Optical device and method for measuring the concentration of a solution

Abstract

The application discloses an optical device and method for measuring solution concentration, relates to the technical field of concentration measurement, and is based on classical refraction and dispersion theory, designs a prism-shaped light-transmitting container capable of causing light path to be translated, and builds an optical device for automatically measuring solution concentration on the basis of the container. The application firstly measures the refractive index of a transparent solution with a known concentration by using the device, establishes a "refractive index-concentration" relationship model, then measures the refractive index of a solution with an unknown concentration, and realizes high-precision measurement of the solution concentration by combining the established quantitative relationship. On the basis, the application also realizes synchronous measurement of the concentration of each component of a multi-solute mixed solution by using two lasers with different wavelengths, provides a simple and effective solution for measurement of unknown solution concentration, is high in automation and precision, convenient for industrialization, and also provides a novel and interesting experimental scheme for teaching of refraction and dispersion theory.

Description

Technical Field

[0001] This invention relates to the field of concentration measurement technology, specifically to an optical device and method for measuring solution concentration based on classical refraction and dispersion theory. Background Technology

[0002] From the use of pesticides in agricultural production to various fuels in the aerospace industry, solutions are ubiquitous, and accurately measuring solution concentration remains an indispensable and crucial topic in production, daily life, and scientific research. Currently, numerous methods exist for measuring solution concentration, including those based on ultrasound, resonant cavities, and conductivity principles. However, these methods generally suffer from drawbacks such as complex operation, high cost, large physical volume, and low accuracy, hindering laboratory teaching and widespread application. Furthermore, existing technologies rarely involve methods for simultaneously determining the concentrations of multiple solutes in a transparent solution.

[0003] Therefore, there is an urgent need to design a concentration measurement device with high accuracy, fast response speed, small size, simple operation, and automation, so as to realize the measurement of the concentration of a single solution, the measurement of the concentration of each component in a mixed solution, and the real-time measurement of dynamic solutions. Summary of the Invention

[0004] The purpose of this invention is to provide an optical device and method for measuring solution concentration, which aims to overcome the aforementioned problems existing in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] An optical device for measuring solution concentration includes a light-transmitting container, which has an incident surface, an exit surface, and a water tank. The water tank includes a first refractive surface and a second refractive surface. The incident surface, the first refractive surface, the second refractive surface, and the exit surface are arranged sequentially along the light path. The incident surface and the exit surface are parallel to each other, the first refractive surface and the second refractive surface are parallel to each other, and an angle is formed between the incident surface and the first refractive surface.

[0007] Furthermore, the angle formed between the incident surface and the first refracting surface simultaneously satisfies the following system of equations:

[0008] n0sinθ0=n1sinθ1;

[0009] n0sinθ0=1.6000sinθ2;

[0010] 0.3L≤D(tanθ1-tanθ2)cosθ0≤0.5L;

[0011] Wherein, θ0 is the angle formed between the incident surface and the first refractive surface, which is also the incident angle of the laser at the first refractive surface when the laser is perpendicularly incident on the incident surface; θ1 is the refraction angle of the laser at the first refractive surface when the water tank is filled with a reference solution; θ2 is the refraction angle of the laser at the first refractive surface when the water tank is filled with a solution with a refractive index of 1.6000; n0 is the refractive index of the transparent container; n1 is the refractive index of the reference solution; D is the straight-line distance between the first refractive surface and the second refractive surface; and L is the length of the photosensitive strip of the displacement sensor.

[0012] In one specific embodiment, the transparent container is made of K9 glass, n0 = 1.5168, the reference solution is deionized water, n1 = 1.3330, D = 8.00 mm, L = 12.00 mm, and D(tanθ1-tanθ2)cosθ0 = 0.5 L; at this time, according to the above equation set, θ0 = 56.4° can be obtained.

[0013] Furthermore, the light-transmitting container includes a first K9 glass block, a first slat, a second slat, a third slat, and a second K9 glass block. Both the first and second K9 glass blocks are triangular prisms. The two facets of the first K9 glass block are the incident surface and the first refractive surface, respectively, while the two facets of the second K9 glass block are the second refractive surface and the exit surface, respectively. The first, second, and third slats are all elongated strips of the same thickness, and are arranged in a U-shape between the first and second K9 glass blocks.

[0014] Furthermore, the first K9 glass block, the first slat, the second slat, the third slat, and the second K9 glass block are fixed together by gluing.

[0015] Preferably, the first, second, and third strips are all made of K9 glass.

[0016] Furthermore, it includes a laser arranged along the light path, the light-transmitting container, and a displacement sensor; it also includes a data acquisition card and a computer, wherein the displacement sensor, the data acquisition card, and the computer are electrically connected in sequence, the data acquisition card is used to acquire the electrical signals fed back by the displacement sensor, and the computer is used to process and analyze the electrical signals.

[0017] Furthermore, it also includes a thermometer used to detect the temperature of the solution inside the transparent container.

[0018] The present invention also discloses a method for measuring solution concentration, using any of the optical devices described in the present invention to measure solution concentration, comprising the following steps:

[0019] 1) Turn on the displacement sensor;

[0020] 2) Turn on the laser;

[0021] 3) Add the reference solution to the water tank in the transparent container;

[0022] 4) Calibrate the optical device so that the laser emitted by the laser enters perpendicularly from the incident surface of the light-transmitting container and exits from the exit surface, illuminating the center position of the photosensitive strip of the displacement sensor.

[0023] It also includes step 5) single solution concentration measurement, specifically:

[0024] (5.1) Prepare solutions of different concentrations, such that the concentrations of each solution are set in a gradient and are known;

[0025] (5.2) Add each solution to the water tank of the transparent container and measure the refractive index of each solution using an optical device;

[0026] (5.3) The nc relationship of each solution is calibrated to obtain the nc calibration curve; the fitting formula of the obtained nc calibration curve is input into the computer; where n is the refractive index and c is the concentration;

[0027] (5.4) Add the test solution of unknown concentration into the water tank of the light-transmitting container, and measure the refractive index of the test solution by optical device;

[0028] (5.5) The computer calculates the concentration of the solution to be tested based on the nc calibration curve and the refractive index of the solution to be tested.

[0029] Furthermore, it also includes step 6) measuring the concentration of each component in the mixed solution, specifically:

[0030] The mixed solution is composed of m kinds of solutes, and the laser includes m kinds of lasers with different wavelengths;

[0031] (6.1) Using m different wavelengths of laser light, plot the nc calibration curves of each solute under the irradiation of m different wavelengths of laser light according to step 5);

[0032] (6.2) Input the fitting formula of the obtained nc calibration curve into the computer;

[0033] (6.3) Add the mixed solution of unknown concentration and the same type of solute to the water tank of the transparent container, and measure the refractive index of the mixed solution under the irradiation of m different wavelengths of laser by optical device;

[0034] (6.4) The computer calculates the concentration of each solute in the mixed solution to be tested based on the fitting formula and the m refractive indices of the mixed solution to be tested.

[0035] Furthermore, it also includes step 7) dynamic solution concentration measurement, specifically:

[0036] (7.1) Plot the nc calibration curve of a single solution containing component A according to step 5), and input the fitting formula into the computer;

[0037] (7.2) Prepare a first solution and a second solution; wherein, the first solution is a single solution containing component A with a mass ratio of X (wt%); the second solution is a single solution containing component A with a mass ratio of Y (wt%), and Y≠X;

[0038] (7.3) Add the first solution into the water tank of the transparent container, measure the refractive index using an optical device, and calculate the concentration value based on the refractive index and the nc calibration curve in step (7.1).

[0039] (7.4) Inject L (ml) of the second solution into the transparent container every T (s) using a pipette, and observe and measure the real-time changes in concentration.

[0040] Compared with the prior art, the beneficial effects of the present invention are:

[0041] This invention, based on classical refraction and dispersion theory, designs a prism-shaped transparent container that allows for optical path translation, and uses this as the basis to build an automated optical device for measuring solution concentration. First, this invention uses this device to measure the refractive index of various transparent solutions with known concentrations, such as NaCl, glucose, and alcohol solutions, establishing a "refractive index-concentration" relationship model. Then, by measuring the refractive index of solutions with unknown concentrations and combining it with the established quantitative relationship, high-precision measurement of solution concentration is achieved. Furthermore, this invention utilizes two laser beams of different wavelengths to simultaneously measure the concentrations of each component in a multi-solute mixture solution. For unknown solutions with continuously changing concentrations, real-time concentration monitoring is achieved through computer software. This invention provides a simple and effective solution for measuring the concentration of unknown solutions, offering high automation, high precision, and ease of industrial application. It also provides a novel and interesting experimental scheme for teaching refraction and dispersion theory.

[0042] Specifically, the innovation of this invention lies in:

[0043] (1) Design a prism-shaped light-transmitting container to eliminate the systematic error caused by the deformation of the light spot due to the tilted emission of light from the prism.

[0044] (2) Based on the principle of dispersion, a linear equation system is established to realize the measurement of the concentration of each component in a multi-solute mixed solution.

[0045] (3) The automation of data measurement and processing is achieved by using computer programs, which is simpler to operate than traditional methods.

[0046] (4) The optical method has the characteristic of fast response to realize real-time monitoring of changes in solution concentration with high precision. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the optical device in this invention.

[0048] Figure 2 This is a top view of the light-transmitting container, displacement sensor, and their optical path in this invention.

[0049] Figure 3 This is a disassembly diagram of the light-transmitting container in this invention.

[0050] Figure 4 This is a top view of a right-angled triangular container, a displacement sensor, and its optical path.

[0051] Figure 5 This is a top view of a cuboid container, a displacement sensor, and its optical path.

[0052] Figure 6 This is the core code for data acquisition in this invention.

[0053] Figure 7 This is the nc calibration curve of NaCl solution under red light.

[0054] Figure 8 This is the nc calibration curve of glucose solution under red light.

[0055] Figure 9 This is the nc calibration curve of the alcohol solution under red light.

[0056] Figure 10 The nc calibration curves of NaCl solution under red and green light are shown.

[0057] Figure 11 The nc calibration curves of glucose solution under red and green light are shown.

[0058] Figure 12 This is the ct curve for NaCl solution.

[0059] Figure 13 This is a curve comparing the measured values ​​and theoretical values ​​of NaCl solution at various concentration levels. Detailed Implementation

[0060] Specific embodiments of the present invention will now be described with reference to the accompanying drawings. Many details are described below to provide a comprehensive understanding of the invention; however, those skilled in the art will be able to implement the invention without these details.

[0061] like Figure 1As shown, an optical device for measuring solution concentration includes a laser 1, a light-transmitting container 2, a displacement sensor 3, a data acquisition card 4, a computer 5, and a thermometer 6. The laser 1, light-transmitting container 2, and displacement sensor 3 are arranged along the light path. The displacement sensor 3, data acquisition card 4, and computer 5 are electrically connected in sequence. The data acquisition card 4 is used to acquire the electrical signals fed back by the displacement sensor 3, and the computer 5 is used to process and analyze the electrical signals. The light-transmitting container 2 is equipped with a water tank 20, and the thermometer 6 extends into the water tank 20 to detect the temperature of the solution inside.

[0062] The key lies in designing a suitable light-transmitting container so that the position of the light spot before and after the light shift can be accurately sensed and recorded by a displacement sensor. To this end, the inventors designed three container models.

[0063] like Figure 4 As shown, (1) Right-angled triangular container: As is well known, the dispersion experiment of a prism is a very important experiment in the history of physics; therefore, the initial design scheme was a right-angled triangular container. However, during the experiment, it was found that the model had two main problems. ① The shape of the light spot on the receiving surface of the displacement sensor changes with the change of the emission angle, which directly leads to the inability to accurately measure the displacement X1 between light spot A and light spot O; ② For the triangular container, in addition to measuring the light spot displacement X1, it is also necessary to measure the vertical distance D1 from the container's emission point C to the displacement sensor in order to measure the refractive index, but D1 is difficult to measure directly and accurately, causing measurement error.

[0064] like Figure 5 As shown, (2) rectangular container: In order to deflect the light, when using this container, the incident light must be kept at a certain angle, which makes the operation cumbersome and difficult to adjust accurately.

[0065] To overcome the problems of the two container models mentioned above, this invention uses a third container model for measurement, as detailed below:

[0066] like Figures 1 to 3 As shown, the light-transmitting container 2 includes an incident surface 21 and an exit surface 24, and the water tank includes a first refractive surface 22 and a second refractive surface 23. The incident surface 21, the first refractive surface 22, the second refractive surface 23, and the exit surface 24 are arranged sequentially along the light path. The incident surface 21 and the exit surface 24 are parallel to each other, the first refractive surface 22 and the second refractive surface 23 are parallel to each other, and an angle θ0 is formed between the incident surface 21 and the first refractive surface 22.

[0067] like Figure 1 and Figure 2As shown, based on the fact that the refractive index of most solutions at room temperature is between 1.3330 and 1.6000, and in order to maximize the measurable range of the photosensitive strip, the light needs to be refracted by two solutions with refractive indices of n1 (n1≥1.3330) and 1.6000 so that it just hits the midpoint and one end point of the photosensitive strip. Let point o be the midpoint, point a be one end point, i.e., oa=0.5L, and let points c and d be the exit points. Then, based on the above conditions, the above system of equations can be listed as follows:

[0068] n0sinθ0=n1sinθ1;

[0069] n0sinθ0=1.6000sinθ2;

[0070] 0.3L≤D(tanθ1-tanθ2)cosθ0≤0.5L;

[0071] Wherein, θ0 is the angle formed between the incident surface and the first refractive surface, which is also the incident angle of the laser at the first refractive surface when the laser is perpendicularly incident on the incident surface; θ1 is the refraction angle of the laser at the first refractive surface when the water tank is filled with a reference solution; θ2 is the refraction angle of the laser at the first refractive surface when the water tank is filled with a solution with a refractive index of 1.6000; n0 is the refractive index of the transparent container; n1 is the refractive index of the reference solution; D is the straight-line distance between the first refractive surface and the second refractive surface; and L is the length of the photosensitive strip of the displacement sensor.

[0072] In one specific embodiment, based on the fact that the refractive index of most solutions at room temperature is n1 = 1.3330, and the length L of the photosensitive strip of the motion sensor used in the experiment is 12 mm; in the light-transmitting container 2, D = 8 mm, and a K9 glass container is used with a refractive index n0 = 1.5168. Therefore, in order to maximize the measurable range of the photosensitive strip, the light needs to be refracted by the two solutions with refractive indices of 1.3330 and 1.6000 so that it just illuminates the midpoint and one end point of the photosensitive strip. Based on the above conditions, the above set of equations can be listed as follows:

[0073] n0sinθ0=1.3330sinθ1;

[0074] n0sinθ0=1.6000sinθ2;

[0075] 8.00(tanθ1-tanθ2)cosθ0=0.5L=6.00;

[0076] The calculation yields θ0 = 56.4°.

[0077] like Figure 2 and Figure 3As shown, in one specific embodiment, the light-transmitting container 2 includes a first K9 glass block 201, a first slat 202, a second slat 203, a third slat 204, and a second K9 glass block 205. Both the first K9 glass block 201 and the second K9 glass block 205 are triangular prisms. The two facets of the first K9 glass block 201 are the incident surface 21 and the first refractive surface 22, respectively. The two facets of the second K9 glass block 205 are the second refractive surface 23 and the exit surface 24, respectively. The first slat 202, the second slat 203, and the third slat 204 are all elongated strips with the same thickness. The first K9 glass block 201 and the second K9 glass block 205 are arranged in a U-shape between the first slat 202, the second slat 203, and the third slat 204.

[0078] like Figure 2 and Figure 3 As shown, specifically, the first K9 glass block 201, the first strip 202, the second strip 203, the third strip 204, and the second K9 glass block 205 are fixed together by adhesive bonding. Preferably, the first strip 202, the second strip 203, and the third strip 204 are all K9 glass products. Of course, the first strip 202, the second strip 203, and the third strip 204 can also be integrally formed U-shaped components.

[0079] like Figure 2 and Figure 3 As shown, the light-transmitting container 2 assembled using the above structure is easy to process for each optical surface, especially the first refractive surface 22 and the second refractive surface 23; and the straight-line distance D between the first refractive surface and the second refractive surface can be precisely set by processing the thickness of the first strip 202, the second strip 203 and the third strip 204. It is also easy to change the straight-line distance D between the first refractive surface and the second refractive surface by changing the first strip 202, the second strip 203 and the third strip 204 with different thicknesses. The assembly is flexible and the applicability is strong.

[0080] A position-sensitive detector (PSD) is a photoelectric device that is sensitive to the position of a light spot and can measure its coordinates. PSDs have fast response speeds, high position resolution, and their output current signal is independent of light intensity, depending only on the position of the light. The displacement sensor used in this invention is a high-precision one-dimensional PSD displacement sensor (including a signal processing module), model DRX-1DPSD-0A02. Its working principle is as follows: the midpoint of the photosensitive strip is the origin, and one side of the origin is taken as the positive direction. The output signal X, after being amplified and processed by the signal processing module, is... c X H The distance from the laser spot to the midpoint can be calculated by substituting the values ​​into the following formula.

[0081]

[0082] The displacement sensor includes a signal processing module that amplifies and processes the output minute current signal into a voltage signal. Its internal circuit board uses a four-layer design and can output both the amplified and processed signal. The module also features a built-in noise background zero-point adjustment circuit to improve measurement accuracy. The functions of each pin are shown in Table 1.

[0083] Table 1. Functions of each pin on the displacement sensor signal processing board

[0084] P1 pin GND <![CDATA[X1]]> <![CDATA[X2]]> Function Grounding Level 1 IV amplified signal Level 1 IV amplified signal P3 pin GND <![CDATA[X H ]]> <![CDATA[X c ]]> Function Grounding Signal after operation Signal after operation

[0085] The data acquisition card 4 used in this invention has a maximum number of 8 channels, and two of these channels are used to measure the voltage V output by the displacement sensor 3. c (i.e. X) c Voltage V H (i.e. X) H The analog signal is collected and then connected to computer 5 via a data cable, so that the collected analog signal is transmitted to computer 5 in the form of a digital signal.

[0086] The software used by Computer 5 includes LabVIEW, Origin, and Python. LabVIEW is used for backend programming to implement data acquisition and visualization, while Origin and Python are mainly used for plotting and image processing. Specifically, by independently developing an automated measurement system using the LabVIEW programming language, it is possible to perform real-time calculations, mapping, and other processing on the acquired digital signals, and visualize the processing results in real time, ultimately achieving high-response-speed real-time monitoring of the experimental measurements. More specifically, through methods such as... Figure 6 The code shown allows setting initialization parameters for the automated measurement system, such as the data storage path, number of sampling points, and sampling frequency, while also meeting the requirements for data acquisition V in this experiment. c and V H The requirement for two output voltages.

[0087] The present invention also discloses a method for measuring solution concentration, which uses an optical device with the structure described above to measure solution concentration, and includes the following steps:

[0088] 1) Turn on displacement sensor 3. Specifically, turn on the regulated power supply (not shown in the figure) to power displacement sensor 3, and adjust the output voltage of the regulated power supply to 12V to enable displacement sensor 3 to work normally.

[0089] 2) Turn on the laser. Specifically, turn on the laser switch and adjust the laser power to 1-5mW.

[0090] 3) Add the reference solution to the water tank 20 of the transparent container 2. Specifically, the reference solution is deionized water. Use a dropper to inject about 8 mL of deionized water into the glass container, control the room temperature at 25°C, and use a thermometer 6 to check whether the temperature of the deionized water is stable. The room temperature is controlled at around 25°C by air conditioning.

[0091] 4) The laser emitted by the laser is directed perpendicularly into the light-transmitting container from the incident surface and out from the exit surface, illuminating the center of the photosensitive strip of the displacement sensor. Specifically, this includes the following sub-steps:

[0092] 4.1) After the deionization temperature stabilizes, place the plane mirror tightly against the incident surface 21 of the light-transmitting container 2;

[0093] 4.2) Adjust laser 1 until the reflected laser spot coincides with the laser emission port of laser 1; preferably, laser 1 is mounted on a three-dimensional adjustment frame for easy adjustment.

[0094] 4.3) Remove the plane mirror, and the laser beam enters the light-transmitting container 2 perpendicularly from the incident surface 21, and then exits from the exit surface 24 to the photosensitive strip 31 of the displacement sensor 3.

[0095] 4.4) Adjust the displacement sensor 3 to change the position of the laser point on the photosensitive strip 31, and simultaneously measure the voltage V output by the displacement sensor 3. c When the output voltage V c When the value is 0, stop adjusting and fix displacement sensor 3; at this time, the laser point is exactly at the center of photosensitive strip 31. The voltage V output by displacement sensor 3 is measured using a numerical multimeter. c Take measurements.

[0096] 5) Single solution concentration measurement, specifically including the following sub-steps:

[0097] (5.1) Prepare solutions of different concentrations, such that the concentrations of each solution are set in a gradient and are known;

[0098] (5.2) Add each solution to the water tank of the transparent container and measure the refractive index of each solution using an optical device;

[0099] (5.3) The nc relationship of each solution is calibrated to obtain the nc calibration curve; the fitting formula of the obtained nc calibration curve is input into computer 5; where n is the refractive index and c is the concentration;

[0100] (5.4) Add the test solution of unknown concentration into the water tank of the light-transmitting container, and measure the refractive index of the test solution by optical device;

[0101] (5.5) The computer calculates the concentration of the solution to be tested based on the nc calibration curve and the refractive index of the solution to be tested.

[0102] In one specific embodiment, three common transparent solutions (NaCl, glucose, and ethanol) were selected for concentration measurement. The calibration process for the nc relationship is illustrated below using NaCl solution as an example: First, 15 groups of NaCl solutions with different concentrations, ranging from 0 wt% to 20 wt%, were prepared for use. During preparation, deionized water and NaCl crystals were weighed using an electronic balance with an accuracy of 0.0001 g, and the small beakers containing the solutions were covered with glass slides to prevent evaporation.

[0103] like Figure 1 , Figure 2 and Figure 7 As shown, a red laser (wavelength 695nm, power adjustable from 0-50mW) was used as laser 1. After calibration and zeroing, the reference solution in the transparent container 2 was replaced with a prepared NaCl solution. The computer 5 was set to set the number of sampling points of the data acquisition card 4 to 1000 and the sampling frequency to 10Hz, and the measurement began. The computer 5 automatically recorded the voltage V output by the displacement sensor 3 for each group of NaCl solutions. c and V H After recording, computer 5 sequentially calculated the distance x from the laser spot to the midpoint and the refractive index n of 15 different concentrations of NaCl solutions, as shown in Table 2. After each solution was measured, the transparent container 2 was washed once with distilled water to reduce the influence of residual solution on the measurement results.

[0104] Table 2. Actual calibration results of NaCl solution.

[0105] Solution number <![CDATA[Theoretical concentration c 理 (wt%)]]> <![CDATA[V C (V)]]> <![CDATA[V H (V)]]> Refractive index n 1 1.6775 -0.1235 2.617 1.3354 2 2.7988 -0.2001 2.600 1.3374 3 4.0649 -0.2851 2.607 1.3396 4 5.0529 -0.3487 2.606 1.3415 5 6.0892 -0.4203 2.658 1.3432 6 7.6987 -0.5116 2.629 1.3461 7 9.0462 -0.5995 2.674 1.3487 8 10.0170 -0.6550 2.656 1.3506 9 11.2948 -0.7362 2.708 1.3531 10 12.6257 -0.8105 2.729 1.3553 11 14.2523 -0.9028 2.764 1.3585 12 15.1918 -0.9699 2.818 1.3600 13 16.9531 -1.0842 2.880 1.3635 14 17.8710 -1.1306 2.867 1.3656 15 20.4564 -1.2966 2.968 1.3707

[0106] The theoretical concentrations in Table 2 were calculated as follows: The masses of NaCl crystals and the reference solution were weighed separately, and the concentrations were calculated according to the formula... The theoretical concentration of the solution was calculated.

[0107] Based on Table 2, plot the nc calibration curve of NaCl solution under red light (wavelength 695 nm), as follows: Figure 7 As shown, it exhibits a linear variation, and the fitting formula is:

[0108] n = 0.00187c + 1.3319

[0109] (R 2 =0.9995)

[0110] Its linear correlation coefficient reached over 0.999, indicating a good linear relationship, which shows that the concentration and refractive index of the NaCl solution are linearly related.

[0111] Subsequently, five more NaCl solutions of different concentrations were prepared. Based on the above nc calibration curve, their refractive index and concentration values ​​were measured by computer and compared with their actual concentrations. The specific data are shown in Table 3.

[0112] Table 3. Measured and Actual Values ​​of NaCl Solutions at Different Concentrations

[0113] Solution number Refractive index n <![CDATA[Measured concentration c 测 (wt%)]]> <![CDATA[Actual concentration c 实 (wt%)]]> <![CDATA[Relative error E c > 1 1.3402 4.41 4.2916 2.7％ 2 1.3503 9.83 9.9328 1.1％ 3 1.3453 7.14 7.0741 1.0％ 4 1.3552 12.43 12.6543 1.8％ 5 1.3607 15.36 15.5801 1.5％

[0114] As shown in Table 3, the errors of all five sets of data are within 3%. This indicates that the experimental results agree well with the theoretical results.

[0115] like Figure 1 , Figure 2 and Figure 8 As shown, a red laser (wavelength 695nm, power adjustable from 0-50mW) was used as laser 1. After calibration and zeroing, the reference solution in the transparent container 2 was replaced with the prepared glucose solution. The number of sampling points on the data acquisition card 4 was set to 1000 and the sampling frequency to 10Hz via computer 5, and the measurement began. Computer 5 automatically recorded the voltage V output by the displacement sensor 3 for each group of glucose solutions. c and V H After recording, computer 5 sequentially calculated the distance x from the laser spot to the midpoint and the refractive index n of 15 groups of glucose solutions with different concentrations, as shown in Table 4. After each group of solutions was measured, the transparent container 2 was washed once with distilled water to reduce the influence of residual solution on the measurement results.

[0116] Table 4. Actual calibration results of glucose solution.

[0117] Solution number <![CDATA[Theoretical concentration c 理 (wt%)]]> <![CDATA[V c (V)]]> <![CDATA[V H (V)]]> Refractive index n 1 1.9223 -0.1143 2.553 1.3352 2 3.0127 -0.1774 2.554 1.3368 3 4.5186 -0.2603 2.541 1.3392 4 5.9495 -0.3451 2.562 1.3415 5 7.1417 -0.4122 2.595 1.3434 6 8.2713 -0.4692 2.593 1.3450 7 9.9582 -0.5617 2.617 1.3479 8 11.1532 -0.6074 2.575 1.3499 9 12.4537 -0.6905 2.666 1.3517 10 13.8073 -0.7603 2.672 1.3541 11 14.4381 -0.8508 2.901 1.3547 12 16.3758 -0.9826 2.994 1.3579 13 17.2403 -1.0554 3.059 1.3596 14 18.3870 -1.1217 3.073 1.3616 15 19.8147 -1.2288 3.152 1.3640

[0118] The nc calibration curve for glucose solution can be obtained from Table 4, as follows: Figure 8 As shown.

[0119] like Figure 8 As shown, the nc calibration curve of the glucose solution exhibits a linear change, and the fitting formula is:

[0120] n = 0.00160c + 1.3319

[0121] (R 2 =0.9996)

[0122] Its linear correlation coefficient reached over 0.999, indicating a good linear relationship, which shows that the concentration and refractive index of the glucose solution are linearly related.

[0123] Subsequently, five additional glucose solutions of different concentrations were prepared. Based on the above nc calibration curve, their refractive index and concentration values ​​were measured by computer 5 and compared with their actual concentrations. The specific data are shown in Table 5.

[0124] Table 5. Measured and Actual Values ​​of Glucose Solutions at Different Concentrations

[0125] Solution number Refractive index n <![CDATA[Measured concentration c 测 (wt%)]]> <![CDATA[Actual concentration c 实 (wt%)]]> <![CDATA[Relative error E c > 1 1.3383 3.99 4.0552 1.7％ 2 1.3430 6.89 7.0703 2.7％ 3 1.3477 9.81 10.0117 2.0％ 4 1.3520 12.50 12.6465 1.2％ 5 1.3570 15.65 15.5073 1.0％

[0126] As shown in Table 5, the errors of all five sets of data are within 3%. This indicates that the experimental results agree well with the theoretical results.

[0127] like Figure 1 , Figure 2 and Figure 9 As shown, a red laser (wavelength 695nm, power adjustable from 0-50mW) was used as laser 1. After calibration and zeroing, the reference solution in the transparent container 2 was replaced with the prepared alcohol solution. The number of sampling points on the data acquisition card 4 was set to 1000 and the sampling frequency to 10Hz via computer 5, and the measurement began. Computer 5 automatically recorded the voltage V output by the displacement sensor 3 for each group of alcohol solutions. c and V H After recording, computer 5 sequentially calculates the distance x from the laser spot to the midpoint and the refractive index n of 10 groups of alcohol solutions with different concentrations, as shown in Table 6. After each group of solutions is measured, the transparent container 2 is washed once with distilled water to reduce the influence of residual solution on the measurement results.

[0128] Table 6. Actual Measurement Results of Alcohol Solution

[0129] Solution number <![CDATA[Theoretical concentration c 理 (wt%)]]> <![CDATA[V C (V)]]> <![CDATA[V H (V)]]> Refractive index n 1 13.6567 -0.1035 3.081 1.3406 2 23.3873 -0.1801 3.127 1.3473 3 27.5642 -0.2177 3.097 1.3505 4 33.2709 -0.2469 3.074 1.3527 5 38.7889 -0.2734 3.052 1.3549 6 49.4413 -0.3371 3.145 1.3592 7 61.2009 -0.3751 3.153 1.3621 8 69.1991 -0.3845 3.127 1.3634 9 85.0816 -0.3899 3.133 1.3638 10 100.0000 -0.3540 3.125 1.3610 .

[0130] As shown in Table 6, the alcohol solution concentration is relatively high. If a linear fit is still performed on the calibration curve under these conditions, the error will be very large. Therefore, this invention uses a quadratic polynomial to fit the data, such as... Figure 9 As shown.

[0131] like Figure 9 As shown, the nc calibration curve of the alcohol solution exhibits a parabolic change, and the fitting formula is:

[0132] n = -0.00000559c 2 +0.000869c+1.3300

[0133] (R 2 =0.998)

[0134] The correlation coefficient is above 0.99, indicating that the concentration and refractive index of the alcohol solution have a nonlinear relationship.

[0135] Subsequently, three more groups of alcohol solutions with different concentrations were prepared. Based on the above nc calibration curve, their refractive index and concentration values ​​were measured by computer 5 and compared with their actual concentrations. The specific data are shown in Table 7.

[0136] Table 7. Measured and Actual Values ​​of Alcohol Solutions at Different Concentrations

[0137] Solution number Refractive index n <![CDATA[Measured concentration c 测 (wt%)]]> <![CDATA[Actual concentration c 实 (wt%)]]> <![CDATA[Relative error E c > 1 1.3535 20.43 20.8233 1.7％ 2 1.3604 34.73 36.0023 4％ 3 1.3646 53.21 54.9363 4％

[0138] As shown in Table 7, the errors of the three sets of data are all within 4%, and the experimental results agree well with the theoretical results. Therefore, the device constructed in this invention is applicable to the concentration measurement of transparent solutions where the relationship between concentration and refractive index is linear or non-linear.

[0139] 6) Measurement of the concentration of each component in the mixed solution, specifically including the following sub-steps:

[0140] The mixed solution is composed of m kinds of solutes, and the laser includes m kinds of lasers with different wavelengths;

[0141] (6.1) Using m different wavelengths of laser light, plot the nc calibration curves of each solute under the irradiation of m different wavelengths of laser light according to step 5);

[0142] (6.2) Input the fitting formula of the obtained nc calibration curve into the computer 5;

[0143] (6.3) Add the mixed solution of unknown concentration and the same type of solute to the water tank of the transparent container, and measure the refractive index of the mixed solution under the irradiation of m different wavelengths of laser by optical device;

[0144] (6.4) The computer calculates the concentration of each solute in the mixed solution to be tested based on the fitting formula and the m refractive indices of the mixed solution to be tested.

[0145] The phenomenon that the refractive index of a medium changes with the frequency of incident light is called "dispersion." According to dispersion theory, different wavelengths of light have different refractive indices in the same solution, and the same wavelength of light also has different refractive indices in different solutions. Assume a mixed solution contains m types of solutes, and a laser can emit m different wavelengths of laser light. If the wavelength λ is measured... i The relationship between the refractive index and concentration of a single solution of the j-th solute under laser irradiation is as follows:

[0146] n ij =k ij c i +b ij (1≤i≤m,1≤j≤m)

[0147] Then at wavelength λ iUnder laser irradiation, the relationship between the refractive index of the mixed solution and the concentration of each component is as follows:

[0148]

[0149] The above equation is a system of m linear equations. Therefore, by measuring the refractive index of the mixed solution under light of different wavelengths, the concentrations of each component can be determined.

[0150] like Figure 1 , Figure 2 , Figure 10 and Figure 11 As shown, in one specific embodiment, the concentration of each component is measured using a mixed solution of NaCl and glucose as an example. Laser 1 includes a red laser (wavelength 695nm, power adjustable from 0-50mW) and a green laser (wavelength 532nm, power adjustable from 0-50mW). First, after zeroing with the red laser, the nc calibration curves of the NaCl solution and glucose solution under red light (wavelength 695nm) are plotted using the above calibration method. Then, after zeroing with the green laser (wavelength 532nm), the nc calibration curves of the NaCl solution and glucose solution under green light (wavelength 532nm) are plotted using the above calibration method.

[0151] like Figure 10 and Figure 11 The fitting formulas for the four obtained calibration curves are as follows:

[0152] NaCl, red light: n = 0.00187c1 + 1.3319

[0153] NaCl, green light: n = 0.00193c1 + 1.3323

[0154] Glucose, red light: n = 0.00160c² + 1.3319

[0155] Glucose, green light: n = 0.00173c² + 1.3320

[0156] Then according to the formula The relationship between the refractive index of the mixed solution under red and green light and the concentration of each component can be obtained as follows:

[0157] Under red light: n1 = 0.00187c1 + 0.00160c2 + 1.3319

[0158] Under green light: n² = 0.00193c₁ + 0.00173c₂ + 1.3322

[0159] And input it into computer 5.

[0160] Finally, three different concentrations of NaCl-glucose mixed solutions were randomly prepared, and the refractive index of the three solutions under red and green light was measured. The concentration values ​​of each component of the mixed solution were calculated, as shown in Table 8.

[0161] Table 8. Measured and Actual Concentrations of Each Component in the Mixed Solution

[0162]

[0163] As shown in Table 8, the measurement method for the mixed solution is novel and the relative errors are small, which is in line with expectations.

[0164] 7) Dynamic solution concentration measurement, specifically including the following sub-steps:

[0165] (7.1) Plot the nc calibration curve of a single solution containing component A according to step 5) and input it into computer 5;

[0166] (7.2) Prepare a first solution and a second solution; wherein, the first solution is a single solution containing component A with a mass ratio of X (wt%); the second solution is a single solution containing component A with a mass ratio of Y (wt%), and Y≠X;

[0167] (7.3) Add the first solution into the water tank of the light-transmitting container, measure the refractive index using an optical device, and calculate the concentration value based on the refractive index and the nc calibration curve in step (7.1).

[0168] (7.4) Inject L (ml) of the second solution into the transparent container every T (s) using a pipette, and observe and measure the real-time changes in concentration.

[0169] like Figure 1 , Figure 2 , Figure 12 and Figure 13 As shown, in one specific embodiment, a high-concentration NaCl solution with a mass ratio of approximately 20 (wt%) is prepared. Using a pipette, 1 (ml) of the high-concentration solution (mass ratio 20.3152 (wt%), density 1.1341 (g / cm³)) is injected into the light-transmitting container 2 approximately every 100 seconds. 3 Let the number of additions be k, then the mass of the solution after addition is m. 溶液 =10+kρ=10+1.1341k, mass of solute m 溶质 =kρc 高 =0.23039k, the actual concentration of the solution is c 理 =0.23039k / (10+1.1341k). Observe and measure the real-time concentration c of the solution in the transparent container 2, as shown in Table 9.

[0170] Table 9. Measured and theoretical values ​​of NaCl solution concentration at different addition times.

[0171] Number of times of liquid addition <![CDATA[Theoretical concentration c 理 (wt%)]]> <![CDATA[Measured concentration c 测 (wt%)]]> <![CDATA[Relative error E c > 1 2.0692 2.12 2.5％ 2 3.7559 3.82 1.7％ 3 5.1571 5.28 2.4％ 4 6.3397 6.19 2.4％

[0172] like Figure 12 As shown, the curve rises in a step-like manner, which is in line with expectations.

[0173] like Figure 13 The errors in concentrations compared to the NaCl solutions at each level in Table 9 are all small.

[0174] Therefore, it can be seen that the optical device constructed in this invention responds quickly to changes in solution concentration and has high measurement accuracy.

[0175] Error Analysis

[0176] (1) Qualitative Analysis

[0177] In the actual experimental operation of this invention, there are two main sources of error:

[0178] ① The light field distribution of the laser beam is Gaussian, and the uniformity of its diffused light spot is poor, which causes the voltage output by the displacement sensor to fluctuate and introduce errors.

[0179] ② The collimation of the optical path is manually adjusted, which cannot accurately ensure that the light is incident perpendicularly along the container wall, causing the incident light point to deviate and introducing errors.

[0180] (2) Quantitative analysis (measurement uncertainty)

[0181] From c = nb / k, according to the uncertainty propagation formula, the uncertainty of the concentration c measured through the refractive index n is:

[0182]

[0183] Taking NaCl solution under red light (wavelength 695nm) as an example, a total of 15 sets of data were measured during calibration. The standard uncertainty of n for the linear fitting is:

[0184]

[0185] The standard uncertainties of the slope k and the intercept b are:

[0186]

[0187]

[0188] The absolute uncertainty of the concentration (pure water) when the concentration is zero is:

[0189]

[0190] When c = 20.4564 (the point of maximum concentration in the fitted line), the absolute uncertainty of the concentration is:

[0191]

[0192] That is, the absolute uncertainty of the NaCl solution concentration measured in this invention is between 0.16wt% and 0.20wt%.

[0193] The above are merely specific embodiments of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention using this concept shall be considered as infringing upon the protection scope of the present invention.

Claims

1. An optical device for measuring solution concentration, characterized in that: It includes a laser, a light-transmitting container, and a displacement sensor arranged along the light path; it also includes a data acquisition card and a computer, wherein the displacement sensor, the data acquisition card, and the computer are electrically connected in sequence, the data acquisition card is used to acquire the electrical signals fed back by the displacement sensor, and the computer is used to process and analyze the electrical signals; The light-transmitting container includes a first K9 glass block, a first slat, a second slat, a third slat, and a second K9 glass block; both the first and second K9 glass blocks are triangular prisms, with the two facets of the first K9 glass block being the incident surface and the first refractive surface, and the two facets of the second K9 glass block being the second refractive surface and the exit surface, respectively; the first, second, and third slats are all elongated strips with the same thickness, and the first, second, and third slats are arranged in a U-shape between the first and second K9 glass blocks; The water tank of the light-transmitting container includes a first refractive surface and a second refractive surface. The incident surface, the first refractive surface, the second refractive surface, and the exit surface are arranged sequentially along the light path. The incident surface and the exit surface are parallel to each other, and the first refractive surface and the second refractive surface are parallel to each other. The angle formed between the incident surface and the first refractive surface satisfies the following system of equations: ； ； ； in, It is the angle formed between the incident surface and the first refractive surface, and it is also the incident angle of the laser at the first refractive surface when the laser is perpendicularly incident on the incident surface; The angle of refraction of the laser at the first refraction surface when the water tank is filled with a reference solution; The water tank is filled with a refractive index of When the solution is in a certain state, the angle of refraction of the laser at the first refractive surface; The refractive index of the transparent container; denoted by , where is the refractive index of the reference solution; and D is the linear distance between the first and second refractive surfaces. The length of the photosensitive strip of the displacement sensor; The transparent container is made of K9 glass. The reference solution is deionized water. , , and ; calculated from the system of equations .

2. The optical device for measuring solution concentration according to claim 1, characterized in that: It also includes a thermometer used to detect the temperature of the solution inside the transparent container.

3. A method for measuring solution concentration, characterized in that, Measuring solution concentration using the optical device as described in claim 1 or 2 includes the following steps: 1) Turn on the displacement sensor; 2) Turn on the laser; 3) Add the standard solution to the water tank in the transparent container; 4) Calibrate the optical device so that the laser emitted by the laser enters perpendicularly from the incident surface of the light-transmitting container and exits from the exit surface, illuminating the center position of the photosensitive strip of the displacement sensor.

4. The method for measuring solution concentration according to claim 3, characterized in that, It also includes step 5) Single solution concentration measurement: (5.1) Prepare solutions of different concentrations, such that the concentrations of each solution are set in a gradient and are known; (5.2) Add each solution to the water tank of the transparent container and measure the refractive index of each solution using an optical device; (5.3) For each solution The relationship is calibrated to obtain Calibration curve; the obtained The fitting formula for the calibration curve is input into the computer; among which, For refractive index, Concentration; (5.4) Add the test solution of unknown concentration into the water tank of the light-transmitting container, and measure the refractive index of the test solution by optical device; (5.5) The computer, according to The concentration of the test solution is calculated using the calibration curve and the refractive index of the test solution.

5. The method for measuring solution concentration according to claim 4, characterized in that, It also includes step 6) measuring the concentration of each component in the mixed solution: The mixed solution is composed of m kinds of solutes, and the laser includes m kinds of lasers with different wavelengths; (6.1) Using m different wavelengths of laser light, plot the results of each solute under the irradiation of m different wavelengths of laser light, following step 5). Calibration curve; (6.2) Each The fitting formula for the calibration curve is input into the computer; (6.3) Add the mixed solution of unknown concentration and the same type of solute to the water tank of the transparent container, and measure the refractive index of the mixed solution under the irradiation of m different wavelengths of laser by optical device; (6.4) The computer calculates the concentration of each solute in the mixed solution to be tested based on the fitting formula and the m refractive indices of the mixed solution to be tested.

6. The method for measuring solution concentration according to claim 4, characterized in that: It also includes step 7) dynamic solution concentration measurement: (7.1) Draw the graph of a single solution containing component A according to step 5). The calibration curve is generated, and the fitting formula is input into the computer. (7.2) Prepare the first solution and the second solution; wherein the first solution is a single solution containing component A with a mass ratio of X (wt%); the second solution is a single solution containing component A with a mass ratio of Y (wt%), and Y≠X; (7.3) Add the first solution to the water tank in the transparent container, measure the refractive index using an optical device, and the computer calculates the refractive index based on the refractive index and the value in step (7.1). The concentration value was calculated from the calibration curve. (7.4) Inject L (ml) of the second solution into the transparent container every T (s) using a pipette, and observe and measure the real-time changes in concentration.

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