Variable-optical-path ultra-large-range liquid concentration measuring system and method

Abstract

The invention relates to a variable-optical-path ultra-wide-range liquid concentration measurement system and method, the system comprises 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 a light signal emitted by a light source into detection light and reference light; the detection light module detects a light signal absorbed by the to-be-detected liquid through a detection light path detector to obtain detection light intensity; the high-precision linear motion module is used for controlling a detection optical fiber to be inserted into a solution to be detected and gradually moves in an optical path length interval according to a set step length, so that high-precision micron-sized variable optical path length is realized; and the data analysis module corrects the detection light intensity through an optical signal fluctuation feedback correction method, fits the change relation of the light intensity along with the optical path length based on the multiple groups of optical path lengths and the corrected detection light intensity through a least square regression algorithm, and calculates the concentration value of the to-be-detected liquid. Compared with the prior art, the invention has the advantages of larger concentration measurement range and more accurate and more stable concentration measurement result.

Description

Technical Field

[0001] The 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 important significance in many fields such as industry and scientific research. Concentration detection based on absorption spectroscopy is a classic liquid concentration measurement technology, and its principle is Beer-Lambert law. This technology uses the absorption of light by the sample solution to quantitatively analyze the sample concentration. Specifically, when light passes through the solution, the substance in the solution absorbs part of the light, and the intensity of the absorbed light is proportional to the concentration of the substance. This non-invasive, fast and accurate concentration detection method is of great significance for promoting scientific research, environmental protection and improving product quality. Therefore, the spectrophotometer developed based on this principle has been widely used and developed rapidly. The spectrophotometer infers the concentration of the solution by measuring the absorbance of the solution. When performing quantitative analysis of the target in the solution, in order to ensure that the result is not affected by the detection container, the same absorption cell is used to hold the sample and reference solution respectively, or two absorption cells with the same paired blank transmittance are used to hold the sample and reference solution.

[0003] The traditional measurement method requires the use of a large-volume cuvette with a fixed optical path length (OPL) (usually 10 mm) and a small concentration measurement range (CN117169147A, CN115406885B) (Li Changhou. UV-visible spectrophotometer and its application [M]. Chemical Industry Press, 2010: 145-153.). The specific process is to first measure the absorbance of a blank solution (or a reference sample), and then measure the absorbance of a target solution by a standard curve calibration method (CN119290853A, CN119290853A). For high-concentration samples, due to the limitation of the range (CN117169147A), the traditional measurement method requires multiple dilutions, which easily leads to dilution errors and limited downstream applications (CN117169147A, CN101832916A). In summary, the solution detection of traditional standards has many shortcomings and limitations, such as the OPL fixation of the cuvette, calibration errors and measurement limitations, and requires a large amount of samples and time, and the concentration measurement range is small (one order of magnitude), which cannot adapt to the measurement of 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 to 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, and at the same time has 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 optical fiber and a Y-type optical 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 optical fiber through the transmission optical fiber. The optical splitter of the Y-type optical fiber divides the received optical signal into detection light and reference light. The detection light and the 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, an optical fiber vertical clamp and a detection platform. The detection light path optical fiber is fixedly connected to the high-precision linear motion module through the optical fiber vertical clamp. A detection container containing a liquid to be tested is placed on the upper part of the detection platform, and a detection light path detector is correspondingly arranged at the lower part. The end of the detection light path optical fiber is immersed in the liquid to be tested, and the detection light is incident into the liquid to be tested through the detection light path optical fiber. The detection light path detector detects the light signal absorbed by the liquid to be tested 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, and the OPL is continuously adjusted 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 end of the reference light and the target surface of the reference light path detector. The reference light path detector has the same specification 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 OPL and corrected detection light intensity, a least squares regression algorithm is used to fit the relationship between the corrected light intensity and 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 detected 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 the 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 tested 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-order derivative at OPL is used to obtain the concentration of the liquid to be measured.

[0017] Furthermore, the process of obtaining the initial position 0OPL 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 step by step in a high-precision driving manner. During this process, each time a step of insertion is completed, the detection optical path detector immediately collects the detection light intensity passing through the standard solution, and the reference optical path detector 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 detection light intensity change rate obtained by continuous multiple measurements is greater than or equal to the set threshold value compared with the initial fixed value change rate calculated theoretically, the position of the detection light path optical fiber is approximately 0 OPL.

[0022] The above process was repeated multiple times under the same concentration of standard solution, and the approximate 0OPL obtained each time was weighted averaged. The weight was determined comprehensively based on factors such as system stability and light intensity fluctuation during each measurement process, and the weighted average was 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 interval and the 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 OPL interval end optical path value 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 can accurately push 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 configured 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 uninterruptedly, and transmit the 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 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 optical fiber through the transmission optical fiber. The optical splitter of the Y-type optical fiber divides the received light signal into detection light and reference light;

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

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

[0033] Correct the detection light intensity according to 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 square 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 broadening 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 according to the light signal fluctuation feedback correction method. Based on multiple groups of precise light intensity data under different optical path, the least squares regression algorithm is used to fit the relationship between light intensity and optical path, overcoming the nonlinear deviation problem of Beer-Lambert's law under high concentration and large optical path (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 obtains the concentration of the liquid to be measured. This synergistic effect enables the present invention to achieve wide-range optical path adjustment and ensure the accuracy of concentration calculation under different ranges, perfectly meeting the concentration measurement requirements of large dynamic range and high-concentration samples, and is widely applicable to various industrial and scientific research fields.

[0037] 2. High-precision measurement: The present invention has unique advantages in achieving high precision. On the one hand, a high-precision stepper motor is used in conjunction with a precision transmission component. The motor is finely regulated by an internal subdivision circuit, and outputs a drive pulse corresponding to a 1-micron step length. 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 deviation of the displacement is strictly controlled within ±0.1 microns; on the other hand, it is equipped with a high-precision closed-loop feedback control system, which uses a high-resolution grating ruler to monitor the position in real time. The control system dynamically adjusts the motor drive pulse parameters according to the deviation, and accurately regulates in multiple dimensions to ensure high-precision motion accuracy throughout the 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 slight fluctuations in the light source power according to the reference light intensity and detection light intensity at the same time, 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, and providing stable guarantees for long-term and continuous measurements. Compared with traditional measurement methods, the stability is significantly improved.

[0039] 4. Improved operational convenience: The system and method of the present invention are simpler and more efficient in terms of operational procedures. The detection platform is set on the xy-axis displacement slide, and the position can be flexibly adjusted. The position of the high-precision linear motion module of the detection optical path can also be preliminarily adjusted through the coarse adjustment slide, and then further accurately adjusted according to the set step size and OPL interval in combination with the control program. Compared with the traditional complex operation of using large-volume cuvettes, frequent sample replacement and calibration, it 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 is a structural schematic diagram of a light source module;

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

[0044] Description 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 light 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 0.1mol / LH 2 SO 4 Solution (step length is 0.005mm) measurement data diagram,

[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 For different concentrations of potassium dichromate (K 2 Cr 2 O 7 ) solution measurement data diagram and measurement data analysis under different OPL (comparison of relative concentration calculation method results),

[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] Fig. 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] Fig.10 The system of the present invention is used to analyze different concentrations of potassium dichromate (K 2 Cr 2 O 7 ) solution measurement,

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

[0056] Fig.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 in conjunction with 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 path ultra-large range liquid concentration measurement system (fs-VOSM), the measurement principle of which is based on Beer-Lambert law. In Beer-Lambert law, the expression of the detection light intensity I is:

[0061] I=I 0 e -εcl (1)

[0062] Among them, I 0 represents the intensity of incident light, 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 concentration, and l represents OPL.

[0063] The expression of absorbance A is:

[0064] A=lg(I 0 / I)=εcl (2)

[0065] It can be seen that when the incident light intensity I 0 When constant, the absorbance is proportional to the OPL of the solution at the measured concentration.

[0066] However, in actual applications, there are interference factors and errors in the detection system and the output intensity of the light source It always fluctuates over time, and the fluctuation factor is recorded as According to the change of absorbance 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 beam splitter 2, and the fluctuation factor is corrected by the reference light path 3. The beam 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 detected light intensity I m (l, t) is measured by two detectors (reference light detector 5 and detection light detector 8) with the same parameter module. In the detection optical path 4, the detection optical fiber is controlled by a high-precision stepper motor 6 to move in different depths of the liquid sample 7 to meet different OPL requirements. 0 (t) is the incident light intensity, that is, the light intensity before the sample absorbs it, and we have:

[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. 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 which are 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. 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 with a core diameter of 600μm and 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 set between the transmission optical fiber 11 and the Y-type optical fiber 13, and the optical power can be controlled by changing the gap between the optical fiber connection ports.

[0076] The detection optical module 25 includes a detection optical path optical fiber 19 and a detection platform 22. In this embodiment, the high-precision linear motion module 18 is a detection optical path stepper motor, and the detection optical path optical fiber 19 is fixed to the detection optical path stepper motor by the optical fiber vertical clamp 20. The coarse adjustment slide 17 can greatly adjust the vertical position of the detection optical 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 arranged 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 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, and the detection light 15 is incident on the liquid to be tested through the detection light path optical fiber 19. The detection light path detector 27 detects the light signal absorbed by the liquid to be tested to obtain the detection light intensity. The end of the detection light path optical fiber 19 uses a bare optical fiber 14, which is convenient for the detection light 15 to be directly incident on the liquid to be tested. The opening of the detection container 21 can 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, which has the same parameters as the detection light path detector 27 and is used to detect the reference light 16 to obtain the reference light intensity. The reference light intensity can correct the influence caused by the fluctuation of the light source 10 and the interference factors in the subsequent calculation 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 for the standard substance acidic potassium dichromate (K 2 Cr 2 O 7 ) solution concentration is measured. In order to verify the performance of the above system, this embodiment is equipped with a standard substance potassium dichromate (K 2 Cr 2 O 7 ) solution and tested it to estimate the concentration. The solution samples were prepared and the concentration was measured in sequence. Potassium dichromate with a purity of ≥99.8% was diluted with 0.1 mol / L sulfuric acid solution to prepare 7 concentrations of acidic potassium dichromate solution, with the concentration range of 101.761 to 0.051 g / L. Then, 8 concentrations of acidic potassium dichromate solution were prepared and measured to evaluate the performance of the concentration estimation model.

[0079] After the system is assembled, the OPL must first be reduced to 0. 2 Cr 2 O 7 ) solution is added to the detection container 21 as the background solution, and the detection light path optical fiber 19 is gradually lowered by the high-precision linear motion module 18. During this process, each time a step of insertion is completed, the detection light path detector immediately collects the detection light intensity 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 continuous multiple measurements is compared with the initial fixed value change rate calculated theoretically, the deviation is greater than or equal to the set threshold value, then the position of the detection light path optical fiber is approximately 0OPL. In order to compare the system measurement performance, the sample solutions of the same batch are also measured on two other commercial UV-visible spectrophotometers. The difference is that before the spectrophotometer is measured, the same colorimetric dish needs to be used 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 under 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 by 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. It can be seen that the photoelectric response of the detection light module 25 and the system is stable and reliable, and the system has high sensitivity and resolution, which is comparable to the performance of commercial equipment.

[0081] This example also tested 0.1 mol / L sulfuric acid (H 2 SO 4 ) solution, which is a solvent with very low absorbance. The measurement step is 0.005mm and the OPL range is 0-0.5mm 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, (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 linear regression and coefficient of variation analysis results of the measured data show that the relative concentration measured by adding the reference light when the step length is 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 for potassium dichromate (K 2 Cr 2 O 7) solution, the step length is 0.005mm, and the OPL is 0~0.5mm. Potassium dichromate (K 2 Cr 2 O 7 ) The measurement data of 7 concentrations of solution are as follows Figure 8 As shown in (8a), (8a) is the measurement data under 0-0.5 mm 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. For this reason, the present embodiment performs a least squares regression on the measured data, and the results show 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) is the measurement data under 0-0.02 mm OPL, including the detection data under 5 OPLs. It can be seen that it is linear in the range of OPL close to 0. The slope of the curve needs to be solved to obtain the relative concentration value of the sample being tested.

[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 the relative error of the relative concentration values ​​is small. The two methods are mutually verified. Even if only the measurement results under 5 OPLs are used, they 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 this system. In order to evaluate the performance of this system (fs-VOSM), the same sample was measured using two commercial UV-visible spectrophotometers (UV2900, Shanghai Sunny Hengping Scientific Instrument Co., Ltd.; LAMBDA1050, PerkinElmer, USA). 2 Cr 2 O 7 ) solution. In order to measure samples with as high concentration as possible, a quartz cuvette with 1 mm OPL was used. The upper limit of the absorbance detected by the UV-visible spectrophotometer is usually around 4. It can be seen that when the concentration is high, it exceeds the upper limit of detection 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. The measurement results of the three systems were subjected to linear regression analysis, and the standard concentration curves obtained were as follows: Fig. 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), the concentration linear range is 0.051-101.761 g / L, which is better than the concentration linear range of the standard curves of the two commercial systems. Due to the limitations of the principle and system, commercial instruments cannot detect higher concentrations. Therefore, the concentration detection range of the system proposed in this embodiment is wider and the concentration estimation is more accurate.

[0085] In order to evaluate the actual concentration estimation capability of the above system, eight potassium dichromate (K 2 Cr 2 O 7 ) concentration sample, the measurement data under 0~0.02mm OPL is as follows Fig.10 (10a) shows that the relative concentration values ​​are shown in Tables 3 and 4. Substituting the results into the standard concentration curve equation for solution, the concentration prediction results detected under 5 OPLs are 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 Fig.10 As shown in (10b), the relative error of the system in concentration estimation is within ±3.6%, which proves that the system has good concentration estimation ability. In summary, the proposed concentration measurement system has a larger concentration measurement range. During the measurement process, data acquisition can be completed by detecting the light intensity under 5 OPLs within a very short OPL interval (0-0.02mm).

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

[0087]

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

[0089]

[0090]

[0091] Note: The data in italic format 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.

[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 by 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 data in italics are the results that are beyond 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 an 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. This 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) With the characteristic of ultra-short OPL measurement, the concentration can be measured by measuring 5 OPL data near the "0" optical path. The concentration value is obtained by performing least square regression on the measured data. This can meet the needs of direct high-precision measurement of high-concentration samples without the need for sample dilution preparation, thus achieving ultra-large dynamic range concentration measurement.

[0108] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and 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 comprises 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) which are connected in sequence, 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), 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 a 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 detected is placed on the upper part of the detection platform (22); 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 detected; the detection light (15) is incident into the liquid to be detected via the detection light path optical fiber (19); the light signal absorbed by the liquid to be detected is detected via 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 via the high-precision linear motion module (18), thereby continuously adjusting the optical path length with micron-level accuracy; The reference light module (24) comprises 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) to obtain a 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 groups of optical path lengths and corrected detection light intensities, a least squares regression algorithm is used to fit the variation 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 through 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 detected 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 effect 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 tested is as follows: According to multiple groups of optical path lengths and corrected detection light intensities, 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 value 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 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 optical path detector (27) immediately collects the detection light intensity that passes through the standard solution, and at the same time, the reference optical 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 detection light intensity change rate obtained by continuous multiple measurements is greater than or equal to the set threshold value compared with the initial fixed value change rate calculated theoretically, 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 0 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 0 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 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 length.

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 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 optical path detector (27) and the reference optical path detector (26) to complete light intensity data collection 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 coordination 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 that can accurately identify a displacement change of 1 micron as a key position feedback element, which is tightly attached to the high-precision linear motion module (18) to capture the actual position information of the detection optical fiber (19) in real time and continuously, and transmit the 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 control 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 variable optical range and ultra-large range liquid concentration measurement method applicable to the variable optical range and ultra-large range liquid concentration measurement system 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), and 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 into 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), so as to obtain 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; Correcting the detection light intensity 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 groups of optical path lengths and corrected detection light intensities, a 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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