Raman spectrometer CCD parameter automatic calibration method based on standard substance spectrum

Abstract

The invention discloses a Raman spectrometer CCD parameter automatic calibration method based on a standard substance spectrum. The method comprises the following steps: measuring an original Raman spectrum by adopting a pure substance standard spectrum, and converting a received optical signal into an electric signal according to a CCD (Charge Coupled Device) pixel array; converting a pixel number corresponding to the Raman signal into a wavelength value according to a parameter of a CCD pixel, and further converting the wavelength value into a wave value required by a Raman spectrum coordinate; according to a pure substance characteristic peak standard wave value provided by a Raman shift standard calibrated by a spectrograph, a measured original spectrum pixel number is corrected, and a least square regression model is constructed according to the standard wave number and the CCD pixel number, so that CCD polynomial parameters are optimally estimated, and calibration of the CCD parameters of the spectrograph is realized. According to the method, the accuracy of the analysis model can be remarkably improved, and the method has the advantages of low training sample demand, high model extrapolation, short analysis time, accurate calibration result and the like, and is suitable for parameter calibration and correction of different spectrograph equipment.

Description

Technical Field

[0001] The present invention relates to the fields of spectrometer parameter calibration and CCD component calibration, and in particular to a Raman spectrometer CCD parameter automatic calibration method based on a standard substance spectrum. Background Art

[0002] At present, Raman spectrometers based on dispersive CCD arrays are widely used in practical applications because of their high detection sensitivity and stable internal components, which can better meet the actual industrial needs on site.

[0003] Dispersive Raman spectroscopy equipment primarily consists of a laser, a Raman probe, a spectrometer, and connecting optical fibers. The position of the characteristic spectral peak is affected by the laser's central wavelength, while the laser power is related to the strength of the spectral signal. Differences in the detection probes can cause variations in signal strength across the entire spectrum and the intensity of light at different pixel locations. Factors such as the spectrometer's detection range, resolution, and CCD array parameters are directly related to the position, shape, and intensity of the characteristic spectral peak. Traditional spectrometer calibration methods typically use halogen elements combined with standard light from specific metal elements to calibrate the spectrometer's resolution and corresponding parameters. These methods, such as tungsten-halogen lamps and argon-mercury lamps, can calibrate the spectrometer's resolution and corresponding parameters. However, variations in elemental purity can lead to deviations in the calibration results. Furthermore, the measurement process is complex, time-consuming, and carries the risk of toxicity and harm. Even for the same sample, spectra obtained using different spectrometer CCD array parameters can differ significantly.

[0004] The collected original spectrum is generally represented by continuous CCD pixel numbers as the horizontal axis of the spectrum, and the CCD parameters convert the pixel numbers into corresponding wavelength values, and then convert them into wavenumber values ​​according to the wavelength of the excitation light to standardize the Raman spectrum image. Although the same type of spectral detection equipment usually uses the same model of spectrometer, that is, each spectrometer has the same nominal resolution, thereby ensuring the consistency of the measured spectral characteristics; however, the error of the spectrometer parameters will affect the peak position and intensity of the final measured spectrum. If the parameters established in the offline detection equipment are directly applied to the online analysis system, the model accuracy will be greatly reduced; and re-collecting samples and re-establishing the quantitative analysis model for the online system will consume a lot of time and cost, thereby damaging economic benefits. Summary of the Invention

[0005] The purpose of the present invention is to address the deficiencies of the prior art and to propose a method for automatically calibrating CCD parameters of a Raman spectrometer based on the spectrum of a standard substance.

[0006] The object of the present invention is achieved through the following technical solution: a method for automatically calibrating CCD parameters of a Raman spectrometer based on the spectrum of a standard substance, comprising the following steps:

[0007] (1) Collect the Raman spectrum of pure substances and obtain the electrical signal corresponding to the Raman spectrum at the CCD pixel number coordinates;

[0008] (2) selecting the left and right endpoint pixels of each characteristic peak spectrum segment according to the shape of the electrical signal spectrum corresponding to the Raman spectrum and the peak height; performing polynomial smoothing on several pixel points before and after the highest point of the characteristic peak, and calculating the CCD sampling pixel number corresponding to the highest point of the main characteristic peak of the pure substance spectrum according to the polynomial fitting result;

[0009] (3) converting the standard wave value of the characteristic peak of the pure substance into a standard wavelength value according to the standard wave value of the characteristic peak of the pure substance provided by the Raman shift standard calibrated by the spectrometer;

[0010] (4) using the CCD sampling pixel number value corresponding to the highest point of each characteristic peak obtained in step (2) and the standard wavelength value obtained in step (3) to establish a regression model using the least squares method, fitting the CCD polynomial parameters, and obtaining the fitted CCD parameters;

[0011] (5) estimating the actual wave value based on the fitted CCD parameters; and verifying the estimated value by combining the variance range of the standard wave value of the characteristic peak of the standard substance calibrated by the spectrometer;

[0012] (6) If the wavenumber estimation value of step (5) is successfully verified, the calibrated CCD parameter value is recorded and stored; otherwise, the spectrum is remeasured and calibration steps (1) to (4) are repeated to ensure that the wavenumber estimation value corresponding to each characteristic peak is within the variance range of the standard wavenumber value of the characteristic peak of the standard substance.

[0013] Furthermore, the polynomial smoothing of several pixel points before and after the highest point of the characteristic peak includes: selecting a characteristic spectrum segment of the standard substance sample, and smoothing the values ​​before and after the highest point of the original characteristic peak to obtain a more accurate characteristic position.

[0014] Furthermore, the step (3) includes:

[0015] Wave number wn(cm -1 ) is calculated as: wn(i) = 10 7 / λ0-10 7 / λ i , where λ0 is the wavelength of the excitation light, λ i is the wavelength corresponding to pixel i;

[0016] Calculate the standard wavelength value according to the standard wave value: λ i,STD =λ0 / (1-10 -7 λ0·wn i,STD );

[0017] Among them, wn i,STD is the standard wave value, λ i,STD is the standard wavelength value.

[0018] Furthermore, the step (4) includes:

[0019] According to the linear relationship Zk=P·λ i,STD , optimally estimate P and obtain the polynomial parameters of the calibrated CCD array;

[0020] Among them, P is the polynomial parameter of the calibrated CCD array, Zk is the polynomial regression matrix of the pixel corresponding to the highest peak after processing of several main characteristic peaks, λ i,STD is the standard wavelength value.

[0021] The present invention also provides an electronic device, comprising a memory and a processor, wherein the memory is coupled to the processor; wherein the memory is used to store program data, and the processor is used to execute the program data to implement the automatic calibration method of the CCD parameters of a Raman spectrometer based on the spectrum of a standard substance.

[0022] The present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method for automatically calibrating CCD parameters of a Raman spectrometer based on the spectrum of a standard substance.

[0023] The beneficial effects of this invention lie in its innovative approach: by rapidly measuring the spectra of reference materials, polynomial smoothing is performed on the raw CCD electrical signal spectrum to obtain the ideal maximum pixel peak value. This is then directly compared and fitted with the reference material wavenumbers to obtain calibrated CCD parameters. This avoids the complex process of traditional halogen lamp calibration and achieves spectral consistency with that described by universal reference materials. Consequently, the calibration process is simple, safe, and highly reliable, and after parameter calibration, high-precision characteristics can be achieved for subsequent spectral measurements of other samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Flowchart of the present invention;

[0025] Figure 2 This is the original Raman spectrum of the standard pure substance cyclohexane;

[0026] Figure 3 This is the Raman spectrum of cyclohexane, a standard pure substance according to ASTM-E1840-96. DETAILED DESCRIPTION

[0027] Exemplary embodiments will be described in detail herein, examples of which are illustrated in the accompanying drawings. In the following description, when referring to the drawings, like numbers in different figures represent like or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all possible embodiments consistent with the present invention. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present invention, as detailed in the appended claims.

[0028] The terms used in this invention are for the purpose of describing specific embodiments only and are not intended to limit the invention. The singular forms "a," "the," and "the" used in this invention and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise. It should also be understood that the term "and / or" as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0029] The present invention will be described in detail below with reference to the accompanying drawings. In the absence of conflict, the features of the following embodiments and implementations can be combined with each other. Figure 1 As shown, an embodiment of the present invention provides a method for automatically calibrating CCD parameters of a Raman spectrometer based on a spectrum of a standard substance, comprising the following steps:

[0030] Step 1. Measure the Raman spectra of 9 samples. The Raman spectrometer uses an Ocean Optics QE65000 grating spectrometer with an optical resolution of 6 cm -1 , a laser with a central wavelength of 785nm is used as the excitation light source, and the detection range is 0-2000cm -1 This experiment takes the standard substance cyclohexane as an example. The pure substance cyclohexane sample is measured nine times in succession. The average of the nine measurement results is taken as the final original Raman spectrum. The integration time for each measurement is 2 seconds. The results are as follows: Figure 2 shown.

[0031] Step 2. Observe the main characteristic peaks of cyclohexane and compare Figure 3 Medium 0-2000cm -1 The spectral band range is compared with that of the standard spectrum, and the measured spectrum has a high degree of similarity with the standard spectrum shape, which can be further analyzed. Figure 2 The measured spectrum shown indicates the characteristic peaks of cyclohexane No. 1-7, and the corresponding standard wave values ​​of these peaks are noted in Table 1.

[0032] Step 3. Select the left and right endpoint pixels of the seven characteristic peak spectrum segments in turn, record them as [LeftIndex, RightIndex], and record the subscript number corresponding to the maximum value in the characteristic peak spectrum segment, i.e. [LeftIndex, RightIndex], record it as maxPeakIndex.

[0033] Step 4. Perform polynomial smoothing on the three pixel points before and after the highest point of the seven characteristic peaks (denoted as Xk), Xk = [maxPeakIndex-3, maxPeakIndex+3], record the corresponding spectral signal value Yk(Xk); and perform second-order polynomial fitting on Yk(Xk).

[0034]

[0035] Therefore, θ * =(A T A) -1 A T ·Yk. Among them, θ is the CCD parameter vector, θ * is the optimal estimated value of the parameter, A is the polynomial regression matrix composed of pixel values, and x is the pixel number in the characteristic peak segment.

[0036] Step 5. According to the standard wave value shown in Table 1, convert it into the standard wavelength value λ according to the following formula i,STD We get: i,STD =λ0 / (1-10 -7 λ0·wn STD ),wn STD is the standard wave value.

[0037] According to the linear relationship Zk=P·λ i,STD , (where P is the CCD polynomial parameter, and Zk is the polynomial regression matrix of the pixel corresponding to the highest peak after processing of several main characteristic peaks), the optimal estimate of P is the polynomial parameter of the calibrated CCD array.

[0038] Table 1: Standard values, standard deviations, and relative signal intensities of cyclohexane Raman shifts according to ASTM-E1840-96

[0039] Wave number mean (cm-1) ± standard deviation Relative Strength 384.1±0.78 2 426.3±0.41 3 801.3±0.96 95 1028.3±0.45 15 1157.6±0.94 6 1266.4±0.58 14 1444.4±0.30 12 2664.4±0.42 8 2852.9±0.32 100 2923.8±0.36 58 2938.3±0.51 67

[0040] Method validation:

[0041] In order to verify the accuracy and reliability of the method of the present invention, the CCD parameter calibration verification evaluation parameters include: maximum error, minimum error, and mean square error (SEP, Standard Error of Prediction). The definitions of each indicator are as follows:

[0042]

[0043] In the above formulas, y i and denote the calibrated estimated value and standard analysis value of the ith wave number, respectively. is the arithmetic mean of the standard analysis value, and M is the number of characteristic peaks.

[0044] The calibration results are shown in Table 2. The maximum error between the calibrated wavenumbers and the standard wavenumber values ​​is 0.183, and the minimum error is -0.168. The error range between the standard analysis values ​​and the model predictions is within the allowable wavenumber standard deviation range shown in Table 1, with a mean square error of 1.123e-06.

[0045] Table 2: Wave values ​​before and after calibration and standard wave values

[0046]

[0047] An embodiment of the present invention also provides an electronic device, including a memory and a processor, wherein the memory is coupled to the processor; wherein the memory is used to store program data, and the processor is used to execute the program data to implement the automatic calibration method of the CCD parameters of a Raman spectrometer based on the spectrum of a standard substance.

[0048] An embodiment of the present invention further provides a computer-readable storage medium having a computer program stored thereon. When the program is executed by a processor, the method for automatically calibrating CCD parameters of a Raman spectrometer based on the spectrum of a standard substance is implemented.

[0049] The computer-readable storage medium may be an internal storage unit of any device with data processing capabilities described in any of the aforementioned embodiments, such as a hard disk or memory. The computer-readable storage medium may also be any device with data processing capabilities, such as a plug-in hard disk, a smart media card (SMC), an SD card, a flash card, etc. equipped on the device. Furthermore, the computer-readable storage medium may also include both an internal storage unit of any device with data processing capabilities and an external storage device. The computer-readable storage medium is used to store the computer program and other programs and data required by any device with data processing capabilities, and may also be used to temporarily store data that has been output or is to be output.

[0050] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the contents disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only.

[0051] It will be understood that the present application is not limited to the exact construction that has been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof.

Claims

1. A method for automatic calibration of CCD parameters of a Raman spectrometer based on the spectrum of a standard substance, characterized in that: The following steps are involved: (1) collecting the Raman spectrum of a pure substance and obtaining an electrical signal corresponding to the Raman spectrum at the CCD pixel number coordinates; (2) selecting the left and right endpoint pixels of each characteristic peak spectrum segment according to the spectrum shape and peak height of the electrical signal corresponding to the Raman spectrum; Perform polynomial smoothing on several pixel points before and after the highest point of the characteristic peak. According to the polynomial fitting results, calculate the CCD sampling pixel number corresponding to the highest point of the main characteristic peak of the pure substance spectrum; (3) converting the standard wave value of the characteristic peak of the pure substance into a standard wavelength value according to the standard wave value of the characteristic peak of the pure substance provided by the Raman shift standard calibrated by the spectrometer; (4) using the CCD sampling pixel number value corresponding to the highest point of each characteristic peak obtained in step (2) and the standard wavelength value obtained in step (3) to establish a regression model using the least squares method, fitting the CCD polynomial parameters, and obtaining the fitted CCD parameters; (5) estimating the actual wave value based on the fitted CCD parameters; and verifying the estimated value by combining the variance range of the standard wave value of the characteristic peak of the standard substance calibrated by the spectrometer; (6) If the wavenumber estimation value of step (5) is successfully verified, the calibrated CCD parameter value is recorded and stored; otherwise, the Raman spectrum of the pure substance is re-collected and steps (1) to (4) are repeated to ensure that the wavenumber estimation value corresponding to each characteristic peak is within the variance range of the standard wavenumber value of the characteristic peak of the standard substance.

2. The method for automatic calibration of CCD parameters of a Raman spectrometer based on a standard material spectrum according to claim 1, characterized in that: The polynomial smoothing of several pixel points before and after the highest point of the characteristic peak includes: selecting a characteristic spectrum segment of the standard substance sample, and smoothing the values ​​before and after the highest point of the original characteristic peak to obtain a more accurate characteristic position.

3. The method for automatic calibration of CCD parameters of a Raman spectrometer based on a standard material spectrum according to claim 1, characterized in that: The step (3) comprises: Wave number wn(cm -1 ) is calculated as: wn(i) = 10 7 / λ0-10 7 / λ i , where λ0 is the wavelength of the excitation light, λ i is the wavelength corresponding to pixel i; Calculate the standard wavelength value according to the standard wave value: λ i,STD =λ0 / (1-10 -7 λ0·wn i,STD ); Among them, wn i,STD is the standard wave value, λ i,STD is the standard wavelength value.

4. The method for automatic calibration of CCD parameters of a Raman spectrometer based on a standard material spectrum according to claim 1, characterized in that: The step (4) comprises: According to the linear relationship Zk=P·λ i,STD , optimally estimate P and obtain the polynomial parameters of the calibrated CCD array; Among them, P is the CCD polynomial parameter, Zk is the polynomial regression matrix of the pixel corresponding to the highest peak after processing of several main characteristic peaks, λ i,STD is the standard wavelength value.

5. An electronic device comprising a memory and a processor, characterized in that: The memory is coupled to the processor; wherein the memory is used to store program data, and the processor is used to execute the program data to implement the automatic calibration method of CCD parameters of a Raman spectrometer based on the spectrum of a standard substance as described in any one of claims 1 to 4.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the method for automatic calibration of CCD parameters of a Raman spectrometer based on the spectrum of a standard substance as described in any one of claims 1 to 4 is implemented.

Images