CN114563355B - Gas detection system and method - Google Patents
Gas detection system and methodInfo
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- CN114563355B CN114563355B CN202210171599.XA CN202210171599A CN114563355B CN 114563355 B CN114563355 B CN 114563355B CN 202210171599 A CN202210171599 A CN 202210171599A CN 114563355 B CN114563355 B CN 114563355B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/314—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
- G01N2021/0106—General arrangement of respective parts
- G01N2021/0112—Apparatus in one mechanical, optical or electronic block
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/314—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths
- G01N2021/3148—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths using three or more wavelengths
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- Investigating Or Analysing Materials By Optical Means (AREA)
Abstract
本申请提供了一种气体检测系统和方法，能够同时避免信号接收模块与气体分子和激光直接接触，既能保护信号接收模块不被腐蚀性气体破坏，又能降低系统的热噪声，从而保证气体检测的精度，进而提高系统的信噪比。该系统包括温控电流源、激光器、气体吸收池、热线式光纤和信号接收及解调模块；所述温控电流源连接所述激光器，所述激光器的输出端光纤连接所述气体吸收池的输入端，所述气体吸收池的输出端光纤连接所述热线式光纤，所述热线式光纤靠近所述信号接收及解调模块，其中，所述热线式光纤能够将光能转化为热能，所述信号接收及解调模块能够利用所述热线式光纤转换的热能检测所述气体吸收池中的待测气体的浓度。
The present application provides a gas detection system and method that can simultaneously prevent a signal receiving module from direct contact with gas molecules and lasers, thereby protecting the signal receiving module from damage by corrosive gases and reducing the system's thermal noise, thereby ensuring the accuracy of gas detection and improving the system's signal-to-noise ratio. The system includes a temperature-controlled current source, a laser, a gas absorption cell, a hot-wire optical fiber, and a signal receiving and demodulation module; the temperature-controlled current source is connected to the laser, the output optical fiber of the laser is connected to the input end of the gas absorption cell, the output optical fiber of the gas absorption cell is connected to the hot-wire optical fiber, and the hot-wire optical fiber is close to the signal receiving and demodulation module, wherein the hot-wire optical fiber can convert light energy into heat energy, and the signal receiving and demodulation module can use the heat energy converted by the hot-wire optical fiber to detect the concentration of the gas to be detected in the gas absorption cell.
Description
Technical Field
The application relates to the field of gas detection, in particular to a gas detection system and a gas detection method.
Background
Along with the development of society and technology, the high-precision monitoring of gas concentration has important significance in the fields of guaranteeing petroleum and natural gas exploitation, biopharmaceutical safety, atmospheric pollution prevention and control, food and drug safety and the like. The current common quartz enhanced photoacoustic spectroscopy gas detection technology is a gas contact measurement technology, and a quartz tuning fork is embedded into a gas sample to be detected, so that the application of the quartz tuning fork in the fields of remote measurement and the like is limited, and if the gas to be detected is corrosive gas, a metal film on the surface of the quartz tuning fork can be damaged, so that the frequency of the quartz tuning fork is drifted or even damaged.
At present, a scholars put forward a quartz enhanced photo-thermal spectrum gas detection technology, the quartz enhanced photo-thermal spectrum gas detection technology is a non-contact gas detection technology, light is directly incident on a quartz tuning fork arm after being absorbed in a gas absorption tank, and gas is detected based on photo-thermal effect, but the method needs laser to be directly contacted with a quartz tuning fork, so that a great amount of thermal noise is inevitably generated, and because a photo-thermal signal is in direct proportion to laser power, but the thermal noise of the quartz tuning fork is in an exponential relation with the laser power, the signal-to-noise ratio of a system is greatly reduced.
Disclosure of Invention
The application provides a gas detection system and a method, which can simultaneously prevent a signal receiving module from being directly contacted with gas molecules and laser, can protect the signal receiving module from being damaged by corrosive gas, and can reduce the thermal noise of the system, thereby ensuring the gas detection precision and further improving the signal to noise ratio of the system.
In a first aspect, the application provides a gas detection system, comprising a temperature-controlled current source, a laser, a gas absorption tank, a hot-wire optical fiber and a signal receiving and demodulating module;
the temperature control current source is connected with the laser, the output end optical fiber of the laser is connected with the input end of the gas absorption tank, the output end optical fiber of the gas absorption tank is connected with the hot wire optical fiber, the hot wire optical fiber is close to the signal receiving and demodulating module, the hot wire optical fiber can convert light energy into heat energy, and the signal receiving and demodulating module can detect the concentration of gas to be detected in the gas absorption tank by utilizing the heat energy converted by the hot wire optical fiber.
Optionally, the signal receiving and demodulating module comprises a signal receiving module and a signal demodulating module, the signal receiving module comprises a quartz tuning fork, and the signal demodulating module comprises a preamplifier, a phase-locked amplifier and an oscilloscope;
The hot wire type optical fiber is arranged around the quartz tuning fork, the output end of the quartz tuning fork is connected with the input end of the preamplifier, the output end of the preamplifier is connected with the input end of the lock-in amplifier, and the output end of the lock-in amplifier is connected with the oscilloscope.
Optionally, the placing the hot wire optical fiber around the quartz tuning fork includes:
The hot wire type optical fiber is placed between two arms of the quartz tuning fork or on the front surface of the quartz tuning fork or on the side surface of the quartz tuning fork.
Optionally, the signal receiving and demodulating module comprises a signal receiving module and a signal demodulating module, the signal receiving module comprises a fiber bragg grating, and the signal demodulating module comprises a broadband light source, a fiber circulator and a spectrum analyzer;
the hot wire type optical fiber is fixed on the optical fiber grating, the broadband light source optical fiber is connected with the input end of the optical fiber circulator, the middle end of the optical fiber circulator is connected with the optical fiber grating, and the output end of the optical fiber circulator is connected with the spectrum analyzer.
Optionally, the fixing the hot wire optical fiber on the fiber bragg grating includes:
the hot wire type optical fiber and the optical fiber grating are adhered together in parallel.
Optionally, the hot wire fiber is a high loss cobalt doped fiber and is overcoated.
In a second aspect, there is provided a gas detection method, using the first aspect and the gas detection system of any of the embodiments, the method comprising:
step S1, connecting the gas detection system, opening the power supply of each part in the gas detection system, and injecting gas to be detected into the gas absorption tank;
And S2, enabling the temperature-controlled current source to generate a driving signal, wherein the driving signal is used for driving the laser, the wavelength of light output by the laser corresponds to the absorption peak of the gas to be detected, the gas absorption tank inputs light absorbed by gas molecules in the gas absorption tank into the hot-wire type optical fiber, the hot-wire type optical fiber converts the light energy of the light absorbed by the gas molecules in the gas absorption tank into heat energy, and the signal receiving and demodulating module detects the concentration of the gas to be detected in the gas absorption tank by utilizing the heat energy converted by the hot-wire type optical fiber.
Optionally, the signal receiving and demodulating module includes a signal receiving module and a signal demodulating module, the signal receiving module includes a quartz tuning fork, the signal demodulating module includes a preamplifier, a phase-locked amplifier and an oscilloscope, the driving signal is a low-frequency sawtooth wave overlapping a high-frequency sine wave of half of the resonance frequency of the quartz tuning fork, and the signal receiving and demodulating module detects the concentration of the gas to be detected in the gas absorbing tank by using the heat energy converted by the hot wire type optical fiber includes:
The heat energy converted by the hot wire type optical fiber causes the temperature of the surrounding environment to periodically change, so that the pressure is periodically changed to generate sound waves, thereby causing the quartz tuning fork to vibrate, the quartz tuning fork generates a piezoelectric current signal, the preamplifier converts the piezoelectric current signal into a voltage signal, and the lock-in amplifier demodulates the voltage signal, so that the concentration of the gas to be detected is inverted on the oscilloscope.
Optionally, the signal receiving and demodulating module includes a signal receiving module and a signal demodulating module, the signal receiving module includes a fiber bragg grating, the signal demodulating module includes a broadband light source, a fiber circulator and a spectrum analyzer, the driving signal is a direct current signal, and the signal receiving and demodulating module detects the concentration of the gas to be detected in the gas absorbing tank by using the heat energy converted by the hot wire type optical fiber includes:
Recording a first wavelength displayed on the spectrum analyzer when the gas absorption cell is free of gas;
Introducing gas to be detected into the gas absorption tank, and after the light output by the laser is absorbed by the gas to be detected, compared with the case that the gas absorption tank does not contain gas, the light intensity of the light input into the hot-wire type optical fiber is attenuated, the temperature of the hot-wire type optical fiber is reduced, the wavelength of the fiber bragg grating is caused to drift, and a second wavelength is displayed on the spectrum analyzer;
and according to the difference value of the first wavelength and the second wavelength, the concentration of the gas to be detected is inverted.
As can be seen from the above embodiments, when in use, the temperature-controlled current source inputs a driving signal to the laser so that the wavelength of the light output by the laser corresponds to the absorption peak of the gas to be measured, the light output by the laser is absorbed by the gas absorption tank and then enters the hot-wire optical fiber, the hot-wire optical fiber converts the light energy into heat energy, and the signal receiving and demodulating module detects the concentration of the gas to be measured in the gas absorption tank by using the heat energy converted by the hot-wire optical fiber, wherein the signal receiving and demodulating module comprises a signal receiving module and a signal demodulating module. In addition, the hot wire type optical fiber converts light energy into heat energy, so that laser is prevented from being directly injected into the signal receiving module, thermal noise of the system can be reduced, and signal to noise ratio of the system is improved.
Drawings
In order to more clearly illustrate the technical solution of the present application, the drawings that are needed in the embodiments will be briefly described below, and it will be obvious to those skilled in the art that other drawings can be obtained from these drawings without inventive effort.
FIG. 1 is a schematic diagram of an exemplary gas detection system provided in accordance with some embodiments of the present application;
FIG. 2 is a schematic diagram of yet another example gas detection system provided in accordance with some embodiments of the present application;
FIG. 3 is a schematic view of the locations of a hot wire optical fiber and a quartz tuning fork;
FIG. 4 is a schematic diagram of yet another example gas detection system provided in accordance with some embodiments of the present application;
FIG. 5 is a diagram of an example of a driving signal of a laser according to the present application;
FIG. 6 is a signal diagram of an exemplary oscilloscope display provided by the application;
FIG. 7 is a schematic diagram of gas concentrations corresponding to different center wavelengths of an example fiber grating provided by the present application.
Reference numerals
1. The device comprises a temperature-controlled current source 2, a laser, 3, a gas absorption tank, 4, a hot wire type optical fiber, 5, a quartz tuning fork, 6, a preamplifier, 7, a lock-in amplifier, 8, an oscilloscope, 9, a fiber bragg grating, 10, a broadband light source, 11, a fiber circulator, 12 and a spectrum analyzer.
Detailed Description
Embodiments of the present application are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are illustrative only and are not to be construed as limiting the application.
As used herein, the singular forms "a", "an", "the" and "the" are intended to include the plural forms as well, unless expressly stated otherwise, as understood by those skilled in the art. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may also be present. Further, "connected" or "coupled" as used herein may include wirelessly connected or wirelessly coupled. The term "and/or" as used herein includes all or any element and all combination of one or more of the associated listed items.
The gas concentration detection has important significance in the fields of biopharmaceutical safety, atmospheric pollution prevention and control, food and drug safety and the like, wherein a quartz enhanced photoacoustic spectroscopy gas detection technology is common, a quartz tuning fork is embedded into a gas sample to be detected, and the quartz tuning fork is vibrated by utilizing a photo-thermal elasticity effect to generate a piezoelectric signal, so that the gas concentration is detected. In the scheme, the application of the quartz tuning fork in the fields of remote measurement and the like is limited, and if the gas to be measured is corrosive gas, a metal film on the surface of the quartz tuning fork can be damaged, so that the frequency of the quartz tuning fork is drifted or even damaged.
Aiming at the problems, a scholars propose a quartz enhanced photo-thermal spectrum gas detection technology, which is a non-contact gas detection technology, light is directly incident on a quartz tuning fork arm after being absorbed in a gas absorption tank, and gas is detected based on photo-thermal effect, but a great amount of thermal noise is generated by a quartz tuning fork in the method, and the signal to noise ratio is low.
Fig. 1 is a schematic diagram of an exemplary gas detection system according to some embodiments of the present application, and as shown in fig. 1, the gas detection system includes a temperature-controlled current source 1, a laser 2, a gas absorption cell 3, a hot wire optical fiber 4, and a signal receiving and demodulating module.
The temperature control current source 1 is connected with the laser 2, the output end of the laser 2 is connected with the input end of the gas absorption tank 3 through optical fibers, the output end of the gas absorption tank 3 is connected with the hot wire type optical fibers 4 through optical fibers, the hot wire type optical fibers 4 are close to the signal receiving and demodulating module, the hot wire type optical fibers 4 can convert light energy into heat energy, and the signal receiving and demodulating module can detect the concentration of gas to be detected in the gas absorption tank 3 through the heat energy converted by the hot wire type optical fibers 4.
Optionally, the temperature controlled current source 1 is electrically or communicatively connected to the laser 2.
Optionally, the hot wire fiber 4 is a high loss cobalt doped fiber and is overcoated. The coating layer is removed to enable the hot wire type optical fiber 4 to dissipate heat better.
Alternatively, the gas to be measured may be acetylene, methane, carbon dioxide, ammonia, or the like.
The signal receiving and demodulating module includes a signal receiving module and a signal demodulating module.
When in use, the temperature-controlled current source 1 inputs a driving signal to the laser 2 so that the wavelength of the light output by the laser 2 corresponds to the absorption peak of the gas to be detected, the light output by the laser 2 is absorbed by the gas absorption tank 3 and then enters the hot-wire type optical fiber 4, the hot-wire type optical fiber 4 converts the light energy into heat energy, and the signal receiving and demodulating module detects the concentration of the gas to be detected in the gas absorption tank 3 by using the heat energy converted by the hot-wire type optical fiber 4. In addition, the hot wire type optical fiber 4 converts light energy into heat energy, so that laser is prevented from being directly injected into the signal receiving module, thermal noise of the system can be reduced, and signal to noise ratio of the system is improved.
Fig. 2 is a schematic diagram of another exemplary gas detection system according to some embodiments of the present application, and optionally, as shown in fig. 2, the signal receiving and demodulating module includes a quartz tuning fork 5, a preamplifier 6, a lock-in amplifier 7, and an oscilloscope 8.
The hot wire type optical fiber 4 is placed around the quartz tuning fork 5, the output end of the quartz tuning fork 5 is connected with the input end of the preamplifier 6, the output end of the preamplifier 6 is connected with the input end of the lock-in amplifier 7, and the output end of the lock-in amplifier 7 is connected with the oscilloscope 8.
In the device, the signal receiving module comprises a quartz tuning fork 5, and the signal demodulation module comprises a preamplifier 6, a lock-in amplifier 7 and an oscilloscope 8.
Fig. 3 is a schematic view of the locations of the hot wire optical fiber and the quartz tuning fork, and optionally, as shown in fig. 3, the placement of the hot wire optical fiber 4 around the quartz tuning fork 5 includes:
the hot wire type optical fiber 4 is placed between both arms of the quartz tuning fork 5 or on the front surface of the quartz tuning fork 5 or on the side surface of the quartz tuning fork 5.
In use, the temperature controlled current source 1 is caused to generate a drive signal which is a drive current signal of a high frequency sine wave of which the low frequency sawtooth wave is superimposed on half the resonant frequency of the quartz tuning fork 5, the drive signal causing the laser 2 to output modulated light of a wavelength corresponding to the absorption peak of the gas to be measured (for example, the central wavelength of the laser 2 is 1368.597nm, corresponding to the absorption peak of water vapour), the modulation frequency of which is half the resonant frequency of the quartz tuning fork 5. The light output from the gas absorption cell 3 is input into the hot wire type optical fiber 4, the hot wire type optical fiber 4 converts light energy into heat energy due to self-heating effect, the temperature of the surrounding environment is caused to periodically change, the pressure is further caused to periodically change, sound waves are generated, the quartz tuning fork 5 is caused to vibrate, the quartz tuning fork 5 generates piezoelectric current signals due to piezoelectric effect, the preamplifier 6 converts the current signals into voltage signals, and the phase-locked amplifier 7 demodulates the voltage signals, so that the concentration of the gas to be detected can be inverted on the oscilloscope 8. The system avoids the direct contact of the quartz tuning fork 5 with the gas to be detected, protects the quartz tuning fork 5 from being damaged by corrosive gas, thereby ensuring the detection precision, on the other hand, converts light energy into heat energy through the hot wire type optical fiber 4, avoids the direct incidence of light on the quartz tuning fork 5, reduces the thermal noise of the system, improves the signal to noise ratio of the system, and overcomes the defect that the quartz enhanced photoacoustic spectroscopy gas detection system is not suitable for the fields of remote measurement, remote sensing, combustion diagnosis and the like.
Wherein, the absorption peak of the light with the wavelength corresponding to the gas to be measured means that the light with the wavelength can be absorbed by the gas at most.
Fig. 4 is a schematic diagram of another exemplary gas detection system according to some embodiments of the present application, and optionally, as shown in fig. 4, the signal receiving and demodulating module includes a fiber grating 9, a broadband light source 10, a fiber circulator 11, and a spectrum analyzer 12.
The hot wire type optical fiber 4 is fixed on the optical fiber grating 9, the broadband light source 10 is connected with the input end of the optical fiber circulator 11 through an optical fiber, the middle end of the optical fiber circulator 11 is connected with the optical fiber grating 9, and the output end of the optical fiber circulator 11 is connected with the spectrum analyzer 12 through an optical fiber.
In the device, the signal receiving module comprises a fiber bragg grating 9, and the signal demodulating module comprises a broadband light source 10, a fiber circulator 11 and a spectrum analyzer 12.
Optionally, the hot wire optical fiber 4 is glued together in parallel with the fiber grating 9.
When in use, the temperature-controlled current source 1 generates a direct current signal as a driving signal of the laser 2, and adjusts the direct current driving signal and the temperature, so that the output wavelength of the laser 2 is located at the gas absorption peak (i.e. the light with the wavelength can be absorbed by the gas at the maximum), and the hot-wire type optical fiber 4 converts the light energy into heat energy due to the self-heating effect, so that the wavelength drift of the fiber bragg grating 9 can be caused. The first wavelength shown on the spectrum analyzer 12 is recorded when the gas absorption cell 3 is free of gas. Then, the gas to be measured is introduced into the gas absorption tank 3, after the light output by the laser 2 is absorbed by the gas to be measured, compared with the case that the gas absorption tank 3 is not filled with the gas, the light intensity of the light input into the hot-wire type optical fiber 4 is attenuated, the temperature of the hot-wire type optical fiber 4 is reduced, so that the wavelength of the fiber bragg grating 9 is caused to drift, and at the moment, the second wavelength is displayed on the spectrum analyzer 12. And inverting the concentration of the gas to be detected according to the difference value of the first wavelength and the second wavelength. The system can respond to light in all wave bands by demodulating signals through the grating, so that the cost of the system is reduced, and the structure of the system is simplified.
Based on the above gas detection system, the present application provides a gas concentration detection method, comprising:
step S1, connecting a gas detection system, turning on power supplies of all parts in the gas detection system, and injecting gas to be detected into a gas absorption tank 3;
Step S2, the temperature-controlled current source 1 is enabled to generate a driving signal, the driving signal is used for driving light output by the laser 2, the wavelength of the light output by the laser 2 corresponds to an absorption peak of the gas to be detected, the gas absorption tank 3 inputs the light processed by the driving signal into the hot-wire type optical fiber 4, the hot-wire type optical fiber 4 converts the light energy of the light processed by the gas absorption tank 3 into heat energy, and the signal receiving and demodulating module detects the concentration of the gas to be detected in the gas absorption tank 3 by utilizing the heat energy converted by the hot-wire type optical fiber 4.
And step S3, turning off the power supply after the signal processing is finished.
Optionally, the signal receiving and demodulating module includes a quartz tuning fork 5, a preamplifier 6, a lock-in amplifier 7 and an oscilloscope 8, fig. 5 is a diagram of a driving signal of an example of the laser provided by the present application, the driving signal (as shown in fig. 5) is a low-frequency sawtooth wave superimposed on a high-frequency sine wave of half of the resonance frequency of the quartz tuning fork 5, and the signal receiving and demodulating module detects the concentration of the gas to be detected in the gas absorbing tank 3 by using the heat energy converted by the hot wire optical fiber 4, where the method includes:
The heat energy converted by the hot wire type optical fiber 4 causes the temperature of the surrounding environment to periodically change, so that the pressure is periodically changed to generate sound waves, thereby causing the quartz tuning fork 5 to vibrate, the quartz tuning fork 5 generates a piezoelectric current signal, the preamplifier 6 converts the piezoelectric current signal into a voltage signal, and the lock-in amplifier 7 demodulates the voltage signal, so that the concentration of the gas to be detected is inverted on the oscilloscope 8. The signals displayed on the oscilloscope 8 are shown in fig. 6, wherein fig. 6 is a signal diagram of an example of the oscilloscope display provided by the application.
Optionally, the signal receiving and demodulating module includes a fiber bragg grating 9, a broadband light source 10, a fiber optic circulator 11 and a spectrum analyzer 12, the driving signal is a direct current signal, and the signal receiving and demodulating module detects the concentration of the gas to be detected in the gas absorption cell 3 by using the heat energy converted by the hot wire type optical fiber 4, and includes:
The light emitted by the broadband light source 10 is monitored by the spectrum analyzer 12 after being reflected by the fiber bragg grating 9, and the first wavelength displayed on the spectrum analyzer 12 is recorded when the gas absorption tank 3 is free of gas;
After the gas to be detected is introduced into the gas absorption tank 3, the light output by the laser 2 is absorbed by the gas to be detected, compared with the case that the gas absorption tank 3 does not contain gas, the light intensity of the light input into the hot-wire type optical fiber 4 is attenuated, the temperature of the hot-wire type optical fiber 4 is reduced, the wavelength of the fiber bragg grating 9 is caused to drift, and the second wavelength is displayed on the spectrum analyzer 12;
and inverting the concentration of the gas to be detected according to the difference value of the first wavelength and the second wavelength.
The above-mentioned laser 2 is illustratively a semiconductor laser 2 having a center wavelength of 1532.83nm corresponding to the absorption peak of acetylene gas. The wavelength range of the broadband light source 10 is 1520nm-1580nm, and the central wavelength of the fiber bragg grating 9 is 1550nm. The center wavelengths of the fiber gratings 9 corresponding to different gas concentrations are different, for example, as shown in fig. 7, where fig. 7 is a schematic diagram of the gas concentrations corresponding to different center wavelengths of an example of the fiber grating provided by the present application.
It should be understood that, although the steps in the flowcharts of the figures are shown in order as indicated by the arrows, these steps are not necessarily performed in order as indicated by the arrows. The steps are not strictly limited in order and may be performed in other orders, unless explicitly stated herein. Moreover, at least some of the steps in the flowcharts of the figures may include a plurality of sub-steps or stages that are not necessarily performed at the same time, but may be performed at different times, the order of their execution not necessarily being sequential, but may be performed in turn or alternately with other steps or at least a portion of the other steps or stages.
The foregoing is only a partial embodiment of the present application, and it should be noted that it will be apparent to those skilled in the art that modifications and adaptations can be made without departing from the principles of the present application, and such modifications and adaptations are intended to be comprehended within the scope of the present application.
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| CN112834568A (en) * | 2021-03-31 | 2021-05-25 | 山东省科学院激光研究所 | A miniature soil moisture content measurement device and system |
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