Solution concentration measuring instrument and method based on white light interference and compensation plate rotation method

Abstract

The invention provides a solution concentration measuring instrument and method based on white light interference and a compensation plate rotation method. The solution concentration measuring instrument comprises a white light source, a convex lens, a beam splitter, a compensation plate, a first reflecting mirror, a sample pipeline, a second reflecting mirror and a color camera, the sample pipeline is arranged in the measuring light path, and a to-be-measured solution is stored in the sample pipeline; the convex lens, the beam splitter, the compensation plate and the first reflector form a measuring light path, and the convex lens, the beam splitter, the sample pipeline and the second reflector form another measuring light path; the convex lens is used for straightening the white light source into parallel light beams, and the beam splitter is used for splitting the light beams into two light beams which pass through different paths and then converge to form interference fringes; the color camera is used for imaging interference fringes; the compensation plate is driven by a motor to rotate, and the imaging position of the interference fringes on the color camera is adjusted by rotating the compensation plate; the motor comprises an encoder, and the encoder is used for reading the rotation angle of the compensation plate.

Description

Technical Field

[0001] The present invention relates to the technical field of optical measurement, and particularly to a solution concentration measuring instrument and method based on white light interference and compensating plate rotation method. Background Art

[0002] Traditional solution concentration measurement methods have significant defects. Handheld refractometers have low accuracy, are significantly affected by environmental temperature, and require frequent calibration. Although fully automatic refractometers improve accuracy, they are costly and cannot continuously monitor, making them unsuitable for dynamic production processes. The conductivity method can only measure the concentration of ionic solutions and is completely ineffective for non-conductive substances (such as sugars and alcohols). The measurement results are significantly affected by temperature and require constant temperature control, increasing the complexity of the system. White light interference technology can achieve high-precision solution concentration measurement by detecting the offset of the zero-order fringe of white light interference or the change in spectral phase, and has advantages such as zero coherence length and wide spectral response, but it has not been widely applied in the field of solution concentration detection. Based on the principle of white light interference, the present invention proposes a novel solution concentration measuring instrument to solve the deficiencies of the prior art. Summary of the Invention

[0003] The main technical problem to be solved by the present invention is to provide a solution concentration measuring instrument and method based on white light interference and compensating plate rotation method based on the principle of white light interference, which can detect the change in the refractive index of the solution with high precision in a non-contact manner, and then calculate its concentration.

[0004] To solve the above technical problems, the present invention provides a solution concentration measuring instrument based on white light interference and compensating plate rotation method, including a white light source, a convex lens, a beam splitter, a compensating plate, a first reflector, a sample pipeline, a second reflector and a color camera;

[0005] The convex lens, the beam splitter, the compensating plate, the first reflector and the second reflector form a measurement optical path, the sample pipeline is placed in the measurement optical path, and the sample pipeline contains the solution to be measured; the convex lens, the beam splitter, the compensating plate and the first reflector form one measurement optical path, and the convex lens, the beam splitter, the sample pipeline and the second reflector form another measurement optical path;

[0006] The convex lens is used to collimate the white light source into a parallel beam, the beam splitter is used to split the beam into two beams of light that converge to form interference fringes after passing through different paths; the color camera is used for imaging the interference fringes;

[0007] The compensating plate can be rotated by a motor, and the imaging position of the interference fringes on the color camera is adjusted by rotating the compensating plate; the motor is equipped with an encoder, and the encoder is used to read the rotation angle of the compensating plate.

[0008] In a preferred embodiment, the solution concentration measuring instrument further includes a temperature sensor and a pressure sensor, and the temperature sensor and the pressure sensor are arranged on the sample pipeline.

[0009] In a preferred embodiment, the temperature sensor includes a thermistor, and the thermistor is placed in the solution to be measured for detecting the change in the solution temperature.

[0010] In a preferred embodiment, a pressure balancing device is installed on the sample pipeline, and the pressure balancing device is used for adjusting the air pressure or hydraulic pressure in the sample pipeline, and the pressure balancing device is electrically connected to the pressure sensor.

[0011] In a preferred embodiment, the pressure balancing device includes a pressure regulating valve or a pressure stabilizer.

[0012] In a preferred embodiment, the encoder adopts a high-precision absolute encoder, and the resolution of the encoder is greater than or equal to 16 bits.

[0013] In a preferred embodiment, the sample pipeline is a closed flow channel made of a light-transmitting material.

[0014] To solve the above technical problems, the present invention also provides a solution concentration measurement method based on white light interference and compensating plate rotation method, including the solution concentration measurement instrument based on white light interference and compensating plate rotation method, and the method includes the following steps:

[0015] Step A: A white light source provides white light, and the white light is calibrated by a convex lens to form parallel light, and the parallel light then passes through a beam splitter and is divided into a first light beam and a second light beam;

[0016] Step B: The first light beam passes through a rotatable compensating plate and a first reflector in sequence, and is reflected by the first reflector to the beam splitter; the second light beam passes through the sample pipeline and a second reflector in sequence, and is reflected by the second reflector to the beam splitter; the first light beam and the second light beam are combined into a beam of light after passing through the beam splitter and then are incident on the color camera to form an interference optical path;

[0017] Step C: The compensating plate is driven to rotate by a motor, and the incident angle of the first light beam is adjusted by rotating the compensating plate to change the compensating optical path, so that the first light beam and the second light beam form white light interference fringes;

[0018] Step D: The rotation angle of the compensating plate is read in real time by the encoder, and in combination with Snell's law and the second-order mathematical model of Taylor expansion, the change amount of the optical path difference is calculated;

[0019] Step E: Based on the correlation between the optical path difference and the refractive index of the solution, the solution concentration is inversely calculated.

[0020] In a preferred embodiment, in step D, the calculation steps of the change amount of the optical path difference are as follows:

[0021] Let the initial tilt angle of the compensator be , the refractive index , and the thickness ; According to Snell's law, the initial refraction angle satisfies: ;

[0022] When the compensator rotates an additional angle around the initial tilt direction, the total incident angle becomes , clockwise rotation is , counterclockwise rotation is , and the corresponding total refraction angle satisfies: ;

[0023] Under the small-angle approximation (Δθ≪1 rad), perform a Taylor expansion on the left side and retain the linear term: ;

[0024] Assume the deviation of the refraction angle is , that is , substitute it into Snell's law to get: ;

[0025] Combine the initial conditions , and finally simplify to:

[0026]

[0027] ;

[0028] The optical path of the compensator when not rotated is: ;

[0029] When rotating clockwise : ;

[0030] When rotating counterclockwise : ;

[0031] Expand The second-order term: ;

[0032] The change in the optical path difference is: ;

[0033] The change in the refractive index of the solution causes the optical path difference: ;

[0034] The solution of the equilibrium condition is:

[0035] 。

[0036] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0037] 1. Solution concentration measurement by white light interference and compensation plate rotation method: A measurement optical path is formed by a convex lens, a beam splitter, a compensation plate, a first reflector, and a second reflector. A sample pipe containing the solution to be measured is placed in the measurement optical path. The convex lens, the beam splitter, the compensation plate, and the first reflector form one measurement optical path, and the convex lens, the beam splitter, the sample pipe, and the second reflector form another measurement optical path. The change in the refractive index of the solution causes a change in the optical path difference. The compensation optical path is changed by rotating the compensation plate, and the solution concentration is inverted through the rotation angle.

[0038] 2. High-precision rotation compensation technology: A rotatable compensation plate driven by an encoder is used to replace the traditional translation device, and combined with a 16-bit resolution encoder, micro-angle adjustment without mechanical wear (accuracy up to 0.0055°) is achieved, significantly improving the optical path compensation accuracy.

[0039] 3. Nonlinear compensation model: A second-order Taylor expansion model of the rotation angle of the compensation plate and the optical path difference is derived based on Snell's law to solve the nonlinear error problem during large-angle rotation.

[0040] 4. Dynamic compensation of environmental parameters: Temperature sensors and pressure sensors are set to monitor environmental parameters in real time and compensate for the influence of temperature and pressure on the measurement through algorithms. The temperature and pressure sensors are integrated, and through the preset temperature-refractive index and pressure-refractive index compensation formulas, environmental interference is eliminated in real time. Description of the Drawings

[0041] Figure 1 It is a schematic structural diagram of a solution concentration measuring instrument in a preferred embodiment of the present invention;

[0042] Figure 2 It is a schematic diagram of the imaging of interference fringes on a color camera in a preferred embodiment of the present invention;

[0043] Figure 3 It is a relationship diagram between alcohol concentration and refractive index in a preferred embodiment of the present invention;

[0044] Figure 4 It is a mathematical model diagram of the rotation angle of the compensation plate and the change value of the refractive index in a preferred embodiment of the present invention;

[0045] Figure 5 It is a relationship diagram between alcohol concentration and rotation angle in a preferred embodiment of the present invention;

[0046] Figure 6 It is a temperature-refractive index compensation curve diagram in a preferred embodiment of the present invention;

[0047] Figure 7This is the pressure-refractive index compensation curve graph in the preferred embodiment of the present invention;

[0048] Explanation of reference numerals: 1. Sample pipeline; 2. Pressure sensor; 3. White light source; 4. Convex lens; 5. Beam splitter; 6. Color camera; 7. Compensation plate; 8. First reflector; 9. Temperature sensor; 10. Motor; 11. Second reflector. Detailed implementation manners

[0049] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention; obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0050] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", "top / bottom end", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation of the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0051] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "provided with", "sheathed / connected", "connected", etc. should be understood in a broad sense. For example, "connected" can be a wall-mounted connection, a detachable connection, or an integral connection, it can be a mechanical connection, an electrical connection, a direct connection, or an indirect connection through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0052] Refer to Figure 1, this embodiment provides a solution concentration measuring instrument based on white light interference and the rotation method of the compensating plate 7, including a white light source 3, a convex lens 4, a beam splitter 5, a compensating plate 7, a first reflector 8, a sample pipe 1, a second reflector 11 and a color camera 6; the convex lens 4, the beam splitter 5, the compensating plate 7, the first reflector 8 and the second reflector 11 form a measurement optical path, the sample pipe 1 is placed in the measurement optical path, and the sample pipe 1 contains the solution to be measured; the convex lens 4, the beam splitter 5, the compensating plate 7 and the first reflector 8 form one measurement optical path, and the convex lens 4, the beam splitter 5, the sample pipe and the second reflector 11 form another measurement optical path; the convex lens 4 is used to collimate the white light source 3 into a parallel beam, and the beam splitter 5 is used to divide the beam into two beams of light, which are recombined to form interference fringes after passing through different paths; the color camera 6 is used for imaging the interference fringes (such as Figure 2 ); the compensating plate 7 can be rotated by driving of a motor 10, and by rotating the compensating plate 7, the imaging position of the interference fringes on the color camera 6 is adjusted to ensure that the two beams of light have a fixed optical path difference and the central wavelength has a zero optical path difference; the motor 10 is equipped with an encoder, and the encoder is used to read the rotation angle of the compensating plate 7.

[0053] This device measures the solution concentration by adopting the method of changing the compensating optical path by rotating the compensating plate 7 until the color fringes appear again at the original pixel position on the target surface of the CMOS camera. Specifically: the white light source 3 is used to provide white light, and the convex lens 4 is used to collimate the white light into a parallel beam to ensure the uniformity of the beam. The beam splitter 5 divides the parallel beam into two beams of light, which are recombined to form interference fringes after passing through different paths respectively. The compensating plate 7 is driven to rotate by the motor 10 to adjust the optical path difference and make the interference fringes return to the initial position. The first reflector 8 and the second reflector 11 reflect the two beams of light respectively, so that they are recombined after passing through different paths. The sample pipe 1 is used to contain the solution to be measured and affects the optical path of one of the beams of light. The color camera 6 is used to capture the image of the interference fringes and record the position change of the fringes. Due to the interference of the two beams of light, interference fringes can be observed on the photosensitive surface of the color camera 6. The refractive index of the solution usually changes with its concentration. When the beam passes through the solution to be measured, due to the change of the refractive index of the solution, the propagation path length of the light in it will change, which will cause the change of the optical path difference. Through the cooperation of the motor 10 and the encoder, the motor 10 drives the compensating plate 7 to rotate, and the encoder reads the rotation angle for calculating the change amount of the optical path difference.

[0054] Let the diameter of the pipeline be R and the refractive index be n. Then the optical path of light in the solution is nd. If the refractive index changes by Δn, the optical path difference will correspondingly change to Δnd. When the light travels back and forth once, the overall optical path difference is 2Δnd. The zero-order fringe corresponds to the position where the optical path difference is zero. The zero-order fringe of white light is still a white stripe, with colored stripes on both sides. When the optical path difference changes, the zero-order fringe will shift accordingly.

[0055] By rotating the compensation plate 7 to change the compensation optical path, the colored stripes reappear at the original pixel positions on the CMOS camera target surface and coincide with the white stripes. There is a certain relationship between the rotation angle and the change amount of the optical path difference. By reading the rotation angle of the encoder, the change amount of the optical path difference can be calculated. Then, based on the relationship between the optical path difference and the refractive index and the relationship between the refractive index and the concentration, the concentration of the solution can be inversely calculated.

[0056] Through the white light interference and the rotation method of the compensation plate 7, high-precision measurement of the solution concentration can be achieved, and there is no need to directly contact the solution, which is suitable for occasions with special requirements for samples. By rotating the compensation plate 7, the change of the interference fringes can be observed in real time, which is convenient for dynamic measurement.

[0057] In order to avoid the influence of the environment on the concentration measurement, in this embodiment, the solution concentration measuring instrument further includes a temperature sensor 9 and a pressure sensor 2, and the temperature sensor 9 and the pressure sensor 2 are arranged on the sample pipeline 1. By measuring the temperature and pressure changes of the solution through the temperature sensor 9 and the pressure sensor 2, environmental compensation can be performed on the measurement results to improve the measurement accuracy. At the same time, by monitoring the temperature and pressure of the solution through the temperature sensor 9 and the pressure sensor 2 simultaneously, more comprehensive experimental data can be provided.

[0058] Specifically, the temperature sensor 9 includes a thermistor, and the thermistor is placed in the solution to be measured for detecting the temperature change of the solution. The thermistor can accurately measure the temperature change of the solution and provide high-precision temperature data.

[0059] A pressure balancing device is installed on the sample pipeline 1. The pressure balancing device is used to adjust the air pressure or hydraulic pressure in the sample pipeline 1. By adjusting the air pressure or hydraulic pressure in the sample pipeline 1 through the pressure balancing device, the stability of the measurement environment can be ensured. The pressure balancing device is electrically connected to the pressure sensor 2, and the pressure can be adjusted in real time according to the feedback of the pressure sensor 2.

[0060] The pressure balancing device includes a pressure regulating valve or a pressure stabilizer. The pressure regulating valve or the pressure stabilizer both adopt existing equipment, which will not be introduced in detail here. Through the pressure regulating valve or the pressure stabilizer, the pressure in the sample pipeline 1 can be accurately adjusted and stabilized. Select a suitable device according to specific requirements to ensure the accurate adjustment of the pressure.

[0061] For high-precision measurement, the encoder adopts a high-precision absolute encoder, and the resolution of the encoder is greater than or equal to 16 bits. In traditional optical path compensation, a translation or tilting device of a mirror is mostly used, which has problems of large mechanical errors and slow response speed. In this embodiment, combining the rotary compensation plate 7 with the encoder can achieve high-precision adjustment without mechanical wear. The compensation plate 7 is fixed on an absolute encoder with an n-bit resolution, such as a 16-bit encoder, with a resolution of 1 / 65,536, corresponding to an angular resolution of 0.0055°.

[0062] The sample pipeline 1 is a closed flow channel made of a light-transmitting material. The sample pipeline 1 made of a light-transmitting material facilitates the passage of light and ensures the accuracy of measurement. The design of the closed flow channel prevents solution leakage and ensures the safety and stability of the measurement environment.

[0063] This embodiment also provides a solution concentration measurement method based on white light interference and the rotation method of the compensation plate 7, including the solution concentration measuring instrument based on white light interference and the rotation method of the compensation plate 7, and the following steps:

[0064] Step A: The white light source 3 provides white light, and the white light is calibrated by the convex lens 4 to form parallel light, and the parallel light is then divided into a first light beam and a second light beam by the beam splitter 5;

[0065] Step B: The first light beam passes through the rotatable compensation plate 7 and the first mirror 8 in sequence, and is reflected by the first mirror 8 to the beam splitter 5 and the convex lens 4; the second light beam passes through the sample pipeline 1 and the second mirror 11 in sequence, and is reflected by the second mirror 11 to the beam splitter 5 and the convex lens 4; the first light beam and the second light beam are combined into one light beam by the beam splitter 5 and then irradiated to the color camera 6 to form an interference optical path;

[0066] Step C: The motor 10 drives the compensation plate 7 to rotate, and the incident angle of the first light beam is adjusted by rotating the compensation plate 7 to change the compensation optical path, so that the first light beam and the second light beam form white light interference fringes;

[0067] Step D: The rotation angle of the compensation plate 7 is read in real time by the encoder, and in combination with Snell's law and the second-order mathematical model of Taylor expansion, the change amount of the optical path difference is calculated;

[0068] Step E: Based on the correlation between the optical path difference and the refractive index of the solution, the solution concentration is inversely calculated.

[0069] Using alcohol as the solution for measurement, according to the relationship between alcohol concentration and refractive index (such as Figure 3 ), in step D, the calculation steps of the change amount of the optical path difference are as follows:

[0070] Let the initial tilt angle of the compensation plate 7 be , refractive index , thickness ; According to Snell's law, the initial refraction angle satisfies: ;

[0071] When the compensation plate 7 rotates by an additional angle around the initial tilt direction, the total incident angle becomes , clockwise rotation is , counterclockwise rotation is , corresponding to the total refraction angle which satisfies: ;

[0072] Under the small angle approximation (Δθ≪1 rad), perform Taylor expansion on the left side and retain the linear term: ;

[0073] Assume that the deviation of the refraction angle is , that is , substituting into Snell's law gives: ;

[0074] Combined with the initial condition , finally simplified to:

[0075]

[0076] ;

[0077] The optical path of the compensation plate 7 when not rotated is: ;

[0078] When rotating clockwise : ;

[0079] When rotating counterclockwise : ;

[0080] Expand to the second order term: ;

[0081] The change in the optical path difference is: ;

[0082] The optical path difference caused by the change in the refractive index of the solution is: ;

[0083] The solution of the equilibrium condition is:

[0084] .

[0085] As Figure 4 , assume that the initial inclination angle of the compensation plate 7 , the thickness t of the compensating plate 7 is 2 mm, the pipe diameter d is 1 cm, the compensating plate 7 is made of glass with a refractive index of 1.5. According to the calculation and derivation of the optical path difference change amount in step D, the relationship diagram between the alcohol concentration and the rotation angle is obtained (as Figure 5 ), when = 0.1° is detected, the data processing unit calculates = 0.0023, corresponding to a 5.7% increase in alcohol concentration.

[0086] In the embodiment, environmental parameter dynamic compensation is also carried out. The temperature sensor 9 and the pressure sensor 2 are set to perform temperature and pressure compensation on the solution concentration measurement. The temperature sensor 9 and the pressure sensor 2 monitor the solution environmental parameters in real time, and compensate for the influence of temperature and pressure on the refractive index through an algorithm. The temperature sensor 9 and the pressure sensor 2 compensate for the influence of temperature and pressure on the solution, as Figure 5 、 Figure 6 .

[0087] As Figure 5 , for temperature compensation, a temperature compensation element, such as a thermistor, is added to the solution concentration measuring instrument and used in cooperation with the sensor. The resistance value of the thermistor changes with the temperature. By measuring the change in the resistance value of the thermistor, the temperature change can be known, and then the measured value of the solution refractive index can be compensated in real time according to the pre-established temperature compensation model. The calculation formula is as follows:

[0088] ;

[0089] where T is the temperature, is the pressure value, is the salinity parameter, is the light source wavelength.

[0090] As Figure 6 , for pressure compensation, a pressure balancing device, such as a gas pressure regulating valve or a liquid pressure stabilizer, is added to keep the pressure in the measurement environment relatively stable and reduce the influence of pressure change on the measurement of the solution refractive index. The calculation formula is as follows:

[0091] ;

[0092] where T is the temperature, is the pressure value, is the salinity parameter, is the light source wavelength.

[0093] The above is only a preferred specific embodiment of the present invention, but the design concept of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention who makes non-substantive modifications to the present invention using this concept shall fall within the scope of infringement of the present invention.

Claims

1. A solution concentration measuring instrument based on white light interference and compensation plate rotation method, characterized in that: It includes a white light source, a convex lens, a beam splitter, a compensating plate, a first reflector, a sample pipe, a second reflector and a color camera; The convex lens, the beam splitter, the compensating plate, the first reflector and the second reflector form a measurement optical path. The sample pipe is placed in the measurement optical path, and a solution to be measured is stored in the sample pipe. The convex lens, the beam splitter, the compensating plate and the first reflector form one measurement optical path, and the convex lens, the beam splitter, the sample pipe and the second reflector form another measurement optical path; The convex lens is used to collimate the white light source into a parallel light beam. The beam splitter is used to split the light beam into two beams of light, which are recombined after passing through different paths to form interference fringes. The color camera is used for imaging the interference fringes; The compensating plate can be rotated by a motor, and the imaging position of the interference fringes on the color camera is adjusted by rotating the compensating plate; The motor is equipped with an encoder, and the encoder is used to read the rotation angle of the compensating plate.

2. The solution concentration measuring instrument based on white light interference and compensation plate rotation method according to claim 1, characterized in that: This solution concentration measuring instrument further includes a temperature sensor and a pressure sensor, and the temperature sensor and the pressure sensor are arranged on the sample pipe.

3. The solution concentration measuring instrument based on white light interference and compensation plate rotation method according to claim 2, characterized in that: The temperature sensor includes a thermistor, and the thermistor is placed in the solution to be measured to detect the temperature change of the solution.

4. The solution concentration measuring instrument based on white light interference and compensation plate rotation method according to claim 2, characterized in that: A pressure balancing device is installed on the sample pipe. The pressure balancing device is used to adjust the air pressure or hydraulic pressure in the sample pipe, and the pressure balancing device is electrically connected to the pressure sensor.

5. The solution concentration measuring instrument based on white light interference and compensation plate rotation method according to claim 4, characterized in that: The pressure balancing device includes a pressure regulating valve or a pressure stabilizer.

6. The solution concentration measuring instrument based on white light interference and compensating plate rotation method according to claim 1, characterized in that: The encoder adopts a high-precision absolute encoder, and the resolution of the encoder is greater than or equal to 16 bits.

7. The solution concentration measuring instrument based on white light interference and compensating plate rotation method according to claim 1, wherein: The sample pipe is a closed flow channel made of a light-transmitting material.

8. A method for measuring the concentration of a solution based on white light interference and the compensation plate rotation method, characterized in that: It includes the solution concentration measuring instrument based on white light interference and compensating plate rotation method according to any one of claims 1-7, and includes the following steps: Step A: The white light source provides white light, and the white light is calibrated by the convex lens to form parallel light, and the parallel light then passes through the beam splitter and is divided into a first light beam and a second light beam; Step B: The first light beam passes through the rotatable compensating plate and the first reflector in sequence, and is reflected by the first reflector to the beam splitter; the second light beam passes through the sample pipe and the second reflector in sequence, and is reflected by the second reflector to the beam splitter; the first light beam and the second light beam are combined into one light beam by the beam splitter and then projected onto the color camera to form an interference optical path; Step C: The compensating plate is rotated by a motor, and the incident angle of the first light beam is adjusted by rotating the compensating plate to change the compensating optical path, so that the first light beam and the second light beam form white light interference fringes; Step D: The rotation angle of the compensating plate is read in real time by the encoder, and the change amount of the optical path difference is calculated by combining Snell's law and the second-order mathematical model of Taylor expansion; Step E: Based on the correlation between the optical path difference and the refractive index of the solution, the solution concentration is inversely calculated.

9. The solution concentration measurement method based on white light interference and compensation plate rotation method according to claim 8, wherein: In step D, the calculation steps of the change amount of the optical path difference are as follows: Let the initial tilt angle of the compensation plate be , refractive index , thickness ; According to Snell's law, the initial refraction angle satisfies: ; When the compensation plate rotates an additional angle around the initial tilt direction , the total incident angle becomes , clockwise rotation is , counterclockwise rotation is corresponding to the total refraction angle satisfying: ; Under the small-angle approximation (Δθ≪1 rad), perform a Taylor expansion on the left side and retain the linear term: ; Assume the refraction angle deviation is , that is . Substituting into Snell's law gives: ; Combined with the initial conditions , finally simplified to: ； The optical path of the compensation plate when not rotated is: ; Rotate clockwise When: ; Counterclockwise rotation When: ; Expand to the second order term: ; The change in optical path difference is: ; Change in refractive index of the solution Optical path difference caused by: ; Equilibrium condition The solution is: 。

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