Multi-gas detection device and method

Abstract

The present application provides a multi-gas detection device and method, which includes a pump source, a wavelength division multiplexer, a doped optical fiber, a gas absorption cell, a wavelength selection and modulation module, a transmission quartz tuning fork light detection module, a preamplifier, a phase-locked amplifier array, and a computer, wherein the wavelength selection and modulation module can simultaneously generate light of multiple wavelengths, each wavelength of light corresponding to the absorption peak of a gas in the mixed gas to be measured in the gas absorption cell, and the modulation frequency of each wavelength of light is different. By setting the wavelength selection and modulation module and the transmission quartz tuning fork light detection module, it is possible to use a single quartz tuning fork to simultaneously detect mixed gases, and the quartz tuning fork is separated from the gas absorption cell, avoiding the problem of being corroded by the gas to be measured, thereby affecting the accuracy of the detection results, and improving the quality factor. The device has the advantages of simple structure, high power, long optical path, and high precision.

Description

Technical Field

[0001] The present application relates to the field of multi-gas detection, and in particular to a multi-gas detection device and method. Background Art

[0002] The development of gas detection technology is of great significance in the fields of atmospheric environment monitoring, human daily life and industrial development. In recent years, with the increasingly complex environmental changes, the development of industrial modernization and the continuous improvement of people's environmental health awareness, traditional single gas detection can no longer meet the requirements, so multi-gas detection has been rapidly developed and promoted.

[0003] The basic operating principle of photothermoelastic spectroscopy gas detection technology is that photons are absorbed by gas molecules in a gas absorption cell, causing light intensity attenuation. The absorbed light then strikes the arms of a quartz tuning fork, creating a temperature field. The photothermoelastic effect causes the tuning fork to vibrate, generating a piezoelectric signal. Photothermoelastic spectroscopy gas detection offers advantages such as high accuracy, full-wavelength response, non-contact gas measurement, and low cost.

[0004] At present, some scholars have proposed a photoacoustic spectroscopy gas detection technology based on multi-tuning fork frequency division multiplexing technology. Three quartz tuning forks respond to sound waves of different frequencies to achieve simultaneous detection of three gases. However, the above method has a complex structure, low excitation light source power, and is difficult to collimate. Summary of the Invention

[0005] The present application provides a multi-gas detection device and method, which realizes the simultaneous detection of multiple gases and has the advantages of simple structure, high power, long optical path, and high precision.

[0006] In a first aspect, a multi-gas detection device is provided, comprising a pump source, a wavelength division multiplexer, a doped optical fiber, a gas absorption cell, a wavelength selection and modulation module, a transmission quartz tuning fork light detection module, a preamplifier, a lock-in amplifier array, and a computer;

[0007] The transmissive quartz tuning fork optical detection module includes a quartz tuning fork, a first collimator, a second collimator, and a transparent glass housing. The first collimator is inserted into a first side of the transparent glass housing, and the second collimator is inserted into a second side of the transparent glass housing opposite to the first side. The quartz tuning fork is encapsulated in the transparent glass housing by vacuum or inert gas and is located between the inner ends of the first collimator and the second collimator. The metal film at the incident point of the quartz tuning fork is removed by chemical etching.

[0008] The output optical fiber of the pump source is connected to the first input end of the wavelength division multiplexer, the output end of the wavelength division multiplexer is connected to the doped optical fiber, the doped optical fiber is connected to the input end of the gas absorption cell, the output optical fiber of the gas absorption cell is connected to the wavelength selection and modulation module, the output optical fiber of the wavelength selection and modulation module is connected to the input end of the transmission quartz tuning fork light detection module, the optical signal output optical fiber of the transmission quartz tuning fork light detection module is connected to the second input end of the wavelength division multiplexer, the electrical signal output end of the transmission quartz tuning fork light detection module is connected to the input end of the preamplifier, the output end of the preamplifier is connected to the input end of the phase-locked amplifier array, and the output end of the phase-locked amplifier array is connected to the computer. The gas absorption cell is filled with a mixed gas to be measured. The wavelength selection and modulation module can simultaneously generate light of multiple wavelengths, each wavelength of light corresponding to the absorption peak of a gas in the mixed gas to be measured, and the modulation frequency of each wavelength of light is different.

[0009] Optionally, the wavelength selection and modulation module includes a temperature-controlled current source, M lasers, a first fiber coupler, and a second fiber coupler, wherein M is an integer and M>1;

[0010] One end of each of the M lasers is connected to the temperature-controlled current source, the other end of each of the M lasers is optically connected to the input end of the first fiber coupler, the output end of the first fiber coupler is optically connected to the input end of the 20% of the second fiber coupler, the output end of the second fiber coupler is optically connected to the input end of the transmission quartz tuning fork light detection module, and the output end of the gas absorption cell is optically connected to the input end of the 80% of the second fiber coupler.

[0011] Optionally, the wavelength selection and modulation module includes N gratings, N piezoelectric ceramics, a piezoelectric ceramic driver and a circulator, wherein N is an integer and N>1;

[0012] The piezoelectric ceramic driver is respectively connected to the N piezoelectric ceramics and drives and controls the N piezoelectric ceramics. One of the N gratings is fixed on each of the N piezoelectric ceramics. The first grating fiber of the N gratings is connected to the second grating of the N gratings. The second grating fiber of the N gratings is connected to the third grating of the N gratings. And so on. The nth grating fiber of the N gratings is connected to the n+1th grating of the N gratings, where n is an integer and 1≤n≤N-1. The output end fiber of the gas absorption cell is connected to the input end of the circulator, the middle end fiber of the circulator is connected to the first grating, and the output end fiber of the circulator is connected to the input end of the transmission quartz tuning fork light detection module.

[0013] Optionally, the wavelengths and modulation frequencies of the output lights of the M lasers are different, wherein the wavelength of the output light of each laser corresponds to the absorption peak of one of the gases in the mixed gas to be measured, and the modulation frequency of the output light of the M lasers is half of the corresponding frequency in the frequency response curve of the quartz tuning fork.

[0014] Optionally, the center wavelengths of the N gratings are different, and the driving frequencies of the N piezoelectric ceramics are different, wherein the center wavelength of each grating corresponds to the absorption peak of a gas in the mixed gas to be measured, and the driving frequency of each of the N piezoelectric ceramics is half of the corresponding frequency in the frequency response curve of the quartz tuning fork.

[0015] In a second aspect, a multi-gas detection method is provided, characterized in that, using the multi-gas detection device described in the first aspect, the method includes:

[0016] Step S1: connecting the multi-gas detection device, turning on the power of the components in the device, and injecting the mixed gas to be detected into the gas absorption cell;

[0017] Step S2: enabling the wavelength selection and modulation module to simultaneously generate light of multiple wavelengths, wherein each wavelength of light corresponds to an absorption peak of one gas in the mixed gas to be measured, and the modulation frequency of each wavelength of light is different;

[0018] Step S3: Light of different modulation frequencies generated in the cavity of the device is absorbed by different gas molecules in the gas absorption cell, causing light intensity attenuation. The light of different modulation frequencies passes through the corrosion point of the quartz tuning fork multiple times, forming temperature fields of different modulation frequencies on the quartz tuning fork. Due to the photothermoelastic effect, the quartz tuning fork vibrates and generates piezoelectric current signals of different frequencies. The preamplifier converts the piezoelectric current signals of different frequencies into voltage signals of different frequencies. The lock-in amplifier array demodulates the voltage signals of different frequencies respectively, thereby inverting the concentrations of different gases on the computer.

[0019] Step S4: After signal processing is completed, turn off the power.

[0020] Optionally, when the wavelength selection and modulation module includes a temperature-controlled current source, M lasers, a first fiber coupler, and a second fiber coupler, step S2 further includes:

[0021] The temperature-controlled current source is used to control the output wavelength and modulation frequency of the M lasers respectively, so that the output wavelength of each laser includes the absorption peak of a gas, and the modulation frequency of each laser is different and each corresponds to half of the corresponding frequency in the frequency response curve of the quartz tuning fork.

[0022] Optionally, when the wavelength selection and modulation module includes a piezoelectric ceramic driver, piezoelectric ceramics, and a grating, step S2 further includes:

[0023] The piezoelectric ceramic driver is caused to generate a sawtooth wave as a low-frequency scanning signal, and the piezoelectric ceramic driver is caused to generate a sine wave as a high-frequency modulation signal. The low-frequency scanning signal and the high-frequency modulation signal are added together to serve as the driving signal for the N piezoelectric ceramics, causing the N piezoelectric ceramics to stretch their corresponding gratings at different frequencies, so that the modulation frequencies of light generated by different gratings are different.

[0024] As can be seen from the above embodiment, when the device is in use, a mixed gas is injected into the gas absorption cell, and the power to each module in the device is turned on. The pump source provides a high-power laser source for the entire laser chamber. The generated pump light is converted into broadband light after passing through the doped optical fiber. The broadband light enters the gas absorption cell, enhancing the optical power absorbed by the gas. The wavelength selection and modulation module modulates the light of different wavelengths corresponding to the mixed gas to a frequency, which is then input into the gas absorption cell through the annular laser chamber, thus selecting the wavelength of the mixed gas to be measured. The light emitted from the gas absorption cell enters the first collimator through the optical fiber. The light emitted from the first collimator passes through the quartz tuning fork and enters the second collimator. The light emitted from the second collimator is then input into the wavelength division multiplexer through the optical fiber. Because the laser circulates in the annular laser chamber, the light passes through the gas absorption cell multiple times, which is equivalent to increasing the absorption optical path. Light of varying modulation frequencies passes through the quartz tuning fork multiple times, creating temperature fields of varying modulation frequencies on the fork. Due to the photothermoelastic effect, the fork vibrates, generating piezoelectric current signals of varying frequencies. A preamplifier converts these piezoelectric current signals into voltage signals of varying frequencies, and a lock-in amplifier array demodulates these voltage signals, thereby inverting the concentrations of the various gases on a computer. As can be seen from the foregoing, the device can simultaneously detect a mixture of multiple gases using only a single quartz tuning fork, offering a simple structure and precise detection results. Furthermore, the transmissive quartz tuning fork optical detection module separates the quartz tuning fork from the gas absorption cell and encapsulates it in a vacuum or inert gas environment, preventing corrosion from the gas being tested, which could affect the accuracy of the detection results, and improving the quality factor. Furthermore, because the transmissive quartz tuning fork optical detection module is located within the laser chamber, it can effectively utilize the high-power laser within the laser chamber as an excitation light source, improving detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0026] Figure 1 is a schematic diagram of a multi-gas detection device provided by the present application according to some embodiments;

[0027] Figure 2 is a schematic diagram of a transmissive quartz tuning fork light detection module provided by the present application according to some embodiments;

[0028] Figure 3 is a schematic diagram of another multi-gas detection device provided by the present application according to some embodiments;

[0029] Figure 4 is another schematic diagram of a multi-gas detection device provided by the present application according to some embodiments;

[0030] Figure 5 It is the frequency response curve of the quartz tuning fork and the three demodulation frequencies selected by the lock-in amplifier.

[0031] Reference numerals

[0032] 1-Pump source, 2-Wavelength division multiplexer, 3-Doped fiber, 4-Circulator, 5-Gas absorption cell, 6.1-First grating, 6.2-Second grating, 6.3-Third grating, 7.1-First piezoelectric ceramic, 7.2-Second piezoelectric ceramic, 7.3-Third piezoelectric ceramic, 8-Piezoelectric ceramic driver, 9-Transmissive quartz tuning fork optical detection module, 10-Preamplifier, 11-Phase-locked amplifier array, 12-Computer, 13-First collimator, 14-Transparent glass housing, 15-Quartz tuning fork, 16-Second collimator, 17-Chemical etching point, 18-Temperature-controlled current source, 19.1-First laser, 19.2-Second laser, 20-First fiber coupler, 21-Second fiber coupler. DETAILED DESCRIPTION

[0033] The following describes in detail embodiments of the present application, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and are not to be construed as limiting the present application.

[0034] It will be understood by those skilled in the art that, unless expressly stated otherwise, the singular forms "a", "an", "said" and "the" used herein may also include the plural forms. It should be further understood that the term "comprising" used in the specification of the present application refers to the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof. It should be understood that when we refer to an element as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element, or there may be intermediate elements. In addition, "connected" or "coupled" as used herein may include wireless connections or wireless couplings. The term "and / or" used herein includes all or any units and all combinations of one or more associated listed items.

[0035] Because single-gas detection is no longer sufficient to meet current detection needs, the demand for simultaneous multi-gas detection is increasing. Photothermoelastic spectroscopy (PTES) gas detection technology utilizes the attenuation of light intensity caused by photons absorbed by gas molecules in a gas absorption cell. The absorbed light is incident on the arms of a quartz tuning fork, forming a temperature field there. The photothermoelastic effect causes the quartz tuning fork to vibrate, generating a piezoelectric signal, which can then be analyzed to infer the gas composition. PTS gas detection technology offers advantages such as high detection accuracy, full-wavelength response, a signal proportional to the incident laser power and absorption pathlength, non-contact gas measurement, and low cost.

[0036] Currently, some scholars have proposed a photoacoustic spectroscopy gas detection technology based on multi-tuning fork frequency division multiplexing. This technology uses three quartz tuning forks to respond to sound waves of different frequencies, enabling simultaneous detection of three gases. However, this method suffers from a complex structure, low-power excitation light source, and difficulty in alignment. Furthermore, the detection module requires contact with the gas, making it susceptible to corrosive gases and dust, leading to inaccurate measurements. Therefore, finding a way to simultaneously detect multiple gases with a simple system structure has become an urgent problem.

[0037] In response to the above problems, the present application proposes a multi-gas detection device, which is described below with reference to the accompanying drawings.

[0038] Figure 1 This is a schematic diagram of a multi-gas detection device provided by the present application according to some embodiments, such as Figure 1 As shown, the device includes:

[0039] Pump source 1, wavelength division multiplexer 2, doped optical fiber 3, gas absorption cell 5, wavelength selection and modulation module, transmission quartz tuning fork light detection module 9, preamplifier 10, phase-locked amplifier array 11 and computer 12.

[0040] The output optical fiber of the pump source 1 is connected to the first input end of the wavelength division multiplexer 2, the output end of the wavelength division multiplexer 2 is connected to the doped optical fiber 3, the doped optical fiber 3 is connected to the input end of the gas absorption cell 5, the output optical fiber of the gas absorption cell 5 is connected to the wavelength selection and modulation module, the output optical fiber of the wavelength selection and modulation module is connected to the input end of the transmission quartz tuning fork light detection module 9, the optical signal output end optical fiber of the transmission quartz tuning fork light detection module 9 is connected to the second input end of the wavelength division multiplexer 2, the electrical signal output end of the transmission quartz tuning fork light detection module 9 is connected to the input end of the preamplifier 10, the output end of the preamplifier 10 is connected to the input end of the phase-locked amplifier array 11, and the output end of the phase-locked amplifier array 11 is connected to the computer 12. The gas absorption cell 5 is filled with a mixed gas to be measured. The wavelength selection and modulation module can simultaneously generate light of multiple wavelengths, each wavelength of light corresponds to the absorption peak of a gas in the mixed gas to be measured, and the modulation frequency of each wavelength of light is different.

[0041] It should be noted that the mixed gas to be tested contains at least two gases.

[0042] In one possible implementation, Figure 2 Schematic diagram of a transmissive quartz tuning fork light detection module provided by the present application according to some embodiments, such as Figure 2 As shown, the transmission type quartz tuning fork light detection module 9 includes a first collimator 13, a quartz tuning fork 15, a second collimator 16 and a transparent glass shell 14. The first collimator 13 is inserted into a first side of the transparent glass shell 14, and the second collimator 16 is inserted into a second side opposite to the first side of the transparent glass shell 14. The quartz tuning fork 15 is encapsulated in the transparent glass shell 14 by vacuum or inert gas and is located between the inner end of the first collimator 13 and the inner end of the second collimator 16. The metal film at the incident point of the quartz tuning fork 15 is removed by chemical etching. The specific position is shown in FIG. Figure 3 Chemical corrosion point 17 is shown.

[0043] The transmissive quartz tuning fork optical detection module 9 encapsulates the quartz tuning fork 15 in a vacuum or inert gas environment, improving the quality factor and avoiding the problem of gas corrosion on the quartz tuning fork 15, which affects the accuracy of the detection results. Furthermore, the provision of the first collimator 13 and the second collimator 16 improves the collimation accuracy.

[0044] During use, the device injects a mixed gas into the gas absorption cell 5 and powers on all modules within the device. The pump source 1 provides a high-power laser source for the entire laser chamber. The generated pump light 1 is converted into broadband light after passing through the doped optical fiber 3. This broadband light enters the gas absorption cell 5, enhancing the optical power absorbed by the gas. The wavelength selection and modulation module modulates the wavelengths of light corresponding to the measured mixed gas to a specific frequency. This light is then input into the gas absorption cell 5 through the annular laser chamber. (As can be seen, because the optical signal output end of the transmissive quartz tuning fork optical detection module 9 is connected to the second input end of the wavelength division multiplexer 2 via an optical fiber, the light in the laser chamber can circulate multiple times through the gas absorption cell 5 and the transmissive quartz tuning fork optical detection module 9, thus selecting wavelengths for the measured mixed gas.) Light emitted from the gas absorption cell 5 enters the first collimator 13 via an optical fiber. The light emitted from the first collimator 13 then passes through the quartz tuning fork 15 and enters the second collimator 16. The light emitted from the second collimator 16 then enters the wavelength division multiplexer 2 via an optical fiber. As the laser circulates through the annular laser chamber, it passes through the gas absorption cell 5 multiple times, effectively increasing the absorption optical path. Light of varying modulation frequencies passes through the quartz tuning fork 15 multiple times, creating temperature fields of varying modulation frequencies on the fork. Due to the photothermoelastic effect, the fork vibrates, generating piezoelectric current signals of varying frequencies. The preamplifier 10 converts these piezoelectric current signals into voltage signals of varying frequencies. The lock-in amplifier array 11 demodulates these voltage signals, respectively, to infer the concentrations of the various gases on the computer 12.

[0045] It can be seen from the above embodiments that the device can simultaneously detect a mixed gas composed of multiple gases using only a single quartz tuning fork, and has the characteristics of simple structure and accurate detection results. Furthermore, the transmission-type quartz tuning fork light detection module separates the quartz tuning fork from the gas absorption cell, thereby avoiding corrosion by the gas to be measured and avoiding the problem of affecting the accuracy of the detection results, thereby improving the quality factor. In addition, since the transmission-type quartz tuning fork light detection module 9 is located in the laser cavity, during the formation process of the laser, the laser can pass through the gas absorption cell 5 multiple times, thereby increasing the absorption optical path and being able to effectively utilize the high-power laser in the laser cavity for gas detection. According to the Beer-Lambert law, It can be seen that in the absorption spectrum, the incident laser power I0 and the absorption optical path L are both beneficial to increasing the absorption signal and can improve the detection accuracy of the system.

[0046] In one possible implementation, Figure 3 This is another schematic diagram of a multi-gas detection device provided by the present application according to some embodiments, such as Figure 3As shown, the wavelength selection and modulation module includes a temperature-controlled current source 18, M lasers, a first fiber coupler 20 and a second fiber coupler 21 for wavelength selection and modulation. Wherein, M is an integer, M>1. The description of other components can be found in the above Figure 1 The relevant content will not be repeated here.

[0047] The output optical fiber of the gas absorption cell 5 is connected to 80% of the input ends of the second optical fiber coupler 21. One end of each of the M lasers is connected to the temperature-controlled current source 18, and the other end is connected to the input end of the first optical fiber coupler 20 (the number of its input ends is greater than or equal to M). For example Figure 3 The first laser 19.1 and the second laser 19.2, and so on, the Mth laser can be represented as 19.m, 1≤m≤M, and m is an integer. The output fiber of the first fiber coupler 20 is connected to the 20% input of the second fiber coupler 21, that is, the second fiber coupler is a 20:80 fiber coupler. The output fiber of the second fiber coupler 21 is connected to the input of the transmission quartz tuning fork light detection module 9. The temperature-controlled current source controls the output wavelength and modulation frequency of the M lasers respectively, so that the output wavelength of each laser includes the absorption peak of a gas, and the modulation frequency of each laser is different, each corresponding to half of the corresponding frequency in the frequency response curve of the above-mentioned quartz tuning fork 15.

[0048] It can be seen from the above embodiments that Figure 3 The wavelength selection and modulation module of the multi-gas detection device includes a temperature-controlled current source 18, M lasers, a first fiber coupler 20, and a second fiber coupler 21, making wavelength selection and modulation more precise. Using only a single quartz tuning fork, a mixed gas composed of multiple gases can be simultaneously detected, resulting in a simple structure and accurate detection results. Furthermore, since the temperature-controlled current source 18 and the M lasers perform wavelength selection, they do not require excessive resources. Therefore, the end of the second fiber coupler 21 with a larger coupling ratio is allocated to the annular laser chamber, while the end with a smaller coupling ratio is connected to the wavelength selection and modulation module. This can maximize the optical power within the laser chamber, thereby further increasing the optical power that can be absorbed by the gas absorption cell and improving the accuracy of the results.

[0049] It should be noted that, because the laser chamber is annular, the connection position of the gas absorption cell is not limited in this application. For example, the gas absorption cell can also be connected between the wavelength selection and modulation module and the transmission quartz tuning fork light detection module 9.

[0050] In one possible implementation, Figure 4 This is another schematic diagram of a multi-gas detection device provided by the present application according to some embodiments, such as Figure 4As shown, the wavelength selection and modulation module includes N gratings, N piezoelectric ceramics, a piezoelectric ceramic driver 8 and a circulator 4, where N is an integer and N>1. The piezoelectric ceramic driver 8 is connected to the N piezoelectric ceramics and drives and controls the N piezoelectric ceramics. One of the N gratings is fixed on each of the N piezoelectric ceramics. The first grating 6.1 of the N gratings is connected to the second grating 6.2 of the N gratings by an optical fiber. The second grating of the N gratings is connected to the third grating 6.3 of the N gratings by an optical fiber. And so on. The nth grating of the N gratings is connected to the n+1th grating of the N gratings by an optical fiber, 1≤n≤N-1. The output end of the gas absorption cell 5 is connected to the input end of the circulator 4 by an optical fiber. The middle end of the circulator 4 is connected to the first grating by an optical fiber. The output end of the circulator 4 is connected to the input end of the transmission quartz tuning fork light detection module 9 by an optical fiber. For descriptions of other components, please refer to the relevant Figure 1 The relevant content will not be repeated here.

[0051] When in use, the piezoelectric ceramic driver 8 generates a sawtooth wave as a low-frequency scanning signal, causing the piezoelectric ceramic driver 8 to generate a sine wave as a high-frequency modulation signal. The low-frequency scanning signal and the high-frequency modulation signal are added together as the driving signal for N piezoelectric ceramics, causing the N piezoelectric ceramics to stretch their corresponding gratings at different frequencies, so that the modulation frequencies of the light generated by different gratings are different.

[0052] In one example, the central wavelengths of the N gratings are different, wherein the central wavelength of each grating corresponds to an absorption peak of one gas in the mixed gas to be measured.

[0053] For example, the central wavelengths of grating 6.1, grating 6.2, and grating 6.3 are 1530.37 nm, 1572.3 nm, and 1568.04 nm, respectively, corresponding to the absorption peaks of acetylene, carbon dioxide, and carbon monoxide gases.

[0054] In one example, the N piezoelectric ceramics are driven at different frequencies.

[0055] In one example, the driving frequency of each of the N piezoelectric ceramics is half of the corresponding frequency in the frequency response curve of the quartz tuning fork 15 .

[0056] Figure 5 The frequency response curve of the quartz tuning fork and the three demodulation frequencies selected by the lock-in amplifier are Figure 5For example, if the three demodulation frequencies are 32.748 kHz, 32.75 kHz, and 32.752 kHz, then the modulation frequencies of the first piezoelectric ceramic 7.1, the second piezoelectric ceramic 7.2, and the third piezoelectric ceramic 7.3 among the N piezoelectric ceramics are 16.374 kHz (half of 32.748 kHz), 16.375 kHz (half of 32.75 kHz), and 16.376 kHz (half of 32.752 kHz), respectively.

[0057] In one possible implementation, Figure 5 As shown, the gas absorption pool 5 is located between the circulator and the grating, that is, the output end of the doped optical fiber 3 is connected to the input end of the circulator 4, the middle end optical fiber of the circulator 4 is connected to the input end of the gas absorption pool 5, and the output end optical fiber of the gas absorption pool 5 is connected to the grating 6.1.

[0058] In the above method, the pump light generated by the pump source 1 is converted into broadband light after passing through the doped optical fiber 3. The broadband light then passes through the circulator 4 and the gas absorption cell 5 and enters N gratings to generate light of different wavelengths. The light is modulated to different frequencies by N piezoelectric ceramics, and the light enters the gas absorption cell 5 again through the optical fiber. The light emitted from the gas absorption cell 5 passes through the circulator 4 and the optical fiber and enters the first collimator 13. The light emitted from the first collimator 13 passes through the quartz tuning fork 15 and enters the second collimator 16. The light emitted from the second collimator 16 passes through the optical fiber and enters the wavelength division multiplexer 2. The gas absorption cell 5 is located between the circulator and the grating, so that the light passes through the gas absorption cell 5 multiple times, which is equivalent to increasing the absorption optical path. As can be seen from the above, the device can simultaneously detect a mixed gas composed of multiple gases using only a single quartz tuning fork 15, and has the characteristics of simple structure and accurate detection results.

[0059] Based on the above-mentioned multi-gas detection device, the present application provides a multi-gas detection method, which includes:

[0060] Step S1: Connect the multi-gas detection device, turn on the power of the components in the device, and inject the mixed gas to be tested into the gas absorption cell 5;

[0061] Step S2: enabling the wavelength selection and modulation module to simultaneously generate light of multiple wavelengths, wherein each wavelength of light corresponds to the absorption peak of one gas in the mixed gas to be measured, and the modulation frequency of each wavelength of light is different;

[0062] Step S3: Light of different modulation frequencies generated within the device cavity is absorbed by different gas molecules in the gas absorption cell 5, causing light intensity attenuation. Light of different modulation frequencies passes through the corrosion points of the quartz tuning fork 15 multiple times, forming temperature fields of different modulation frequencies on the quartz tuning fork 15. Due to the photothermoelastic effect, the quartz tuning fork 15 vibrates and generates piezoelectric current signals of different frequencies. The preamplifier 10 converts the piezoelectric current signals of different frequencies into voltage signals of different frequencies. The lock-in amplifier array 11 demodulates the voltage signals of different frequencies respectively, thereby inverting the concentrations of different gases on the computer 12.

[0063] Step S4: After signal processing is completed, turn off the power.

[0064] In the case where the wavelength selection and modulation module includes a piezoelectric ceramic driver 8, piezoelectric ceramics and a grating, step S2 further includes:

[0065] The piezoelectric ceramic driver 8 generates a sawtooth wave as a low-frequency scanning signal, and generates a sine wave as a high-frequency modulation signal. The low-frequency scanning signal and the high-frequency modulation signal are added together as the driving signal of N piezoelectric ceramics, causing the N piezoelectric ceramics to stretch their corresponding gratings at different frequencies, so that the modulation frequencies of the light generated by different gratings are different.

[0066] In the case where the wavelength selection and modulation module includes a temperature-controlled current source, M lasers, a first fiber coupler, and a second fiber coupler, step S2 further includes:

[0067] The temperature-controlled current source is used to control the output wavelength and modulation frequency of the M lasers respectively, so that the output wavelength of each laser includes the absorption peak of a gas, and the modulation frequency of each laser is different and each corresponds to half of the corresponding frequency in the frequency response curve of the quartz tuning fork.

[0068] It should be understood that although the steps in the flowcharts of the accompanying drawings are shown in sequence as indicated by the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some of the steps in the flowcharts of the accompanying drawings may include multiple sub-steps or multiple stages, and these sub-steps or stages are not necessarily executed at the same time, but can be executed at different times, and their execution order is not necessarily sequential, but can be executed in turn or alternately with other steps or at least a portion of the sub-steps or stages of other steps.

[0069] The above description is only part of the implementation methods of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A multi-gas detection device, characterized in that: It includes pump source, wavelength division multiplexer, doped optical fiber, gas absorption cell, wavelength selection and modulation module, transmission quartz tuning fork light detection module, preamplifier, lock-in amplifier array and computer; The transmissive quartz tuning fork optical detection module includes a quartz tuning fork, a first collimator, a second collimator, and a transparent glass housing. The first collimator is inserted into a first side of the transparent glass housing, and the second collimator is inserted into a second side of the transparent glass housing opposite to the first side. The quartz tuning fork is encapsulated in the transparent glass housing by vacuum or inert gas and is located between the inner ends of the first collimator and the second collimator. The metal film at the incident point of the quartz tuning fork is removed by chemical etching. The output optical fiber of the pump source is connected to the first input end of the wavelength division multiplexer, the output end of the wavelength division multiplexer is connected to the doped optical fiber, the doped optical fiber is connected to the input end of the gas absorption cell, the output optical fiber of the gas absorption cell is connected to the wavelength selection and modulation module, the output optical fiber of the wavelength selection and modulation module is connected to the input end of the transmission quartz tuning fork light detection module, the optical signal output optical fiber of the transmission quartz tuning fork light detection module is connected to the second input end of the wavelength division multiplexer, the electrical signal output end of the transmission quartz tuning fork light detection module is connected to the input end of the preamplifier, the output end of the preamplifier is connected to the input end of the phase-locked amplifier array, and the output end of the phase-locked amplifier array is connected to the computer. The gas absorption cell is filled with a mixed gas to be measured. The wavelength selection and modulation module can simultaneously generate light of multiple wavelengths, each wavelength of light corresponding to the absorption peak of a gas in the mixed gas to be measured, and the modulation frequency of each wavelength of light is different.

2. A multi-gas detection device according to claim 1, characterized in that: The wavelength selection and modulation module includes a temperature-controlled current source, M lasers, a first fiber coupler, and a second fiber coupler, wherein M is an integer and M>1; One end of each of the M lasers is connected to the temperature-controlled current source, the other end of each of the M lasers is optically connected to the input end of the first fiber coupler, the output end of the first fiber coupler is optically connected to the input end of the 20% of the second fiber coupler, the output end of the second fiber coupler is optically connected to the input end of the transmission quartz tuning fork light detection module, and the output end of the gas absorption cell is optically connected to the input end of the 80% of the second fiber coupler.

3. The multi-gas detection device according to claim 1, characterized in that: The wavelength selection and modulation module includes N gratings, N piezoelectric ceramics, a piezoelectric ceramic driver and a circulator, wherein N is an integer and N>1; The piezoelectric ceramic driver is respectively connected to the N piezoelectric ceramics and drives and controls the N piezoelectric ceramics. One of the N gratings is fixed on each of the N piezoelectric ceramics. The first grating fiber of the N gratings is connected to the second grating of the N gratings. The second grating fiber of the N gratings is connected to the third grating of the N gratings. And so on. The nth grating fiber of the N gratings is connected to the n+1th grating of the N gratings, where n is an integer and 1≤n≤N-1. The output end fiber of the gas absorption cell is connected to the input end of the circulator, the middle end fiber of the circulator is connected to the first grating, and the output end fiber of the circulator is connected to the input end of the transmission quartz tuning fork light detection module.

4. A multi-gas detection device according to claim 2, characterized in that: The wavelengths and modulation frequencies of the output lights of the M lasers are different, wherein the wavelength of the output light of each laser corresponds to the absorption peak of one of the gases in the mixed gas to be measured, and the modulation frequency of the output light of the M lasers is half of the corresponding frequency in the frequency response curve of the quartz tuning fork.

5. The multi-gas detection device according to claim 3, characterized in that: The central wavelengths of the N gratings are different, and the driving frequencies of the N piezoelectric ceramics are different, wherein the central wavelength of each grating corresponds to the absorption peak of one gas in the mixed gas to be measured, and the driving frequency of each of the N piezoelectric ceramics is half of the corresponding frequency in the frequency response curve of the quartz tuning fork.

6. A multi-gas detection method, characterized in that: Utilizing the multi-gas detection device according to any one of claims 1 to 5, the method comprises: Step S1: connecting the multi-gas detection device, turning on the power of the components in the device, and injecting the mixed gas to be detected into the gas absorption cell; Step S2: enabling the wavelength selection and modulation module to simultaneously generate light of multiple wavelengths, wherein each wavelength of light corresponds to an absorption peak of one gas in the mixed gas to be measured, and the modulation frequency of each wavelength of light is different; Step S3: Light of different modulation frequencies generated in the cavity of the device is absorbed by different gas molecules in the gas absorption cell, causing light intensity attenuation. The light of different modulation frequencies passes through the corrosion point of the quartz tuning fork multiple times, forming temperature fields of different modulation frequencies on the quartz tuning fork. Due to the photothermoelastic effect, the quartz tuning fork vibrates and generates piezoelectric current signals of different frequencies. The preamplifier converts the piezoelectric current signals of different frequencies into voltage signals of different frequencies. The lock-in amplifier array demodulates the voltage signals of different frequencies respectively, thereby inverting the concentrations of different gases on the computer. Step S4: After signal processing is completed, turn off the power.

7. The method according to claim 6, characterized in that When the multi-gas detection device according to claim 2 is used, step S2 further includes: A temperature-controlled current source is used to control the output wavelength and modulation frequency of the M lasers respectively, so that the output wavelength of each laser includes an absorption peak of a gas, and the modulation frequency of each laser is different and each corresponds to half of the corresponding frequency in the frequency response curve of the quartz tuning fork.

8. The method according to claim 6, characterized in that When the multi-gas detection device according to claim 3 is used, step S2 further includes: The piezoelectric ceramic driver is caused to generate a sawtooth wave as a low-frequency scanning signal, and the piezoelectric ceramic driver is caused to generate a sine wave as a high-frequency modulation signal. The low-frequency scanning signal and the high-frequency modulation signal are added together to serve as the driving signal for the N piezoelectric ceramics, causing the N piezoelectric ceramics to stretch their corresponding gratings at different frequencies, so that the modulation frequencies of light generated by different gratings are different.

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