Displacement sensor-based liquid refractive index real-time measurement method and device

Abstract

The invention discloses a liquid refractive index real-time measurement method and a liquid refractive index real-time measurement device based on a displacement sensor, which are used for solving the problem that the liquid refractive index cannot be accurately measured in real time in the prior art and can capture and monitor the tiny change of the liquid refractive index in real time. Through high-speed data processing and analysis, the instrument can quickly respond to the change of the refractive index of the liquid and provide continuous and real-time measurement data; according to the technical scheme, the problem that in the prior art, a rectangular container is not obvious in light beam refraction capacity is solved, the circular container is selected as the sample container, and the measurement accuracy is improved. According to the technical scheme, traditional refraction angle measurement is converted into laser beam transverse displacement measurement, and the innovative method not only improves the measurement precision, but also effectively avoids interference of ambient light. The instrument can provide more accurate refractive index data by accurately measuring the displacement change of the laser beam after penetrating through the liquid.

Description

Technical Field

[0001] The invention belongs to the technical field of optical measurement of liquid refractive index, and in particular relates to a method and device for real-time measurement of liquid refractive index based on a displacement sensor. Background Art

[0002] Refractive index is an important optical property parameter of a substance, which can often reflect the state and changes of relevant physical properties of the substance, such as concentration and temperature. Accurate measurement of refractive index is crucial in fields such as optics, chemistry and materials science. Measuring the refractive index of liquids is crucial to advancing scientific exploration and plays a core role in industrial manufacturing and environmental monitoring. Since the refractive index of liquids is extremely sensitive to changes in factors such as temperature and concentration, it has become an extremely valuable physical indicator that can help us accurately monitor and control various states of liquids. Traditional methods for measuring refractive index, such as Abbe refractometry, total reflection technology, and Michelson interferometry, have limitations in accuracy and ease of use, and cannot accurately observe changes in the refractive index of liquids in real time. Therefore, a reliable and user-friendly method is needed to measure the refractive index of liquids.

[0003] In the field of scientific research, the real-time measurement device for the refractive index of liquids can be used to study the refractive index variation of optical materials under different conditions and states, explore the optical properties of new materials, and provide important data support for material science research. In the field of engineering applications, the real-time measurement device for the refractive index of liquids can be used to monitor the refractive index variation of products on the production line in real time, help optimize product production and design, and improve product performance and stability. In the field of medical diagnosis, the real-time measurement device for the refractive index of liquids can be used to detect the refractive index variation of biological tissues or drugs, and achieve accurate diagnosis and treatment.

[0004] The patent with publication number CN 114062318 A provides a device and method for measuring the refractive index of liquid using a linear array CCD (schematic diagram as shown in FIG. Figure 1 As shown in the figure, first let the light pass through the liquid, and then observe the radius of the beam formed after the light is refracted. Due to the refraction of the light beam in the liquid, its radius will change. By measuring the radius of the refracted light beam with a high-precision linear array CCD camera, the refractive index information of the liquid can be indirectly obtained.

[0005] Existing technologies cannot measure the refractive index of liquids in real time, especially for situations where the refractive index of liquids changes rapidly, such as in industrial production processes, the device cannot achieve real-time and fast dynamic measurement;

[0006] Existing technologies have limitations in accuracy and applicability, and cannot accurately observe the measurement of liquid refractive index in real time;

[0007] Existing technology can only use rectangular containers, which have a weak refractive ability for liquids, resulting in low accuracy of the final measurement results; the measurement of the beam radius by the linear array CCD may be affected by the interference of ambient light, which will affect the accuracy of its measurement.

[0008] The existing technology is limited by its principle and is only applicable to the measurement of a certain aspect of the liquid, such as only the concentration or only the refractive index, and its application scope is relatively narrow. Summary of the invention

[0009] In view of this, the purpose of the present invention is to provide a real-time measurement method and device for liquid refractive index based on a displacement sensor. Based on the principle of the displacement sensor, using its high sensitivity and fast response characteristics, it can capture the refractive index changes of optical materials in real time and realize accurate monitoring of optical properties. Compared with the traditional refractive index measurement method, the present invention has the advantages of fast measurement speed, high accuracy, non-contact measurement, etc. It can work stably in various complex environments, and provides important technical support for research and application in related fields.

[0010] A real-time measurement method for liquid refractive index based on a displacement sensor. The laser light emitted by a laser light source passes through a transparent glass cylindrical sample container, is reflected by a reflective plate, and then passes through the transparent glass cylindrical sample container again. Finally, the laser signal is received by the CCD of the displacement sensor. After the transparent glass cylindrical container is filled with the liquid to be measured, the returned laser light is received again to obtain the displacement of the laser signal on the CCD before and after the liquid to be measured is filled, thereby calculating the refractive index of the liquid to be measured.

[0011] Preferably, the method for calculating the refractive index of the liquid to be measured includes:

[0012] Let the sample container be close to the sample container, take the center of the bottom disk of the sample container as the origin, take the diameter of the bottom disk parallel to the CCD surface as the x-axis, and the y-axis perpendicular to the x-axis; R represents the radius of the cylindrical glass container; no represents the refractive index of air; ns represents the refractive index of liquid; h represents the distance between the displacement sensor CCD screen plane and the sample container; xn represents the x-axis coordinate value of the light at the junction of the two media during the nth refraction; yn represents the y-axis coordinate value of the light at the junction of the two media during the nth refraction; θin-n represents the incident angle of the nth refraction; θout-n represents the exit angle of the nth refraction; θn-n represents the normal direction of the nth refraction; θrn represents the direction of the laser light during the nth refraction; x5 represents the x-axis coordinate value of the light spot when the laser is projected onto the CCD screen; d represents the distance d from the y-axis when the laser light is emitted parallel to the y-axis; Δd represents the displacement in the x-axis direction when the laser is emitted and when it returns to the CCD screen after 5 refractions;

[0013] For the first refraction:

[0014] x1=d

[0015] For the second refraction:

[0016]

[0017] For the third refraction:

[0018]

[0019] For the fourth refraction:

[0020]

[0021]

[0022] For the fifth refraction:

[0023]

[0024] Then the relationship between the displacement Δd and the refractive index ns of the liquid to be measured is expressed as: Δd=x5-x1; the refractive index ns of the liquid to be measured is calculated based on this equation.

[0025] Preferably, for a certain solution to be tested, the corresponding relationship between the refractive index and the displacement Δd of the solution at different temperatures and / or different concentrations is first stored, and when the displacement Δd is calculated based on the laser signal received on the CCD of the displacement sensor, the refractive index of the current solution to be tested is obtained.

[0026] Preferably, for a certain solution to be tested, the corresponding relationship between the refractive index and the displacement Δd of the solution at different temperatures and / or different concentrations is first stored, and the displacement Δd is calculated based on the laser signal received on the CCD of the displacement sensor to obtain the refractive index of the current solution to be tested.

[0027] Preferably, for a certain solution to be tested, when it is placed in a fixed temperature environment, the refractive index of the current solution to be tested is obtained after the displacement Δd is calculated based on the laser signal received on the CCD of the displacement sensor, and the concentration of the solution is determined based on the concentration and refractive index relationship curve of the solution to be tested.

[0028] Preferably, for a certain solution to be tested, when its concentration is fixed, the refractive index of the current solution to be tested is obtained after calculating the displacement Δd based on the laser signal received on the CCD of the displacement sensor, and the temperature of the solution is determined based on the relationship curve between the temperature and the refractive index of the solution to be tested.

[0029] A real-time measurement device for liquid refractive index based on a displacement sensor, a laser light source, a reflector, a sample container, a displacement sensor, a base and a data acquisition and processing unit;

[0030] The reflector is fixed vertically on the base, the sample container is placed in front of the reflector, and the laser light source is placed in front of the sample container; the sample container is a transparent cylindrical glass container; the laser light emitted by the laser light source is parallel to the surface of the base, and is emitted to the reflector through the sample container; after being reflected by the reflector, the light enters and passes through the sample container again, and is received by the CCD of the displacement sensor; the data acquisition processing unit converts the optical signal received on the CCD into an electrical signal, and calculates the displacement Δd of the receiving light spot caused by the change of the refractive index in the sample container before and after, and obtains the refractive index in the sample container in real time according to the relationship between the displacement Δd and the refractive index curve pre-stored in the data acquisition processing unit.

[0031] Preferably, the laser light source is a laser of any wavelength.

[0032] Preferably, the sample container is a cylindrical glass container with a wall thickness of 0.1 mm.

[0033] The present invention has the following beneficial effects:

[0034] The technical solution of the present invention is used to solve the problem that the prior art cannot measure the precise refractive index of liquids in real time, and can capture and monitor small changes in the refractive index of liquids in real time. Through high-speed data processing and analysis, the instrument can quickly respond to changes in the refractive index of liquids and provide continuous and real-time measurement data.

[0035] The technical solution of the present invention is used to solve the problem in the prior art that the rectangular container has an unclear light beam refraction ability, and a circular container is selected as a sample container to improve the measurement accuracy.

[0036] The technical solution of the present invention converts the traditional refraction angle measurement into the measurement of the lateral displacement of the laser beam. This innovative method not only improves the measurement accuracy, but also effectively avoids the interference of ambient light. By accurately measuring the displacement change of the laser beam after passing through the liquid, the instrument can provide more accurate refractive index data. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic diagram of a device for real-time measurement of liquid refractive index;

[0038] FIG2( a ) and FIG2( b ) are three-dimensional images of the liquid refractive index real-time measurement device from two viewing angles, respectively;

[0039] FIG3(a) and FIG3(b) are schematic diagrams of the lateral displacement of the laser landing point before and after the addition of the liquid to be tested;

[0040] Figure 4 is the refraction light path diagram of the present invention;

[0041] Figure 5 The laser landing point displacement-refractive index curves of the two containers;

[0042] Figure 6 is the laser point displacement-salt water concentration;

[0043] Figure 7 is the refractive index-laser landing point displacement fitting curve.

[0044] Among them, 1-reflector, 2-sample container, 3-laser source, 4-displacement measuring instrument, 5-base. DETAILED DESCRIPTION

[0045] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0046] 1. Measuring device

[0047] The schematic diagram of the real-time measurement device for liquid refractive index proposed by the present invention is as follows Figure 1 As shown in the figure, it consists of several key components: laser light source, reflector, sample container, displacement sensor, base and data acquisition and processing unit.

[0048] The reflector is fixed vertically on the base, the sample container is placed in front of the reflector, and the laser light source is placed in front of the sample container; the laser light emitted by the laser light source is parallel to the surface of the base, and passes through the sample container to the reflector; after being reflected by the reflector, the light enters the sample container again and passes through the sample container, and the light is received by the CCD of the displacement sensor. The sample container is a cylindrical glass container with a thickness of 0.1mm and high light transmittance, and the liquid to be tested is contained inside it; when there is no liquid in the sample container and when there is liquid to be tested in the sample container, due to the refraction of the liquid on the light, the returned laser light is received by the CCD of the displacement sensor, and the data acquisition processing unit converts the optical signal received on the CCD into an electrical signal, and calculates the displacement Δd of the receiving light spot caused by the change of the refractive index in the sample container before and after. According to the relationship between the displacement Δd and the refractive index curve pre-stored in the data acquisition processing unit, the refractive index in the sample container can be obtained in real time.

[0049] The principle of the measuring device is as follows: The measuring principle of the device is based on the law of refraction of light. When a laser beam is directed at a liquid interface at a preset angle, the degree of its refraction will vary depending on the refractive index of the liquid. When the refractive index of the liquid changes, the propagation path of the laser beam in the liquid is deflected, thereby causing the position of the terminal laser landing point at the detection end to change (as shown in Figure 3). By accurately measuring the horizontal displacement of the laser landing point, the refractive index of the liquid can be calculated.

[0050] 2. Optical Path Analysis

[0051] In order to calculate the specific relationship between the laser landing point and the refractive index, a detailed optical path analysis was carried out.

[0052] The optical path diagram is as follows Figure 4As shown. After the laser light source emits the laser, it passes through the sample container wall for the first time and enters the liquid to be measured, then passes through the sample container for the second time and hits the reflector. After being reflected by the reflector, it passes through the sample container wall for the third time and propagates through the liquid. It passes through the sample container wall for the fourth time and finally exits and enters the CCD of the displacement sensor. It can be seen that four refractions and one reflection occur in this optical path. Since the sample container wall is very thin, the influence on the distance measurement can be ignored. Therefore, the refraction on the container wall is not considered in the analysis.

[0053] right Figure 4 The parameters are set as follows:

[0054] Take the center of the bottom disk of the sample container as the origin, the diameter of the bottom disk parallel to the CCD surface as the x-axis, and the perpendicular x-axis as the y-axis; R: the radius of the cylindrical glass container; no: the refractive index of air; ns: the refractive index of liquid; h: the distance between the displacement sensor CCD screen plane and the sample container; xn: the x-axis coordinate value of the light at the junction of the two media during the nth refraction; yn: the y-axis coordinate value of the light at the junction of the two media during the nth refraction; θin-n: the incident angle of the nth refraction; θout-n: the exit angle of the nth refraction; θn-n: the normal direction of the nth refraction; θrn: the direction of the laser light during the nth refraction; x5: the x-axis coordinate value of the spot when the laser is projected onto the CCD screen. d: when the laser light is emitted parallel to the y-axis, the distance from the y-axis is d; Δd is used to represent the displacement in the x-axis direction when the laser is emitted and when it returns to the CCD screen after 5 refractions.

[0055] For the first refraction:

[0056] x1=d

[0057] For the second refraction:

[0058]

[0059] For the third refraction:

[0060] In the optical path design, the reflector c is actually close to the disk, so the displacement deviation caused by 2 to 3 is ignored in the analysis of the optical path. Therefore, it can be known that:

[0061]

[0062] For the fourth refraction:

[0063] The fourth refraction is the key refraction that affects the CCD receiving position:

[0064] x4≈x3+2R·tanθr3=

[0065]

[0066] For the fifth refraction:

[0067]

[0068] Δd=x5-x1.

[0069] We therefore established a mathematical relationship between the horizontal displacement of the laser spot and the refractive index of the liquid. Using this relationship, we can calculate the correspondence between the change in the liquid refractive index and the change in the value measured by the displacement sensor. By using the pre-calibrated liquid refractive index data, we can draw a calibration curve between the laser spot position and the refractive index. In order to further improve the accuracy of the measurement, we can also compare the measured value with the fitted curve to optimize the accuracy of the measurement result. The real-time data obtained during the measurement process can be quickly processed by the computer system and presented in real time, allowing the user to keep abreast of the latest changes in the liquid refractive index. Through these steps, we have successfully developed a device that can measure the refractive index changes of liquids in real time.

[0070] 3. Computer simulation:

[0071] Based on the optical path, we derived the relationship between the liquid refractive index ns and the horizontal distance Δd of the laser landing point on the CCD display, and simulated and fitted the curve fitting diagram of the liquid laser landing point displacement and refractive index. Figure 5 As shown, the slope can be used to determine the sensitivity of the change in laser landing point displacement relative to the change in refractive index. We define measurement sensitivity = unit laser position change / unit refractive index change. Calculation shows the average sensitivity between refractive indices of 1 and 2: the average sensitivity of cylindrical sample containers is 2.8935; the average sensitivity of rectangular containers is 0.2994. It can be seen that the method of using cylindrical sample containers for refraction measurement can be more accurate than that of rectangular containers, and the sensitivity is about one order of magnitude higher. This conclusion can also be seen directly from the image. It can be seen that the method of selecting cylindrical sample containers to carry liquids can improve measurement accuracy.

[0072] At room temperature of 20°C, the laser landing point of salt water with different concentrations was measured. The measurement data are as follows: Figure 6 As shown:

[0073] according to Figure 6 It can be seen that the laser point displacement is nearly linearly related to the concentration of the NaCl solution. From the literature, it can be seen that the refractive index and concentration of the sodium chloride solution are nearly linearly related. Therefore, the relationship between the refractive index and the displacement can be normalized according to the known data to obtain the relationship between the refractive index and the laser point ( Figure 7). It can be clearly seen from the figure that as the refractive index increases, the laser landing position also increases accordingly. Therefore, as long as the laser landing position is measured, compared with the laser landing position of pure water (i.e., 0% NaCl solution), the displacement distance of the laser landing point is calculated, and then the refractive index of the liquid to be measured can be easily determined by referring to the change curve. We have established a fitting curve between the refractive index and the laser landing position by the curve fitting method. Using this curve and the real-time collected laser landing data, the refractive index value of the liquid can be obtained in real time.

[0074] The refractive index of a series of NaCl solutions with different concentrations was measured according to the method of the present invention, as shown in Table 1.

[0075] Table 1: Refractive index and laser point displacement of NaCl solutions with different concentrations

[0076]

[0077]

[0078] In terms of measuring accuracy, the accuracy of the refractive index measuring instrument developed in the present invention mainly depends on the measuring accuracy of the laser landing position. According to experimental results, the measuring accuracy of the laser landing position of the instrument has reached 0.01 mm. This level of accuracy corresponds to a refractive index measurement accuracy of 0.0001, indicating that the instrument can sensitively capture small changes in the refractive index. The measurement accuracy of the laser landing point is a key factor affecting the refractive index measurement results. Therefore, if the measurement accuracy of the laser landing point can be improved through technical improvements, the measurement accuracy of the refractive index is expected to be significantly improved. For example, the use of higher resolution displacement sensors may push the measurement accuracy to a higher level. It should also be noted that the laser light source in the present invention is a laser of any wavelength.

[0079] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A real-time measurement method of liquid refractive index based on a displacement sensor, characterized in that: The laser light emitted by the laser light source passes through the transparent glass cylindrical sample container, is reflected by the reflective plate, and then passes through the transparent glass cylindrical sample container again, and finally the laser signal is received by the CCD of the displacement sensor; after the transparent glass cylindrical container is filled with the liquid to be tested, the returned laser light is received again, and the displacement of the laser signal on the CCD before and after the liquid to be tested is obtained, thereby calculating the refractive index of the liquid to be tested.

2. A method for real-time measurement of liquid refractive index based on a displacement sensor as claimed in claim 1, characterized in that: Methods for calculating the refractive index of the liquid to be measured include: Let the sample container be close to the sample container, take the center of the bottom disk of the sample container as the origin, take the diameter of the bottom disk parallel to the CCD surface as the x-axis, and the y-axis perpendicular to the x-axis; R represents the radius of the cylindrical glass container; no represents the refractive index of air; ns represents the refractive index of liquid; h represents the distance between the displacement sensor CCD screen plane and the sample container; xn represents the x-axis coordinate value of the light at the junction of the two media during the nth refraction; yn represents the y-axis coordinate value of the light at the junction of the two media during the nth refraction; θin-n represents the incident angle of the nth refraction; θout-n represents the exit angle of the nth refraction; θn-n represents the normal direction of the nth refraction; θrn represents the direction of the laser light during the nth refraction; x5 represents the x-axis coordinate value of the light spot when the laser is projected onto the CCD screen; d represents the distance d from the y-axis when the laser light is emitted parallel to the y-axis; Δd represents the displacement in the x-axis direction when the laser is emitted and when it returns to the CCD screen after 5 refractions; For the first refraction: x1=d For the second refraction: For the third refraction: For the fourth refraction: For the fifth refraction: Then the relationship between the displacement Δd and the refractive index ns of the liquid to be measured is expressed as: Δd=x5-x1; the refractive index ns of the liquid to be measured is calculated based on this equation.

3. A method for real-time measurement of liquid refractive index based on a displacement sensor as claimed in claim 1, characterized in that: For a certain solution to be tested, the corresponding relationship between the refractive index and the displacement Δd of the solution at different temperatures and / or different concentrations is first stored. After the displacement Δd is calculated based on the laser signal received on the CCD of the displacement sensor, the refractive index of the current solution to be tested is obtained.

4. A method for real-time measurement of liquid refractive index based on a displacement sensor as claimed in claim 1, characterized in that: For a certain solution to be tested, the corresponding relationship between the refractive index and displacement Δd of the solution at different temperatures and / or different concentrations is first stored, and the displacement Δd is calculated based on the laser signal received on the CCD of the displacement sensor to obtain the refractive index of the current solution to be tested.

5. The method for real-time measurement of liquid refractive index based on displacement sensor according to claim 1, characterized in that: For a certain solution to be tested, when it is placed in a fixed temperature environment, the displacement Δd is calculated based on the laser signal received on the CCD of the displacement sensor, and the refractive index of the current solution to be tested is obtained. The concentration of the solution is determined based on the relationship curve between the concentration and refractive index of the solution to be tested.

6. A method for real-time measurement of liquid refractive index based on a displacement sensor as claimed in claim 1, characterized in that: For a certain solution to be tested, when its concentration is fixed, the displacement Δd is calculated based on the laser signal received on the CCD of the displacement sensor to obtain the refractive index of the current solution to be tested, and the temperature of the solution is determined based on the relationship curve between the temperature and the refractive index of the solution to be tested.

7. A real-time measurement device for liquid refractive index based on a displacement sensor, characterized in that: Laser light source, reflector, sample container, displacement sensor, base and data acquisition and processing unit; The reflector is fixed vertically on the base, the sample container is placed in front of the reflector, and the laser light source is placed in front of the sample container; the sample container is a transparent cylindrical glass container; the laser light emitted by the laser light source is parallel to the surface of the base, and is emitted to the reflector through the sample container; after being reflected by the reflector, the light enters and passes through the sample container again, and is received by the CCD of the displacement sensor; the data acquisition processing unit converts the optical signal received on the CCD into an electrical signal, and calculates the displacement Δd of the receiving light spot caused by the change of the refractive index in the sample container before and after, and obtains the refractive index in the sample container in real time according to the relationship between the displacement Δd and the refractive index curve pre-stored in the data acquisition processing unit.

8. The device for real-time measurement of liquid refractive index based on displacement sensor according to claim 1, characterized in that: The laser light source is a laser of any wavelength.

9. The device for real-time measurement of liquid refractive index based on displacement sensor according to claim 1, characterized in that: The sample container is a cylindrical glass container with a wall thickness of 0.1 mm.

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