CN115523958A - Gas temperature and concentration synchronous measurement method based on spectrum fast-slow separation principle - Google Patents

Abstract

The invention discloses a method for synchronously measuring gas temperature and concentration based on the principle of fast and slow separation of spectra, comprising the steps of: acquiring and normalizing the differential absorption spectra of chlorobenzene with unknown concentration and temperature information at different wavelength points; The differential absorption cross section corresponding to the differential absorption spectrum of each wavelength point; the differential absorption cross section of each wavelength point at different temperatures is normalized; the differential absorption spectrum of the unknown concentration and temperature information after normalization and After normalization, each differential absorption cross ^- section is compared with the coefficient of determination R2 one by one, and the temperature corresponding to the differential absorption cross ^- section corresponding to the maximum value of the determination coefficient R2 found is used as the predicted temperature; the difference corresponding to the predicted temperature Absorption cross section, the chlorobenzene concentration corresponding to the differential absorption cross section was calculated according to Beer-Lambert's law. The invention considers the temperature specificity of the differential absorption section, and realizes the simultaneous measurement of the temperature and concentration of p-chlorobenzene.

Description

A Synchronous Measurement Method of Gas Temperature and Concentration Based on the Principle of Spectral Fast and Slow Separation

technical field

The invention relates to the technical field of chlorobenzene gas measurement, in particular to a method for synchronously measuring gas temperature and concentration based on the principle of spectral fast-slow separation.

Background technique

Chlorobenzene is the main raw material for the production of pesticides, and it is also an intermediate in the organic synthesis of chemical raw materials such as phenol, nitrophenol, and aniline. Chlorobenzene is often used as rubber additives, solvents for paints, coatings and varnishes, quick-drying inks and dry cleaning agents, etc., and is used in many fields such as dyes, medicines, spices and other production fields. Chlorobenzene is widely used, but with the development of my country's industry, the pollution of chlorobenzene compounds in soil and groundwater has become more and more serious, and chlorobenzene has strong volatility, and gaseous chlorobenzene in industrial environments also greatly threatens the environment and human body Healthy, it has an anesthetic effect on the central nervous system, has a stimulating effect on human skin and mucous membranes, and will increase the morbidity and mortality of chronic diseases. Second, in the field of waste disposal, chlorobenzene is considered a precursor of persistent organic pollutants such as dioxins. Therefore, the accurate measurement of p-chlorobenzene concentration is of great significance for the prevention and control of pollutants and the understanding of the generation of persistent organic pollutants in the process of waste disposal. Although mass spectrometry, gas chromatography, high performance liquid chromatography, ion mobility spectrometry and other methods in the existing methods have been used to measure the concentration of chlorobenzene, the accuracy is not high, and it is impossible to measure the concentration of chlorobenzene at the same time. Measurement of the temperature of p-chlorobenzene.

Contents of the invention

The invention aims at realizing the synchronous and accurate measurement of p-chlorobenzene concentration and temperature, and provides a method for synchronous measurement of gas temperature and concentration based on the principle of fast and slow separation of spectra.

For reaching this purpose, the present invention adopts following technical scheme:

Provide a method for synchronous measurement of gas temperature and concentration based on the principle of spectral fast and slow separation, including steps:

L1, obtain the differential absorption spectrum of chlorobenzene with unknown concentration and temperature information and perform normalization processing;

L2, calculating the differential absorption cross section corresponding to the differential absorption spectrum of the chlorobenzene at each wavelength point of the known concentration and temperature in the experiment;

L3, normalizing the differential absorption cross section at different temperatures in the experiment;

L4, compare the differential absorption spectrum of the unknown concentration and temperature information after normalization with each of the differential absorption cross-sections after normalization with the coefficient of determination R ² one by one, and determine the determined ^The temperature corresponding to the differential absorption cross section corresponding to the maximum value of coefficient R2 is used as the predicted temperature of the chlorobenzene of unknown temperature in step L1;

L5. For the differential absorption cross section corresponding to the predicted temperature, calculate the chlorobenzene concentration corresponding to the differential absorption cross section according to the Beer-Lambert law.

As a preference, in step L2, the method for calculating the differential absorption cross section corresponding to the differential absorption spectrum is expressed by the following formula (5):

In formula (1), Δσ(λ) represents the differential absorption cross-section obtained when light with a wavelength of λ is incident on chlorobenzene gas;

N represents the chlorobenzene number density;

L represents the absorption optical path length;

DOD denotes the differential absorption spectrum.

As preferably, in step L3, the method for normalizing the differential absorption cross section at each wavelength point at the same temperature is expressed by the following formula (2):

In formula (2), Δσ _{Normalization} represents the normalization result of Δσ;

i represents the differential absorption cross section corresponding to the i-th wavelength point at a specified temperature and a specified concentration;

n represents the number of wavelength points selected within the 201-220nm band range at a specified concentration and a specified temperature.

As preferably, the method for normalizing the differential absorption spectrum of p-chlorobenzene is:

ΔDOD _{Normalization} represents the normalization result of DOD;

DOD _i represents the differential absorption spectrum corresponding to the ith wavelength point at a specified temperature and a specified concentration.

Preferably, in step L4, the method for obtaining the predicted temperature corresponding to the differential absorption cross-section includes the steps of:

S1, constructing a fitting function of the differential absorption cross section with respect to temperature;

S2. Calculate the temperature corresponding to the differential absorption cross section according to the fitting function as the predicted temperature.

As preferably, the fitting function constructed in step S1 is the first fitting function characterizing the relationship between the chlorobenzene differential absorption cross section and temperature at each wavelength point, and the first fitting function is expressed by the following formula (1):

In the formula (3), Δσ represents the differential absorption cross section of the chlorobenzene;

T means temperature;

a, b, c represent item coefficients, d is a constant;

λ ₁ represents a specific wavelength point;

f represents the first fitting function.

Preferably, when λ ₁ =201.24 nm, a=2.99×10 ^-25 , b=-3.70×10 ^-22 , c=1.43×10 ^-19 , d=-1.55×10 ^-17 .

As preferably, the fitting function of construction is the second fitting function characterizing the relationship between the chlorobenzene differential absorption cross section and the wavelength of each temperature point, and the second fitting function is expressed by the following formula (4):

In formula (4), T ₁ represents specific described temperature point;

λ represents the wavelength;

Δσ _298K represents the chlorobenzene differential absorption cross section at the λ wavelength point position at a temperature of 298K;

a represents the quadratic term coefficient of the second fitting function _of the fitting relationship between temperature T and 298K differential absorption cross section,

b represents the _first -order coefficient of the second fitting function of the fitting relationship between temperature T and 298K differential absorption cross section,

C represents the constant term of the second fitting function _of the fitting relationship between temperature T and 298K differential absorption cross section,

m _Q , m _P , m _C respectively represent the corresponding parameters a, b, c and the cubic coefficient in the temperature fitting process;

n _Q , n _P , and n _C respectively represent the corresponding parameters a, b, c and the quadratic term coefficients in the temperature fitting process;

P _Q , P _P , and P _C respectively represent the corresponding parameters a, b, c and the first-order coefficients in the temperature fitting process;

w _Q , w _P , and w _C represent corresponding parameters a, b, c and constant items in the temperature fitting process, respectively.

Preferably, when constructing the fitting function, the light incident into the chlorobenzene gas is ultraviolet light with a wavelength of 201nm-220nm.

The present invention has the following beneficial effects:

1. Considering the temperature specificity of the differential absorption cross section, the present invention creatively proposes a method for simultaneous measurement of temperature and concentration, and the measurement deviation of the method for temperature is within 1.89%. Due to the spectral resolution of the instrument and other reasons, some deviations in the concentration inversion results are relatively large, but this method can basically realize the simultaneous measurement of temperature and concentration, which provides a new idea for the extension of differential absorption spectroscopy to the field of simultaneous measurement of temperature and concentration. 2. As the temperature changes, the differential absorption spectrum of chlorobenzene not only shows changes in amplitude, but also shows differences in its shape. In order to further understand the spectral absorption characteristics of chlorobenzene, the present invention calculates the important spectral parameters at different temperatures, that is, the differential absorption cross section, and constructs a binary function of the differential absorption cross section with respect to temperature and wavelength, respectively under the conditions of fixed temperature and wavelength The dimensionality reduction of the binary function was fitted to obtain the differential absorption cross section of chlorobenzene at continuous temperature in the target detection band. The two fitting methods provided show that the method of fitting with a single wavelength point has a relatively large error, because the spectral acquisition of a single point is easily affected by instrument fluctuations, but both fitting methods achieve a concentration inversion error within Within 2.74%, it is highly consistent with the differential absorption section shape obtained in the experiment.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the following will briefly introduce the drawings that are used in the embodiments of the present invention. Apparently, the drawings described below are only some embodiments of the present invention, and those skilled in the art can obtain other drawings according to these drawings without creative efforts.

Fig. 1 is the structural representation of fitting data generation device;

Fig. 2 is the schematic diagram of the differential absorption spectrum of 50ppm chlorobenzene under different temperatures;

Figure a in Figure 3 is the differential absorption cross-section of chlorobenzene recorded in the MPI-Mainz UV database at a specified band and at a temperature of 298K. Figure b is the database differential absorption cross-section after convolution. Figure c is the differential absorption cross-section obtained by the experiment;

Fig. 4 is the bar graph of the chlorobenzene concentration and the actual concentration comparison obtained by using the standard absorption cross-section inversion and the curve graph of the variation trend of the calculated deviation with temperature;

Fig. 5 is a fitting curve diagram of the relationship between temperature compensation coefficient K (T) and temperature T;

Fig. 6 is a schematic diagram of a fitting curve of temperature and differential absorption cross section at a wavelength of 201.24nm;

Fig. 7 is a schematic flow chart of the relationship between temperature and chlorobenzene differential absorption cross-section under continuous wavelengths;

Fig. 8 is a schematic diagram of dividing the differential absorption cross section of chlorobenzene into 8 sections of monotonic intervals;

Fig. 9 is a fitting relationship curve diagram of different temperatures and 298K differential absorption cross sections;

Fig. 10 is the fitting relationship curve diagram between the quadratic term coefficient, the first term coefficient, the constant term and temperature of the second fitting function;

Fig. 11 is a schematic flow chart for constructing the fitting relationship between different temperatures and the differential absorption cross section of chlorobenzene at 298K;

Figure 12 is a schematic diagram of the results and deviations of the two fitting methods used in this embodiment to invert the concentration of chlorobenzene;

Figure 13 is a schematic diagram of the variation of the differential absorption cross-section at the continuous temperature from 288K to 473K in the 201-220nm band drawn according to the second fitting method;

Figure 14 is a schematic diagram of the normalized chlorobenzene differential absorption cross section at different temperatures;

Fig. 15 is the flowchart of synchronously measuring chlorobenzene temperature and concentration;

Fig. 16 is a diagram of the implementation steps of the method for inversion of gas concentration based on the fast-changing absorption cross section of the spectrum provided by an embodiment of the present invention;

Fig. 17 is a diagram of the implementation steps of a method for synchronously measuring gas temperature and concentration based on the principle of spectral fast-slow separation provided by an embodiment of the present invention.

detailed description

The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and through specific implementation methods.

Wherein, the accompanying drawings are only for illustrative purposes, showing only schematic diagrams, rather than physical drawings, and should not be construed as limitations on this patent; in order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings will be omitted, Enlargement or reduction does not represent the size of the actual product; for those skilled in the art, it is understandable that certain known structures and their descriptions in the drawings may be omitted.

In the drawings of the embodiments of the present invention, the same or similar symbols correspond to the same or similar components; , "inner", "outer" and other indicated orientations or positional relationships are based on the orientations or positional relationships shown in the drawings, which are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred devices or elements must It has a specific orientation, is constructed and operated in a specific orientation, so the terms describing the positional relationship in the drawings are for illustrative purposes only, and should not be understood as limitations on this patent. For those of ordinary skill in the art, the understanding of the specific meaning of the above terms.

In the description of the present invention, unless otherwise clearly stipulated and limited, if the term "connection" or the like indicates the connection relationship between parts, the term should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection. Connection, or integration; it can be mechanical connection or electrical connection; it can be direct connection or indirect connection through an intermediary, and it can be the internal communication of two parts or the interaction relationship between two parts. Those of ordinary skill in the art can understand the specific meanings of the above terms in the present invention in specific situations.

Since chlorobenzene has strong absorption characteristics in the ultraviolet wavelength range, differential absorption spectroscopy is suitable for the measurement of chlorobenzene concentration. The main absorption of chlorobenzene is located between 170-220nm, and there is another characteristic absorption band between 240-280nm, but its intensity is 2 orders of magnitude lower than the main absorption band. Considering that the increase of Rayleigh scattering in the atmosphere and the absorption of _O2 in the air make the light intensity of short-wave ultraviolet light within 200nm decay faster, the 201nm-220nm band was selected for the analysis of chlorobenzene concentration inversion in the experiment. The absorption cross section of chlorobenzene can be calculated using the Beer-Lambert law (Beer-Lambert law) in the absorption measurement. When the beam passes through chlorobenzene, the ratio of the incident light intensity to the transmitted light intensity can be expressed as:

I(λ)/I ₀ (λ)＝exp(-σ(λ)NL) (1)

Where I ₀ (λ) and I(λ) represent the intensity of incident light and the intensity of transmitted light, respectively;

λ represents the wavelength of the incident light;

σ(λ)(cm ² /molecule) represents the absorption cross section; N(molecule/cm ³ ) represents the number density of chlorobenzene; L(cm) represents the absorption optical path length.

In order to avoid the slow-changing absorption effect caused by factors such as scattering and light source instability on the measurement results, the differential absorption spectrum was obtained by polynomial fitting of the detection spectrum. The overall absorption cross section of chlorobenzene can be decomposed into fast-changing absorption and slow-changing absorption:

σ(λ)=σ ₀ (λ)+Δσ(λ) (2)

In formula (2), σ ₀ (λ) represents slowly varying absorption;

Δσ(λ) represents fast-changing absorption;

From formula (2), formula (1) can be rewritten as:

I(λ)＝I ₀ (λ)exp[-σ ₀ (λ)NL]exp[-Δσ(λ)NL] (3)

Removing the slow variation and only retaining the item that varies drastically with the wavelength, the formula (3) can be evolved as:

The DOD is defined as the differential absorption spectrum, which can be obtained by polynomial fitting of the detected spectral curve. The differential absorption cross section Δσ of chlorobenzene can be calculated according to the DOD, particle number density N and optical path length L in the experiment. However, the spectral data available in the experiment is limited, and it is impossible to exhaustively detect the differential absorption spectrum of chlorobenzene at all temperatures. Therefore, it is necessary to obtain the chlorine at other temperatures by theoretically deriving and calculating from the existing absorption cross section of chlorobenzene. Differential absorption cross section of benzene at various wavelengths. According to the pre-experiment and molecular absorption line theory, the change of temperature and wavelength can affect the intensity change of the differential absorption cross section, so the differential absorption cross section of chlorobenzene is a binary function of temperature and wavelength, which can be expressed as:

Δσ=f(T,λ) (5)

In the formula (5), f represents the mapping function of the differential absorption cross section changing with temperature and wavelength;

In order to accurately solve the differential absorption cross section Δσ, the embodiment of the present invention provides two fitting methods to determine the differential absorption cross section of chlorobenzene at different temperatures:

The first is to first fit the absorption cross section and temperature of each wavelength point to obtain the function of the absorption cross section and temperature of each wavelength point. In the present embodiment, the differential absorption cross section and the unary function _of temperature under specific wavelength λ Such as formula (6). Then arrange these unary functions in ascending order of the wavelength λ, and finally obtain the binary function of the absorption cross section with respect to temperature and wavelength.

The second is to firstly fit the differential absorption cross-section and wavelength at each temperature point to obtain the function of the differential absorption cross-section and wavelength at each temperature point. The unary function of the differential absorption cross-section and wavelength at a specific temperature T ₁ is shown in Equation (7 ), and then fit the parameters of these unary functions with temperature, and finally obtain the binary function of the differential absorption cross section with respect to temperature and wavelength.

However, since the shape of the differential absorption cross section of chlorobenzene is relatively complex, it is difficult to express it with a single functional expression, so the differential absorption cross section at 298K is used as the standard, and the formula (7) is transformed into the difference between the differential absorption cross section and the temperature T and the temperature at 298K Binary function of the differential absorption cross section at the λ wavelength point position:

In formula (8), Δσ _298K represents the chlorobenzene differential absorption cross section at the λ wavelength point position at a temperature of 298K;

a represents the quadratic term coefficient of the second fitting function _of the fitting relationship between temperature T and 298K differential absorption cross section,

b represents the _first -order coefficient of the second fitting function of the fitting relationship between temperature T and 298K differential absorption cross section,

m_Q、m_P、m_C分别表示对应的参数a、b、c与温度拟合过程中的三次项系数；C represents the constant term of the second fitting function _of the fitting relationship between temperature T and 298K differential absorption cross section,

m _Q , m _P , m _C respectively represent the corresponding parameters a, b, c and the cubic coefficient in the temperature fitting process;

n _Q , n _P , and n _C respectively represent the corresponding parameters a, b, c and the quadratic term coefficients in the temperature fitting process;

P _Q , P _P , and P _C respectively represent the corresponding parameters a, b, c and the first-order coefficients in the temperature fitting process;

w _Q , w _P , and w _c represent corresponding parameters a, b, c and constant items in the temperature fitting process, respectively.

From the above formulas (6)-(8), it can be seen that the differential absorption cross section of chlorobenzene is related to the wavelength and temperature. After obtaining the ultraviolet light wavelength data and the chlorobenzene temperature data incident on the chlorobenzene, the above formula ( 6) or formula (8) to solve the differential absorption cross section of chlorobenzene. After the differential absorption cross section is obtained, the concentration of chlorobenzene corresponding to the differential absorption cross section can be calculated according to the Beer-Lambert law (Beer-Lambert law). Whether the two fitting relations expressed by formulas (6) and (8) can accurately characterize the mapping relationship between the differential absorption cross-section and temperature and wavelength, the key is to accurately solve the coefficients a, b, c and constant d, for example, in formula (6), under a specific wavelength λ ₁ , the temperature T and the corresponding differential absorption cross section Δσ are used as fitting points to solve a, b, c, d, the more fitting points , the smoother the curve represented by the formula (6), the more accurate the values of a, b, c, and d obtained by inversion. Therefore, in order to easily obtain a sufficient number of data fitting points, the present invention specifically provides a method as shown in Figure 1 The fitting data generation device shown, the experimental principle of the device is as follows:

A high-pressure deuterium lamp (Hamamatsu, L9815) with a broadband emission spectrum was used as a light source, and the light emitted by the deuterium lamp was converted into parallel light through a quartz lens 1 (Thorlab, LA4545) with a focal length of 100 mm. The parallel light passes through a gas absorption cell 2 with a length of 50 cm and a diameter of 2 cm. After passing through the gas absorption cell 2, the optical path enters the optical fiber 5 connected to the spectrometer through the focusing lens 3. In order to improve the coupling efficiency and reduce the dissipation of the light beam, a quartz collimator 6 (74-UV collimator lens) is installed at the end of the fiber, and the transmission light wavelength range is 200-2000nm. The gas mixing unit consists of a highly stable mass flow controller 7 (MFC, Seven Stars) and a preheated mixing chamber 8, and the chlorobenzene standard gas is premixed with chlorobenzene and nitrogen at a nominal 100ppm. It is preferred to use two MFCs to achieve further dilution of the sample gas with nitrogen, resulting in different concentrations of chlorobenzene for the experiment. The temperature of the outside of the gas absorption cell 2 is preferably controlled by a glass fiber heating belt, and the temperature range that can be controlled by the temperature controller 9 is 273K-673K. Spectrometer 4 (Ocean Optics, Maya pro) has a detection range of 200nm-340nm and a resolution of 0.6nm, covering the narrow absorption band of chlorobenzene at 200-220nm. Reference numeral "10" in Fig. 1 is an air tank. Figure 2 shows the differential absorption spectra of 50ppm chlorobenzene at different temperatures. It can be seen from Figure 2 that the positions of the absorption peaks of chlorobenzene are the same at different temperatures, but the absorption peaks become smaller as the temperature increases, because at room temperature, the molecules are mainly in their ground state vibration energy levels. As the temperature increases, the number of molecules in the ground state vibration level decreases, and the temperature affects the density of the gas, so the temperature change affects the absorption of gas molecules. Although the absorption peak position is the same, as the temperature increases, the absorption peak The amplitude decreases, the absorption tends to be smoothed, and the differential structure is smoothed.

In order to understand the influence of temperature change on the concentration measurement of chlorobenzene, concentration inversion was performed on the obtained differential absorption spectrum with the corresponding absorption cross section at room temperature according to BeerLambert's law. The absorption cross section of chlorobenzene in a specified band at a temperature of 298K can be obtained from the MPI-Mainz ultraviolet database. In order to correct the instrument error, the system instrument function is convolved with the absorption cross-section in the database to obtain the standard absorption cross-section after convolution. Figure a in Fig. 3 shows the chlorobenzene recorded in the MPI-Mainz ultraviolet database at a temperature of 298K and The absorption cross-section under the specified band, the figure b is the standard absorption cross-section after the absorption cross-section shown in figure a is convolved with the system instrument function, what needs to be explained here is that the convolution process is to correct the instrument error, and the convolution is obtained by convolution The method of the standard absorption section is not within the scope of the claims of the present invention, so no specific description will be given. Figure c in Figure 3 is a schematic diagram of the differential absorption cross-section of chlorobenzene obtained through experiments in the specified band and also at a temperature of 298K in the present invention, and the experimental results expressed in figure c basically match the absorption cross-section shown in figure a, illustrating The absorption cross-section experimental method provided by the invention is effective. However, since there is a certain resolution with the original spectrum in the database, there are still errors in the standard absorption cross section obtained after convolution, and the principle of calculating the absorption cross section by using the fitting method and convolution to obtain the standard absorption cross section provided by this application is completely Different, the influence of the error that still exists due to convolution on the accuracy of the inversion results of chlorobenzene concentration is solved.

Concentration inversion was performed on the obtained differential absorption spectra using standard absorption cross-sections. After measuring the differential absorption spectrum DOD, the optical path L and the standard differential absorption cross section at 298K, according to the formula (4), that is, the Beer-Lambert law (Beer Lambert Law), it can be obtained:

Where N (molecule/cm ³ ) is the number density of chlorobenzene, the conversion relationship between volume fraction C (ppm) and number density N (molecule/cm ³ ) can be expressed as:

Wherein C _C is the calculated concentration of chlorobenzene (ppm); T is the gas temperature (K) during measurement; V _A is 22.4L of 1 mol gas volume at 273K; N _A is Avogadro's constant 6.02×10 ²³ ; T ₀ is 273K. The obtained results are shown in Table 1 below. From the histogram of the comparison between the actual concentration and the calculated concentration shown in Figure 4 corresponding to Table 1 and the curve of the deviation versus temperature, it can be seen that as the temperature deviates from 298K, the concentration reverses. The larger the error (deviation) will be. When the temperature rises to 473K, if the standard absorption cross section is used for concentration inversion, the deviation will reach more than 70%.

Table 1

According to the above analysis, it can be seen that the temperature has a significant impact on the results of concentration inversion. In order to obtain more accurate chlorobenzene concentration measurement results, the present invention adopts the method of temperature compensation to the measurement results, by calculating the concentration of chlorobenzene under different temperatures. The ratio fitting between the actual concentration and the temperature compensation coefficient K (T) is obtained, and the relationship between the calculated concentration _C of chlorobenzene and the actual concentration _CA is expressed by the following formula (9):

C _C ＝C _A ×K(T) formula (9)

Adopt the standard chlorobenzene gas of known concentration to measure K (T), measuring method is as shown in following formula (10):

Then measure the K(T) value at different temperatures, and use the temperature and the corresponding K(T) as the fitting point to solve the term coefficient and constant of the fitting function of K(T) with respect to the temperature, and solve the obtained Item coefficients and constants are substituted into the fitting function of K(T) with respect to temperature to obtain the final fitting function of K(T) with respect to temperature. After repeated experiments, the fitting function of K(T) with respect to temperature is obtained as follows (11 )Express:

K(T)＝exp(-0.000017527×T ² +0.0073569×T-0.63957) (11)

In order to verify the applicability of the temperature compensation coefficient, the present invention adopts 55ppm chlorobenzene standard gas to study the concentration compensation under four temperature conditions of 318K, 333K, 383K and 473K, and the verification results are shown in Table 2 below:

Table 2

The temperature compensation coefficient K(T) can be obtained according to the measured temperature. After temperature compensation is performed on the calculated concentration, the detection error of the chlorobenzene concentration is reduced to less than 3.2%, which effectively eliminates the nonlinear influence of temperature on the detection of chlorobenzene and improves the difference. Accuracy of detection of p-chlorobenzene concentration at temperature.

The temperature compensation method mentioned above only considers the influence of temperature on its amplitude, and regards the shapes of differential absorption spectra at different temperatures as the same. However, it has been shown in Fig. 2 that with the increase of temperature, the fluctuation range of the differential absorption spectrum of chlorobenzene decreases. So in fact, the temperature also affects the shape of the differential absorption spectrum. By analyzing this effect, the error of using differential absorption spectroscopy to predict the concentration of chlorobenzene when the temperature is known can be further reduced. More importantly, the gas temperature and the concentration of chlorobenzene can be obtained through the spectrum at the same time when the concentration is unknown.

According to the theory of molecular spectroscopy, the absorption spectrum is mainly affected by the analytical absorption cross section. The following will emphatically illustrate how the present invention specifically uses the fitting method expressed by formula (6) or formula (8) to obtain the relationship between the differential absorption cross section and temperature in the 288-473K interval, and then obtain the measured chlorine by inversion The concentration of benzene gas.

The present invention utilizes the fitting method one expression of formula (6) to invert the step of chlorobenzene concentration as follows:

1. According to the data obtained from the experiment, fit the relationship between temperature and the differential absorption cross-section intensity at a single wavelength (such as a specific wavelength λ ₁ ), and obtain the functional relationship of the differential absorption cross-section intensity at a single wavelength as a function of temperature. Taking the wavelength point 201.24nm in the range of 201nm-220nm as an example, the differential absorption cross section corresponding to 288K-473K at this wavelength point is shown in Table 3 below. Fitting the functional relational expression of temperature and differential absorption cross section at this wavelength, if the fitting number is too low, it will affect the accuracy of the solution result of the relational expression, and if the fitting number is too high, the fitting curve will oscillate. Therefore, after repeated experiments, this paper concludes that The embodiment selects the best fitting times as 3 times.

table 3

2. According to the fitting curve of temperature and differential absorption cross section at the wavelength of 201.24nm shown in Figure 6, the fitting relationship between temperature and differential absorption cross section at this wavelength point can be obtained, and the relational expression is as follows:

Δσ＝2.99×10 ^-25 ×T ³ -3.70×10 ^-22 ×T ² +1.43×10 ^-19 ×T-1.55×10 ^-17 Formula (12)

According to the cubic function expression expressed in formula (12), input any temperature within the range of 288-473K, and the chlorobenzene differential absorption cross section corresponding to the temperature at the wavelength of 201.24nm can be obtained.

3. Use MATLAB programming to sequentially fit the relationship between the differential absorption cross-section intensity and temperature at each wavelength point between 201nm and 220nm, so that the single wavelength can be extended to the target detection band, and the continuous change with the wavelength can be obtained. Chlorobenzene differential absorption cross section.

Fitting method 1. Steps 1-3 of inverting the concentration of chlorobenzene are the flow chart for constructing the relationship between the temperature at continuous wavelength and the differential absorption cross section of chlorobenzene as shown in FIG. 7 .

The present invention utilizes the fitting method two of formula (8) expression to reverse the step of chlorobenzene concentration as follows:

1. By observing the absorption spectrum at 201nm-220nm, it can be found that the differential absorption cross section of chlorobenzene presents an obvious quasi-periodicity, and it is difficult to use a single function to characterize the relationship with temperature. Therefore, as shown in FIG. 8, the present invention divides the differential absorption cross section of chlorobenzene into 8 sections of monotone intervals, so that each section can be characterized by a monotone function.

2. The change of each segment of the differential absorption cross section is more complicated, and a simple function cannot accurately describe the characteristics of the absorption cross section. Therefore, in order to more accurately describe the characteristics of the absorption cross section at different temperatures, the present invention compares the absorption at different temperatures with the absorption at 298K, and obtains the fitting relationship between the two. The absorption cross section of is represented by the absorption cross section at 298K. Taking the spectrum of the sixth segment (VI segment) in Figure 8 as an example, the differential absorption cross section at 298K and different experimental temperatures is fitted, and it is found that the relationship between the two can be expressed by a quadratic function in this segment, and the rest of the segment It can also be characterized by the quadratic function relationship with the differential absorption cross-section at 298K, so it can be realized that each absorption cross-section at different temperatures can be obtained by solving the relationship of the absorption cross-section at 298K.

3. Because the differential absorption cross-section shows obvious regular changes with temperature, the parameters (term coefficients, constants) and temperature in the function expression will also show certain regular changes. In the present invention, the parameters are extracted and fitted with the temperature, and the differential absorption cross-section expression at the temperature can be constructed by inputting any temperature. Taking the sixth paragraph in Fig. 8 as an example, each fitting point in the following table 3 is fitted The quadratic function relational expression (namely the second fitting function) between each temperature and the differential absorption cross section at 298K was obtained, and the quadratic term coefficient, the first-order term coefficient and the constant term in the relational formula were obtained by sorting out. Then fit the temperature with the coefficient of the quadratic term and the coefficient of the first term, that is, the constant term. Here, in order to maintain consistency and facilitate operation, each parameter and temperature are fitted into a cubic function relationship. The function expression is written as follows:

Wherein, a, b, and c respectively represent the quadratic term coefficient, the first-order term coefficient and the constant term of the second fitting function of the fitting relationship between different temperatures and 298K differential absorption cross-section;

m _Q , m _P , m _C respectively represent the corresponding parameters a, b, c and the cubic coefficient in the temperature fitting process;

n _Q , n _P , and n _C respectively represent the corresponding parameters a, b, c and the quadratic term coefficients in the temperature fitting process;

P _Q , P _P , and P _C respectively represent the corresponding parameters a, b, c and the first-order coefficients in the temperature fitting process;

w _Q , w _P , and w _C represent corresponding parameters a, b, c and constant items in the temperature fitting process, respectively.

table 3

4. According to formulas (13)-(15), input any temperature within the range of 288-473K to obtain the specific values of a, b, and c at this temperature, and substitute the specific values into the differential absorption cross section at different temperatures and 298K The second fitting function of can get the differential absorption cross section at this temperature.

To sum up, steps 1-4 of the fitting method 2 inversion of chlorobenzene concentration are the flow chart for constructing the fitting relationship between different temperatures and the differential absorption cross section at 298K as shown in Fig. 11 .

The present invention also compares and analyzes the experimental results of the two fitting methods. In the experiment, 55 ppm of chlorobenzene is used to compare the chlorobenzene concentration measurement results of the two fitting methods under the temperature conditions of 318, 333, 383 and 473K. , the specific comparison method is divided into two steps: firstly, the coefficient of determination R ² is used to measure the correlation between the differential absorption cross section obtained by the experiment and the differential absorption cross section of the two fitting methods at the corresponding temperature, and secondly, the comparison between the two fitting methods The accuracy of the chlorobenzene concentration obtained by the inversion of the differential absorption cross section obtained by the method.

See Table 4 below for the comparison of the coefficient of determination R2 of the ^two fitting methods:

Table 4

It can be seen from Table 4 that the differential absorption cross sections obtained by the two fitting methods are in good agreement with the experimental data, and the correlation coefficients are all above 0.99. The correlation coefficient of fitting method 2 is slightly higher than that of fitting method 1, indicating that the shape and intensity of the differential absorption section obtained by fitting method 2 are more accurate.

See Table 5 and Figure 12 below for the results and deviations of the two fitting methods inversion of the concentration of chlorobenzene:

table 5

It can be seen from Table 5 that the concentration deviation of chlorobenzene obtained by fitting method 1 inversion is within 2.74%, while the concentration deviation obtained by fitting method 2 is within 2.7%. Both further improve the accuracy of concentration inversion. It can be seen from the concentration calculation deviations of the two that the second fitting method is slightly better than the first fitting method, and the smallest deviation reaches 0.13%, which proves the validity of the fitting method provided by the present invention.

To sum up, the first fitting method is to construct a fitting relationship (that is, the first fitting function) based on the differential absorption cross section of a single wavelength point at different temperatures. Since the single-point measurement is easily affected by environmental interference, the fitting Method 2 Constructing a fitting relationship based on multiple wavelength points (ie, the second fitting function) can effectively reduce the uncertainty in the measurement results and improve the signal-to-noise ratio. According to the second fitting method, the present invention draws the differential absorption cross section of the 201-220nm band under continuous temperatures from 288K-473K, and the drawing results are shown in FIG. 13 .

To sum up, the method for inversion of gas concentration based on the fast-changing absorption cross section of the spectrum provided in this embodiment is shown in Figure 16, including steps:

S1, constructing a fitting function of the differential absorption cross section with respect to temperature;

S2. Calculate the temperature corresponding to the differential absorption cross section according to the fitting function as the predicted temperature.

In the above scheme, the differential absorption cross section of chlorobenzene is solved by fitting method 1 or fitting method 2, and then the chlorobenzene concentration corresponding to the differential absorption cross section is inverted based on the Beer-Lambert law, and the measurement of the temperature of chlorobenzene is still This needs to be achieved by a temperature controller as shown in Figure 1 or an additional temperature sensor. In order to realize the simultaneous measurement of p-chlorobenzene concentration and temperature, the invention also provides a method for synchronous measurement of chlorobenzene concentration and temperature based on ultraviolet differential absorption spectrum.

In the experiment, after observing the differential absorption cross section at different temperatures, it was found that as the temperature increases, the most significant change feature of the differential absorption cross section is that the differential absorption peak becomes lower, and different temperatures are observed after normalizing the differential absorption cross section. There are still differences in the shape of the lower section, indicating that temperature can not only change the size of the absorption section, but also cause characteristic differences in the shape of the absorption section. Based on the above-mentioned phenomena observed, the chlorobenzene concentration and temperature synchronous measurement method based on ultraviolet differential absorption spectrum provided in this embodiment includes the following steps:

1. Obtain the differential absorption spectrum of chlorobenzene with unknown concentration and temperature information through experiments. At this time, because the temperature is unknown, the concentration cannot be calculated by using the differential absorption cross section corresponding to the temperature according to the Beer-Lambert law (the concentration calculation process refers to the above formula (4) ).

2. Normalize the differential absorption cross section of chlorobenzene at each wavelength point at the same temperature (please refer to Figure 14 for the schematic diagram of the normalized differential absorption cross section at different temperatures), assuming that the differential absorption cross section at a certain wavelength is used Δσ, then the normalization method is:

In formula (22), Δσ _{Normalization} represents the normalization result of Δσ;

i represents the differential absorption cross section corresponding to the i-th wavelength point at a specified temperature and a specified concentration;

n represents the number of wavelength points selected within the 201-220nm band range at a specified concentration and a specified temperature.

The chlorobenzene differential absorption spectrum of unknown concentration and temperature information obtained in the experiment is normalized, and the normalization method is:

In formula (17), ΔDOD _{Normalization} represents the normalization result to DOD;

i represents the differential absorption spectrum corresponding to the i-th wavelength point at the specified temperature and specified concentration;

n represents the number of wavelength points selected within the 201-220nm band range at a specified concentration and a specified temperature. 3. Through the pre-written program language, compare the chlorobenzene differential absorption spectrum of unknown concentration and temperature information after the experiment normalization with the normalized chlorobenzene differential absorption cross-section one by one with the coefficient of determination R ^2. The coefficient of determination is the description For the variables of the correlation between the two, if the coefficient of determination is larger, it indicates that the shapes of the two are closer. The specific calculation formula is shown in formula (18). Find the standard differential absorption cross section with the largest determination coefficient of the experimental data, and the temperature corresponding to the standard differential absorption cross section is the predicted temperature;

^The calculation method of the coefficient of determination R2 is shown in the following formula (18):

表示201-220nm波段第i个波长点的拟合差分吸收截面；In formula (18),

Indicates the fitting differential absorption cross section of the i-th wavelength point in the 201-220nm band;

y _i represents the experimental differential absorption cross section of the i-th wavelength point in the 201-220nm band;

表示201-220nm波段实验差分吸收截面的平均值。

Indicates the average value of the experimental differential absorption cross section in the 201-220nm band.

4. For the differential absorption cross section corresponding to the predicted temperature, the corresponding chlorobenzene concentration can be measured synchronously according to the Beer-Lambert law.

In short, the data processing flow for synchronous measurement of chlorobenzene temperature and concentration is shown in Figure 15 and Figure 17, including steps:

L1, obtain the differential absorption spectrum of chlorobenzene with unknown concentration and temperature information;

L2, calculate the differential absorption cross section corresponding to the differential absorption spectrum of chlorobenzene at each wavelength point in the experiment of known concentration and temperature;

L3, normalize the experimental differential absorption cross section at the same temperature;

L4, compare the differential absorption spectrum of the unknown concentration and temperature information after normalization with each differential absorption cross section after normalization with the coefficient of determination R ² one by one, and find the maximum value of the coefficient of determination R ² The temperature corresponding to the corresponding differential absorption cross section is used as the predicted temperature of chlorobenzene of unknown temperature in step L1;

L5, for the differential absorption cross section corresponding to the predicted temperature, calculate the chlorobenzene concentration corresponding to the differential absorption cross section according to the Beer-Lambert law.

In order to verify the feasibility of the chlorobenzene temperature and concentration synchronous measurement provided by the present invention, two groups of experiments have been done respectively: 1, under the same temperature, the chlorobenzene of different concentrations is carried out temperature and concentration measurement simultaneously; 2, under the same concentration Simultaneous measurement of temperature and concentration of chlorobenzene at different temperatures. The following Tables 6 and 7 respectively show the prediction results and deviations of the chlorobenzene concentration and temperature synchronous measurement method based on differential absorption spectroscopy provided by this embodiment at the same temperature and the same concentration:

Table 6

Table 7

Through the two sets of experimental data in Table 6 and Table 7, it can be found that the deviation of the temperature prediction is within 1.89%, but some data of the concentration prediction deviate far from the actual concentration, and the deviation reaches 12.27%. The chlorobenzene concentration and temperature synchronous measurement method based on the differential absorption spectrum provided by the present invention first predicts the temperature according to the shape of the differential absorption structure, and then solves the concentration through the temperature and the differential absorption spectrum, according to the law of influence of the temperature on the differential absorption spectrum , the deviation of temperature prediction results is low, and the corresponding deviation of concentration prediction results is also low. In the experiment, due to external factors such as instrument resolution, there are certain instrument errors, so there may be large errors in the concentration prediction process, but in general, this method realizes the simultaneous measurement of p-chlorobenzene temperature and concentration.

In summary, aiming at the problem that temperature affects the gas absorption spectrum, thus making the measurement concentration inaccurate, the present invention takes the differential absorption characteristics of chlorobenzene in the ultraviolet 201-220nm band as an object, and studies its differential absorption characteristics in the temperature range of 288K-473K. Variation of absorption cross section with temperature. A calculation method for the differential absorption cross section of chlorobenzene at continuous temperature was established, and a method for synchronous inversion of temperature and concentration based on the differential absorption spectrum was obtained, which mainly has the following beneficial effects:

1. As the temperature changes, the differential absorption spectrum of chlorobenzene not only shows changes in amplitude, but also shows differences in its shape. In order to further understand the spectral absorption characteristics of chlorobenzene, the present invention calculates the important spectral parameters at different temperatures, that is, the differential absorption cross section, and constructs a binary function of the differential absorption cross section with respect to temperature and wavelength, respectively under the conditions of fixed temperature and wavelength The dimensionality reduction of the binary function was fitted to obtain the differential absorption cross section of chlorobenzene at continuous temperature in the target detection band. The two fitting methods provided show that the method of fitting with a single wavelength point has a relatively large error, because the spectral acquisition of a single point is easily affected by instrument fluctuations, but both fitting methods achieve a concentration inversion error within Within 2.74%, it is highly consistent with the differential absorption section shape obtained in the experiment.

1. Considering the temperature specificity of the differential absorption cross section, the present invention creatively proposes a method for simultaneous measurement of temperature and concentration, and the measurement deviation of the method for temperature is within 1.89%. Due to the spectral resolution of the instrument and other reasons, some deviations in the concentration inversion results are relatively large, but this method can basically realize the simultaneous measurement of temperature and concentration, which provides a new idea for the extension of differential absorption spectroscopy to the field of simultaneous measurement of temperature and concentration.

It should be declared that the above specific implementation manners are only preferred embodiments of the present invention and applied technical principles. Those skilled in the art should understand that various modifications, equivalent replacements, changes and the like can be made to the present invention. However, as long as these changes do not deviate from the spirit of the present invention, they should all be within the protection scope of the present invention. In addition, some terms used in the specification and claims of this application are not limiting, but are only for convenience of description.

Claims (9)

1. A gas temperature and concentration synchronous measurement method based on a spectrum fast-slow separation principle is characterized by comprising the following steps:

l1, acquiring a differential absorption spectrum of chlorobenzene with unknown concentration and temperature information and performing normalization treatment;

l2, calculating a differential absorption cross section corresponding to the differential absorption spectrum of the chlorobenzene at each wavelength point with known concentration and temperature in the experiment;

l3, normalizing the differential absorption cross sections at different temperatures in the experiment;

l4, determining coefficient R for the differential absorption spectrum of the normalized unknown concentration and temperature information and each normalized differential absorption section ² Comparing one by one, and finding out the decision coefficient R ² The temperature corresponding to the differential absorption cross section corresponding to the maximum value of (a) is taken as the predicted temperature of the chlorobenzene at the unknown temperature in the step L1;

and L5, calculating the chlorobenzene concentration corresponding to the differential absorption cross section for the differential absorption cross section corresponding to the predicted temperature according to the beer-Lambert law.

2. The method for synchronously measuring the temperature and the concentration of the gas based on the spectrum fast-slow separation principle according to claim 1, wherein in the step L2, the method for calculating the differential absorption cross section corresponding to the differential absorption spectrum is expressed by the following formula (5):

in the formula (1), Δ σ (λ) represents a differential absorption cross section obtained by incidence of light having a wavelength λ into chlorobenzene gas;

n represents chlorobenzene number density;

l represents an absorption optical path length;

DOD represents the differential absorption spectrum.

3. The method for synchronously measuring the temperature and the concentration of a gas based on the spectrum fast-slow separation principle in claim 1, wherein in the step L3, the method for normalizing the differential absorption cross section of each wavelength point at the same temperature is expressed by the following formula (2):

in the formula (2), Δ σ _{Normalization} Represents the result of normalization on Δ σ;

i represents a differential absorption cross section corresponding to the ith wavelength point at a specified temperature and a specified concentration;

n represents the number of wavelength points selected in the wavelength band range of 201-220nm at a specified concentration and a specified temperature.

4. The method for synchronously measuring the gas temperature and the concentration based on the spectrum fast-slow separation principle of claim 2, wherein the method for normalizing the differential absorption spectrum of chlorobenzene comprises the following steps:

ΔDOD _{Normalization} represents the normalized result for DOD;

DOD _i and the differential absorption spectrum corresponding to the ith wavelength point at the specified concentration at the specified temperature is represented.

5. The method for synchronously measuring chlorobenzene concentration and temperature based on differential absorption spectrum according to claim 1, wherein in step L4, the method for obtaining the predicted temperature corresponding to the differential absorption cross section comprises the steps of:

s1, constructing a fitting function of a differential absorption cross section with respect to temperature;

and S2, solving the temperature corresponding to the differential absorption cross section according to the fitting function to serve as the predicted temperature.

6. The method for synchronously measuring gas temperature and concentration based on the spectrum fast-slow separation principle according to claim 5, characterized in that the fitting function constructed in step S1 is a first fitting function representing the relationship between the chlorobenzene differential absorption cross section and the temperature at each wavelength point, and the first fitting function is expressed by the following formula (1):

in the formula (3), Δ σ represents the chlorobenzene differential absorption cross section;

t represents a temperature;

a. b and c represent term coefficients, and d is a constant;

λ ₁ representing a particular said wavelength point;

f represents the first fitting function.

7. The method for synchronously measuring the temperature and the concentration of the gas based on the spectrum fast-slow separation principle of claim 6, characterized in that λ ₁ A =2.99 × 10 when =201.24nm ^-25 ，b＝-3.70×10 ^-22 ，c＝1.43×10 ^-19 ，d＝-1.55×10 ^-17 。

8. The method for synchronously measuring the temperature and the concentration of the gas based on the spectrum fast-slow separation principle according to claim 5, wherein the constructed fitting function is a second fitting function which characterizes the relationship between the chlorobenzene differential absorption cross section and the wavelength of each temperature point, and the second fitting function is expressed by the following formula (4):

in the formula (4), T ₁ Represents a specific said temperature point;

λ represents a wavelength;

Δσ _298K the chlorobenzene differential absorption cross section representing the position of a lambda wavelength point at a temperature of 298K;

a represents the temperature T ₁ Coefficients of the second fitting function fitted to the 298K differential absorption cross-section,

b represents the temperature T ₁ The first order coefficient of the second fitting function fitted to the 298K differential absorption cross-section,

c represents the temperature T ₁ A constant term of the second fitting function fitted to the 298K differential absorption cross-section,

m _Q 、m _P 、m _C respectively representing the corresponding parameters a, b and c and cubic term coefficients in the temperature fitting process;

n _Q 、n _P 、n _C respectively representing the corresponding parameters a, b and c and quadratic term coefficients in the temperature fitting process;

P _Q 、P _P 、P _C respectively representing the corresponding parameters a, b and c and the first-order coefficient in the temperature fitting process;

w _Q 、w _P 、w _C respectively representing the constant terms in the fitting process of the corresponding parameters a, b and c and the temperature.

9. The method for synchronously measuring the gas temperature and the concentration based on the spectrum fast-slow separation principle of claim 5, wherein when the fitting function is constructed, the light incident into the chlorobenzene gas is ultraviolet light with the wavelength of 201nm-220 nm.

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