A full-range deep-sea dissolved CH4 in-situ sensor

Abstract

This application discloses a full-range deep-sea dissolved CH4 in-situ sensor, belonging to the field of deep-sea dissolved gas in-situ detection technology. The full-range deep-sea dissolved CH4 in-situ sensor includes a circuit system unit, a trace gas measurement chamber unit, and a water-gas separation unit. The circuit system unit includes a microcontroller, a frequency synthesizer, an adder, a laser and a laser driver circuit, two analog lock-in amplifiers, two preamplifiers, and two analog-to-digital converters. The trace gas measurement chamber unit includes a trace gas measurement chamber, an optical fiber collimator, a tuning fork, a coaxial microresonator, a temperature, humidity, and pressure sensor, a photodetector, two solenoid valves, and a miniature air pump. The water-gas separation unit includes a base, a sintered block, filter paper, and a water-gas separation membrane. This disclosure provides a miniaturized, high-sensitivity, full-range in-situ sensor for deep-sea dissolved CH4 with low gas consumption, featuring high sensitivity, full range, low gas consumption, strong anti-interference ability, fast response, low power consumption, and small size.

Description

Technical Field

[0001] This application belongs to the field of in-situ detection technology of dissolved gas in deep sea, and particularly relates to a full-range in-situ sensor for dissolved CH4 in deep sea. Background Technology

[0002] The carbon cycle in the deep-sea environment reflects the processes of marine life and Earth's geological evolution, exerting a profound impact on the atmospheric environment. CH4, a high-energy-density carbon energy source, exists in deep-sea sediments in the form of natural gas hydrates. Due to the extreme instability of natural gas hydrates, factors such as seafloor activities easily lead to their decomposition into CH4 gas, which is released from the sediments. Furthermore, as a greenhouse gas, CH4's cycling into the atmosphere will exacerbate the risk of global warming. Therefore, studying the distribution of dissolved CH4 concentrations in the deep-sea environment is helpful for better managing and protecting Earth's ecosystems and addressing global challenges such as climate change.

[0003] Traditional deep-sea dissolved gas detection methods, such as "in-situ sampling-laboratory analysis," suffer from susceptibility to external interference and low temporal and spatial resolution. To meet the need for continuous temporal and spatial observation of deep-sea dissolved gaseous substances, in-situ online detection technology based on membrane separation and enrichment techniques has emerged. This technology utilizes the gas-selective permeability of membranes to separate and enrich dissolved CH4 in seawater, and combines this with gas detection technologies such as mass spectrometry, spectroscopy, and semiconductor gas sensors to achieve rapid measurement of dissolved CH4 in seawater. Currently, in-situ detection technology for dissolved CH4 in deep-sea based on membrane separation mainly quantifies the concentration of dissolved CH4 in seawater by measuring the water-gas separation flux. This method requires establishing a correlation between the concentration difference across the membrane and the system's permeation flux, but this correlation is easily affected by external factors. The membrane's own characteristics, installation method, and changes in the deep-sea environment such as temperature, pressure, and salinity all influence the membrane permeation flux. Furthermore, it is difficult to calibrate a concentration quantification model for the deep-sea environment. The equilibrium measurement method using the "dissolution-diffusion" model eliminates the influence of membrane properties and environmental factors on the measurement results. However, currently reported sensors suffer from response times on the order of hours due to the large volume of the measurement chamber. Therefore, reducing the volume of the measurement chamber is the best option to improve the system's response time and eliminate the influence of membrane properties and environmental factors. Furthermore, current spectroscopic techniques have limited measurement ranges, making it difficult to meet the long-term measurement needs for large dynamic range changes in dissolved CH4 concentration in seawater under extreme environments such as cold seeps.

[0004] Therefore, it is necessary to provide a new full-range in-situ sensor for dissolved CH4 in the deep sea to solve the above-mentioned technical problems. Summary of the Invention

[0005] The purpose of this disclosure is to provide a full-range deep-sea dissolved CH4 in-situ sensor to solve the above-mentioned problems.

[0006] This disclosure achieves the above objectives through the following technical solutions:

[0007] A full-range deep-sea dissolved CH4 in-situ sensor includes a water-gas separation unit, a trace gas measurement chamber unit, and a circuit system unit connected in sequence.

[0008] The water-gas separation unit is used to separate dissolved CH4 from seawater and introduce it into the trace gas measurement chamber unit;

[0009] The trace gas measurement chamber unit is used for storing CH4 and acquiring parameters, and the trace gas measurement chamber unit includes a tuning fork;

[0010] The circuit system unit is used to collimate the modulated laser beam and incident it into the trace gas measurement cavity unit using wavelength modulation technology, causing the tuning fork to vibrate and generate a piezoelectric current to realize the concentration detection of CH4.

[0011] As a further optimization of this disclosure, the water-gas separation unit includes a water-gas separation membrane, filter paper, sintered block and base arranged sequentially from top to bottom;

[0012] The trace gas measurement chamber unit includes an optical fiber collimator, a trace gas measurement chamber, a second solenoid valve, and a micro gas pump connected in sequence; it also includes a first solenoid valve, and the water-gas separation unit is connected to the trace gas measurement chamber through the first solenoid valve; the trace gas measurement chamber is equipped with the tuning fork, coaxial micro-resonant tube, photodetector, and temperature, humidity, and pressure sensor;

[0013] The circuit system unit includes a microcontroller, a frequency synthesizer, an adder, a laser driver circuit, and a laser connected in sequence; the laser is connected to the fiber collimator; the circuit system unit also includes a first preamplifier, a second preamplifier, a first analog lock-in amplifier, a second analog lock-in amplifier, a first analog-to-digital converter, and a second analog-to-digital converter; both the first preamplifier and the second preamplifier are connected to the trace gas measurement cavity; the first preamplifier, the first analog lock-in amplifier, the second analog-to-digital converter, and the microcontroller are connected in sequence; the second preamplifier, the second analog lock-in amplifier, the first analog-to-digital converter, and the microcontroller are connected in sequence; both the first analog lock-in amplifier and the second analog lock-in amplifier are connected to the frequency synthesizer.

[0014] As a further optimization of this disclosure, the first preamplifier has a tuning fork frequency calibration function. When the analog switch is set to a low level via the microcontroller's GPIO port, one pin of the tuning fork is connected to the calibration signal input terminal, which can realize the tuning fork response frequency calibration. fCalibration of 0; when the analog switch is set to high level, one pin of the tuning fork is connected to ground, which enables the detection of sound wave signals.

[0015] As a further optimization of this disclosure, the photodetector is an indium gallium arsenide infrared sensor with a response wavelength of 800 μm to 1700 μm.

[0016] As a further optimization of this disclosure, both the first analog lock-in amplifier and the second analog lock-in amplifier include a preamplifier, two multipliers, and two low-pass filters; the preamplifier has a gain greater than 1×10⁻⁶. 4 .

[0017] As a further optimization of this disclosure, the microcontroller is connected to a host computer to enable data uploading.

[0018] As a further optimization of this disclosure, the workflow includes the following steps:

[0019] Power is supplied, and when the current stabilizes, it is determined whether the current value is less than the preset value. If the current value is greater than the preset value, the power is cut off.

[0020] The operating temperature of the laser is set by outputting a DC level through the microcontroller. When the indicator light of the temperature control module of the laser driver circuit lights up, it indicates that the laser temperature control is stable.

[0021] The response frequency of the tuning fork is calibrated, and the response frequency value is used as... f 0 represents;

[0022] The microcontroller controls the frequency synthesizer to generate four signals, namely the laser scanning signal. f s Modulation signal f 0 / 2, and demodulated signal f 0 and f 1, and f 1 and f They have the same frequency but are 90° out of phase.

[0023] The scan signal is converted by an adder. f s and modulated signal f The 0 and 2 signals are added together, and the resulting signal is output to the laser drive current control module to enable the laser to emit light normally.

[0024] The laser pigtail is connected to the fiber collimator via a flange. After the beam is collimated, it enters the micro gas measurement cavity, passes between the coaxial micro-resonator tube and the tuning fork arm, and the transmitted light is received by the photodetector.

[0025] The water-gas separation membrane is attached to the surface of the filter paper, and then the filter paper is tightly attached to the surface of the sintered block and installed in the base in sequence. The base surface is engraved with a base guide track to transmit the separated gas to the micro gas measurement chamber.

[0026] Simultaneously activate the first and second solenoid valves and the micro air pump. Under the action of the micro air pump, control the air pressure in the base guide rail and the trace gas measurement chamber within the preset pressure, and then close the first and second solenoid valves and the micro air pump. Seawater flows over the surface of the water-gas separation membrane, forming a stable CH4 concentration field on the membrane surface. Under the driving force of concentration difference and pressure difference, the dissolved CH4 molecules dissolve into the water-gas separation membrane and diffuse into the base guide rail to complete the gas-liquid separation. When the concentration on both sides of the water-gas separation membrane reaches equilibrium, open the first and second solenoid valves and the micro air pump to draw the equilibrium CH4 gas into the trace gas measurement chamber for measurement.

[0027] CH4 molecules absorb laser light to generate an acoustic signal. This signal is amplified by a coaxial microresonator, and the acoustic wave causes a tuning fork to vibrate, generating a piezoelectric current to detect CH4. The transmitted light is then used to measure the full range of CH4 and the laser intensity through a photodetector.

[0028] The piezoelectric current generated by the tuning fork and the photocurrent generated by the photodetector are converted into voltage signals by the first and second preamplifiers, and then amplified by the transimpedance amplifier circuit. The amplified direct absorption signal is divided into two paths. One path is directly acquired by the first and second analog-to-digital converters, and the laser intensity is measured by calculating the background amplitude. The other path, along with the photoacoustic signal, is demodulated by the first and second analog lock-in amplifiers to obtain the second harmonic component X2 of the quartz-enhanced photoacoustic spectrum. f _QEPAS and orthogonal component Y2 f _QEPAS And the second harmonic co-directional component X of the wavelength modulation spectrum 2f _WMS and orthogonal component Y 2f _WMS Four signals;

[0029] The temperature, humidity and air pressure sensors upload environmental parameters to the microcontroller;

[0030] The first analog-to-digital converter and the second analog-to-digital converter respectively process X2 f _QEPAS Y2 f _QEPAS X 2f _WMS Y 2f _WMS Data is acquired from four signals;

[0031] Based on X2 f _QEPAS Y2 f _QEPAS X 2f _WMS Y 2f _WMS Calculate the second harmonic amplitude R2 of the quartz-enhanced photoacoustic spectrum. f _QEPAS The second harmonic amplitude R2 of the wavelength modulation spectrum f _WMS Using the background amplitude of the directly absorbed signal to adjust R2 f _QEPAS R2 f _WMS The signal amplitude is normalized; the normalized R² is adjusted according to environmental parameters. f _QEPAS The signal amplitude is corrected to obtain the final gas concentration value;

[0032] The microcontroller communicates with the host computer in real time via RS485 communication to upload data.

[0033] As a further optimization of this disclosure, the response frequency of the tuning fork is calibrated, including:

[0034] The analog switch of the first preamplifier is set to low level via the GPIO port. One pin of the tuning fork is connected to the input of the calibration signal. The microcontroller controls the frequency synthesizer to generate a frequency of [frequency value missing]. f ± f The calibration sine signal is used to calibrate the frequency response of the tuning fork. f The pre-set center response frequency of the tuning fork f The frequencies were set to 0, 0.1 Hz, 0.2 Hz, 0.3 Hz, 0.4 Hz, and 0.5 Hz, respectively. The responses of the tuning fork at different frequencies were collected, and the center response frequency was obtained by fitting the data. f 0, and will f 0 is set as the default value.

[0035] As a further optimization of this disclosure, the temperature, humidity and air pressure sensor uploads environmental parameters to the microcontroller via I2C communication, and the environmental parameters include temperature, humidity and air pressure.

[0036] As a further optimization of this disclosure, based on X2 f _QEPAS Y2 f _QEPAS X 2f_WMS Y 2f _WMS Calculate R2 f _QEPAS R2 f _WMS The calculation formula is as follows:

[0037] ;

[0038] .

[0039] The beneficial effects of this disclosure are as follows:

[0040] This invention has the advantages of high sensitivity, full range, low gas consumption, strong anti-interference ability, fast response, low power consumption and small size. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of the overall structure in an embodiment of this disclosure;

[0043] Figure 2 This is a schematic diagram of the overall circuit system structure of the sensor in the embodiments of this disclosure;

[0044] Figure 3 This is a schematic diagram of the analog lock-in amplifier structure in an embodiment of this disclosure;

[0045] Figure 4 This is a flowchart illustrating the working principle of the sensor in an embodiment of this disclosure.

[0046] In the diagram: 1. Water-gas separation unit; 101. Water-gas separation membrane; 102. Filter paper; 103. Sintered block; 104. Base;

[0047] 2. First solenoid valve; 3. Second solenoid valve; 4. Miniature air pump;

[0048] 5. Trace gas measurement chamber; 501. Tuning fork; 502. Coaxial microresonator; 503. Photodetector; 504. Temperature, humidity and pressure sensor;

[0049] 6. First preamplifier; 7. Second preamplifier; 8. First analog lock-in amplifier; 9. Second analog lock-in amplifier; 10. First analog-to-digital converter; 11. Second analog-to-digital converter; 12. Microcontroller; 13. Host computer; 14. Frequency synthesizer; 15. Adder; 16. Laser driver circuit; 17. Laser; 18. Fiber collimator. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0051] like Figure 1 As shown, a full-range deep-sea dissolved CH4 in-situ sensor includes a water-gas separation unit 1, a trace gas measurement chamber unit, and a circuit system unit connected in sequence.

[0052] The water-gas separation unit 1 includes a water-gas separation membrane 101, filter paper 102, sintered block 103 and base 104 arranged sequentially from top to bottom. The base 104 has a base guide track engraved on its surface.

[0053] The trace gas measurement chamber unit includes an optical fiber collimator 18, a trace gas measurement chamber 5, a second solenoid valve 3, and a micro air pump 4 connected in sequence; it also includes a first solenoid valve 2, and the water-gas separation unit 1 is connected to the trace gas measurement chamber 5 through the first solenoid valve 2; the trace gas measurement chamber 5 is equipped with a tuning fork 501, a coaxial micro resonant tube 502, a photodetector 503, and a temperature, humidity, and pressure sensor 504;

[0054] The circuit system unit includes a microcontroller 12, a frequency synthesizer 14, an adder 15, a laser driver circuit 16, and a laser 17 connected in sequence; the laser 17 is connected to the fiber collimator 18; the circuit system unit also includes a first preamplifier 6, a second preamplifier 7, a first analog lock-in amplifier 8, a second analog lock-in amplifier 9, a first analog-to-digital converter 10, and a second analog-to-digital converter 11; the first preamplifier 6 and the second preamplifier 7 are both connected to the trace gas measurement cavity 5; the first preamplifier 6, the first analog lock-in amplifier 8, the second analog-to-digital converter 11, and the microcontroller 12 are connected in sequence; the second preamplifier 7, the second analog lock-in amplifier 9, the first analog-to-digital converter 10, and the microcontroller 12 are connected in sequence; the first analog lock-in amplifier 8 and the second analog lock-in amplifier 9 are both connected to the frequency synthesizer 14.

[0055] like Figure 2 As shown, it also includes an independent power supply unit with an input voltage of 24V-36V. It has five independent power supply outputs and a current detection function. If the current is less than 1 A, the system is operating stably; if the current is greater than 1 A, the system will automatically power off.

[0056] Simultaneously start the first solenoid valve 2, the second solenoid valve 3, and the micro air pump 4. Under the action of the micro air pump 4, the air pressure in the base guide rail and the micro gas measurement chamber 5 is controlled at 30 kPa, and the first solenoid valve 2, the second solenoid valve 3, and the micro air pump 4 are closed. Seawater flows over the surface of the water-gas separation membrane 101, forming a stable CH4 concentration field on its surface. Driven by the concentration and pressure differences, the CH4 molecules dissolved in the seawater dissolve into the water-gas separation membrane 101 and diffuse into the base guide rail, completing the gas-liquid separation. When the concentrations on both sides of the water-gas separation membrane 101 reach equilibrium, open the first solenoid valve 2, the second solenoid valve 3, and the micro air pump 4 to pump the balanced CH4 gas into the micro gas measurement chamber 5 for measurement.

[0057] The first preamplifier 6 has a tuning fork frequency calibration function. When the analog switch is set to low level through the microcontroller's 12GPIO port, one pin of the tuning fork 501 is connected to the calibration signal input terminal, which can realize the calibration of the tuning fork response frequency. f 0 calibration; when the analog switch is set to high level, one pin of the tuning fork 501 is connected to ground, which can realize the detection of sound wave signals;

[0058] Microcontroller 12 sets the frequency synthesizer 14 to output four sinusoidal signals of different frequencies via the SPI communication protocol, which are laser scanning signals. f s Modulation signal f0 / 2, and demodulated signal f 0、 f 1, and f 1 and f They have the same frequency but are 90° out of phase.

[0059] The scan signal is processed by adder 15 f s and modulated signal f The 0 / 2 are added together, and the driving current is applied to the laser 17 through the laser driving circuit 16 to achieve modulation of the laser 17;

[0060] Laser 17 is collimated by fiber collimator 18 and incident into the trace gas measurement cavity 5. The laser beam passes between the two forks of coaxial microresonator 502 and tuning fork 501, achieving highly sensitive measurement of CH4 through tuning fork 501. The coaxial microresonator is 90 mm long, and the overall effective optical path length reaches 100 mm. The transmitted light is received by photodetector 503. Therefore, the full range of CH4 measurement and laser intensity measurement can be achieved through photodetector 503.

[0061] The generated photoacoustic signal and direct absorption signal are converted from current signals to voltage signals and amplified by the first preamplifier 6 and the second preamplifier 7, respectively. The amplified direct absorption signal is divided into two paths. One path is directly acquired by the first analog-to-digital converter 10 and the second analog-to-digital converter 11, and the laser intensity is measured by calculating the background amplitude of the signal. The other path and the photoacoustic signal are demodulated by the first analog lock-in amplifier 8 and the second analog lock-in amplifier 9, respectively.

[0062] The second harmonic in-phase component X2 of the demodulated quartz-enhanced photoacoustic spectrum (QEPAS) f _QEPAS Orthogonal component Y2 f _QEPAS and the second harmonic co-directional component X of wavelength modulation spectrum (WMS) 2f _WMS Orthogonal component Y 2f _WMS The four signals are acquired by the first analog-to-digital converter 10 and the second analog-to-digital converter 11, and the spectral data is processed by the microcontroller 12 to obtain the second harmonic amplitude R2 of QEPAS. f _QEPAS The second harmonic amplitude R of WMS 2f _WMS The gas concentration and light intensity information are obtained, and the influence of light intensity is eliminated by normalizing the concentration information.

[0063] The microcontroller 12 communicates with the host computer 13 in real time via the RS485 communication protocol to upload data.

[0064] The water-air separation membrane 101 is a polydimethylsiloxane (PDMS) membrane with a thickness of 10 μm and a diameter greater than or equal to 100 mm.

[0065] Laser 17 is a near-infrared continuously tunable single longitudinal mode output laser with a center wavelength of 1653.72 nm.

[0066] The laser driving circuit 16 has a temperature control sensitivity of 0.001 ℃, a driving current sensitivity of 0.1mA, and a frequency sensitivity of 0.05Hz.

[0067] The tuning fork 501 has a resonant frequency range of 3.86 kHz and a full width at half maximum (FWHM) of less than 0.5 Hz. The tuning fork 501 has a total length of 28 mm, a thickness of 0.55 mm, and fork arm length and width of 20 mm and 1.57 mm, respectively.

[0068] The coaxial microresonator 502 consists of two tubes with a diameter of 2 mm and a length of 45 mm, with a total resonator length of 90 mm.

[0069] The photodetector 503 is an indium gallium arsenide (InGaAs) infrared sensor with a response band of 800 μm to 1700 μm.

[0070] The frequency synthesizer 14, model AD9959, can simultaneously output four sine signals of different frequencies and phases, with a frequency tuning resolution better than 0.12Hz.

[0071] like Figure 3 As shown, both the first analog lock-in amplifier 8 and the second analog lock-in amplifier 9 include a preamplifier, two multipliers, and two low-pass filters. The preamplifier has a gain greater than 1 × 10⁻⁶. 4 The center frequency of the bandpass filter was set to 3.86 kHz, and the -3 dB bandwidth was 3.8 kHz; the integration time of the low-pass filter was greater than 500 ms. Two multipliers and two low-pass filters were used to obtain 2... f X / 1 f X 2 f Y / 1 f Y .

[0072] The first analog-to-digital converter 10 and the second analog-to-digital converter 11 have an effective resolution better than 16 bits and a sampling rate better than 1MHz, which meets the requirements for 4-channel acquisition.

[0073] The power supply voltage is 24V-36V, and the current is less than 1A.

[0074] like Figure 4 As shown, the workflow includes the following steps:

[0075] S1. Power on the system. Once the current stabilizes, check if the current value is less than 1 A. If the current value is greater than 1 A, the system will power off.

[0076] S2. Set the laser operating temperature by outputting a DC level through the microcontroller 12. When the indicator light of the temperature control module of the laser drive circuit 16 lights up, it indicates that the temperature control of the laser 17 is stable.

[0077] S3. Calibrate the response frequency of tuning fork 501. Set the analog switch of the first preamplifier 6 to low level via GPIO port. Connect one pin of tuning fork 501 to the input terminal of the calibration signal. The microcontroller 12 controls the frequency synthesizer 14 to generate a frequency of... f ± f The calibration sine signal is used to calibrate the frequency response of the tuning fork. f The pre-set center response frequency of the tuning fork f The frequencies were set to 0, 0.1 Hz, 0.2 Hz, 0.3 Hz, 0.4 Hz, and 0.5 Hz, respectively. The responses of the tuning fork 501 at different frequencies were collected, and the center response frequency was obtained by fitting the data. f 0, and will f 0 is set as the default value;

[0078] S4, the microcontroller 12 controls the frequency synthesizer 14 to generate four signals, namely the laser scanning signal. f s Modulation signal f 0 / 2, and demodulated signal f 0 and f 1, and f 1 and f They have the same frequency but are 90° out of phase.

[0079] S5, using adder 15 to... f s , f The 0 and 2 signals are added together, and the resulting signal is output to the laser drive current control module, allowing laser 17 to emit light normally.

[0080] S6. The laser 17 pigtail is connected to the fiber collimator 18 via a flange. After the beam is collimated, it enters the micro gas measurement cavity 5 and passes between the coaxial micro resonator tube 502 and the fork arm of the tuning fork 501. The transmitted light is received by the photodetector 503.

[0081] S7. Attach the water-gas separation membrane 101 to the surface of the filter paper 102, then attach the filter paper 102 tightly to the surface of the sintered block 103, and install them in the base 104 in sequence. The base 104 has a base guide track engraved on its surface, which can transmit the separated gas to the micro gas measuring chamber 5.

[0082] S8. Simultaneously start the first solenoid valve 2, the second solenoid valve 3, and the micro air pump 4. Under the action of the micro air pump 4, control the air pressure of the base guide rail and the micro gas measurement chamber 5 at 30 kPa, and close the first solenoid valve 2, the second solenoid valve 3, and the micro air pump 4. Seawater flows over the surface of the water-gas separation membrane 101, forming a stable CH4 concentration field on the membrane surface. Under the driving force of concentration difference and pressure difference, the dissolved CH4 molecules dissolve into the water-gas separation membrane 101 and diffuse into the base guide rail to complete the gas-liquid separation. When the concentration on both sides of the water-gas separation membrane 101 reaches equilibrium, open the first solenoid valve 2, the second solenoid valve 3, and the micro air pump 4 to draw the balanced CH4 gas into the micro gas measurement chamber 5 for measurement.

[0083] S9 and CH4 molecules absorb laser light to generate acoustic signals. These signals are amplified by a coaxial microresonator 502, causing a tuning fork 501 to vibrate and generate a piezoelectric current, enabling highly sensitive detection of CH4. The coaxial microresonator 502 is 90 mm long, and the overall effective optical path length reaches 100 mm. Therefore, the transmitted light passes through a photodetector 503 to achieve full-range measurement of CH4 and to measure the laser intensity.

[0084] The piezoelectric current generated by S10 and tuning fork 501, and the photocurrent generated by photodetector 503, are converted into voltage signals by first preamplifier 6 and second preamplifier 7, and then amplified by transimpedance amplifier circuit. The amplified direct absorption signal is divided into two paths. One path is directly acquired by first analog-to-digital converter 10 and second analog-to-digital converter 11, and the laser intensity is measured by calculating the background amplitude. The other path, along with the photoacoustic signal, is demodulated by first analog lock-in amplifier 8 and second analog lock-in amplifier 9 to obtain X2. f _QEPAS Y2 f _QEPAS X 2f _WMS Y 2f _WMS Four signals;

[0085] S11. The temperature, humidity and pressure sensor 504 inside the trace gas measurement chamber 5 transmits environmental parameter information such as temperature, humidity and pressure to the microcontroller 12 via I2C communication.

[0086] S12, analog-to-digital converters 10 and 11 respectively process X2 f _QEPAS Y2 f _QEPAS X 2f _WMS Y 2f _WMS Data is acquired from four signals;

[0087] S13, based on X2 f _QEPAS Y2 f _QEPAS X 2f _WMS Y 2f _WMS Calculate R2 f _QEPAS R2 f _WMS Using the background amplitude of the directly absorbed signal to adjust R2 f _QEPAS R2 f _WMS The signal amplitude is normalized to eliminate the impact of light intensity fluctuations on the measurement. The normalized R² is then calculated based on temperature, humidity, and air pressure data. f _QEPAS The signal amplitude is corrected to obtain the final gas concentration value; based on X2 f _QEPAS Y2 f _QEPAS X 2f _WMS Y 2f _WMS Calculate R2 f _QEPAS R2 f _WMS The formula is as follows:

[0088] ;

[0089] .

[0090] S14. The microcontroller 12 can communicate with the host computer 13 in real time via RS485 communication to upload data.

[0091] The embodiments described above are merely examples of several implementations of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent disclosure. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and these modifications and improvements all fall within the protection scope of this disclosure.

Claims

1. A full-range in-situ sensor for deep-sea dissolved CH4, characterized in that, It includes a water-gas separation unit (1), a trace gas measurement chamber unit, and a circuit system unit connected in sequence; The water-gas separation unit (1) is used to separate dissolved CH4 from seawater and introduce it into the trace gas measuring chamber unit; The trace gas measurement chamber unit is used for storing CH4 and collecting parameters, and the trace gas measurement chamber unit includes a tuning fork (501). The circuit system unit is used to collimate the modulated laser beam and then incident it into the trace gas measurement cavity unit using wavelength modulation technology, so as to cause the tuning fork (501) to vibrate and generate piezoelectric current to realize the concentration detection of CH4. The water-gas separation unit (1) includes a water-gas separation membrane (101), filter paper (102), sintered block (103) and base (104) arranged from top to bottom. The trace gas measurement chamber unit includes an optical fiber collimator (18), a trace gas measurement chamber (5), a second solenoid valve (3), and a micro air pump (4) connected in sequence; it also includes a first solenoid valve (2), and the water-gas separation unit (1) is connected to the trace gas measurement chamber (5) through the first solenoid valve (2); the trace gas measurement chamber (5) is equipped with the tuning fork (501), a coaxial micro resonant tube (502), a photodetector (503), and a temperature, humidity, and pressure sensor (504); The circuit system unit includes a microcontroller (12), a frequency synthesizer (14), an adder (15), a laser driver circuit (16), and a laser (17) connected in sequence; the laser (17) is connected to the fiber collimator (18); the circuit system unit also includes a first preamplifier (6), a second preamplifier (7), a first analog lock-in amplifier (8), a second analog lock-in amplifier (9), a first analog-to-digital converter (10), and a second analog-to-digital converter (11); the first preamplifier (6) and the second preamplifier (7) are both connected to the trace gas measurement cavity (5); the first preamplifier (6), the first analog lock-in amplifier (8), the second analog-to-digital converter (11), and the microcontroller (12) are connected in sequence; the second preamplifier (7), the second analog lock-in amplifier (9), the first analog-to-digital converter (10), and the microcontroller (12) are connected in sequence; the first analog lock-in amplifier (8) and the second analog lock-in amplifier (9) are both connected to the frequency synthesizer (14); The first preamplifier (6) has a tuning fork frequency calibration function. When the analog switch is set to low level through the GPIO port of the microcontroller (12), one pin of the tuning fork (501) is connected to the calibration signal input terminal, which can realize the tuning fork response frequency calibration. f 0 calibration; when the analog switch is set to high level, one pin of the tuning fork (501) is connected to ground, which can realize the detection of sound wave signals; The response frequency of the tuning fork (501) is calibrated, including: The analog switch of the first preamplifier (6) is set to low level via the GPIO port. One pin of the tuning fork (501) is connected to the input of the calibration signal. The microcontroller (12) controls the frequency synthesizer (14) to generate a frequency of f ± f The calibration sine signal is used to calibrate the frequency response of the tuning fork. f The pre-set center response frequency of the tuning fork f The frequencies were set to 0, 0.1 Hz, 0.2 Hz, 0.3 Hz, 0.4 Hz, and 0.5 Hz, respectively. The responses of the tuning fork (501) at different frequencies were collected, and the center response frequency was obtained by fitting the data. f 0, and will f 0 is set as the default value.

2. A full-range in-situ sensor for dissolved CH4 in deep sea according to claim 1, characterized in that, The photodetector (503) is an indium gallium arsenide infrared sensor with a response band of 800 μm to 1700 μm.

3. The full-range deep-sea dissolved CH4 in-situ sensor according to claim 1, characterized in that, Both the first analog lock-in amplifier (8) and the second analog lock-in amplifier (9) include a preamplifier, two multipliers, and two low-pass filters; the preamplifier has a gain greater than 1×10⁻⁶. 4 .

4. The in-situ sensor for full range deep ocean dissolved CH4 according to claim 1, wherein, The microcontroller (12) is connected to a host computer (13) to enable data uploading.

5. The in-situ sensor for full range deep ocean dissolved CH4 according to claim 1, wherein, The workflow includes the following steps: Power is supplied, and when the current stabilizes, it is determined whether the current value is less than the preset value. If the current value is greater than the preset value, the power is cut off. The operating temperature of the laser (17) is set by outputting a DC level through the microcontroller (12). When the indicator light of the temperature control module of the laser drive circuit (16) lights up, it indicates that the temperature control of the laser (17) is stable. The response frequency of the tuning fork (501) is calibrated, and the response frequency value is indicated by f 0. The microcontroller (12) controls the frequency synthesizer (14) to generate four signals, namely the laser scanning signal. f s Modulation signal f 0 / 2 and demodulated signal f 0 and f 1, and f 1 and f They have the same frequency but are 90° out of phase. The scan signal is processed by adder (15). f s and modulated signal f The 0 and 2 signals are added together, and the added signal is output to the laser drive current control module to enable the laser (17) to emit light normally. The laser (17) pigtail is connected to the fiber collimator (18) through a flange. After the beam is collimated, it enters the micro gas measurement cavity (5), passes between the coaxial micro resonator tube (502) and the tuning fork (501) fork arm, and the transmitted light is received by the photodetector (503). The water-gas separation membrane (101) is attached to the surface of the filter paper (102), and then the filter paper (102) is tightly attached to the surface of the sintered block (103), and then installed in the base (104) in sequence. The base (104) has a base guide track engraved on its surface, which can transmit the separated gas to the micro gas measuring chamber (5). Start the first solenoid valve (2), the second solenoid valve (3) and the micro air pump (4) at the same time. Under the action of the micro air pump (4), control the air pressure of the base guide rail and the micro gas measurement chamber (5) within the preset pressure and close the first solenoid valve (2), the second solenoid valve (3) and the micro air pump (4); seawater flows over the surface of the water-gas separation membrane (101) and forms a stable CH4 concentration field on the membrane surface; under the driving force of concentration difference and pressure difference, the dissolved CH4 molecules dissolve into the water-gas separation membrane (101) and diffuse into the base guide rail to complete the gas-liquid separation; when the concentration on both sides of the water-gas separation membrane (101) reaches equilibrium, open the first solenoid valve (2), the second solenoid valve (3) and the micro air pump (4) to draw the balanced CH4 gas into the micro gas measurement chamber (5) for measurement; CH4 molecules absorb laser light to generate an acoustic signal. The acoustic signal is amplified by a coaxial micro-resonator (502). The acoustic wave causes the tuning fork (501) to vibrate, generating a piezoelectric current to detect CH4. The transmitted light is used to measure the full range of CH4 through a photodetector (503), and the laser intensity is also measured. The piezoelectric current generated by the tuning fork (501) and the photocurrent generated by the photodetector (503) are converted into voltage signals by the first preamplifier (6) and the second preamplifier (7), and then amplified by the transimpedance amplifier circuit. The amplified direct absorption signal is divided into two paths. One path is directly acquired by the first analog-to-digital converter (10) and the second analog-to-digital converter (11), and the laser intensity is measured by calculating the background amplitude of the signal. The other path and the photoacoustic signal are demodulated by the first analog lock-in amplifier (8) and the second analog lock-in amplifier (9) to obtain the second harmonic component X2 of the quartz-enhanced photoacoustic spectrum. f _QEPAS and orthogonal component Y2 f _QEPAS And the second harmonic co-directional component X of the wavelength modulation spectrum 2f _WMS and orthogonal component Y 2f _WMS Four signals; The temperature, humidity and pressure sensor (504) uploads environmental parameters to the microcontroller (12). The first analog-to-digital converter (10) and the second analog-to-digital converter (11) respectively process X2 f _QEPAS Y2 f _QEPAS X 2f _WMS Y 2f _WMS Data is acquired from four signals; Based on X2 f _QEPAS Y2 f _QEPAS X 2f _WMS Y 2f _WMS Calculate the second harmonic amplitude R2 of the quartz-enhanced photoacoustic spectrum. f _QEPAS The second harmonic amplitude R2 of the wavelength modulation spectrum f _WMS Using the background amplitude of the directly absorbed signal to adjust R2 f _QEPAS R2 f _WMS The signal amplitude is normalized; the normalized R² is adjusted according to environmental parameters. f _QEPAS The signal amplitude is corrected to obtain the final gas concentration value; The microcontroller (12) communicates with the host computer (13) in real time via RS485 communication to upload data.

6. A full-range in-situ sensor for dissolved CH4 in deep sea according to claim 1, characterized in that, The temperature, humidity and air pressure sensor (504) uploads environmental parameters to the microcontroller (12) via I2C communication. The environmental parameters include temperature, humidity and air pressure.

7. A full-range in-situ sensor for dissolved CH4 in deep sea according to claim 5, characterized in that, Based on X2 f _QEPAS Y2 f _QEPAS X 2f _WMS Y 2f _WMS Calculate R2 f _QEPAS R2 f _WMS The calculation formula is as follows: ； 。

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