CN113310922A - NO concentration measuring system based on ultraviolet differential absorption spectrum and concentration calculating method - Google Patents
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Abstract
The invention relates to an NO concentration measuring system and a concentration calculating method based on ultraviolet differential absorption spectrum. The system comprises a gas distribution system, a gas mixing chamber, an ultraviolet light source, a gas detection tank, tail gas treatment, an ultraviolet spectrometer and a PC (personal computer) terminal, wherein the absorbance of NO standard gas is calculated by obtaining a background spectrum and a light source original spectrum of a measurement system and an ultraviolet spectrum of NO standard gas, polynomial fitting is used for realizing spectrum fast-slow change separation, Fourier conversion is carried out on the fast-changing spectrum, a NO concentration calculation formula is obtained by linearly fitting a standard gas concentration value and a Fourier conversion extreme point to a standard, the calculated gas concentration value is corrected to obtain a final NO concentration value, the steps of spectrum separation and Fourier conversion are repeated to obtain an NO gas extreme point with unknown concentration, and the NO gas extreme point is substituted into the calculation formula and the correction formula to calculate the final NO concentration value. The scheme of the invention has simple structure, convenient operation and accurate final calculation result, and the calculation error value is less than 0.5 percent.
Description
Technical Field
The invention relates to the technical field of NO gas concentration measurement, in particular to an NO concentration measurement system and a concentration calculation method based on ultraviolet differential absorption spectrum.
Background
When light emitted by a light source passes through a certain gas, the light intensity is attenuated due to the absorption of the gas, the attenuation of the light intensity follows the Lambert-Bell law, and in actual measurement, due to the complex smoke components, the attenuation of the light intensity is not only due to the characteristic absorption of polluted gas, but also to Rayleigh scattering caused by O2 or N2 and Mie scattering caused by smoke and aerosol particles. At this time, the Lambert-Bell law can be expressed as:
the absorbance of the gas can be obtained through the ratio of the original light intensity of the light source to the attenuated light intensity, the absorbance consists of two parts of gas scattering and ultraviolet characteristic absorption, the absorbance and the ultraviolet characteristic absorption can be separated through a mathematical method, so that a fast-varying spectrum only containing gas concentration information is obtained, and finally accurate concentration information of the gas can be obtained through mathematical methods such as Fourier transform and polynomial fitting.
At present, in the inversion process of an ultraviolet differential spectrum, a least square method is sampled to calculate the gas concentration most of the time, but in the difference process, a characteristic spectrum peak containing concentration information is translated on a horizontal coordinate relative to an original spectrum, so that a large error is caused when the concentration is calculated by the least square method, and if the characteristic spectrum peak is translated according to the unknown original spectrum peak, the calculation process is complicated.
Disclosure of Invention
The invention aims to solve the technical problem of providing an NO concentration measuring system and a concentration calculating method based on ultraviolet differential absorption spectrum, which are used for solving the problems of complex structure and low measuring accuracy of the existing gas concentration measuring system of ultraviolet differential absorption spectrum, so that more accurate concentration information of NO gas can be obtained.
Technical objects that can be achieved by the present invention are not limited to what has been particularly described above, and other technical objects that are not described herein will be more clearly understood by those skilled in the art from the following detailed description.
The technical scheme for solving the technical problems is as follows:
according to a first aspect of the present disclosure, the present invention provides an NO concentration measurement system based on ultraviolet differential absorption spectroscopy, characterized in that the system comprises:
the gas distribution system is used for configuring NO standard gas, the NO standard gas is uniformly mixed through the gas mixing chamber and then is introduced into the gas detection cell, gas discharged from the gas detection cell passes through the tail gas treatment device and then is discharged into the atmosphere, the ultraviolet light source and the ultraviolet spectrometer are both connected with the computing equipment, the computing equipment controls the starting of the ultraviolet light source to emit ultraviolet light, the ultraviolet light passes through the gas detection cell and then is received by the ultraviolet spectrometer, and spectral data generated by the ultraviolet spectrometer are transmitted into the computing equipment and are stored in the computing equipment;
the NO concentration measurement system is configured to perform a NO concentration calculation method, the method including the steps of:
step 1: obtaining a background spectrum I of the NO concentration measurement system and an original spectrum I of the ultraviolet light source0Wherein, in the step (A),
firstly, under the condition that the ultraviolet light source is not started, starting the ultraviolet spectrometer to obtain a background spectrum of the NO concentration measurement system, and then starting the ultraviolet light source to obtain an original spectrum of the ultraviolet light source;
step 2: obtaining ultraviolet spectrum I after NO standard gas1，I2…ImWhich isIn (1),
respectively introducing m NO standard gases with different concentrations, and receiving and storing the ultraviolet spectrum I attenuated after passing through the m NO standard gases with different concentrations by the ultraviolet spectrometer1，I2…Im；
And step 3: calculating the absorbance of the NO standard gas, wherein,
obtaining standard gas absorbances of NO with different concentrations, wherein the standard gas absorbances comprise NO concentration information of NO causing ultraviolet spectrum signal attenuation;
and 4, step 4: the fast-changing spectrum and the slow-changing spectrum are separated, wherein,
fast-changing spectrum information including NO standard gas concentration information can be obtained by carrying out difference after NO absorbance is processed through polynomial fitting;
and 5: fast-varying spectral fourier transforms, in which,
performing Fourier transformation on the fast-changing spectrum obtained under the NO standard gas with different concentrations, and extracting an extreme point after the Fourier transformation;
step 6: the extreme points and the concentration value of the NO standard gas establish a functional relation through linear fitting, wherein,
enabling the extreme points of Fourier transform obtained under the NO standard gas with different concentrations to correspond to the concentration values of the NO standard gas, and establishing a functional relation through linear fitting to be used as an NO concentration inversion calculation formula;
and 7: and calculating the concentration value of the standard gas by the NO concentration inversion calculation formula for error correction,
correspondingly substituting the Fourier transform extreme points into an NO concentration inversion calculation formula to calculate and obtain a concentration calculation value, and performing function fitting corresponding to the actual concentration of the standard gas to obtain an NO inversion concentration correction formula after concentration correction;
and 8: the concentration of NO gas of unknown concentration is calculated, wherein,
and (3) acquiring a Fourier transform extreme point of NO gas with unknown concentration through steps 1 to 5, substituting the numerical value of the Fourier transform extreme point into the NO concentration inversion calculation formula in step 7 to acquire an NO concentration calculation value, and substituting the NO concentration calculation value into the NO concentration inversion correction formula in step 8 to acquire a final NO concentration value.
Optionally, in the system as described above, in step 2, NO standard gas with concentration of 200ppm, 300ppm, 400ppm and 500ppm is respectively introduced.
Alternatively, in the system as described above, in step 3, the standard gas absorbances of different concentrations of NO are obtained by the following calculation formula: ln (I)0-I)/(In-I), wherein n is a natural number less than or equal to m.
Optionally, in the system as described above, in step 4, the cause of the attenuation of the ultraviolet spectral intensity passing through the NO standard gas includes characteristic absorption of the NO standard gas and Rayleigh scattering and Mie scattering.
According to a second aspect of the present disclosure, the present invention provides a method for calculating an NO concentration based on an ultraviolet differential absorption spectrum, the method comprising the steps of:
step 1: obtaining a background spectrum I of the NO concentration measurement system and an original spectrum I of the ultraviolet light source0Wherein, in the step (A),
firstly, under the condition that the ultraviolet light source is not started, starting the ultraviolet spectrometer to obtain a background spectrum of the NO concentration measurement system, and then starting the ultraviolet light source to obtain an original spectrum of the ultraviolet light source;
step 2: obtaining ultraviolet spectrum I after NO standard gas1，I2…ImWherein, in the step (A),
respectively introducing m NO standard gases with different concentrations, and receiving and storing the ultraviolet spectrum I attenuated after passing through the m NO standard gases with different concentrations by the ultraviolet spectrometer1，I2…Im；
And step 3: calculating the absorbance of the NO standard gas, wherein,
obtaining standard gas absorbances of NO with different concentrations, wherein the standard gas absorbances comprise NO concentration information of NO causing ultraviolet spectrum signal attenuation;
and 4, step 4: the fast-changing spectrum and the slow-changing spectrum are separated, wherein,
fast-changing spectrum information including NO standard gas concentration information can be obtained by carrying out difference after NO absorbance is processed through polynomial fitting;
and 5: fast-varying spectral fourier transforms, in which,
performing Fourier transformation on the fast-changing spectrum obtained under the NO standard gas with different concentrations, and extracting an extreme point after the Fourier transformation;
step 6: the extreme points and the concentration value of the NO standard gas establish a functional relation through linear fitting, wherein,
enabling the extreme points of Fourier transform obtained under the NO standard gas with different concentrations to correspond to the concentration values of the NO standard gas, and establishing a functional relation through linear fitting to be used as an NO concentration inversion calculation formula;
and 7: and calculating the concentration value of the standard gas by the NO concentration inversion calculation formula for error correction,
correspondingly substituting the Fourier transform extreme points into an NO concentration inversion calculation formula to calculate and obtain a concentration calculation value, and performing function fitting corresponding to the actual concentration of the standard gas to obtain an NO inversion concentration correction formula after concentration correction;
and 8: the concentration of NO gas of unknown concentration is calculated, wherein,
and (3) acquiring a Fourier transform extreme point of NO gas with unknown concentration through steps 1 to 5, substituting the numerical value of the Fourier transform extreme point into the NO concentration inversion calculation formula in step 7 to acquire an NO concentration calculation value, and substituting the NO concentration calculation value into the NO concentration inversion correction formula in step 8 to acquire a final NO concentration value.
Optionally, in the method as described above, in step 2, NO standard gas with the concentration of 200ppm, 300ppm, 400ppm and 500ppm is respectively introduced.
Alternatively, in the method as described above, in step 3, the standard gas absorbances of different concentrations of NO are obtained by the following calculation formula: ln (I)0-I)/(In-I), wherein n is a natural number less than or equal to m.
Optionally, in the method as described above, in step 4, the cause of the attenuation of the ultraviolet spectral intensity passing through the NO standard gas includes characteristic absorption of the NO standard gas and Rayleigh scattering and Mie scattering.
The above-described embodiments are only some of the embodiments of the present invention, and those skilled in the art can derive and understand various embodiments including technical features of the present invention from the following detailed description of the present invention.
The NO concentration measuring system and the concentration calculating method based on the ultraviolet differential absorption spectrum have the advantages of simple structure, easiness in installation and replacement and the like; compared with the least square method which is widely used at present, the method has the advantages of small calculation error and simple and convenient calculation process.
It will be appreciated by persons skilled in the art that the effects that can be achieved by the present invention are not limited to what has been particularly described hereinabove and other advantages of the present invention will be more clearly understood from the following detailed description.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention.
FIG. 1 is a schematic structural diagram of an NO concentration measurement system based on ultraviolet differential absorption spectroscopy according to the present invention;
FIG. 2 is a flow chart of a method for calculating NO concentration based on ultraviolet differential absorption spectroscopy according to the present invention;
FIG. 3 is an original spectrum of an ultraviolet light source according to the present invention;
FIG. 4 is a dark field spectrum of the measurement system of the present invention;
FIG. 5 is a NO signature spectrum according to the present invention;
FIG. 6 is a NO signature spectrum difference process according to the present invention;
FIG. 7 is a characteristic NO absorption spectrum according to the present invention;
fig. 8 is a NO spectral feature transform waveform according to the present invention.
Detailed Description
Reference will now be made in detail to exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. The detailed description, which will be given below with reference to the accompanying drawings, is intended to explain exemplary embodiments of the present invention, rather than to show the only embodiments that can be implemented according to the present invention. The following detailed description includes specific details in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details.
In some instances, well-known structures and devices are omitted or shown in block diagram form, focusing on important features of the structures and devices so as not to obscure the concept of the present invention. The same reference numbers will be used throughout the specification to refer to the same or like parts.
The principles and features of this invention are described below in conjunction with the following drawings, which are set forth by way of illustration only and are not intended to limit the scope of the invention.
In the description of the present invention, it is to be understood that the terms "upper", "lower", "center", "inner", "outer", "top", "bottom", and the like, indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience in describing the present invention and simplifying the description, but do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
Fig. 1 shows a schematic structural diagram of an NO concentration measurement system based on ultraviolet differential absorption spectroscopy according to the present invention. As shown in fig. 1, the invention provides an NO concentration measurement system based on ultraviolet differential absorption spectrum, the measurement system comprises a gas distribution system 1, a gas mixing chamber 2, an ultraviolet light source 3, a gas detection cell 4, a tail gas treatment 5, an ultraviolet spectrometer 6 and a PC end 7, the gas distribution system 1 is used for configuring NO standard gas, the NO standard gas is uniformly mixed by the gas mixing chamber 2 and then is introduced into the gas detection cell 4, gas discharged from the gas detection cell 4 is discharged into the atmosphere after being treated by the tail gas treatment 5, both the ultraviolet light source 3 and the ultraviolet spectrometer 6 are connected with the PC end 7, the PC end controls the start of the ultraviolet light source 3 to emit ultraviolet light, the ultraviolet light is received by the ultraviolet spectrometer 6 after passing through the gas detection cell 4, and the spectrum data is transmitted into the PC end 7 and stored;
fig. 2 shows a flowchart of a method for calculating the NO concentration based on the ultraviolet differential absorption spectrum according to the present invention. Firstly, under the condition that the ultraviolet light source 3 is not started, starting the ultraviolet spectrometer 6 to obtain a background spectrum I (shown in figure 3) of the measurement system, and then starting the ultraviolet light source 3 to obtain an original spectrum I0 (shown in figure 4) of the ultraviolet light source 3; respectively introducing 4 ultraviolet spectrum signals with the concentration of 200ppm, 300ppm, 400ppm and 500ppm, obtaining ultraviolet spectrum signals attenuated after NO, and marking as I1，I2…I4(as shown in FIG. 5), for example, m is equal to 4 and n is less than or equal to m, by calculating the formula Ln (I) according to Lambert-Bell's Law0-I)/(In-I) the absorbance of standard gas with different concentrations of NO can be obtained, and the absorbance contains NO concentration information causing the attenuation of ultraviolet spectrum signals; fast-varying spectrum information (shown in figures 6 and 7) only containing NO standard gas concentration information can be obtained by carrying out difference after NO absorbance is processed through polynomial fitting, fast-varying spectra obtained under NO standard gases with different concentrations are subjected to Fourier transformation (shown in figure 8), extreme values after Fourier transformation are extracted, Fourier transformation extreme values obtained under the NO standard gases with different concentrations correspond to standard gas concentration values, a functional relation is established through linear fitting, and a fitting function is an NO concentration inversion calculation formula; substituting the Fourier transform extreme points into an NO concentration inversion calculation formula one by one to calculate and obtain a concentration calculation value, performing function fitting corresponding to the actual concentration of the standard gas to obtain a concentration correction NO inversion concentration correction formula, obtaining the Fourier transform extreme points of NO gas with unknown concentration through the steps 1 to 5, substituting the numerical values of the extreme points into the NO concentration inversion calculation formula in the step 7 to obtain the NO concentration calculation value, wherein the obtained calculation concentration value and the obtained error are shown in the table 1, substituting the calculation value into the NO concentration inversion correction formula in the step 8 to obtain a final NO concentration value (shown in the table 2), and the final NO concentration value can be obtained (shown in the table 2), wherein the final NO concentration value is obtained by substituting the calculation value into the NO concentration inversion correction formula in the step 8The final calculation error is less than 0.5%, and the high accuracy is shown.
TABLE 1-results of the NO concentration inversion calculation
TABLE 2 NO concentration inversion correction results
From the above description of the embodiments, it is obvious for those skilled in the art that the present application can be implemented by software and necessary general hardware, and of course, can also be implemented by hardware. Based on such understanding, the technical solutions of the present application may be embodied in the form of a software product, which may be stored in a computer-readable storage medium, such as a floppy disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a FLASH Memory (FLASH), a hard disk or an optical disk of a computer, and includes several instructions for enabling a computer device (which may be a personal computer, a server, or a network device) to execute the methods described in the embodiments of the present application.
As mentioned above, a detailed description of the preferred embodiments of the invention has been given to enable those skilled in the art to make and practice the invention. Although the present invention has been described with reference to exemplary embodiments, those skilled in the art will appreciate that various modifications and changes can be made in the present invention without departing from the spirit or scope of the invention described in the appended claims. Thus, the present invention is not intended to be limited to the particular embodiments shown and described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (8)
1. An ultraviolet differential absorption spectroscopy-based NO concentration measurement system, comprising:
the gas distribution system is used for configuring NO standard gas, the NO standard gas is uniformly mixed through the gas mixing chamber and then is introduced into the gas detection cell, gas discharged from the gas detection cell passes through the tail gas treatment device and then is discharged into the atmosphere, the ultraviolet light source and the ultraviolet spectrometer are both connected with the computing equipment, the computing equipment controls the starting of the ultraviolet light source to emit ultraviolet light, the ultraviolet light passes through the gas detection cell and then is received by the ultraviolet spectrometer, and spectral data generated by the ultraviolet spectrometer are transmitted into the computing equipment and are stored in the computing equipment;
the NO concentration measurement system is configured to perform a NO concentration calculation method, the method including the steps of:
step 1: obtaining a background spectrum I of the NO concentration measurement system and an original spectrum I of the ultraviolet light source0Wherein, in the step (A),
firstly, under the condition that the ultraviolet light source is not started, starting the ultraviolet spectrometer to obtain a background spectrum of the NO concentration measurement system, and then starting the ultraviolet light source to obtain an original spectrum of the ultraviolet light source;
step 2: obtaining ultraviolet spectrum I after NO standard gas1，I2…ImWherein, in the step (A),
respectively introducing m NO standard gases with different concentrations, and receiving and storing the ultraviolet spectrum I attenuated after passing through the m NO standard gases with different concentrations by the ultraviolet spectrometer1，I2…Im；
And step 3: calculating the absorbance of the NO standard gas, wherein,
obtaining standard gas absorbances of NO with different concentrations, wherein the standard gas absorbances comprise NO concentration information of NO causing ultraviolet spectrum signal attenuation;
and 4, step 4: the fast-changing spectrum and the slow-changing spectrum are separated, wherein,
fast-changing spectrum information including NO standard gas concentration information can be obtained by carrying out difference after NO absorbance is processed through polynomial fitting;
and 5: fast-varying spectral fourier transforms, in which,
performing Fourier transformation on the fast-changing spectrum obtained under the NO standard gas with different concentrations, and extracting an extreme point after the Fourier transformation;
step 6: the extreme points and the concentration value of the NO standard gas establish a functional relation through linear fitting, wherein,
enabling the extreme points of Fourier transform obtained under the NO standard gas with different concentrations to correspond to the concentration values of the NO standard gas, and establishing a functional relation through linear fitting to be used as an NO concentration inversion calculation formula;
and 7: and calculating the concentration value of the standard gas by the NO concentration inversion calculation formula for error correction,
correspondingly substituting the Fourier transform extreme points into an NO concentration inversion calculation formula to calculate and obtain a concentration calculation value, and performing function fitting corresponding to the actual concentration of the standard gas to obtain an NO inversion concentration correction formula after concentration correction;
and 8: the concentration of NO gas of unknown concentration is calculated, wherein,
and (3) acquiring a Fourier transform extreme point of NO gas with unknown concentration through steps 1 to 5, substituting the numerical value of the Fourier transform extreme point into the NO concentration inversion calculation formula in step 7 to acquire an NO concentration calculation value, and substituting the NO concentration calculation value into the NO concentration inversion correction formula in step 8 to acquire a final NO concentration value.
2. The system of claim 1,
in step 2, NO standard gases with the concentrations of 200ppm, 300ppm, 400ppm and 500ppm are respectively introduced.
3. The system of claim 1,
in step 3, the absorbance of the standard gas with different concentrations of NO is obtained through the following calculation formula: ln (I)0-I)/(In-I), wherein n is a natural number less than or equal to m.
4. The system of claim 1,
in step 4, the reasons for the attenuation of the ultraviolet spectral intensity through the NO standard gas include the characteristic absorption of the NO standard gas and Rayleigh scattering and Mie scattering.
5. A method for calculating NO concentration based on ultraviolet differential absorption spectroscopy, the method comprising the steps of:
step 1: obtaining a background spectrum I of the NO concentration measurement system and an original spectrum I of the ultraviolet light source0Wherein, in the step (A),
firstly, under the condition that the ultraviolet light source is not started, starting the ultraviolet spectrometer to obtain a background spectrum of the NO concentration measurement system, and then starting the ultraviolet light source to obtain an original spectrum of the ultraviolet light source;
step 2: obtaining ultraviolet spectrum I after NO standard gas1，I2…ImWherein, in the step (A),
respectively introducing m NO standard gases with different concentrations, and receiving and storing the ultraviolet spectrum I attenuated after passing through the m NO standard gases with different concentrations by the ultraviolet spectrometer1，I2…Im；
And step 3: calculating the absorbance of the NO standard gas, wherein,
obtaining standard gas absorbances of NO with different concentrations, wherein the standard gas absorbances comprise NO concentration information of NO causing ultraviolet spectrum signal attenuation;
and 4, step 4: the fast-changing spectrum and the slow-changing spectrum are separated, wherein,
fast-changing spectrum information including NO standard gas concentration information can be obtained by carrying out difference after NO absorbance is processed through polynomial fitting;
and 5: fast-varying spectral fourier transforms, in which,
performing Fourier transformation on the fast-changing spectrum obtained under the NO standard gas with different concentrations, and extracting an extreme point after the Fourier transformation;
step 6: the extreme points and the concentration value of the NO standard gas establish a functional relation through linear fitting, wherein,
enabling the extreme points of Fourier transform obtained under the NO standard gas with different concentrations to correspond to the concentration values of the NO standard gas, and establishing a functional relation through linear fitting to be used as an NO concentration inversion calculation formula;
and 7: and calculating the concentration value of the standard gas by the NO concentration inversion calculation formula for error correction,
correspondingly substituting the Fourier transform extreme points into an NO concentration inversion calculation formula to calculate and obtain a concentration calculation value, and performing function fitting corresponding to the actual concentration of the standard gas to obtain an NO inversion concentration correction formula after concentration correction;
and 8: the concentration of NO gas of unknown concentration is calculated, wherein,
and (3) acquiring a Fourier transform extreme point of NO gas with unknown concentration through steps 1 to 5, substituting the numerical value of the Fourier transform extreme point into the NO concentration inversion calculation formula in step 7 to acquire an NO concentration calculation value, and substituting the NO concentration calculation value into the NO concentration inversion correction formula in step 8 to acquire a final NO concentration value.
6. The system of claim 5,
in step 2, NO standard gases with the concentrations of 200ppm, 300ppm, 400ppm and 500ppm are respectively introduced.
7. The system of claim 5,
in step 3, the absorbance of the standard gas with different concentrations of NO is obtained through the following calculation formula: ln (I)0-I)/(In-I), wherein n is a natural number less than or equal to m.
8. The system of claim 5,
in step 4, the reasons for the attenuation of the ultraviolet spectral intensity through the NO standard gas include the characteristic absorption of the NO standard gas and Rayleigh scattering and Mie scattering.
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| CN115523958A (en) * | 2022-10-15 | 2022-12-27 | 浙江大学 | Gas temperature and concentration synchronous measurement method based on spectrum fast-slow separation principle |
| CN117388204A (en) * | 2023-12-13 | 2024-01-12 | 杭州泽天春来科技股份有限公司 | Nitric oxide gas analysis system, method and computer readable storage medium |
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