A method and system for wavelength drift correction in a deuterium lamp gas analyzer

Abstract

This invention relates to a method and system for correcting wavelength drift in a deuterium lamp gas analyzer. The method includes: acquiring the deuterium lamp spectrum after attenuation by filtering, as a reference background spectrum; periodically acquiring the deuterium lamp spectrum after attenuation by filtering, as the background spectrum to be corrected; extracting a pixel interval including the absorption band of the gas to be measured as a wavelength window; interpolating the wavelength window to obtain the interpolated background spectrum to be corrected; calculating the wavelength offset between the interpolated background spectrum to be corrected and the reference background spectrum; and shifting the background spectrum to be corrected according to the wavelength offset to correct the wavelength drift of the deuterium lamp gas analyzer. The system includes a deuterium lamp, a filter, a measuring cell, a spectrometer, a storage module, a timing module, a calculation module, and a correction module. This invention solves the problem of inaccurate wavelength drift calculation in the automatic zeroing stage of the gas analyzer by sequentially calculating the coarse and fine drift amounts of the background spectrum to be corrected from the deuterium lamp after attenuation by filtering.

Description

Technical Field

[0001] This invention relates to a gas analyzer, specifically to a wavelength drift correction method and system for a deuterium lamp gas analyzer, belonging to the field of environmental monitoring technology. Background Technology

[0002] A spectrometer is a device that detects the wavelength position and intensity of spectral lines, and is widely used in gas analyzers for online monitoring of gas concentration. Currently, many gas analyzers employ Differential Absorption Spectroscopy (DOAS). The basic principle of DOAS technology is to identify the gas using its absorption cross-section and deduce the gas concentration based on the absorption intensity. During the deduction process, the wavelength positions of the measured gas absorption spectrum and the standard gas absorption spectrum must be strictly matched. However, with prolonged operation of the gas analyzer, temperature changes and minor deformations of optical components and mechanical structures can cause wavelength drift in the measured spectrum. This results in a mismatch between the waveforms of the differential spectrum of the measured gas and the standard absorption cross-section, affecting the measurement results.

[0003] To address the wavelength drift problem, existing gas analyzers typically employ an automatic zero-calibration process before concentration inversion. This process corrects the wavelength drift of the analyte's absorption spectrum by calculating the wavelength drift between the reference background spectrum measured at the factory and the currently measured background spectrum to be calibrated, thus avoiding real-time wavelength drift correction during concentration calculation and simplifying the real-time inversion process. However, for deuterium lamp gas analyzers, the background spectrum in the absorption band of the analyte is almost a smooth, monotonic curve with no obvious peaks or troughs. Figure 2 As shown, when performing waveform matching, it is impossible to accurately compare the wavelength drift between the reference background spectrum and the background spectrum to be corrected, which affects the measurement accuracy of the gas analyzer. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention provides a wavelength drift correction method and system for a deuterium lamp gas analyzer, which can correct the wavelength drift of the background spectrum during the zeroing process of the deuterium lamp gas analyzer and improve the measurement accuracy of the gas analyzer.

[0005] A method for correcting wavelength drift in a deuterium lamp gas analyzer includes the following steps:

[0006] S1. Background gas is introduced into the measuring cell, and the deuterium lamp spectrum after filtering and attenuation is collected and stored in the gas analyzer as a reference background spectrum.

[0007] S2, Background gas is periodically introduced into the measuring cell, and the deuterium lamp spectrum after filtering and attenuation is collected as the background spectrum to be corrected;

[0008] S3, extract all pixel intervals in the background spectrum to be corrected that include the absorption band of the gas to be measured, select a wider interval than the above pixel interval as a wavelength window, interpolate all pixels in the background spectrum to be corrected within the wavelength window to obtain the interpolated background spectrum to be corrected.

[0009] S4, calculate the wavelength offset between the interpolated background spectrum to be corrected and the reference background spectrum;

[0010] S5, adjust the background spectrum to be corrected based on the wavelength shift to correct the wavelength drift of the deuterium lamp gas analyzer.

[0011] Furthermore, the wavelength shift mentioned in step S4 is the sum of the coarse wavelength shift and the fine wavelength shift.

[0012] Furthermore, the coarse wavelength shift between the interpolated background spectrum to be corrected and the reference background spectrum is calculated using the correlation coefficient method or the least squares method, with an accuracy of 1 interpolation point; the fine wavelength shift between the interpolated background spectrum to be corrected and the reference background spectrum is calculated using the polynomial fitting method, with an accuracy of 0.0001 interpolation points.

[0013] Optionally, the coarse wavelength shift is calculated as follows:

[0014] S411, starting from the leftmost pixel of the wavelength window and ending at the rightmost pixel of the wavelength window, extract one interpolation point every n pixels of the background spectrum to be corrected after interpolation, and obtain s new background spectrum curves.

[0015] S421, calculate the correlation coefficient between each of the new background spectrum curves and the reference background spectrum;

[0016] S431, compare all correlation coefficients and select the m-th background spectrum curve with the largest correlation coefficient to the reference background spectrum. The wavelength coarse offset is the m interpolation points, 1≤m≤s.

[0017] Optionally, the coarse wavelength shift is calculated as follows:

[0018] S412, starting from the leftmost pixel of the wavelength window and ending at the rightmost pixel of the wavelength window, extract one interpolation point every n pixels of the background spectrum to be corrected after interpolation, and obtain s new background spectrum curves.

[0019] S422, calculate the residual sum of squares between each of the new background spectrum curves and the reference background spectrum to obtain a set of residual sum of squares arrays;

[0020] S432, compare all values ​​in the residual sum of squares array, select the smallest residual sum of squares, and record its position m' in the array. The wavelength coarse offset is m' interpolation points, 1≤m'≤s.

[0021] Optionally, the wavelength shift can be calculated as follows:

[0022] S441, using the polynomial fitting method, defines the origin and the symmetrical points to the left and right of the origin as X values, takes the maximum correlation coefficient between the background spectrum curve and the reference background spectrum and the correlation coefficients to the left and right of the maximum correlation coefficient as Y values, and performs polynomial fitting on X and Y.

[0023] S451, calculate the x-coordinate of the extreme points of the multinomial fitting curve as the wavelength fine shift.

[0024] Optionally, the wavelength shift can be calculated as follows:

[0025] S442 uses a polynomial fitting method, defining the origin and the points symmetrical to the left and right of the origin as X values, taking the minimum residual sum of squares and the residual sum of squares adjacent to the minimum residual sum of squares as Y values, and performing polynomial fitting on X and Y.

[0026] S452 calculates the x-coordinate of the extreme points of the multinomial fitting curve as the wavelength fine drift.

[0027] Furthermore, the deuterium lamp spectrum collected in steps S1 and S2 after filtering and attenuation involves attenuating the light in the 222-237nm wavelength band.

[0028] A wavelength drift correction system for a deuterium lamp gas analyzer includes a deuterium lamp, a filter, a measuring cell, and a spectrometer. The deuterium lamp is connected sequentially to the filter, the measuring cell, and the spectrometer. The system also includes a storage module, a timing module, a calculation module, and a correction module. Background gas is introduced into the measuring cell. Light emitted from the deuterium lamp is filtered and attenuated by the filter before passing through the measuring cell, where it is received by the spectrometer and converted into a digital signal, which is then input into the storage module. The timing module is used to periodically acquire the background spectrum to be corrected after the deuterium lamp filters and attenuates the light. The calculation module is used to calculate the wavelength shift of the background spectrum to be corrected and send it to the correction module. The correction module moves the background spectrum to be corrected according to the wavelength shift.

[0029] The method and system provided by this invention are based on the principle of calculating the coarse and fine drift amounts of the background spectrum to be corrected from the deuterium lamp after filter attenuation. This allows for the accurate drift amount of the background spectrum to be corrected, with an accuracy of 0.0001 interpolation points. This solves the problem that gas analyzers cannot accurately calculate the wavelength drift of the background spectrum to be corrected relative to the reference background spectrum during the automatic zeroing stage, thus improving the accuracy of wavelength drift correction, simplifying the online concentration inversion process, and ensuring the reliability of the gas analyzer. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the method flow provided by the present invention;

[0031] Figure 2 This is a comparison diagram of the reference background spectrum of the deuterium lamp before and after filtering in a specific embodiment of the present invention;

[0032] Figure 3 This is a comparison diagram of the reference background spectrum and the background spectrum to be corrected in a specific embodiment of the present invention;

[0033] Figure 4 This is a comparison diagram of the reference background spectrum and the background spectrum after correcting the wavelength drift in a specific embodiment of the present invention;

[0034] Figure 5 This is a schematic diagram of the system provided by the present invention. Detailed Implementation

[0035] To more clearly illustrate the present invention, the invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0036] Example 1

[0037] like Figure 1 As shown, a wavelength drift correction method for a deuterium lamp gas analyzer includes the following steps:

[0038] S1, background gas is introduced into the measuring cell, and the deuterium lamp spectrum after filtering and attenuation is collected and stored as a reference background spectrum in the gas analyzer. In this embodiment, the background gas is air, and the reference background spectrum is mostly collected when the gas analyzer leaves the factory or during the first use. Since the background spectrum is almost a smooth monotonic curve in the absorption band of the gas to be measured, without obvious peaks and troughs, in this embodiment, a filter is added between the deuterium lamp and the measuring cell to achieve filtering and attenuation of light in the 222-237nm band. Figure 2 As shown, the reference background spectrum exhibits a noticeable notch in the 222-237nm band due to attenuation, thus enabling more accurate comparison of spectral curves at peaks and troughs.

[0039] S2, Background gas is periodically introduced into the measuring cell, and the deuterium lamp spectrum after filtering and attenuation is collected as the background spectrum to be corrected;

[0040] After a period of use, gas analyzers may exhibit wavelength drift in their spectra. This method addresses this by periodically acquiring the background spectrum to be corrected during the automatic zeroing phase and comparing it with a reference background spectrum to calculate the amount of wavelength drift, thereby correcting the wavelength drift of the gas being measured. Similarly, the background spectrum to be corrected is a spectral curve obtained by filtering and attenuating light in the 222-237 nm wavelength band, as shown below. Figure 3 As shown, the background spectrum to be corrected, compared with the reference background spectrum, exhibits both lateral wavelength shift and longitudinal amplitude stretching.

[0041] S3, extract all pixel intervals in the background spectrum to be corrected that include the absorption band of the gas to be measured, select a wider interval than the above pixel interval as a wavelength window, interpolate all pixels in the background spectrum to be corrected within the wavelength window to obtain the interpolated background spectrum to be corrected.

[0042] In this embodiment, the absorption band of the gas to be measured is 213-296nm, and the range of all pixels in the background spectrum to be corrected corresponding to the above band is 15-99. Since the background spectrum to be corrected has undergone wavelength drift, it needs to be shifted left and right according to the offset and compared with the reference background spectrum for correction. In order to facilitate comparison and make the calculation more accurate, a range wider than the above pixel range needs to be selected as the wavelength window. In this embodiment, the wavelength window pixel range is selected as 5-132. In this embodiment, the FFT interpolation method is used to interpolate 16 points between every two adjacent pixels to obtain the interpolated background spectrum to be corrected.

[0043] S4. Calculate the wavelength shift between the interpolated background spectrum to be corrected and the reference background spectrum using the correlation coefficient method; the wavelength shift is the sum of the coarse wavelength shift and the fine wavelength shift; the specific calculation steps are as follows:

[0044] S411, starting from the leftmost pixel of the wavelength window and ending at the rightmost pixel of the wavelength window, extract one interpolation point every n pixels of the interpolated background spectrum to be corrected to obtain s new background spectrum curves; in this embodiment, extract one interpolation point every 16 pixels of the interpolated background spectrum to be corrected to obtain 321 new background spectrum curves.

[0045] S421, calculate the correlation coefficient between each of the new background spectrum curves and the reference background spectrum;

[0046] S431, compare all correlation coefficients and select the m-th background spectrum curve with the largest correlation coefficient with the reference background spectrum. The wavelength coarse shift is the m interpolation points, 1≤m≤s; in this embodiment, the maximum correlation coefficient with the reference background spectrum is 0.9957, and it is the 23rd background spectrum, so the wavelength coarse shift is 23 interpolation points.

[0047] S441, using the polynomial fitting method, defines the origin and the symmetrical points to the left and right of the origin as X values, takes the maximum correlation coefficient between the background spectrum curve and the reference background spectrum and the correlation coefficients to the left and right of the maximum correlation coefficient as Y values, and performs polynomial fitting on X and Y.

[0048] In this embodiment, a quadratic polynomial fitting method is used. X = {-1, 0, 1} is defined, and the maximum correlation coefficient and its left and right neighboring correlation coefficients are taken as the Y value, Y = {0.9954, 0.9957, 0.9956}. A quadratic polynomial fitting a0 + a1*x + a2*x is performed on X and Y. 2 We obtain a0 = 0.9957, a1 = 8.9339e-5, and a2 = -9.2028e-5;

[0049] S451, calculate the abscissa value of the extreme point of the multivariate fitting curve as the wavelength fine drift.

[0050] In this embodiment, the x-coordinates of the extreme points of the quadratic curve are calculated. The wavelength shift is then 0.4854 interpolation points;

[0051] The wavelength shift of the background spectrum to be corrected = 23 + 0.479 = 23.4854 interpolation points;

[0052] S5, adjusts the background spectrum to be corrected based on the wavelength shift to correct the wavelength drift of the deuterium lamp gas analyzer. For example... Figure 4 As shown, the background spectrum after wavelength drift correction and the reference background spectrum are basically overlapped, which solves the problem that the gas analyzer cannot accurately calculate the wavelength drift between the two background spectra during the automatic zeroing stage, improves the accuracy of wavelength drift, simplifies the online concentration inversion process, and greatly improves the performance of the analyzer.

[0053] Example 2

[0054] The difference between this embodiment and Embodiment 1 is that:

[0055] S4. The wavelength shift between the interpolated background spectrum to be corrected and the reference background spectrum is calculated using the least squares method; the wavelength shift is the sum of the coarse wavelength shift and the fine wavelength shift; the specific calculation steps are as follows:

[0056] S412, starting from the leftmost pixel of the wavelength window and ending at the rightmost pixel of the wavelength window, extract one interpolation point every n pixels of the interpolated background spectrum to be corrected to obtain s new background spectrum curves; in this embodiment, extract one interpolation point every 16 pixels of the interpolated background spectrum to be corrected to obtain 321 new background spectrum curves.

[0057] S422, calculate the residual sum of squares between each of the new background spectrum curves and the reference background spectrum to obtain a set of residual sum of squares arrays;

[0058] S432, compare all values ​​in the residual sum of squares array, select the smallest residual sum of squares, and record its position m' in the array. The wavelength coarse shift is m' interpolation points, 1≤m'≤s; In this embodiment, the smallest residual sum of squares is 1945.59, and its position in the array is 23, so the wavelength coarse shift is 23 interpolation points;

[0059] S442 uses a polynomial fitting method, defining the origin and the points symmetrical to the left and right of the origin as X values, taking the minimum residual sum of squares and the residual sum of squares adjacent to the minimum residual sum of squares as Y values, and performing polynomial fitting on X and Y.

[0060] In this embodiment, a quadratic polynomial fitting method is used. X = {-1, 0, 1} is defined, and the minimum sum of squared residuals and the sums of squared residuals of its left and right neighbors are taken as the Y value, Y = {2001.09, 1945.59, 1951.41}. A quadratic polynomial fitting a0 + a1*x + a2*x is performed on X and Y. 2 We obtain a0 = 1945.59, a1 = -27.83, and a2 = 29.05;

[0061] S452, calculate the x-coordinate of the extreme points of the multivariate fitted curve as the wavelength fine shift.

[0062] In this embodiment, the x-coordinates of the extreme points of the quadratic curve are calculated. The wavelength shift is then 0.479 interpolation points;

[0063] The wavelength shift of the background spectrum to be corrected is 23 + 0.479 = 23.4790 interpolation points.

[0064] like Figure 5 As shown, this application also discloses a wavelength drift correction system for a deuterium lamp gas analyzer, including a deuterium lamp, a filter, a measuring cell, and a spectrometer. The deuterium lamp is connected to the filter, the measuring cell, and the spectrometer in sequence. The system also includes a storage module, a timing module, a calculation module, and a correction module. Background gas is introduced into the measuring cell. The light emitted by the deuterium lamp is filtered and attenuated by the filter before passing through the measuring cell, where it is received by the spectrometer and converted into a digital signal, which is then input into the storage module. The timing module is used to periodically collect the background spectrum to be corrected after the deuterium lamp filter attenuation. The calculation module is used to calculate the wavelength shift of the background spectrum to be corrected and send it to the correction module. The correction module moves the background spectrum to be corrected according to the wavelength shift.

[0065] A non-transitory computer-readable storage medium includes instructions for performing the wavelength drift correction method for a deuterium lamp gas analyzer as described in any of the above embodiments.

[0066] An electronic device includes a non-transitory computer-readable storage medium; and one or more processors capable of executing the instructions of the non-transitory computer-readable storage medium.

[0067] The method and system provided by this invention are based on the principle of calculating the coarse and fine drift amounts of the background spectrum to be corrected from the deuterium lamp after filter attenuation. This allows for the accurate drift amount of the background spectrum to be corrected, with an accuracy of 0.0001 interpolation points. This solves the problem that gas analyzers cannot accurately calculate the wavelength drift of the background spectrum to be corrected relative to the reference background spectrum during the automatic zeroing stage, thus improving the accuracy of wavelength drift correction, simplifying the online concentration inversion process, and ensuring the reliability of the gas analyzer.

[0068] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product 7 embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0069] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0070] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0071] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0072] Specific embodiments have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A wavelength drift correction method for a deuterium lamp gas analyzer, characterized in that, Includes the following steps: S1. Background gas is introduced into the measuring cell, and the deuterium lamp spectrum after filtering and attenuation is collected and stored in the gas analyzer as a reference background spectrum. S2, Background gas is periodically introduced into the measuring cell, and the deuterium lamp spectrum after filtering and attenuation is collected as the background spectrum to be corrected; S3, extract all pixel intervals in the background spectrum to be corrected that include the absorption band of the gas to be measured, select a wider interval than the above pixel interval as a wavelength window, interpolate all pixels in the background spectrum to be corrected within the wavelength window to obtain the interpolated background spectrum to be corrected. S4, calculate the wavelength shift between the interpolated background spectrum to be corrected and the reference background spectrum; wherein the wavelength shift is the sum of the coarse wavelength shift and the fine wavelength shift; calculate the coarse wavelength shift between the interpolated background spectrum to be corrected and the reference background spectrum using the correlation coefficient method or the least squares method, with an accuracy of 1 interpolation point; calculate the fine wavelength shift between the interpolated background spectrum to be corrected and the reference background spectrum using the polynomial fitting method, with an accuracy of 0.0001 interpolation points; S5, adjust the background spectrum to be corrected based on the wavelength shift to correct the wavelength drift of the deuterium lamp gas analyzer.

2. The wavelength drift correction method for a deuterium lamp gas analyzer according to claim 1, characterized in that, The wavelength coarse shift is calculated as follows: S411, starting from the leftmost pixel of the wavelength window and ending at the rightmost pixel of the wavelength window, extract one interpolation point every n pixels of the background spectrum to be corrected after interpolation, and obtain s new background spectrum curves. S421, calculate the correlation coefficient between each of the new background spectrum curves and the reference background spectrum; S431, compare all correlation coefficients and select the m-th background spectrum curve with the largest correlation coefficient to the reference background spectrum. The coarse wavelength offset is the m interpolation points. .

3. The wavelength drift correction method for a deuterium lamp gas analyzer according to claim 1, characterized in that, The wavelength coarse shift is calculated as follows: S412, starting from the leftmost pixel of the wavelength window and ending at the rightmost pixel of the wavelength window, extract one interpolation point every n pixels of the background spectrum to be corrected after interpolation, and obtain s new background spectrum curves. S422, calculate the residual sum of squares between each of the new background spectrum curves and the reference background spectrum to obtain a set of residual sum of squares arrays; S432, compare all values ​​in the residual sum of squares array, select the smallest residual sum of squares, and record its position m' in the array. The wavelength coarse offset is the m' interpolation points. .

4. The wavelength drift correction method for a deuterium lamp gas analyzer according to claim 2, characterized in that, The wavelength shift is calculated as follows: S441, using the polynomial fitting method, defines the origin and the symmetrical points to the left and right of the origin as X values, and takes the maximum correlation coefficient between the background spectrum curve and the reference background spectrum and the correlation coefficients to the left and right of the maximum correlation coefficient as Y values, and performs polynomial fitting on X and Y. S451, calculate the x-coordinate of the extreme points of the multinomial fitting curve as the wavelength fine shift.

5. The wavelength drift correction method for a deuterium lamp gas analyzer according to claim 3, characterized in that, The wavelength shift is calculated as follows: S442 uses a polynomial fitting method, defining the origin and the points symmetrical to the left and right of the origin as X values, and taking the minimum residual sum of squares and the residual sum of squares adjacent to the minimum residual sum of squares as Y values, and performing polynomial fitting on X and Y. S452 calculates the x-coordinate of the extreme points of the multinomial fitting curve as the wavelength fine drift.

6. The wavelength drift correction method for a deuterium lamp gas analyzer according to claim 1, characterized in that, The deuterium lamp spectrum collected in steps S1 and S2 after filtering and attenuation is light in the 222-237nm wavelength band that has been attenuated.

7. A wavelength drift correction system for a deuterium lamp gas analyzer, utilizing the wavelength drift correction method for a deuterium lamp gas analyzer as described in any one of claims 1 to 6, comprising a deuterium lamp, a filter, a measuring cell, and a spectrometer, wherein the deuterium lamp is sequentially connected to the filter, the measuring cell, and the spectrometer, characterized in that... It also includes a storage module, a timing module, a calculation module, and a calibration module; background gas is introduced into the measurement cell, and the light emitted by the deuterium lamp is filtered and attenuated before passing through the measurement cell, being received by the spectrometer and converted into a digital signal input into the storage module; the timing module is used to periodically collect the background spectrum to be calibrated after the deuterium lamp filtering and attenuation, the calculation module is used to calculate the wavelength shift of the background spectrum to be calibrated and send it to the calibration module, and the calibration module moves the background spectrum to be calibrated according to the wavelength shift.

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