laser output end of the QCL laser 3 is connected with the laser incidence end of the differential optical sound cell 11, and the incidence laser of the QCL laser 3 directly enters the differential optical sound cell 11;

[0033] The laser output end of the DFB laser 4 is connected with the laser input end of the collimator 19, the laser output end of the collimator 19 is connected with the laser incidence end of the differential optical sound cell 11, and the incidence laser of the DFB laser 4 enters the differential optical sound cell 11 after being focused by the collimator 19;

[0034] The laser output end of the helium-neon laser 5 is connected with the laser input end of the chopper 18, the laser output end of the chopper 18 is connected with the laser incidence end of the differential optical sound cell 11, and the incidence laser of the helium-neon laser 5 enters the differential optical sound cell 11 after being frequency-modulated by the chopper 18;

[0035] The photoacoustic cell module comprises a differential optical sound cell 11, a gas control unit and a sound signal acquisition unit, wherein the differential optical sound cell 11 is used for accommodating background gas and the carbon dioxide gas to be measured, and generating a sound signal after the carbon dioxide gas to be measured absorbs the incidence laser energy; the gas control unit is used for controlling and conveying the carbon dioxide gas to be measured; and the sound signal acquisition unit is used for converting the collected sound signal into an electric signal;

[0036] The gas control unit includes a gas cylinder 9, a flow rate controller 8, a humidity controller 7 and a pressure controller 6; the gas cylinder 9 is used to store the carbon dioxide gas to be detected; the flow rate controller 8 is used to control the gas to pass through the differential photoacoustic cell 11 at a specified flow rate; the humidity controller 7 is used to control the gas to pass through the differential photoacoustic cell 11 at a specified humidity; and the pressure controller 6 is used to control the pressure in the differential photoacoustic cell 11 and keep it stable;

[0037] As shown in Figure 2 The differential photoacoustic cell 11 includes a first buffer cavity 20 and a second buffer cavity 21 in a cylindrical shape arranged at both ends along the direction of gas flow, and the two buffer cavities are communicated through two first and second resonant cavities 22 and 23 arranged in parallel; the carbon dioxide gas enters the buffer cavities of the differential photoacoustic cell 11 through the gas inlet 12 of the differential photoacoustic cell 11, and the gas outlets 13 of the differential photoacoustic cell 11 are communicated with the buffer cavities of the differential photoacoustic cell 11 and the gas inlet of the exhaust pump 10 to exhaust the carbon dioxide gas after absorbing the laser energy; the laser output end of the differential photoacoustic cell 11 is connected with the laser input end of the optical garbage can 16 for absorbing excess laser and preventing laser from scattering; and the first and second resonant cavities of the differential photoacoustic cell 11 are respectively provided with the first and second microphones 14 and 15;

[0038] The sound signal acquisition unit includes the first and second microphones 14 and 15 and an adder differential circuit 17 for subtracting the signals of the two microphones; the electrical signal output ends of the first and second microphones 14 and 15 are connected with the electrical signal input end of the adder differential circuit 17, and the electrical signal output end of the adder differential circuit 17 is connected with the electrical signal input end of the control and receiving module 2;

[0039] The electrical signal output end of the control and receiving module 2 is connected with the electrical signal input ends of the QCL laser 3, the DFB laser 4 and the helium-neon laser 5, respectively, for controlling the laser light source module to emit specific laser; the electrical signal output end of the sound signal acquisition module is connected with the electrical signal input end of the control and receiving module 2 for locking and demodulating the sound signal from the sound signal acquisition unit;

[0040] The electrical signal output end of the control and receiving module 2 is connected with the electrical signal input end of the chopper controller, and the electrical signal output end of the chopper controller is connected with the electrical signal input end of the chopper 18; the control and receiving module 2 controls the incident laser emitted by the helium-neon laser 5 to be modulated into pulsed light with a certain period through the chopper 18 by the chopper controller;

[0041] The control and receiving module 2 is equipped with a self-designed electronic circuit based on an FPGA chip (Altera, EP4CE15F256), as shown in Figure 3As shown, including laser drive module 27, signal acquisition module 24, signal modulation and demodulation module 25 and signal input and output module 26;The signal output end of computer 1 is connected with the input end of laser drive module 27 through signal input and output module 26, and the power supply of QCL laser 3, DFB laser 4 and helium-neon laser 5 is controlled by laser drive module 27 through computer 1, and the temperature and current of the laser are controlled;The output end of signal acquisition module 24 is connected with the input end of signal modulation and demodulation module 25, and the output end of signal modulation and demodulation module 25 is connected with the signal input end of computer 1 through signal input and output module 26, signal acquisition module 24 supplies power for the microphone arranged on the differential photoacoustic cell 11, and the electrical signal collected by the microphone is transmitted to computer 1 after being analyzed and calculated by signal modulation and demodulation module 25;Signal modulation and demodulation module 25 includes signal generator, adder and lock-in amplifier, the sine wave for frequency modulation and the sawtooth wave for wavelength scanning are output by the signal generator, the frequency, amplitude and bias of the output wave are set according to the situation, the sine wave and the sawtooth wave emitted by the signal generator are added by the adder to form a signal and are transmitted to the laser in the laser light source module, and the sine wave signal output by the signal generator and the electrical signal of the sound signal acquisition unit are received by the lock-in amplifier and are output to computer 1 after lock-in amplification;The sine wave and the ramp signal generated by the FPGA chip are used for signal modulation of QCL laser 3, DFB laser 4 and helium-neon laser 5 respectively, and the frequency of the chopper is adjusted by changing the bias of the sine signal;Signal input and output module 26 and computer 1 carry out signal input and output;

[0042] Computer 1: the signal output end of control and receiving module 2 is connected with the signal input end of computer 1, which is used for receiving and processing the sound signal demodulated from control and receiving module 2 to obtain the concentration of the measured carbon dioxide gas;The signal output end of computer 1 is connected with the signal input end of control and receiving module 2, which is used for transmitting control signal to control and receiving module 2 to make control and receiving module 2 control laser light source module to emit specific laser.

[0043] The working principle of the utility model is:

[0044] According to photoacoustic spectrum theory, in the experimental process, the light emitted by the laser light source module irradiates on the gas sample in the differential photoacoustic cell 11, the gas molecules can absorb light of a specific wavelength, absorb light energy and convert it into heat energy, and the gas molecules absorbing light will produce periodic expansion and contraction due to local heating, thereby generating sound waves;The QCL laser 3 and DFB laser 4 in the carbon dioxide gas detection device can detect the carbon dioxide concentration by emitting specific waveband laser; Figure 4As shown, based on the HITRAN database of carbon dioxide and water vapor spectral distribution characteristics, at a temperature of 296K and a pressure of 1 atm, carbon dioxide molecules have strong absorption bands in the near-infrared region 4989.971 cm -1 and the mid-infrared region 2364.106 cm -1 Both have strong absorption bands, and water vapor has fewer absorption lines in this spectral band, which will not cause spectral interference to the detection of carbon dioxide, so the DFB laser 4 with a wavelength of 2004 nm and the QCL laser 3 with a wavelength of 4230 nm are used for detection; but when the gas concentration increases to a certain concentration, the absorption of light by the gas may reach a saturation state, that is, the degree of light absorption reaches a limit and cannot be effectively increased, and in the case of high concentration of gas, the distance of the light beam propagating in the gas is short, so the attenuation effect of the light beam will be more obvious; At this time, the acoustic signal may no longer increase with the concentration, thereby affecting the linearity range and accuracy of detection, so the frequency tracking method is used to detect the gas concentration at high concentration.

[0045] The principle of frequency tracking is based on the solid photoacoustic theory (Rosencwaig-Gersho theorem, RG theorem). When the light is modulated and irradiates the gas sample in the differential photoacoustic cell 11, the laser energy is absorbed by the sample, thereby generating heat energy. The spectral range of the visible light source is usually between 400 nm and 700 nm, which is not absorbed by carbon dioxide. Since the gas inside the photoacoustic cell does not absorb the laser, the laser interacts with the inner wall of the resonant cavity of the differential photoacoustic cell 11, part of the energy is diffused in the resonant cavity, and the rest of the energy is transferred to the gas in contact with the resonant cavity. This interaction forms a boundary layer between the gas and the surface of the resonant cavity, which produces a thermal response to temperature changes. When the incident laser is periodically modulated, the boundary layer is also periodically heated, thereby producing an acoustic piston effect, affecting the residual gas in the photoacoustic cell, and generating acoustic signals, which are then detected by the microphone. The frequency and amplitude of these acoustic waves are affected by the properties of the gas, and changes in the resonant frequency will significantly affect the acoustic response. By analyzing the size of the resonant frequency, the concentration of the gas can be determined. In order to eliminate gas absorption and improve the universality of the sensor, a helium-neon laser 5 with a wavelength of 632.8 nm is selected to irradiate the resonant cavity wall of the differential photoacoustic cell 11. The resonant frequency is an important performance parameter of the photoacoustic cell, which is affected by factors such as the concentration and type of gas in the differential photoacoustic cell 11, and the expression is as follows:

[0046]

[0047] where v represents the speed of sound; L effrepresents the effective optical length, i.e. the distance that light effectively propagates in the carbon dioxide (medium) considering the absorption and scattering, etc., representing the length of interaction between light and medium; the velocity v depends on the specific heat capacity ratio γ under constant pressure and constant volume, the ideal gas constant R, the temperature T and the molar mass M of the gas; the resonance frequency of the differential photoacoustic cell 11 varies significantly with the concentration of carbon dioxide gas.

[0048] The frequency tracking detects the concentration by inversely measuring the resonance frequency of the differential photoacoustic cell 11, making up for the deficiency that the photoacoustic spectrum cannot realize linear detection of high concentration; the combination of the photoacoustic spectrum and the frequency tracking can realize linear detection of carbon dioxide with high precision and full range.

[0049] In the experiment, the photoacoustic spectrum mode is to excite a photoacoustic signal in the differential photoacoustic cell 11, and the sound wave signals captured by the first microphone 14 and the second microphone 15 are subtracted by the adder differential circuit 17. Since the photoacoustic signal in the differential photoacoustic cell 11 is reversed and the noise signal is in the same direction, the photoacoustic signal can be amplified and the same frequency noise can be eliminated by subtracting processing. After the amplification processing of the adder differential circuit 17, the electrical signal is transmitted to the control and collection module 2. By comparing the electrical signal with the signal of the standard sample with known concentration, the concentration of the gas is quantitatively analyzed. The frequency tracking mode is to measure the resonance frequency of the differential photoacoustic cell 11, and to determine the concentration of carbon dioxide from the determined resonance frequency.

[0050] The measurement results of the standard sample are shown in Figure 5 Figure 5 (a) can be seen, the detection of QCL laser 3, i.e. QCL mode (photoacoustic spectrum), the relationship between the concentration of 0-80 ppm carbon dioxide and the photoacoustic signal shows that the saturation concentration of carbon dioxide is 80 ppm; in the concentration range of 0-50 ppm, the linearity of concentration and photoacoustic signal is more than 0.9993; as Figure 5 (b) shows, the detection of DFB laser, i.e. DFB mode (photoacoustic spectrum), the linearity of 0-20% concentration and photoacoustic signal is 0.9999, indicating that the sensor has good linear response to carbon dioxide with concentration less than 20%, and the concentration of carbon dioxide below 20% is detected by photoacoustic spectrum mode, and the concentration of carbon dioxide is determined by checking the photoacoustic signal detected by the sensor; when the concentration exceeds 20%, the photoacoustic signal under the photoacoustic spectrum mode and the change of carbon dioxide concentration show a nonlinear relationship, and the helium-neon laser 5 is used for detection, i.e. He-Ne mode (frequency tracking), as Figure 3 ​(c) the 0-100% concentration-resonance frequency graph measured in the frequency tracking mode, within 20%-100% concentration, the linearity of concentration and resonance frequency is 0.9994, so when the carbon dioxide concentration is higher than 20%, the carbon dioxide concentration is inferred by measuring the resonance frequency of the differential photoacoustic cell 11 using the frequency tracking mode.

[0051] The present utility model simulates three environments: microbial growth environment (low concentration), factory production environment (medium concentration) and metal smelting environment (high concentration). The temperature in the simulated environment is set to 30℃, and the pressure is set to 1 atm. According to the characteristics of each environment, low, medium and high concentration carbon dioxide leakage is set, and the results are continuously monitored using a carbon dioxide gas detection device, as shown in Figure 6 The initial mode of the detection device is the frequency tracking mode. If the detection frequency remains below 1126Hz (corresponding to a concentration of 20%), the frequency tracking mode is enabled, otherwise it is automatically switched to the photoacoustic spectroscopy mode of the DFB laser 4, that is, it is automatically switched by changing the sinusoidal signal used by the helium-neon laser 5 to a sinusoidal signal with a sawtooth waveform applied to the DFB laser 4. If the result in the photoacoustic spectroscopy mode of the DFB laser 4 is below 0.0535mV (corresponding to a concentration of 50ppm), it is automatically switched to the photoacoustic spectroscopy mode of the QCL laser 3, that is, it is automatically switched by changing the sinusoidal and double sinusoidal waveform signal of the DFB laser 4 to the sinusoidal and double sinusoidal waveform signal of the QCL laser 3. The expression of the corresponding detection concentration range of the three modes is as follows:

[0052]

[0053] Figure 6 To measure the results of carbon dioxide at different concentrations by the present utility model, wherein, Figure 6 (a) is 30ppm, Figure 6 (b) is 10%, Figure 6 (c) is 80%, PAS represents photoacoustic spectroscopy, and RFT represents frequency tracking; first, pure nitrogen gas (0% carbon dioxide) is injected into the carbon dioxide gas detection device, and after stabilizing for 20s inside, as shown in Figure 6 (a), carbon dioxide with a concentration of 30ppm is immediately injected at a flow rate of 440sccm, the resonance frequency stabilizes after about 5s in the RFT mode, it is switched to the photoacoustic spectroscopy mode of the DFB laser 4 for detection, which is completed in 7s, and it is switched to the photoacoustic spectroscopy mode of the QCL laser 3 for detection, which is completed in 8s; as shown in Figure 6 (b), carbon dioxide with a concentration of 10% is immediately injected at a flow rate of 440sccm, the resonance frequency stabilizes after about 5s in the RFT mode, it is switched to the photoacoustic spectroscopy mode of the DFB laser 4 for detection, which is completed in 7s; as shown inFigure 6 (c) As shown in FIG. 44, carbon dioxide with a concentration of 80% was injected at a flow rate of 440 seem, and the detection was completed after the resonance frequency was stabilized for about 5 s in the RFT mode. The total detection time ranged from a minimum of 5 s to a maximum of 20 s, which was determined by the gas concentration.

Claims

1. A photoacoustic spectroscopy and frequency tracking based full-range carbon dioxide detection device, characterized by, It comprises: A laser light source module: including a QCL laser (3), a DFB laser (4) and a helium-neon laser (5), wherein the QCL laser (3) and the DFB laser (4) are used to emit infrared light, and the helium-neon laser (5) is used to emit visible light; A photoacoustic cell module: including a differential photoacoustic cell (11), a gas control unit and a sound signal acquisition unit, wherein the differential photoacoustic cell (11) is used to accommodate background gas and the carbon dioxide gas to be measured, and to generate a sound signal after the carbon dioxide gas to be measured absorbs the incident laser energy; the gas control unit is used to control and transport the carbon dioxide gas to be measured; the sound signal acquisition unit is used to convert the collected sound signal into an electrical signal; A control and receiving module (2): the electrical signal output end of the control and receiving module (2) is connected with the electrical signal input end of the QCL laser (3), the DFB laser (4) and the helium-neon laser (5) respectively, for controlling the laser light source module to emit specific laser; the electrical signal output end of the sound signal acquisition unit is connected with the electrical signal input end of the control and receiving module (2), for locking and demodulating the sound signal from the sound signal acquisition unit; A computer (1): the signal output end of the control and receiving module (2) is connected with the signal input end of the computer (1), for receiving and processing the sound signal demodulated from the control and receiving module (2), to obtain the concentration of the carbon dioxide gas to be measured; the signal output end of the computer (1) is connected with the signal input end of the control and receiving module (2), for transmitting control signals to the control and receiving module (2), so that the control and receiving module (2) controls the laser light source module to emit specific laser.

2. The full-range carbon dioxide detection device based on photoacoustic spectroscopy and frequency tracking according to claim 1, wherein: The laser output end of the QCL laser (3) is connected with the laser incidence end of the differential photoacoustic cell (11), and the incident laser of the QCL laser (3) directly enters the differential photoacoustic cell (11); The laser output end of the DFB laser (4) is connected with the laser input end of the collimator (19), the laser output end of the collimator (19) is connected with the laser incidence end of the differential photoacoustic cell (11), and the incident laser of the DFB laser (4) enters the differential photoacoustic cell (11) after being focused by the collimator (19); The laser output end of the helium-neon laser (5) is connected with the laser input end of the chopper (18), the laser output end of the chopper (18) is connected with the laser incidence end of the differential photoacoustic cell (11), and the incident laser of the helium-neon laser (5) enters the differential photoacoustic cell (11) after being frequency modulated by the chopper (18). 3.The all-range carbon dioxide detection device based on photoacoustic spectroscopy and frequency tracking according to claim 1, wherein: The differential photoacoustic cell (11) includes a first buffer cavity (20) and a second buffer cavity (21) in a cylindrical shape arranged at both ends along the direction of the gas flow, and the two buffer cavities are communicated through two parallel arranged first resonant cavity (22) and second resonant cavity (23); the carbon dioxide gas is introduced into the buffer cavity of the differential photoacoustic cell (11) through the gas inlet (12) of the differential photoacoustic cell (11), and the gas outlet (13) of the differential photoacoustic cell (11) is communicated with the buffer cavity of the differential photoacoustic cell (11) and the gas inlet of the exhaust pump (10), and the carbon dioxide gas after absorbing the laser energy is extracted.

4. A device for detecting carbon dioxide in a full range based on photoacoustic spectroscopy and frequency tracking according to any one of claims 1-3, characterized in that: The laser output end of the differential photoacoustic cell (11) is connected with the laser input end of the optical garbage can (16), which is used for absorbing excess laser and preventing laser dispersion.

5. The device according to claim 1, wherein the device is a photoacoustic spectroscopy and frequency tracking based full-range carbon dioxide detection device. The gas control unit includes a gas cylinder (9), a flow rate controller (8), a humidity controller (7) and a pressure controller (6); the gas cylinder (9) is used for storing the carbon dioxide gas to be detected; the flow rate controller (8) is used for controlling the gas to pass through the differential photoacoustic cell (11) at a specified flow rate; the humidity controller (7) is used for controlling the gas to pass through the differential photoacoustic cell (11) at a specified humidity; and the pressure controller (6) is used for controlling the pressure in the differential photoacoustic cell (11) and keeping it stable. 6.The all-range carbon dioxide detection device based on photoacoustic spectroscopy and frequency tracking of claim 1, wherein: The sound signal acquisition unit includes a first microphone (14), a second microphone (15) and an adder differential circuit (17) for subtracting the signals of the two microphones; the first microphone (14) and the second microphone (15) are arranged in the middle of the two resonant cavities of the differential photoacoustic cell (11); the electrical signal output ends of the first microphone (14) and the second microphone (15) are connected with the electrical signal input end of the adder differential circuit (17), and the electrical signal output end of the adder differential circuit (17) is connected with the electrical signal input end of the control and receiving module (2). 7.The all-range carbon dioxide detection device based on photoacoustic spectroscopy and frequency tracking of claim 1, wherein: The electrical signal output end of the control and receiving module (2) is connected with the electrical signal input end of the chopping controller, the electrical signal output end of the chopping controller is connected with the electrical signal input end of the chopper (18), and the control and receiving module (2) controls the incident laser emitted by the helium-neon laser (5) to be modulated into pulsed light with a certain period through the chopper (18) through the chopping controller. 8.The all-range carbon dioxide detection device based on photoacoustic spectroscopy and frequency tracking of claim 1, wherein: The control and receiving module (2) comprises a laser driving module (27), a signal collecting module (24), a signal modulation and demodulation module (25) and a signal input and output module (26); the signal output end of the computer (1) is connected with the input end of the laser driving module (27) through the signal input and output module (26), the laser driving module (27) is controlled by the computer (1) to supply power to the QCL laser (3), the DFB laser (4) and the helium-neon laser (5), and the temperature and current of the laser are controlled; the output end of the signal collecting module (24) is connected with the input end of the signal modulation and demodulation module (25), the output end of the signal modulation and demodulation module (25) is connected with the signal input end of the computer (1) through the signal input and output module (26), the signal collecting module (24) supplies power to the microphone arranged on the differential photoacoustic cell (11), and the electrical signal collected by the microphone is transmitted to the computer (1) after being analyzed and calculated by the signal modulation and demodulation module (25).

9. The device according to claim 8, wherein the device is a photoacoustic spectroscopy and frequency tracking based full-range carbon dioxide detection device. The signal modulation and demodulation module (25) comprises a signal generator, an adder and a lock-in amplifier, wherein the signal generator outputs a sine wave used for frequency modulation and a sawtooth wave used for wavelength sweeping; the adder is used for adding the sine wave and the sawtooth wave output by the signal generator into a signal and transmitting the signal to the laser in the laser light source module; and the lock-in amplifier is used for receiving the sine wave signal output by the signal generator and the electrical signal of the sound signal collecting unit and performing lock-in amplification.

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