CN112557322A - Dual-light-path gas concentration measuring device and method based on off-axis integral cavity system - Google Patents
Dual-light-path gas concentration measuring device and method based on off-axis integral cavity system Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 18
- 230000003287 optical effect Effects 0.000 claims abstract description 36
- 239000013307 optical fiber Substances 0.000 claims abstract description 29
- 238000001514 detection method Methods 0.000 claims abstract description 13
- 238000012545 processing Methods 0.000 claims abstract description 3
- 238000000862 absorption spectrum Methods 0.000 claims description 5
- 238000002310 reflectometry Methods 0.000 claims description 5
- 230000009977 dual effect Effects 0.000 claims description 4
- 238000006243 chemical reaction Methods 0.000 claims description 3
- 239000004065 semiconductor Substances 0.000 claims description 3
- JBRZTFJDHDCESZ-UHFFFAOYSA-N AsGa Chemical compound [As]#[Ga] JBRZTFJDHDCESZ-UHFFFAOYSA-N 0.000 claims description 2
- 239000000835 fiber Substances 0.000 claims description 2
- 229910052738 indium Inorganic materials 0.000 claims description 2
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 claims description 2
- 239000007789 gas Substances 0.000 abstract description 32
- 239000000126 substance Substances 0.000 abstract description 7
- 238000004458 analytical method Methods 0.000 abstract description 4
- 238000005259 measurement Methods 0.000 description 7
- 229910002092 carbon dioxide Inorganic materials 0.000 description 5
- 238000010586 diagram Methods 0.000 description 4
- 238000005516 engineering process Methods 0.000 description 4
- 238000012986 modification Methods 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 230000010354 integration Effects 0.000 description 2
- 238000000691 measurement method Methods 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 238000010792 warming Methods 0.000 description 2
- 229910000530 Gallium indium arsenide Inorganic materials 0.000 description 1
- KXNLCSXBJCPWGL-UHFFFAOYSA-N [Ga].[As].[In] Chemical group [Ga].[As].[In] KXNLCSXBJCPWGL-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 239000003245 coal Substances 0.000 description 1
- 238000013480 data collection Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000004069 differentiation Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 231100000331 toxic Toxicity 0.000 description 1
- 230000002588 toxic effect Effects 0.000 description 1
- 239000002912 waste gas Substances 0.000 description 1
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- 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
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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
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Abstract
The invention discloses a double-light-path gas concentration measuring device and method based on an off-axis integral cavity system. The device mainly comprises a computer (1), an arbitrary function generator (2), a temperature current controller (3), a laser, optical fibers, an optical resonant cavity (10) with a built-in gas to be measured, a photoelectric sensor (12) and a data collector (13) which are connected in sequence, wherein the laser is a first laser (4) and a second laser (5) which output different wavelengths, and the optical fibers are a first optical fiber (6) and a second optical fiber (7); the method comprises the steps of collecting and processing photoelectric sensor signals, particularly generating two groups of sawtooth wave signals with the same frequency, waveform and phase difference of 180 degrees by a computer, converting the sawtooth wave signals into electric signals by an arbitrary function generator, and sending the electric signals to a temperature current controller for controlling a first laser and a second laser to alternately output laser signals. The device can simultaneously carry out high-efficiency detection of the concentration of two trace gases and accurate analysis of chemical components of substances.
Description
Technical Field
The invention relates to a gas concentration measuring device and a method, in particular to a double-light-path gas concentration measuring device and a method based on an off-axis integral cavity system.
Background
The detection of the concentration of trace gas is the subject of current hot scientific research, and with the continuous development of urban industrialization, industries such as petroleum, coal, chemical industry and the like continuously generate a large amount of toxic and harmful waste gas which pollutes the environment and destroys the ecology in the production process. These gases, although present in very low concentrations in the atmosphere, have profound effects on the atmospheric environment, global climate and human health. Excessive carbon dioxide emissions from industrial activities, for example, can cause global warming, causing arctic glaciers to melt and cause combustible ice to release a large amount of methane, again causing global warming to form a chain of vicious cycles. Therefore, it is necessary to quantitatively, qualitatively, quantitatively detect and analyze the gas concentration.
The off-axis integrating cavity absorption spectrum technology in the absorption spectrum technology has the basic characteristics of high sensitivity and good stability, and can be used for high-precision detection of low-concentration gas in the atmosphere, for example, the wavelength locking device for the laser in the off-axis integrating cavity system and the locking method thereof, which are published in 2019, 7, month and 30 by the applicant of the Chinese patent application CN 110068548A. The locking device mentioned in the patent application comprises a laser with an input end electrically connected with a temperature current controller and an output end connected with an optical fiber, and a gas to be detected and a photoelectric sensor on an optical fiber output optical path, wherein the gas to be detected is arranged in an optical resonant cavity with an optical axis deviating from the optical fiber output optical path, the temperature current controller and the photoelectric sensor are electrically connected with each other through a wavelength locking component consisting of a data acquisition and analysis device, an analog PID (proportion integration differentiation) device and an adder which are sequentially connected in series, and a sawtooth wave generator with an output end electrically connected with the adder; the locking method is that the laser is modulated by sawtooth wave, the collected signal is intercepted according to the data segment containing the complete absorption peak of the gas to be measured and the same length, and the linear correlation operation is carried out on the intercepted first data segment and the intercepted data segment added with a data point subsequently to obtain the drift signal of the central wavelength of the laser. Although the wavelength locking device and the method can stabilize the frequency output by the laser on a specific absorption peak so as to be widely used for trace gas concentration detection and substance chemical component analysis based on an off-axis integration cavity system, the wavelength locking device and the method have the defect that the detection efficiency is low because only one laser can be used for measuring gas.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a dual-light-path gas concentration measuring device based on an off-axis integral cavity system, which has high gas concentration detection efficiency and is convenient to use.
The invention provides a method for measuring the concentration of a dual-optical-path gas based on an off-axis integral cavity system.
In order to solve the technical problem of the invention, the technical scheme is that the dual-optical-path gas concentration measuring device based on the off-axis integral cavity system comprises a temperature current controller, a laser, an optical fiber, an optical resonant cavity internally provided with gas to be measured, a photoelectric sensor and a data acquisition unit which are connected in sequence, and particularly comprises:
the laser is a first laser and a second laser which output different wavelengths;
the optical fiber is a first optical fiber connected with the first laser and a second optical fiber connected with the second laser;
and a computer and an arbitrary function generator are sequentially connected between the data collector and the temperature current controller, so that two groups of sawtooth wave signals with the same frequency, waveform and phase difference of 180 degrees are sent out by the computer, converted into electric signals by the arbitrary function generator and then sent to the temperature current controller, and the temperature current controller is used for controlling the first laser and the second laser to alternately output laser signals.
The device is further improved as a dual-light-path gas concentration measuring device based on an off-axis integral cavity system:
preferably, the first laser and the second laser are both distributed feedback semiconductor lasers.
Preferably, a first adjustable focusing lens group and a second adjustable focusing lens group with adjustable focal lengths of 7.5mm are respectively arranged between the first optical fiber and the optical resonant cavity and between the second optical fiber and the optical resonant cavity.
Preferably, the optical resonant cavity is a tube with optical axes deviating from the output optical axes of the first optical fiber and the second optical fiber, the tube side of the optical resonant cavity is provided with an air inlet and an air outlet respectively, the two end faces of the tube are provided with a front high reflecting mirror and a rear high reflecting mirror respectively, wherein the tube length of the tubular optical resonant cavity is 28cm, the inner diameter of the tube is 2cm, the diameters of the air inlet and the air outlet are 1cm, and the reflectivity of the front high reflecting mirror and the reflectivity of the rear high reflecting mirror are both more than or equal to 99.99%.
Preferably, a focusing lens with a fixed focal length of 25mm is arranged between the optical resonant cavity and the photoelectric sensor.
Preferably, the photosensor is an indium gallium arsenide photosensor.
Preferably, the data collector is a single chip microcomputer with A/D and D/A conversion.
Preferably, the arbitrary function generator is a signal output device with a programming function and an analog output function.
In order to solve another technical problem of the present invention, another technical solution is that a dual optical path gas concentration measurement method based on an off-axis integrating cavity system includes acquiring and processing signals of a photoelectric sensor, and in particular:
the modulation of the laser output is such that,
generating a sawtooth wave signal a, setting a section from an initial value to a middle value as a non-emergent section and a section from the middle value to a tail value as a scanning section by taking the middle value of the sawtooth wave signal a as a demarcation point;
keeping the frequency and the waveform of the sawtooth wave signal a unchanged, and generating a sawtooth wave signal b by changing the 180-degree phase of the sawtooth wave signal a, so that the scanning section of the sawtooth wave signal b is positioned in the light-emitting-free section of the sawtooth wave signal a, and the light-emitting-free section is positioned in the scanning section of the sawtooth wave signal a;
converting the sawtooth wave signal a and the sawtooth wave signal b into voltage signals, and enabling the voltage output by the light-emitting-free section to be 0V and the voltage output by the scanning section to be scanning voltage required by detection of the absorption spectrum;
the scan voltage is converted into a scan current that alternately drives the first laser and the second laser.
The method for measuring the concentration of the gas in the double light paths based on the off-axis integral cavity system is further improved as follows:
preferably, the frequency of the sawtooth wave signal a and the sawtooth wave signal b is 160 Hz.
Compared with the prior art, the beneficial effects are that:
firstly, after the device adopts the structure, two paths of laser with different wavelengths are all incident into the optical resonant cavity with the built-in gas to be detected to detect different types of gas, so that the detection efficiency is greatly improved, and the measurement time is saved.
Secondly, the measuring method is simple, convenient and efficient. The output of the laser is modulated by adopting a time division multiplexing technology, two beams of laser are strictly divided in time in the optical resonant cavity on the basis of ensuring the detection precision of the gas concentration, so that two paths of light can be effectively distinguished on a single photoelectric sensor, the problem of signal confusion caused by light intensity superposition is avoided, and the invention can simultaneously carry out high-efficiency detection on the concentration of two trace gases and accurate analysis on the chemical composition of substances.
Drawings
Fig. 1 is a schematic diagram of a basic structure of the measuring device of the present invention.
Fig. 2 is a schematic diagram of time division multiplexing of the measurement method of the present invention. FIG. 2a is a schematic diagram of a generated sawtooth wave signal a and a sawtooth wave signal b; fig. 2b is a schematic diagram of the photoelectric signal actually collected by the photoelectric sensor.
FIG. 3 is a graph showing the use of the present invention for CH at a concentration of 1840ppb4And 439.5ppm CO2A measurement result graph with a sampling interval of 20 seconds and a time duration of 20 hours was performed. Wherein, FIG. 3a is the pair CH4The concentration measurement result of (a); FIG. 3b is CH4The Allan variance of the concentration measurements of (1), wherein the minimum detection limit reaches 0.34ppb at 3580 seconds; FIG. 3c is for CO2The concentration measurement result of (a); FIG. 3d is CO2The Allan variance of the concentration measurement results of (1), wherein the minimum detection limit reached 0.05ppm at 2040 seconds.
Detailed Description
Preferred embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.
Referring to fig. 1, 2 and 3, the dual-optical-path gas concentration measuring apparatus based on the off-axis integral cavity system is configured as follows:
the computer 1 is a microcomputer;
any function generator 2 is a signal output device with a programming function and an analog output function;
the laser is a first laser 4 and a second laser 5 which output different wavelengths and are both distributed feedback semiconductor lasers;
the optical fibers are a first optical fiber 6 connected with the first laser 4 and a second optical fiber 7 connected with the second laser 5;
the adjustable focusing lens group comprises a first adjustable focusing lens group 8 and a second adjustable focusing lens group 9, the adjustable focal lengths of which are both 7.5 mm;
the optical resonant cavity 10 is a tube with optical axes deviating from the output optical axes of the first optical fiber 6 and the second optical fiber 7, the tube side of the optical resonant cavity is provided with an air inlet and an air outlet respectively, the two end faces of the tube are provided with a front high reflecting mirror 101 and a rear high reflecting mirror 102 respectively, the tube length of the tubular optical resonant cavity 10 is 28cm, the inner diameter of the tube is 2cm, the diameters of the air inlet and the air outlet are both 1cm, and the reflectivity of the front high reflecting mirror 101 and the reflectivity of the rear high reflecting mirror 102 are both more than or equal to 99.99%;
the fixed focal length of the focusing lens 11 is 25 mm;
the photoelectric sensor 12 is an indium gallium arsenic photoelectric sensor;
the data collector 13 is a single chip with A/D and D/A conversion.
During measurement, the process of modulating the output of the laser by adopting the time division multiplexing technology comprises the following steps: the computer 1 generates a sawtooth wave signal a with the frequency of 160Hz, and takes the median of the sawtooth wave signal a as a demarcation point, and sets a section from an initial value to the median as a light-out section and a section from the median to a tail value as a scanning section; keeping the frequency and the waveform of the sawtooth wave signal a unchanged, and generating a sawtooth wave signal b by changing the 180-degree phase of the sawtooth wave signal a, so that the scanning section of the sawtooth wave signal b is positioned in the light-emitting-free section of the sawtooth wave signal a, and the light-emitting-free section is positioned in the scanning section of the sawtooth wave signal a. Then, the sawtooth wave signal a and the sawtooth wave signal b are converted into voltage signals by an arbitrary function generator 2, the voltage output by the light-emitting-free section is 0 volt, the voltage output by the scanning section is scanning voltage required for detecting absorption spectrum, and then the voltage signals are sent to a temperature current controller 3, and the temperature current controller 3 is used for converting the scanning voltage into scanning current for alternately driving a first laser 4 and a second laser 5.
The process of detecting the gas concentration comprises the following steps: the light beams output by the first laser 4 and the second laser 5 which alternately emit light respectively pass through the first optical fiber 6, the first adjustable focusing lens group 8, the second optical fiber 7 and the second adjustable focusing lens group 9, then are injected into the optical resonant cavity 10 in a time-sharing manner through the front high-reflection mirror 101, and the gas CH to be measured in the optical resonant cavity 104And CO2The front high-reflection mirror 101 and the rear high-reflection mirror 102 make contact with each other many times, and after the contact is transmitted by the rear high-reflection mirror 102 and focused by the focusing lens 11, the contact is converted into an electric signal by the photoelectric sensor 12, and then the electric signal is collected and analyzed by the data collector 13, so that the result shown in fig. 3 is obtained.
It is apparent that those skilled in the art can make various changes and modifications to the apparatus and method for measuring a gas concentration of a two-optical path based on an off-axis integrating cavity system of the present invention without departing from the spirit and scope of the present invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include such modifications and variations.
Claims (10)
1. The utility model provides a two light path gas concentration measuring device based on off-axis integral cavity system, includes temperature current controller (3), laser instrument, optic fibre, built-in optical resonator (10), photoelectric sensor (12) and the data acquisition unit (13) of the gas that awaits measuring that connect gradually, its characterized in that:
the laser is a first laser (4) and a second laser (5) which output different wavelengths;
the optical fibers are a first optical fiber (6) connected with the first laser (4) and a second optical fiber (7) connected with the second laser (5);
the laser temperature and current controller is characterized in that a computer (1) and an arbitrary function generator (2) are sequentially connected between the data collector (13) and the temperature and current controller (3), so that the computer (1) sends out two groups of sawtooth wave signals with the same frequency, the same wave form and the phase difference of 180 degrees, the sawtooth wave signals are converted into electric signals by the arbitrary function generator (2) and then sent to the temperature and current controller (3) for controlling the first laser (4) and the second laser (5) to alternately output laser signals.
2. The dual optical path gas concentration measuring device based on the off-axis integral cavity system as claimed in claim 1, wherein the first laser (4) and the second laser (5) are both distributed feedback semiconductor lasers.
3. The dual-optical-path gas concentration measuring device based on the off-axis integral cavity system as claimed in claim 1, wherein a first adjustable focusing lens group (8) and a second adjustable focusing lens group (9) with adjustable focal lengths of 7.5mm are respectively arranged between the first optical fiber (6), the second optical fiber (7) and the optical resonant cavity (10).
4. The dual-optical-path gas concentration measuring device based on the off-axis integral cavity system as claimed in claim 1, wherein the optical resonant cavity (10) is a tube with optical axes both deviating from the output optical axes of the first optical fiber (6) and the second optical fiber (7), the tube side of the optical resonant cavity is provided with a gas inlet and a gas outlet respectively, the two end faces of the tube are provided with a front high reflecting mirror (101) and a rear high reflecting mirror (102) respectively, wherein the tube length of the tubular optical resonant cavity (10) is 28cm, the tube inner diameter is 2cm, the diameters of the gas inlet and the gas outlet are both 1cm, and the reflectivities of the front high reflecting mirror (101) and the rear high reflecting mirror (102) are both greater than or equal to 99.
5. The dual optical path gas concentration measuring device based on the off-axis integral cavity system as claimed in claim 1, wherein a focusing lens (11) with a fixed focal length of 25mm is disposed between the optical resonant cavity (10) and the photoelectric sensor (12).
6. The dual optical path gas concentration measuring device based on the off-axis integral cavity system as claimed in claim 1, wherein the photoelectric sensor (12) is an indium gallium arsenic photoelectric sensor.
7. The dual-optical-path gas concentration measuring device based on the off-axis integral cavity system as claimed in claim 1, wherein the data collector (13) is a single chip with A/D and D/A conversion.
8. The dual-optical-path gas concentration measuring device based on the off-axis integral cavity system as claimed in claim 1, wherein the arbitrary function generator (2) is a signal output device with a programming function and an analog output function.
9. A dual-light-path gas concentration measuring method based on an off-axis integral cavity system comprises the steps of collecting signals of a photoelectric sensor and processing the signals, and is characterized in that:
the modulation of the laser output is such that,
generating a sawtooth wave signal a, setting a section from an initial value to a middle value as a non-emergent section and a section from the middle value to a tail value as a scanning section by taking the middle value of the sawtooth wave signal a as a demarcation point;
keeping the frequency and the waveform of the sawtooth wave signal a unchanged, and generating a sawtooth wave signal b by changing the 180-degree phase of the sawtooth wave signal a, so that the scanning section of the sawtooth wave signal b is positioned in the light-emitting-free section of the sawtooth wave signal a, and the light-emitting-free section is positioned in the scanning section of the sawtooth wave signal a;
converting the sawtooth wave signal a and the sawtooth wave signal b into voltage signals, and enabling the voltage output by the light-emitting-free section to be 0V and the voltage output by the scanning section to be scanning voltage required by detection of the absorption spectrum;
the scan voltage is converted into a scan current that alternately drives the first laser and the second laser.
10. The method of claim 9, wherein the frequencies of the sawtooth wave signal a and the sawtooth wave signal b are 160 Hz.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114279996A (en) * | 2021-12-28 | 2022-04-05 | 哈尔滨工业大学 | Gas-phase hydrogen peroxide concentration detection system based on off-axis integration cavity |
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2020
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Application publication date: 20210326 |