A variable optical range and ultra-large range liquid concentration measurement system and method

Abstract

The present invention relates to a variable optical path ultra-large range liquid concentration measurement system and method. The system includes a light source module, a detection light module, a reference light module, a high-precision linear motion module, and a data analysis module. The light source module divides the light signal emitted by the light source into detection light and reference light; the detection light module detects the light signal absorbed by the liquid to be measured through a detection light path detector to obtain the detection light intensity; the high-precision linear motion module controls the detection light fiber to be inserted into the solution to be measured, and gradually moves within the optical path length interval with a set step size to achieve high-precision micron-level variable optical path length; the data analysis module corrects the detection light intensity through an optical signal fluctuation feedback correction method. Based on multiple sets of optical path lengths and the corrected detection light intensity, a least squares regression algorithm is used to fit the relationship between light intensity and optical path length to calculate the concentration value of the liquid to be measured. Compared with the prior art, the present invention has a larger concentration measurement range and more accurate and stable concentration measurement results.

Description

Technical Field

[0001] The present invention belongs to the field of liquid concentration measurement, and in particular relates to a variable optical range and ultra-large range liquid concentration measurement system and method. Background Art

[0002] Liquid concentration measurement has wide applications and significant significance in numerous fields, including industry and scientific research. Absorption spectroscopy is a classic liquid concentration measurement technique, based on the Beer-Lambert law. This technique uses the absorption of light by a sample solution to quantitatively analyze sample concentration. Specifically, when light passes through a solution, substances in the solution absorb some of the light, and the intensity of the absorbed light is proportional to the concentration of the substance. This non-invasive, rapid, and accurate concentration measurement method is of great significance for promoting scientific research, environmental protection, and improving product quality. Consequently, spectrophotometers developed based on this principle have been widely used and rapidly developed. Spectrophotometers infer the concentration of a solution by measuring its absorbance. When quantitatively analyzing a target substance in a solution, to ensure that the results are not affected by the test container, the sample and reference solutions are held in the same absorption cell, or in two absorption cells with the same transmittance after pairing blanks.

[0003] Traditional measurement methods require the use of large cuvettes with a fixed optical path length (OPL) (typically 10 mm), resulting in a small concentration measurement range (CN117169147A, CN115406885B) (Li Changhou. Ultraviolet-visible spectrophotometer and its applications [M]. Chemical Industry Press, 2010: 145-153). The specific process involves first measuring the absorbance of a blank solution (or reference sample), and then measuring the absorbance of the target solution using a standard curve calibration method (CN119290853A, CN119290853A). For high-concentration samples, due to the limited measurement range (CN117169147A), traditional measurement methods require multiple dilutions, which can easily lead to dilution errors and limit downstream applications (CN117169147A, CN101832916A). In summary, traditional standard solution testing has many shortcomings and limitations, such as cuvette OPL fixation, calibration errors, and measurement limitations. It also requires a large amount of sample and time, and has a narrow concentration measurement range (one order of magnitude), making it unsuitable for measuring high-concentration samples. Therefore, it is necessary to design a liquid concentration measurement method with a wider concentration measurement range and more accurate concentration measurement results. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a variable optical path and ultra-large range liquid concentration measurement system and method, which has a wider concentration measurement range and more accurate concentration measurement results, while having reliable measurement repeatability and stability.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] The present invention provides a variable optical range and ultra-large range liquid concentration measurement system, comprising a light source module, a detection light module, a reference light module and a data analysis module;

[0007] The light source module includes a light source controller, a light source, a transmission fiber, and a Y-type fiber connected in sequence. The light source controller is used to control the output power of the light source. The optical signal output by the light source is coupled to the Y-type fiber through the transmission fiber. The optical splitter of the Y-type fiber divides the received optical signal into detection light and reference light. The detection light and reference light have a bare fiber protection mechanism.

[0008] The detection light module includes a high-precision linear motion module, a detection light path optical fiber, a vertical fiber clamp, and a detection platform. The detection light path optical fiber is fixedly connected to the high-precision linear motion module via the vertical fiber clamp. A detection container containing a liquid to be tested is placed on the upper portion of the detection platform, and a detection light path detector is correspondingly provided on the lower portion. The end of the detection light path optical fiber is immersed in the liquid to be tested. The detection light is incident into the liquid to be tested through the detection light path optical fiber. The detection light signal absorbed by the liquid to be tested is detected by the detection light path detector to obtain the detection light intensity. The end position of the detection light path optical fiber is controlled by the high-precision linear motion module, thereby continuously adjusting the OPL with micron-level accuracy.

[0009] The reference light module includes the reference light and a reference light path detector. There is no test sample between the reference light end and the target surface of the reference light path detector. The reference light path detector has the same specifications and parameters as the detection light path detector and is used to detect the reference light and obtain the reference light intensity.

[0010] The data analysis module is used to correct the detection light intensity according to the OPL, the detection light intensity and the reference light intensity through the light signal fluctuation feedback correction method, and based on multiple groups of OPLs and the corrected detection light intensity, use the least squares regression algorithm to fit the relationship between the corrected light intensity and the OPL to calculate the concentration value of the liquid to be tested.

[0011] Furthermore, the optical signal fluctuation feedback correction method is as follows:

[0012] Get the detection light intensity I m (l,t), where I0(t) is the intensity of the detection light before entering the liquid to be tested, ε is the molar absorption coefficient, c is the liquid concentration, l is the OPL, is the light source fluctuation factor, α m is the spectral coefficient of the detection light, I set is the output light intensity of the light source, I set Set up through the light source controller;

[0013] Get reference light intensity I r (t), and the reference light intensity I r The change of (t) is fed back to the light source controller in real time;

[0014] The reference light intensity I r (t) and the detection light intensity I m The ratio of (l,t) is logarithmically transformed: lg(I r (t) / I m (l,t))=εcl+lgα, and then differentiate: εc=Δlg(I r (t) / I m (l,t)) / Δl=ΔA / Δl to eliminate the light source fluctuation factor For detection light intensity I m (l, t), where the splitting ratio α = α r / α m is a constant value, α r is the spectral coefficient of the reference light.

[0015] Furthermore, the process of calculating the concentration value of the liquid to be measured is as follows:

[0016] According to multiple groups of optical pathlengths and corrected detection light intensity, the least squares regression algorithm is used to fit the relationship between the corrected detection light intensity and OPL. + The first derivative at OPL is used to obtain the concentration of the liquid to be measured.

[0017] Furthermore, the process of obtaining the initial position 00PL is as follows:

[0018] The detection optical path optical fiber is in an initial standby position, and the initial standby position OPL is greater than the estimated 0OPL;

[0019] Selecting a standard solution of known concentration, placing it in the detection container, and placing the detection container on the detection platform;

[0020] The high-precision linear motion module is controlled to vertically insert the detection optical fiber into the standard solution in a high-precision driving manner. During this process, each time an insertion step is completed, the detection light path detector immediately collects the detection light intensity transmitted through the standard solution, and the reference light path detector simultaneously monitors the reference light intensity in real time to calibrate the influence of light source fluctuations;

[0021] Calculate and monitor the detection light intensity change rate in real time. If the deviation of the detection light intensity change rate obtained by multiple consecutive measurements from the initial fixed value change rate calculated theoretically is greater than or equal to the set threshold, the position of the detection light path optical fiber is approximately 0 OPL.

[0022] Repeat the above process multiple times with the same concentration of standard solution, and perform weighted averaging on the approximate 0OPL obtained each time. The weight is determined based on factors such as system stability and light intensity fluctuation during each measurement process, and the weighted average is used as the final initial position 0OPL.

[0023] Furthermore, the specific process of continuously adjusting the OPL with micron-level precision is as follows:

[0024] After receiving the variable optical path instruction, the high-precision linear motion module drives the detection optical fiber to gradually insert it into the liquid to be tested in a direction perpendicular to the detection platform according to the preset OPL range and set step size.

[0025] Furthermore, during the process of inserting the detection optical fiber into the liquid to be tested, each time a step of movement is completed, a preset time interval is paused to wait for the detection optical path detector and the reference optical path detector to complete the light intensity data collection until the preset end optical path value of the OPL interval is reached or a stop command is received.

[0026] Furthermore, the high-precision linear motion module is constructed based on a high-precision stepper motor and a precision transmission component. The high-precision stepper motor achieves fine control through its internal subdivision circuit, and the internal subdivision circuit is used to output a driving pulse corresponding to a 1-micron step length. The output shaft of the selected high-precision stepper motor is rigidly connected to a high-precision ball screw. The pitch of the high-precision ball screw is optimized through theoretical calculations and multiple experiments to ensure that when the high-precision stepper motor receives a driving pulse corresponding to a 1-micron step length, it accurately pushes the detection optical fiber fastened to it to achieve a 1-micron linear displacement on the OPL, and the long-term repeatability deviation of the displacement is strictly controlled within ±0.1 microns.

[0027] Furthermore, the high-precision linear motion module is also equipped with a high-precision closed-loop feedback control system, which uses a grating ruler that can accurately identify 1 micron displacement changes as a key position feedback element. It is tightly attached to the high-precision linear motion module to capture the actual position information of the detection optical fiber in real time and continuously, and transmit this information back to the control system at a response speed of microseconds. The control system has a built-in difference comparison algorithm for real-time analysis of the deviation between the preset position and the real-time feedback position, and then dynamically adjusts the drive pulse parameters of the high-precision stepper motor to regulate the speed and torque of the high-precision stepper motor.

[0028] Furthermore, the detection platform is arranged on an xy-axis displacement slide, and the position of the detection platform is adjusted by the xy-axis displacement slide.

[0029] The present invention also provides a variable optical range and ultra-large range liquid concentration measurement method applicable to the above-mentioned variable optical range and ultra-large range liquid concentration measurement system, comprising the following steps:

[0030] Turn on the light source, and the light signal output by the light source is coupled to the Y-type fiber through the transmission fiber. The Y-type fiber's optical splitter divides the received light signal into detection light and reference light;

[0031] The position of the detection optical fiber is adjusted by a high-precision linear motion module. The detection light is incident into the liquid to be tested through the detection optical fiber. The detection optical path detector detects the light signal absorbed by the liquid to be tested, and the detection light intensity under different OPL is obtained.

[0032] Detect the reference light through a reference light path detector to obtain the reference light intensity;

[0033] The detection light intensity is corrected according to the OPL, detection light intensity and reference light intensity by using the light signal fluctuation feedback correction method;

[0034] According to multiple groups of OPL and corrected detection light intensity, the least squares regression algorithm is used to fit the relationship between the corrected light intensity and OPL, and the concentration value of the liquid to be tested is calculated.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. Compared with the traditional measurement method with fixed optical path (usually 10mm) and narrow concentration measurement range (only one order of magnitude), the present invention relies on high-precision linear motion module to set the step size to accurately control OPL, realize high-precision micron-level variable optical path adjustment, and can flexibly adapt the optical path according to the concentration of the liquid to be measured, avoiding the errors caused by multiple dilutions of high-concentration samples, and greatly widening the measurement range. More importantly, the data analysis module and unique concentration calculation method equipped in the present invention provide a solid backing for ultra-large range measurement. The data analysis module corrects the detection light intensity based on the light signal fluctuation feedback correction method, and based on multiple sets of precise light intensity data at different optical paths, uses the least squares regression algorithm to fit the relationship between light intensity and optical path, overcoming the nonlinear deviation problem of Beer-Lambert's law at high concentrations and large optical paths (Li Changhou. Ultraviolet Visible Spectrophotometer and Its Application [M]. Chemical Industry Press, 2010: 9-14.), by 0 + The first-order derivative at the OPL accurately determines the concentration of the liquid being measured. This synergistic effect enables the present invention to achieve wide-range optical path adjustment while ensuring the accuracy of concentration calculations across different ranges. This perfectly meets the concentration measurement requirements of samples with a large dynamic range and high concentrations, making it widely applicable to various industrial and scientific research fields.

[0037] 2. High-precision measurement: This invention has unique advantages in achieving high precision. On the one hand, it uses a high-precision stepper motor in conjunction with a precision transmission component. The motor is finely controlled by an internal subdivision circuit and outputs a drive pulse corresponding to a 1-micron step size. Combined with a ball screw with an optimized pitch, it ensures that the displacement deviation of the detection optical fiber is extremely small and the long-term repeatability of the displacement is strictly controlled within ±0.1 micron. On the other hand, it is equipped with a high-precision closed-loop feedback control system, which monitors the position in real time with a high-resolution grating ruler. The control system dynamically adjusts the motor drive pulse parameters based on the deviation, and multi-dimensional precise control ensures high-precision motion accuracy throughout the entire process, making the measurement results more accurate and reliable, and effectively overcoming the accuracy limitations of traditional measurement methods caused by calibration errors, cuvettes, and devices.

[0038] 3. High measurement stability: Through a unique optical signal fluctuation feedback correction method, Y-type optical fiber splitting is used to form reference light and detection light. The reference light detector captures the reference light intensity in real time and feeds it back to the control system. Based on the Beer-Lambert law, an optical signal correction algorithm is constructed. This algorithm can eliminate the influence of small fluctuations in the light source power according to the reference light intensity and detection light intensity at the same moment, ensuring that the output detection light signal has high precision and high stability, avoiding measurement deviations caused by unstable light sources. In addition, the least squares regression algorithm fits the rate of change of the detection light intensity with the optical path after correction, avoiding measurement errors caused by device interference factors, providing stable guarantee for long-term, continuous measurement, and significantly improving stability compared to traditional measurement methods.

[0039] 4. Improved operational convenience: The system and method of the present invention are simpler and more efficient in terms of operational process. The detection platform is set on the xy-axis displacement slide, which can be flexibly adjusted. The coarse adjustment slide can also be used to preliminarily adjust the position of the high-precision linear motion module of the detection optical path. Then, combined with the control program, further precise adjustment is made according to the set step size and OPL range. Compared with the traditional complex operation that requires the use of large-volume cuvettes, frequent sample replacement and calibration, this greatly simplifies the measurement steps, reduces the sample amount and time required for measurement, improves work efficiency, and reduces the difficulty and intensity of the operator's work. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a front view of the system of the present invention;

[0041] Figure 2 It is a left side view of the system of the present invention;

[0042] Figure 3 Schematic diagram of the structure of the light source module;

[0043] Figure 4 It is a schematic diagram of the present invention;

[0044] Explanation of reference numerals: 1. light source; 2. 1×2 optical splitter; 3. reference optical path; 4. detection optical path; 5. reference optical detector; 6. stepper motor; 7. sample; 8. detection optical detector; 9. light source controller; 10. light source; 11. transmission optical fiber; 12. optical attenuator; 13. Y-type optical fiber; 14. bare optical fiber; 15. detection light; 16. reference light; 17. coarse adjustment slide; 18. high-precision linear motion module; 19. detection optical path optical fiber; 20. optical fiber vertical clamping; 21. detection container; 22. detection platform; 23. xy-axis displacement slide; 24. reference light module; 25. detection optical module; 26. reference optical path detector; 27. detection optical path detector;

[0045] Figure 5 is the emission spectrum of the light source;

[0046] Figure 6 Schematic diagram of the correlation between reference light intensity and detection light intensity under different optical power outputs.

[0047] Among them, (6a) is the correlation between the reference light intensity measurement value and the detection light intensity measurement value when there is no sample at different light power outputs; (6b) is the correlation between the reference light intensity measurement value and the light power of the test module detection light at different light source output powers;

[0048] Figure 7 This is the measurement data diagram of 0.1mol / L H2SO4 solution (step size is 0.005mm),

[0049] Among them, (7a) is the measurement data without the reference optical module, and (7b) is the measurement data with the reference optical module added;

[0050] Figure 8 The following are the measurement data of potassium dichromate (K2Cr2O7) solutions with different concentrations and the analysis of measurement data under different OPL (comparison of the results of relative concentration calculation method).

[0051] Among them, (8a) is the measurement data of 0-0.5 mm OPL, (8b) is the measurement data of 0-0.02 mm OPL, (8c) is the linear correlation degree of relative concentration obtained by different regression methods, and (8d) is the relative error of relative concentration obtained by different regression methods;

[0052] Figure 9 The concentration standard curve established for the same sample in different measurement systems,

[0053] Among them, (9a) is the concentration standard curve of the system of the present invention (few-step variable optical-path-length slope method, fs-VOSM) at 0-0.02 mm OPL, (9b) is the concentration standard curve of UV 2900, and (9c) is the concentration standard curve of LAMBDA1050;

[0054] Figure 10 The system of the present invention measures potassium dichromate (K2Cr2O7) solutions with different concentrations.

[0055] Among them, (10a) is the measurement data from 0 to 0.02 mm, and (10b) is the relationship curve between the concentration gold standard and the estimated value when the OPL is 0.020 mm;

[0056] Figure 11 Comparison of concentration estimates of the same sample using different measurement methods.

[0057] Where, (11a) is the relative error of concentration measurement using fs-VOSM and commercial instrument system, and (11b) is the repeatability of concentration measurement. DETAILED DESCRIPTION

[0058] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0059] Example:

[0060] This embodiment provides a variable optical range ultra-large range liquid concentration measurement system (fs-VOSM), the measurement principle of which is based on the Beer-Lambert law. In the Beer-Lambert law, the expression of the detection light intensity I is

[0061] I=I0e -εcl (1)

[0062] Among them, I0 represents the incident light intensity, ε represents the molar absorption coefficient, which is a physical quantity related to the properties of the substance itself and is used to describe the degree of absorption of light of a specific wavelength per molar concentration of the substance, c represents the concentration, and l represents OPL.

[0063] The expression of absorbance A is:

[0064] A=lg(I0 / I)=εcl (2)

[0065] It can be seen that when the incident light intensity I0 is constant, the absorbance is proportional to the OPL of the measured concentration solution.

[0066] However, in actual applications, there are interference factors and errors in the detection system and the output light intensity of the light source It always fluctuates over time, where the fluctuation factor is As the absorbance changes with OPL, this requires that the incident light intensity be constant, and the changes in OPL and detection light intensity be accurately measured to eliminate the influence of interfering factors.

[0067] In view of the above problems, this embodiment proposes a solution, such as Figure 4 As shown, the light source 1 is divided into a reference light path 3 and a detection light path 4 by a 1×2 optical splitter 2, and the fluctuation factor is corrected by the reference light path 3. The splitting coefficients of the reference light path 3 and the detection light path 4 are set to α r and α m . Reference light intensity I r (t) and the detection light intensity I m (l, t) is measured by two detectors with identical parameter modules (reference light detector 5 and detection light detector 8). In the detection optical path 4, a high-precision stepper motor 6 controls the movement of the detection optical fiber into the liquid sample 7 at different depths to achieve different OPL requirements. I0(t) is the incident light intensity, that is, the light intensity before the sample absorbs it, and is given by:

[0068]

[0069] After logarithmic calculation, we can get:

[0070] lg(I r (t) / I m (l, t))=εcl+lgα (4)

[0071] The splitting ratio α=α r / α m , where lg(I r (t) / I m (l,t)) is defined as the relative concentration value, and differentiating the above formula yields:

[0072] εc= Δlg(I r (t) / I m (l, t)) / Δl=ΔA / Δl (5)

[0073] By Δlg(I r (t) / I m (l, t)) = ΔA, it can be seen that this method can be used to eliminate the influence of light source fluctuations and device interference factors.

[0074] Based on the above method, this embodiment proposes a method as follows Figure 1 The variable optical range and ultra-large range liquid concentration measurement system shown includes a light source module, a detection light module 25, a reference light module 24, and a data analysis module. The specific description of each module is as follows:

[0075] like Figure 3 As shown, the light source module includes a light source controller 9, a light source 10, a transmission optical fiber 11 and a Y-type optical fiber 13 connected in sequence. The central wavelength of the light source 10 is 465nm, the half-height width is 26nm, and the emission spectrum is as shown in FIG. Figure 5 As shown in the figure, the light source controller 9 is used to control the output power of the light source 10. The optical signal output by the light source 10 is coupled to the Y-type optical fiber 13 through the transmission fiber 11 with a core diameter of 600μm and a 0.22NA. The optical splitter of the Y-type optical fiber 13 divides the received optical signal into detection light 15 and reference light 16. An optical attenuator 12 is provided between the transmission fiber 11 and the Y-type optical fiber 13. The optical power can be controlled by changing the gap between the optical fiber connection ports.

[0076] The detection light module 25 includes a detection light path optical fiber 19 and a detection platform 22. In this embodiment, the high-precision linear motion module 18 is a detection light path stepper motor, and the detection light path optical fiber 19 is fixed to the detection light path stepper motor by the optical fiber vertical clamp 20. The coarse adjustment slide 17 can greatly adjust the vertical position of the detection light path stepper motor. Furthermore, the control program is developed using the LabVIEW platform to realize the movement of the stepper motor within a given step length and distance range, and the position parameters of the stepper motor and the response values ​​of the two detectors are returned to the data analysis module in real time. When the step length is 0.005mm, it takes 16 seconds to complete the scanning detection of 0-0.5mm OPL. When the step length is 0.005mm, it takes 0.8 seconds to complete the scanning detection of 0-0.02mm OPL. The detection platform 22 is set on the xy-axis displacement slide 23, and the position of the detection platform 22 can be adjusted by the xy-axis displacement slide 23. A detection container 21 containing the test liquid is placed on the upper portion of the detection platform 22, and a detection light path detector 27 is located on the lower portion. The end of the detection light path optical fiber 19 is immersed in the test liquid, and the detection light 15 is incident on the test liquid through the detection light path optical fiber 19. The detection light path detector 27 detects the light signal absorbed by the test liquid and obtains the detection light intensity. The end of the detection light path optical fiber 19 uses a bare optical fiber 14 to facilitate direct injection of the detection light 15 into the test liquid. The opening of the detection container 21 only needs to be slightly larger than the end of the detection light path optical fiber 19.

[0077] like Figure 2 As shown, the reference light module 24 includes a reference light path detector 26. The reference light path detector 26 has the same parameters as the detection light path detector 27 and is used to detect the reference light 16 to obtain a reference light intensity. The reference light intensity can be used to correct the effects of light source 10 fluctuations and interference factors in subsequent calculations and analysis.

[0078] The variable optical range ultra-large range liquid concentration measurement system and method (fs-VOSM) of this embodiment is specifically described below using an example of measuring the concentration of a standard substance, acidic potassium dichromate (K2Cr2O7) solution. In order to verify the performance of the above system, this embodiment configures a standard substance, potassium dichromate (K2Cr2O7) solution and performs detection to estimate the concentration. The solution samples are diluted and prepared and the concentration is measured in sequence. Potassium dichromate with a purity of ≥99.8% is diluted with 0.1 mol / L sulfuric acid solution as a diluent to prepare 7 concentrations of acidic potassium dichromate solution. The solution concentration range is 101.761 to 0.051 g / L. Then, 8 concentrations of acidic potassium dichromate solution are configured and measured to evaluate the performance of the concentration estimation model.

[0079] After the system is assembled, the OPL needs to be reduced to 0 first. The standard substance potassium dichromate (K2Cr2O7) solution is added to the detection container 21 as the background solution, and the detection light path fiber 19 is gradually lowered through the high-precision linear motion module 18. During this process, each time the insertion action is completed, the detection light path detector immediately collects the detection light intensity passing through the standard solution, and at the same time, the reference light path detector monitors the reference light intensity in real time to calibrate the influence of light source fluctuations; the detection light intensity change rate is calculated and monitored in real time. If the detection light intensity change rate obtained by multiple consecutive measurements is compared with the initial fixed value change rate calculated theoretically, the deviation is greater than or equal to the set threshold value. At this time, the position of the detection light path fiber is approximately 0 OPL. In order to compare the measurement performance of the system, the sample solutions of the same batch were also measured on two other commercial UV-visible spectrophotometers. The difference is that before the spectrophotometer is measured, it is necessary to first use the same cuvette to add solvent for baseline calibration (return to 0).

[0080] When the OPL of the detection light module 25 is fixed, the correlation between the reference light intensity and the detection light intensity measured at different light source output powers is as follows: Figure 6 As shown in (6a). The linear regression results show that the splitting ratio is relatively stable and can be regarded as a constant, which verifies the stability and reliability of the system proposed in this embodiment. In addition, the detection light path detector 27 of the detection light module 25 is replaced with an optical power meter to measure the light intensity. Figure 6 As shown in (6b), the linearity between the reference light intensity and the optical power of the test module is very high. This shows that the photoelectric response of the detection optical module 25 and the system is stable and reliable. The system has high sensitivity and resolution, which is comparable to the performance of commercial equipment.

[0081] This example also tests a 0.1 mol / L sulfuric acid (H2SO4) solution, which is a very low absorbance solvent. The measurement step is 0.005 mm and the OPL range is 0-0.5 mm to verify the resolution of the system in liquid concentration measurement. The measurement data of the system for sulfuric acid solution are as follows: Figure 7 As shown in Figure 7, (7a) is the measurement data without the reference light module 24, and (7b) is the measurement data with the reference light module 24 added. The results of linear regression and coefficient of variation analysis of the measured data show that the relative concentration measured with the reference light added at a step size of 0.005 mm is more stable and reliable, and the sensitivity and resolution of the detection system are very high.

[0082] The system was used to measure potassium dichromate (K2Cr2O7) solution with a step size of 0.005mm and an OPL of 0 to 0.5mm. The measurement data of 7 concentrations of potassium dichromate (K2Cr2O7) solution are as follows: Figure 8As shown. Among them, (8a) is the measurement data under 0~0.5mm OPL, and the measurement of each concentration sample is completed under 101 OPL. It can be seen from (8a) that lg(I r / I m ) and OPL are linearly related, and the higher the concentration of the solution, the greater the relative absorbance (slope) per unit OPL. When the concentration is greater than 28.056 g / L, the rate of change of the relative absorbance decreases monotonically. This is consistent with the theoretical application of Beer-Lambert's law, that is, when the solution concentration is high, the absorbance becomes nonlinear. To this end, this embodiment performed a least squares regression on the measured data, and the results showed that it satisfies the cubic polynomial relationship well (Table 1). The higher-order terms of the polynomial regression of low-concentration data can be ignored, which is equivalent to linear regression. Because the larger the OPL, the more serious the cumulative effect of inhibition and interference factors on the light absorption performance of the substance, and the greater the deviation from the theoretical law, especially for high-concentration samples. Figure 8 (8b) shows the measured data at 0 to 0.02 mm OPL, including the detection data at 5 OPLs. It can be seen that it is linear in the range where the OPL is close to 0. The slope of the curve needs to be solved to obtain the relative concentration value of the measured sample.

[0083] To this end, this embodiment proposes a concentration calculation method, including two methods: (1) For the case of a larger OPL, the first-order derivative of the polynomial regression equation at OPL = 0 is the relative concentration value; (2) For the measured data of the OPL close to the "0" position (only the detection data under a 5-micron step length is required), a linear regression analysis is performed, and the slope value is the relative concentration value of the measured sample. The linear correlation degree and relative error of the relative concentration values ​​obtained by the two methods are compared and analyzed, and the results are as follows: Figure 8 As shown in (8c) and (8d) (Table 2), it can be seen that the relative concentration values ​​of multiple samples have a high linear correlation and a small relative error. The two methods are mutually verified. Even if the measurement results under only 5 OPLs are equivalent to the analysis results under 101 OPLs, the experiment proves that the system has good stability and high resolution.

[0084] For the estimation of sample concentration, it is usually necessary to develop a standard curve based on the system. In order to evaluate the performance of the system (fs-VOSM), two commercial UV-visible spectrophotometers (UV2900, Shanghai Sunny Hengping Scientific Instrument Co., Ltd.; LAMBDA1050, PerkinElmer, USA) were used to measure the same sample. Due to the high absorbance of potassium dichromate (K2Cr2O7) solution, in order to measure samples with high concentrations as much as possible, a 1mm OPL quartz cuvette was used. The upper limit of the absorbance detection of the UV-visible spectrophotometer is usually around 4. It can be seen that when the concentration is high, it exceeds the detection limit and returns an erroneous measurement value (Table 2). In addition, the results of low-concentration samples are negative, which exceeds its resolution. In terms of detection, the system has a larger dynamic range and higher resolution. Linear regression analysis was performed on the measurement results of the three systems, and the standard concentration curves obtained were as follows: Figure 9 The results show that the linear regression determination coefficient of the standard curve of the system proposed in this embodiment is the highest (R 2 =0.99999), with a concentration linear range of 0.051–101.761 g / L, exceeding the concentration linear range of the standard curves for both commercial systems. Due to theoretical and system limitations, commercial instruments cannot detect higher concentrations. Therefore, the system proposed in this embodiment offers a wider concentration detection range and more accurate concentration estimation.

[0085] In order to evaluate the actual concentration estimation capability of the above system, the system was used to measure the concentration of eight potassium dichromate (K2Cr2O7) samples. The measurement data at 0-0.02 mm OPL are shown in Figure 2. Figure 10 (10a) shows that the relative concentration values ​​are shown in Tables 3 and 4. The results are substituted into the standard concentration curve equation to solve the concentration prediction results under 5 OPLs as shown in Tables 5 and 6, which further proves that the system has good stability and high resolution. When the OPL is 0.02 mm, the comparison between the concentration prediction and the actual concentration of the system is as follows: Figure 10 As shown in (10b), the system achieves a relative concentration estimation error within ±3.6%, demonstrating its robust concentration estimation capabilities. In summary, the proposed concentration measurement system offers a wider concentration measurement range. During measurement, data acquisition is accomplished by simply measuring the light intensity at five OPLs within a very short OPL interval (0 to 0.02 mm).

[0086] Table 1 Comparison of least squares regression results of measurement data

[0087]

[0088] Table 2 Measurement data of potassium dichromate samples under different systems

[0089]

[0090]

[0091] Note: Data in italics are results beyond the measurement range of the instrument. AVG is the mean, SD is the standard deviation, and CV is the coefficient of variation.

[0092] Table 3 Linear regression of known concentrations using the proposed system

[0093]

[0094] Table 4 Determination results of potassium dichromate samples by different systems

[0095]

[0096]

[0097] Note: The data in italics are the results beyond the measurement range of the instrument, AVG is the average value, SD is the standard deviation, and CV is the coefficient of variation.

[0098] Table 5 Estimated concentration results of potassium dichromate samples measured using different instruments

[0099]

[0100] Note: The data in italics are the results beyond the measurement range of the instrument, AVG is the average value, SD is the standard deviation, and CV is the coefficient of variation.

[0101] Table 6 Relative error of potassium dichromate sample concentration measured by different instruments

[0102]

[0103] *1c is the concentration gold standard, c e The values ​​in italics are the results that exceed the measurement range of the system.

[0104] Compared with the prior art, the above solution has the following beneficial effects:

[0105] (1) On the basis of the variable spectrum method, the reference light module is added to correct the influence of light source ratio fluctuation and device interference, realize the concentration measurement under variable OPL in ultra-large dynamic range, and improve the measurement precision, accuracy and reliability.

[0106] (2) It has the function of OPL "0" position. By returning to the "0" model through data analysis, the stepper motor drive displacement and OPL are matched. It can meet the measurement needs under extremely short OPL (relative to "0 optical path"), improve the accuracy and precision of concentration measurement, and increase the dynamic range of concentration measurement.

[0107] (3) It has the characteristics of ultra-short OPL measurement. It only needs to measure 5 OPL data near the "0" optical path to achieve concentration measurement. The measured data is subjected to least squares regression to obtain the concentration value. It can meet the needs of direct high-precision measurement of high-concentration samples without the need for sample dilution preparation, and achieve ultra-large dynamic range concentration measurement.

[0108] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A variable optical range and ultra-large range liquid concentration measurement system, characterized in that: It includes a light source module, a detection light module (25), a reference light module (24) and a data analysis module; The light source module comprises a light source controller (9), a light source (10), a transmission optical fiber (11) and a Y-type optical fiber (13) connected in sequence, wherein the light source controller (9) is used to control the output power of the light source (10), the optical signal output by the light source (10) is coupled to the Y-type optical fiber (13) through the transmission optical fiber (11), and the optical splitter of the Y-type optical fiber (13) divides the received optical signal into detection light (15) and reference light (16), and the detection light (15) and the reference light (16) are provided with an optical fiber bare fiber protection mechanism; The detection light module (25) comprises a high-precision linear motion module (18), a detection light path optical fiber (19), an optical fiber vertical clamp (20) and a detection platform (22). The detection light path optical fiber (19) is fixedly connected to the high-precision linear motion module (18) via the optical fiber vertical clamp (20). A detection container (21) containing a liquid to be tested is placed on the upper part of the detection platform (22), and a detection light path detector (27) is correspondingly arranged at the lower part. The end of the detection light path optical fiber (19) is immersed in the liquid to be tested. The detection light (15) is incident on the liquid to be tested through the detection light path optical fiber (19). The light signal absorbed by the liquid to be tested is detected by the detection light path detector (27) to obtain the detection light intensity. The end position of the detection light path optical fiber (19) is controlled by the high-precision linear motion module (18), thereby continuously adjusting the optical path length with micron-level accuracy. The reference light module (24) includes the reference light (16) and a reference light path detector (26), there is no test sample between the end of the reference light (16) and the target surface of the reference light path detector (26), the reference light path detector (26) has the same specification parameters as the detection light path detector (27), and is used to detect the reference light (16) and obtain reference light intensity; The data analysis module is used to correct the detection light intensity according to the optical path length, the detection light intensity and the reference light intensity through an optical signal fluctuation feedback correction method, and based on multiple sets of optical path lengths and corrected detection light intensities, use a least squares regression algorithm to fit the relationship between the corrected detection light intensity and the optical path length to calculate the concentration value of the liquid to be tested.

2. The variable optical range and ultra-large range liquid concentration measurement system according to claim 1, characterized in that: The optical signal fluctuation feedback correction method is as follows: Get the detection light intensity I m (l,t), where I m (l,t)=I0(t)e -εcl =I set φ(t)α m e -εcl , I0(t) is the intensity of the detection light (15) before entering the liquid to be tested, ε is the molar absorption coefficient, c is the liquid concentration, l is the optical path length, φ(t) is the light source fluctuation factor, α m is the spectral coefficient of the detection light (15), I set is the output light intensity of the light source (10), I set Setting is performed via a light source controller (9); Get reference light intensity I r (t), and the reference light intensity I r The change of (t) is fed back to the light source controller (9) in real time; The reference light intensity I r (t) and the detection light intensity I m The ratio of (l,t) is logarithmically transformed: lg(I r (t) / I m (l,t))=εcl+lgα, and then differentiate: εc=Δlg(I r (t) / I m (l,t)) / Δl=ΔA / Δl, to eliminate the influence of light source fluctuation factor φ(t) on the detected light intensity I m (l, t), where the splitting ratio α = α r / α m is a constant value, α r is the spectral coefficient of the reference light (16).

3. The variable optical range and ultra-large range liquid concentration measurement system according to claim 1, characterized in that: The process of calculating the concentration value of the liquid to be measured is as follows: According to multiple groups of optical path lengths and the corrected detection light intensity, the least squares regression algorithm is used to fit the relationship between the corrected detection light intensity and the optical path length. + The first-order derivative at the optical path length is used to obtain the concentration of the liquid to be measured.

4. The variable optical range and ultra-large range liquid concentration measurement system according to claim 3, characterized in that: The process of obtaining the initial position 0 optical path length is as follows: The detection optical path optical fiber (19) is in an initial standby position, and the optical path length of the initial standby position is greater than the estimated zero optical path length; Selecting a standard solution of known concentration, placing it in the detection container (21), and placing the detection container (21) on the detection platform (22); The high-precision linear motion module (18) is controlled to vertically insert the detection light path optical fiber (19) into the standard solution step by step in a high-precision driving manner. During this process, each time a step of insertion is completed, the detection light path detector (27) immediately collects the detection light intensity passing through the standard solution, and at the same time, the reference light path detector (26) monitors the reference light intensity in real time to calibrate the influence of light source fluctuations; Calculate and monitor the detection light intensity change rate in real time. If the deviations of the detection light intensity change rate obtained by multiple consecutive measurements compared with the initial fixed value change rate calculated theoretically are greater than or equal to a set threshold, the position of the detection light path optical fiber (19) is approximately 0 optical path length. The above process is repeated multiple times under the same concentration of standard solution, and the approximate zero optical path length obtained each time is weighted averaged. The weight is comprehensively determined based on factors such as system stability and light intensity fluctuation during each measurement process, and the weighted average is used as the final initial position zero optical path length.

5. The variable optical range and ultra-large range liquid concentration measurement system according to claim 1, characterized in that: The specific process of continuously adjusting the optical path length with micron-level precision is as follows: After receiving the variable optical path instruction, the high-precision linear motion module (18) drives the detection optical fiber (19) to gradually insert the detection optical path into the liquid to be tested in a direction perpendicular to the detection platform (22) according to a preset optical path length interval and a set step size.

6. The variable optical range and ultra-large range liquid concentration measurement system according to claim 5, characterized in that: During the process of inserting the detection light path optical fiber (19) into the liquid to be tested, each time a step of movement is completed, a preset time interval is paused to wait for the detection light path detector (27) and the reference light path detector (26) to complete light intensity data acquisition until the end optical path value of the preset optical path length interval is reached or a stop instruction is received.

7. The variable optical range and ultra-large range liquid concentration measurement system according to claim 1, characterized in that: The high-precision linear motion module (18) is constructed based on a high-precision stepper motor in conjunction with a precision transmission component. The high-precision stepper motor achieves fine control through its internal subdivision circuit, and the internal subdivision circuit is used to output a driving pulse corresponding to a 1-micron step length. The output shaft of the selected high-precision stepper motor is rigidly connected to a high-precision ball screw. The pitch of the high-precision ball screw is optimized through theoretical calculations and multiple experiments to ensure that when the high-precision stepper motor receives a driving pulse corresponding to a 1-micron step length, it accurately pushes the detection optical fiber (19) fastened thereto to achieve a 1-micron linear displacement in the optical path length, and the long-term repeatability deviation of the displacement is strictly controlled within ±0.1 microns.

8. The variable optical range and ultra-large range liquid concentration measurement system according to claim 7, characterized in that: The high-precision linear motion module (18) is also equipped with a high-precision closed-loop feedback control system, which uses a grating ruler capable of accurately identifying a displacement change of 1 micron as a key position feedback element. The grating ruler is tightly attached to the high-precision linear motion module (18), and the actual position information of the detection optical fiber (19) is captured in real time and continuously, and the information is transmitted back to the control system at a response speed of microseconds. The control system has a built-in difference comparison algorithm for real-time analysis of the deviation between the preset position and the real-time feedback position, and then dynamically adjusts the driving pulse parameters of the high-precision stepper motor to regulate the speed and torque of the high-precision stepper motor.

9. The variable optical range and ultra-large range liquid concentration measurement system according to claim 1, characterized in that: The detection platform (22) is arranged on an xy-axis displacement slide (23), and the position of the detection platform (22) is adjusted by the xy-axis displacement slide (23).

10. A method for measuring liquid concentration with a variable optical range and a large range applicable to the liquid concentration measurement system with a variable optical range and a large range according to any one of claims 1 to 9, characterized in that: The following steps are involved: The light source (10) is turned on, and the optical signal output by the light source (10) is coupled to the Y-type optical fiber (13) through the transmission optical fiber (11). The optical splitter of the Y-type optical fiber (13) splits the received optical signal into detection light (15) and reference light (16); The position of the detection light path optical fiber (19) is adjusted by a high-precision linear motion module (18), the detection light (15) is incident on the liquid to be tested through the detection light path optical fiber (19), and the light signal absorbed by the liquid to be tested is detected by the detection light path detector (27), thereby obtaining the detection light intensity under different optical path lengths; Detecting the reference light (16) through a reference light path detector (26) to obtain a reference light intensity; The detection light intensity is corrected according to the optical path length, the detection light intensity and the reference light intensity by using the light signal fluctuation feedback correction method; According to multiple sets of optical path lengths and corrected detection light intensities, the least squares regression algorithm is used to fit the relationship between the corrected light intensity and the optical path length to calculate the concentration value of the liquid to be tested.

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