CN108760653A - A kind of method that spectrometer accurately measures concentration of SO 2 gas - Google Patents

Abstract

The invention relates to a method for accurately measuring the concentration of sulfur dioxide gas with dual wavelengths and narrow pulse widths, comprising the following steps: one beam of pumping light is incident on a first resonant cavity to form a first detection laser; another beam of pumping light is incident on a second The resonant cavity forms the second detection laser; the first and second detection lasers are directly transmitted to the sample cell (22), and after multiple reflections in the sample cell (22), the light from the sample cell (22) exits Port (23) emits, converges in the absorption spectrometer (25) through the adjustable converging lens (24), and the spectrometer (25) converts the received optical signal into an electrical signal and transmits it to the computer (26), and the computer (26) passes the Analyzing and calculating the measured value N ₁ of the first detection laser and the measured value N ₂ of the second detection laser to obtain an accurate gas concentration value N. The present invention adopts dual wavelengths for measurement and uses each other as reference standards for pulse width correction, thereby obtaining accurate measurement results and meeting the detection of sulfur dioxide gas under high precision.

Description

A method for accurately measuring the concentration of sulfur dioxide gas with a spectrometer

technical field

The invention relates to a method for detecting the concentration of sulfur dioxide gas, in particular to a method for accurately measuring the concentration of sulfur dioxide gas with dual wavelengths and narrow pulse width.

Background technique

Industry and commerce usually require accurate measurement of harmful gases in a certain space to ensure the safety of this space. Currently, harmful gases that need to be prevented include SO ₂ , H ₂ S, CO, etc. Whether the claimed hazardous gases meet certain purity limits and/or whether the emissions of these gases comply with environmental regulations. Typical applications such as process control, emissions and environmental monitoring, security, and air conditioning require accurate concentration measurement.

Wavelength modulation spectroscopy is a way to enhance the sensitivity of gas measurements, especially when measuring smaller concentrations. Usually, the concentration of the gas to be measured is calculated by measuring the spectral intensity of the incident light and the outgoing light. However, the accuracy of the existing measurement methods is not high, which is acceptable for some situations with low requirements, but for some environments with high precision requirements, the existing measurement methods often cannot accurately measure the concentration of harmful gases in the space, so , it is necessary to develop a systematic method for accurate measurement.

Contents of the invention

The invention aims to solve the technical problem of inaccurate measurement of the existing sulfur dioxide gas concentration. A method for accurately measuring the concentration of sulfur dioxide gas with a dual-wavelength narrow pulse width is proposed, including the following steps:

A fiber laser 1 with a spectral line width of 0.1nm outputs 1064nm linearly polarized laser light, which is divided into two beams of pumping light by a 1064nm half mirror 2;

A beam of pump light is incident to the first resonant cavity, the first resonant cavity includes a first reflector 4, a second reflector 9, a third reflector 3 and a fourth reflector 10, and the incident light passes through the first reflector 4 is transmitted to the first crystal 8; the first crystal 8 generates 3980nm idler light and 1452nm signal light by adjusting the temperature controller; the 3980nm idler light, 1452nm signal light and 1064nm pump light Resonant cavity oscillation; the first optical isolator 5, the first 1/2 wave plate 6, and the first Fabry-Perot etalon 7 are also included in the first resonant cavity, and the first optical isolator 5 controls The transmission direction of light, the first 1/2 wave plate 6 controls the polarization direction of the pump light 1064nm laser, and the first Fabry-Perot etalon 7 controls the spectral line width of the 3980nm idler light to be 0.0001nm , the 3980nm idler light is emitted from the second mirror 9 to form the first detection laser light;

The first detection laser light is directly transmitted to the first entrance 11 of the sample cell 22, and after multiple reflections in the sample cell 22, it is emitted from the light exit port 23 of the sample cell 22, and passed through the adjustable converging lens 24. Converging in the absorption spectrometer 25, the spectrometer 25 converts the received optical signal into _an electrical signal and transmits it to the computer 26, and uses the following _formula to calculate the SO gas concentration to obtain the SO gas concentration N ₁ ,

I(λ ₁ )=A(λ ₁ )I ₀ (λ ₁ )eσ1N1+B(L1)(1)

In the formula, σ ₁ is the absorption cross section of the SO2 gas to be measured under the laser wavelength of 3980nm, A(λ ₁ ) is the first interference factor, B(L ₁ ) is the second interference factor, and I ₀ (λ ₁ ) is the incident light Intensity, I(λ ₁ ) is the outgoing light intensity, L ₁ is the optical path of the laser in the sample cell;

Another beam of pumping light is reflected by the half-mirror 2 to the 1064nm total reflection mirror 12, and then enters the second resonant cavity. The second resonant cavity includes the fifth reflector 13, the sixth reflector 19, the seventh reflector Mirror 14 and the eighth reflection mirror 20, the incident light is transmitted to the second crystal 16 through the fifth reflection mirror 13; The second crystal 16 is made to produce 2466nm idle frequency light and 1871nm signal light by adjusting the temperature controller; the 2466nm idle frequency Frequency light, 1871nm signal light and 1064nm pump light oscillate in the second resonant cavity; the second resonant cavity also includes a second optical isolator 15, a second 1/2 wave plate 17, a second Fabry -Perot etalon 18, the second optical isolator 15 controls the transmission direction of light, the second 1/2 wave plate 17 controls the polarization direction of pump light 1064nm laser, the second Fabry-Perot Luo etalon 18 controls the spectral line width of the 2466nm idler light to be 0.0001nm, and the 2466nm idler light is emitted from the sixth reflector 19 to form the second detection laser light;

The second detection laser is directly transmitted to the second entrance 21 of the sample cell 22, and after multiple reflections in the sample cell 22, it is emitted from the light exit port 23 of the sample cell 22, passed through the adjustable converging lens 24 Converging in the absorption spectrometer 25, the spectrometer 25 converts the received optical signal into an electrical signal and transmits it to the computer ₂₆ , and uses the following _formula to calculate the SO2 gas concentration to obtain the SO2 gas concentration _N2 ,

In the formula, σ ₂ is the absorption cross section of the SO2 gas to be measured under the laser wavelength of 2466nm, A(λ ₂ ) is the first interference factor, B(L ₂ ) is the second interference factor, and I ₀ (λ ₂ ) is the incident light Intensity, I(λ ₂ ) is the outgoing light intensity, L ₂ is the optical path of the laser in the sample cell;

The computer 26 obtains an accurate gas concentration value N by analyzing and calculating the measurement value N ₁ of the first detection laser and the measurement value N ₂ of the second detection laser.

Further, the following steps are also included:

Adjust the measured values I(λ ₁ ), I(λ ₂ ) at different wavelengths under different absorption peaks, and then determine the values of the first interference factors A(λ ₁ ), A(λ ₂ );

In conjunction with formula (1) (2) and the value calculation of the above-mentioned first interference factor A(λ ₁ ), A(λ ₂ ), the SO gas concentrations N ₁ , N ₂ under different wavelengths are obtained _;

Accurate SO2 gas concentration N is calculated by weighted average.

Further, the weighted average coefficient is 0.5, that is, N=0.5N ₁ +0.5N ₂ .

Further, by increasing the optical path L ₁ or L ₂ of the detection light in the measurement gas, the measurement result is more accurate.

Further, the temperature control device is controlled by a computer, so that the control temperature is accurate at 0.01° C., thereby ensuring the stability of the wavelength of the detection laser, thereby ensuring the accuracy of the concentration measurement.

Beneficial effects of the present invention: the present invention uses dual wavelengths for measurement and uses each other as a reference standard for pulse width calibration to obtain accurate pulse width alignment detection, and through multiple measurements, it can eliminate the corresponding interference factors, and through temperature The controller precisely controls the detection laser wavelength to obtain accurate measurement results, which meets the high-precision detection of sulfur dioxide gas. This method is more accurate than measurements at a single wavelength.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings that need to be used in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For Those of ordinary skill in the art can also obtain other drawings based on these drawings without any creative effort.

Fig. 1 is a structural schematic diagram of a sulfur dioxide gas detection device according to the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

As shown in Figure 1, the present invention aims to solve the technical problem of inaccurate measurement of the existing sulfur dioxide gas concentration. A method for accurately measuring the concentration of sulfur dioxide gas with a dual-wavelength narrow pulse width is proposed, including the following steps:

A fiber laser 1 with a spectral line width of 0.1nm outputs 1064nm linearly polarized laser light, which is divided into two beams of pumping light by a 1064nm half mirror 2;

A beam of pump light is incident to the first resonant cavity, the first resonant cavity includes a first reflector 4, a second reflector 9, a third reflector 3 and a fourth reflector 10, and the incident light passes through the first reflector 4 is transmitted to the first crystal 8; the first crystal 8 generates 3980nm idler light and 1452nm signal light by adjusting the temperature controller; the 3980nm idler light, 1452nm signal light and 1064nm pump light Resonant cavity oscillation; the first optical isolator 5, the first 1/2 wave plate 6, and the first Fabry-Perot etalon 7 are also included in the first resonant cavity, and the first optical isolator 5 controls The transmission direction of light, the first 1/2 wave plate 6 controls the polarization direction of the pump light 1064nm laser, and the first Fabry-Perot etalon 7 controls the spectral line width of the 3980nm idler light to be 0.0001nm , the 3980nm idler light is emitted from the second mirror 9 to form the first detection laser light;

The first detection laser light is directly transmitted to the first entrance 11 of the sample cell 22, and after multiple reflections in the sample cell 22, it is emitted from the light exit port 23 of the sample cell 22, and passed through the adjustable converging lens 24. Converging in the absorption spectrometer 25, the spectrometer 25 converts the received optical signal into _an electrical signal and transmits it to the computer 26, and uses the following _formula to calculate the SO gas concentration to obtain the SO gas concentration N ₁ ,

In the formula, σ ₁ is the absorption cross section of the SO2 gas to be measured under the laser wavelength of 3980nm, A(λ ₁ ) is the first interference factor, B(L ₁ ) is the second interference factor, and I ₀ (λ ₁ ) is the incident light Intensity, I(λ ₁ ) is the outgoing light intensity, L ₁ is the optical path of the laser in the sample cell;

Another beam of pumping light is reflected by the half-mirror 2 to the 1064nm total reflection mirror 12, and then enters the second resonant cavity. The second resonant cavity includes the fifth reflector 13, the sixth reflector 19, the seventh reflector Mirror 14 and the eighth reflection mirror 20, the incident light is transmitted to the second crystal 16 through the fifth reflection mirror 13; The second crystal 16 is made to produce 2466nm idle frequency light and 1871nm signal light by adjusting the temperature controller; the 2466nm idle frequency Frequency light, 1871nm signal light and 1064nm pump light oscillate in the second resonant cavity; the second resonant cavity also includes a second optical isolator 15, a second 1/2 wave plate 17, a second Fabry -Perot etalon 18, the second optical isolator 15 controls the transmission direction of light, the second 1/2 wave plate 17 controls the polarization direction of pump light 1064nm laser, the second Fabry-Perot Luo etalon 18 controls the spectral linewidth of the 2466nm idler light to be 0.0001nm, and the 2466nm idler light is emitted from the sixth reflector 19 to form the second detection laser light;

The second detection laser light is directly transmitted to the second entrance 21 of the sample cell 22, and after multiple reflections in the sample cell 22, it is emitted from the light exit port 23 of the sample cell 22, passed through the adjustable converging lens 24 Converging in the absorption spectrometer 25, the spectrometer 25 converts the received optical signal into an electrical signal and transmits it to the computer ₂₆ , and uses the following _formula to calculate the SO gas concentration to obtain the SO gas concentration N ₂ ,

In the formula, σ ₂ is the absorption cross section of the SO2 gas to be measured under the laser wavelength of 2466nm, A(λ ₂ ) is the first interference factor, B(L ₂ ) is the second interference factor, and I ₀ (λ ₂ ) is the incident light Intensity, I(λ ₂ ) is the outgoing light intensity, L ₂ is the optical path of the laser in the sample cell;

The computer 26 obtains an accurate gas concentration value N by analyzing and calculating the measurement value N ₁ of the first detection laser and the measurement value N ₂ of the second detection laser.

The 45-degree surface of the high-reflection mirror 4 of the resonator is coated with a 1064nm high-transparency, 2000-4300nm high-reflection film, and the first and second crystals are nonlinear MgO:PPLN crystals.

The pulse widths of the first detection light and the second detection light are both 0.001nm, so as to better match the absorption peak of sulfur dioxide gas, absorb accurately, reduce the interference of other absorbing gases, and ensure the accuracy of measurement. By precisely controlling the angle and thickness accuracy of the first and second Fabry-Perot etalons to meet the pulse width compression, the incident angle is usually controlled to 45 degrees and the thickness is 3-4mm.

In addition, the following steps are also included:

By adjusting the spectrometer to obtain measured values I(λ ₁ ), I(λ ₂ ) at different wavelengths under different absorption peaks, and then obtain the first interference factors A(λ ₁ ), A(λ 2 ) through multiple iterations ₂ ), the calculation precision is 0.001.

Combine formula (1) (2) and the value calculation of above-mentioned first interference factor A (λ ₁ ), A (λ ₂ ) to get SO under different wavelengths gas concentration N ₁ , N _{2 ;}

Accurate SO2 gas concentration N is calculated by weighted average. The weighted average coefficient is between 0.495-0.505, preferably 0.5, namely N=0.5N ₁ +0.5N ₂ .

In a further method, the measurement result is more accurate by increasing the optical path L ₁ or L ₂ of the detection light in the measurement gas, and the length of L ₁ or L ₂ can usually be set to 0.5-5 meters.

In addition, the temperature control device is controlled by a computer, so that the control temperature is accurate at 0.01°C, so as to ensure the stability of the wavelength of the detection laser and the accuracy of the concentration measurement.

The test lasers with two wavelengths of 3980.0nm and 2466.0nm with a spectral line width of 0.1pm test SO2 gas at the same time. The laser of one wavelength is used as the test light source, and the laser of the other wavelength is used as the reference light source. Out of SO2 gas, but also improve the accuracy of the test gas to 0.1ppb.

The absorption intensity values of the two SO2 gases after the test are displayed on the computer software, compared with the standard intensity values of the SO2 gas, and the spectrometer is used as the calibration value of the test method to obtain the concentration of the SO2 gas.

Beneficial effects of the present invention: the present invention uses dual wavelengths for measurement and uses each other as a reference standard for pulse width calibration to obtain accurate pulse width alignment detection, and through multiple measurements, it can eliminate the corresponding interference factors, and through temperature The controller precisely controls the detection laser wavelength to obtain accurate measurement results, which meets the high-precision detection of sulfur dioxide gas.

The device embodiments described above are only illustrative, and the units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in One place, or it can be distributed to multiple network elements. Part or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still be Modifications are made to the technical solutions described in the foregoing embodiments, or equivalent replacements are made to some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims (5)

1. A method for accurately measuring the concentration of sulfur dioxide gas with a narrow pulse width of two wavelengths, is characterized in that it comprises the steps: A fiber laser (1) with a spectral line width of 0.1nm outputs 1064nm linearly polarized laser light, which is divided into two beams of pumping light by a 1064nm half mirror (2); A beam of pumping light is incident to the first resonant cavity, and the first resonant cavity includes a first reflective mirror (4), a second reflective mirror (9), a third reflective mirror (3) and a fourth reflective mirror (10) , the incident light is transmitted to the first crystal (8) through the first reflector (4); the first crystal (8) is produced by adjusting the temperature controller to produce 3980nm idler light and 1452nm signal light; the 3980nm idler light , 1452nm signal light and 1064nm pump light oscillate in the first resonant cavity; the first resonant cavity also includes a first optical isolator (5), a first 1/2 wave plate (6), a first method The Brie-Perot etalon (7), the first optical isolator (5) controls the transmission direction of light, and the first 1/2 wave plate (6) controls the polarization direction of the pump light 1064nm laser, so The first Fabry-Perot etalon (7) controls the spectral line width of the 3980nm idler light to be 0.0001nm, and the 3980nm idler light is emitted from the second reflector (9) to form the first detection laser light; The first detection laser light is directly transmitted to the first entrance (11) of the sample cell (22), and after multiple reflections in the sample cell (22), it is emitted from the light exit port (11) of the sample cell (22). 23) emit, converge in the absorption spectrometer (25) through the adjustable converging lens (24), and the spectrometer (25) converts the received optical signal into an electrical signal and transmits it to the computer (26), and utilizes the following _formula for SO gas gas The concentration is calculated to obtain the SO ₂ gas concentration N ₁ , In the formula, σ ₁ is the absorption cross section of the SO2 gas to be measured under the laser wavelength of 3980nm, A(λ ₁ ) is the first interference factor, B(L ₁ ) is the second interference factor, and I ₀ (λ ₁ ) is the incident light Intensity, I(λ ₁ ) is the outgoing light intensity, L ₁ is the optical path of the laser in the sample cell; Another beam of pumping light is reflected by the half mirror (2) to the 1064nm total reflection mirror (12), and then enters the second resonant cavity. The second resonant cavity includes the fifth reflector (13), the sixth reflector mirror (19), the seventh reflector (14) and the eighth reflector (20), the incident light is transmitted to the second crystal (16) through the fifth reflector (13); The crystal (16) produces 2466nm idler light and 1871nm signal light; the 2466nm idler light, 1871nm signal light and 1064nm pump light oscillate in the second resonant cavity; the second resonant cavity also includes a second light Isolator (15), the second 1/2 wave plate (17), the second Fabry-Perot etalon (18), the second optical isolator (15) controls the transmission direction of light, the first Two 1/2 wave plates (17) control the polarization direction of the pump light 1064nm laser, and the spectral linewidth of the second Fabry-Perot etalon (18) controlling the 2466nm idler light is 0.0001nm, and the 2466nm The idler light is emitted from the sixth reflector (19) to form the second detection laser light; The second detection laser is directly transmitted to the second entrance (21) of the sample cell (22), and after multiple reflections in the sample cell (22), it is emitted from the light exit port (22) of the sample cell (22). 23) emit, converge in the absorption spectrometer (25) through the adjustable converging lens (24), and the spectrometer (25) converts the received optical signal into an electrical signal and transmits it to the computer (26), and utilizes the following _formula for SO gas gas The concentration is calculated to obtain the SO ₂ gas concentration N ₂ , In the formula, σ ₂ is the absorption cross section of the SO ₂ gas to be measured under the laser wavelength of 2466nm, A(λ ₂ ) is the first interference factor, B(L ₂ ) is the second interference factor, and I ₀ (λ ₂ ) is the incident Light intensity, I(λ ₂ ) is the outgoing light intensity, L ₂ is the optical path of the laser in the sample cell; The computer (26) obtains an accurate gas concentration value N by analyzing and calculating the measured value N ₁ of the first detection laser and the measured value N ₂ of the second detection laser. 2. The method according to claim 1, further comprising the steps of: Adjust the measured values I(λ ₁ ), I(λ ₂ ) at different wavelengths under different absorption peaks, and then determine the values of the first interference factors A(λ ₁ ), A(λ ₂ ); In conjunction with formula (1) (2) and the value calculation of the above-mentioned first interference factor A(λ ₁ ), A(λ ₂ ), the SO gas concentrations N ₁ , N ₂ under different wavelengths are obtained _; Accurate _SO2 gas concentration N is obtained by weighted average. 3. The method according to claim 2, wherein the weighted average coefficient is 0.5, ie N=0.5N ₁ +0.5N ₂ . 4 . The method according to claim 3 , wherein the measurement result is made more accurate by increasing the optical path L ₁ or L ₂ of the detection light in the measurement gas. 5. The method according to claim 4, characterized in that, the temperature control device is controlled by a computer so that the control temperature is accurate at 0.01°C, thereby ensuring the stability of the wavelength of the detection laser and the accuracy of the concentration measurement.