A solution concentration real-time detection method based on composite lens focusing offset

Abstract

The application provides a solution concentration real-time detection method based on composite lens focusing offset, which comprises the following steps: step A, laser emitted by a laser diode is collimated into parallel light by a plano-convex lens, the parallel light is injected into a sample cell through a glass window, and then is shot out by a composite lens to form an image on an image sensor; step B, the parallel light is imaged as two light spots on the image sensor by the composite lens, the distance between the two light spots on the image sensor is recorded, and the solution concentration is inversely calculated through the distance between the two light spots; step C, a temperature sensor and a pressure sensor are used to detect the temperature and the pressure of the solution to be measured respectively, and the influence of the temperature and the pressure on the measurement is compensated through an algorithm; the application is based on the light spot shape analysis of the composite lens, and then inversely calculates the solution concentration, improves the resolution capability for low-concentration transparent solutions, and improves the detection stability of transparent solutions such as alcohol.

Description

Technical Field

[0001] The present invention relates to the technical field of optical detection, and in particular to a real-time detection method for solution concentration based on composite lens focus offset. Background Art

[0002] Existing transparent solution detection technologies have significant shortcomings. Contact-type detection instruments (such as densitometers) require direct immersion in the solution, are susceptible to chemical corrosion, and are difficult to clean. They also suffer from volatilization errors when detecting volatile solutions such as alcohol. Traditional refractometers can measure concentration, but they require manual sampling and the detection process is significantly affected by ambient light, making them unsuitable for continuous production scenarios such as wine brewing and chemical distillation. Chromatographic analysis offers high precision but expensive equipment and long detection cycles, making it difficult to meet the real-time control requirements of production lines. Laser interferometry is highly sensitive to changes in solution concentration, but optical path adjustment is complex and its stability is extremely poor in vibrating environments. Spot analysis, which measures concentration by analyzing the differences in spot shape after a beam of light is transmitted, offers the advantages of non-contact and fast response, lacks moving parts, and requires no back-and-forth motion. It can directly measure increases and decreases in solution concentration. However, existing technologies have weak resolution for low-concentration transparent solutions and are susceptible to temperature fluctuations. The present invention improves resolution for low-concentration transparent solutions by introducing a composite lens design, significantly enhancing the detection stability of transparent solutions such as alcohol. Summary of the Invention

[0003] The present invention aims to address the deficiencies of the prior art and provide a real-time detection method for solution concentration based on focus offset of a composite lens. The method analyzes the spot morphology of the composite lens and then inverts the solution concentration, thereby improving the resolution of low-concentration transparent solutions and enhancing the detection stability of transparent solutions such as alcohol.

[0004] In order to solve the above technical problems, the present invention provides a real-time detection method for solution concentration based on focus offset of a composite lens, which comprises the following steps:

[0005] Step A: The laser light emitted by the laser diode is collimated into parallel light by a plano-convex lens. The parallel light is incident on the sample cell through a glass window and then emitted by a compound lens to form an image on the image sensor.

[0006] Step B: Parallel light is projected onto the image sensor through a compound lens to form two light spots, and the distance s between the two light spots on the image sensor is recorded. The concentration of the solution is inverted by the distance s between the two light spots;

[0007] Step C: Detect the temperature and pressure of the solution to be measured by a temperature sensor and a pressure sensor respectively, and compensate for the influence of temperature and pressure on the measurement by an algorithm.

[0008] In a preferred embodiment, in step B, the calculation steps for inverting the solution concentration are as follows:

[0009] Assume that the parameters of the compound lens are: the base angle of the compound lens is α, the curvature radius of the compound lens is R; the initial state: when the concentration of the test solution is c0, the refractive index of the test solution is n0, and when propagating in the compound lens, the angle between the light passing through the center of the compound lens and the horizontal direction is γ0, and the distance between the two light spots is D0;

[0010] When the laser passes through the solution to be tested and is incident on the inclined incident point A in the compound lens, the geometric relationship shows that the incident angle is the base angle α of the compound lens, and the refraction angle in the compound lens is β;

[0011] According to the law of refraction: nsinα=n L sinβ; where n is the refractive index of the solution to be measured, n L is the refractive index of the compound lens; when the angle is small, sinα≈α;

[0012] The internal refraction angle β of the compound lens is calculated as: When the small angle approximation is used,

[0013]

[0014] The angle γ between the light passing through the center of the compound lens and the horizontal direction is:

[0015] When the laser passes through the solution to be tested and is incident on the compound lens from the inclined incident point A, it forms a light spot at point B of the image sensor through the compound lens. Let the distance from point B to the optical axis be s.

[0016] Let the straight-line distance from the image sensor to the center of the compound lens be L; let the distance between the two light spots be D. According to symmetry, D = 2s; the calculation formula is:

[0017]

[0018] In a preferred embodiment, the detection method further comprises a solution concentration measuring device, wherein the solution concentration measuring device comprises a laser diode, a plano-convex lens, a sample cell, a compound lens, and an image sensor arranged in sequence along the optical path;

[0019] The sample cell includes a test solution channel containing a test solution; a glass window is provided on one side of the test solution channel facing the plano-convex lens; the composite lens is provided on one side of the test solution channel facing the image sensor, with the curved convex surface of the composite lens facing away from the test solution;

[0020] The laser light emitted by the laser diode passes through the plano-convex lens, the sample cell, and the compound lens in sequence, and is imaged as two light spots on the image sensor;

[0021] A temperature sensor and a pressure sensor are provided at the bottom of the sample pool; the temperature sensor and the pressure sensor are used to detect the temperature and pressure of the solution to be tested respectively.

[0022] In a preferred embodiment, the compound lens is a combination of a prism and two cylindrical lenses, and the two cylindrical lenses are combined at an angle δ on one side of the prism facing away from the solution to be tested, and δ=

[0023] 180°-2α.

[0024] In a preferred embodiment, the image sensor is a linear array CMOS image sensor.

[0025] In a preferred embodiment, the measured value of the refractive index of the solution is compensated in real time according to the temperature change of the temperature sensor; the calculation formula is as follows:

[0026] n temperature (λ,T)=(b1+b2λ 2 +b3λ 4 )(TT b )+(b4+b5λ 2 +b6λ 4 )(T-

[0027] T b ) 2 +(b7+b8λ 2 +b9λ 4 )(TT b ) 3 ;

[0028] Where b1-b9 is the temperature-wavelength coupling coefficient, T b is the reference temperature and T is the temperature.

[0029] In a preferred embodiment, the measured value of the refractive index of the solution is compensated in real time according to the pressure change measured by the pressure sensor; the calculation formula is as follows:

[0030] n pressure (λ,T,p)=[c1+c2λ 2 +(c3+c4λ 2 )T](pp b )+(c5+c6λ 2 )(p-

[0031] p b ) 2 ;

[0032] Where c1-c6 are correction coefficients, p b is the reference pressure, p is the pressure;

[0033]

[0034] Among them, a1-a5 is the compensation coefficient, λ a is the characteristic wavelength, and λ is the wavelength of incident light.

[0035] In a preferred embodiment, the pressure sensor includes a pressure balancing device, and the pressure balancing device includes a gas pressure regulating valve or a liquid pressure stabilizer.

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

[0037] 1. The present invention provides a real-time detection method for solution concentration. The laser light emitted by a laser diode is collimated into parallel light by a plano-convex lens. The parallel light is emitted into a sample cell through a glass window and then emitted by a compound lens to be imaged on an image sensor. The image is imaged as two light spots on the image sensor. The solution concentration is inverted by the distance s between the two light spots. The entire process is optically measured without contact with the solution. The method is suitable for non-contact rapid measurement of liquid concentration, and is particularly suitable for concentration detection of transparent to translucent liquids such as alcohol and sugar solutions.

[0038] 2. This invention uses a composite lens to analyze the spot shape and infer solution concentration, improving the resolution of low-concentration transparent solutions and enhancing the detection stability of transparent solutions such as alcohol. Temperature and pressure sensors are also included, and algorithms are used to compensate for the effects of temperature and pressure on measurement, effectively suppressing temperature drift.

[0039] 3. This invention introduces a composite lens design, comprising a prism and two tilted cylindrical lenses. The cylindrical lenses focus the light beam, significantly improving the signal-to-noise ratio, thereby increasing the system's detection sensitivity and enhancing the resolution of low-concentration transparent solutions. The entire optical assembly is integrated, preventing optical path misalignment, greatly improving system reliability and significantly enhancing the detection stability of transparent solutions such as alcohol. The composite lens is an integrated device, rather than a separate component, thus avoiding vibration interference, improving vibration resistance, and preventing thermal drift caused by ambient temperature changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a structural distribution diagram of a solution concentration measuring device in a preferred embodiment of the present invention;

[0041] Figure 2 This is a light spot morphology analysis diagram of the compound lens in the preferred embodiment of the present invention;

[0042] Figure 3 is a graph showing the relationship between alcohol concentration and refractive index in a preferred embodiment of the present invention;

[0043] Figure 4 This is a graph showing the change in the distance of the image sensor spot versus the refractive index of alcohol in a preferred embodiment of the present invention;

[0044] Figure 5 A graph showing a change in alcohol concentration versus spot spacing on an image sensor in a preferred embodiment of the present invention;

[0045] Figure 6 This is a temperature and refractive index compensation curve diagram in a preferred embodiment of the present invention;

[0046] Figure 7 This is a pressure and refractive index compensation curve diagram in a preferred embodiment of the present invention.

[0047] Explanation of the accompanying symbols: 1. Laser diode; 2. Plano-convex lens; 3. Glass window; 4. Channel for the solution to be tested; 5. Compound lens; 6. Image sensor; 7. Temperature sensor; 8. Pressure sensor. DETAILED DESCRIPTION

[0048] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0049] In the description of the present invention, it should be noted that the terms "upper," "lower," "inner," "outer," "top / bottom," and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0050] In the description of the present invention, it should be noted that, unless otherwise clearly stipulated and limited, the terms "installed", "provided with", "set / connected", "connected", etc. should be understood in a broad sense. For example, "connection" can be a wall-mounted connection, a detachable connection, or an integral connection. It can be a mechanical connection or an electrical connection. It can be a direct connection or an indirect connection through an intermediate medium. It can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0051] refer to Figure 1-Figure 7This embodiment provides a real-time solution concentration detection method based on composite lens focus offset, which is used for non-contact rapid measurement of liquid concentration. It is particularly suitable for concentration detection of transparent to translucent liquids such as alcohol and sugar solutions, and is suitable for real-time monitoring of parameters such as the concentration gradient of alcohol solutions, the purity level of organic solvents, and the ion concentration of electrolyte solutions.

[0052] The detection method also includes a solution concentration measuring device (such as Figure 1 ), the solution concentration measuring device includes a laser diode, a plano-convex lens, a sample cell, a compound lens and an image sensor arranged in sequence along the optical path; the sample cell includes a channel for a solution to be tested, and the channel for a solution to be tested contains a solution to be tested; a glass window is provided on one side of the channel for a solution to be tested facing the plano-convex lens, and the compound lens is provided on one side of the channel for a solution to be tested facing the image sensor, with the arc-shaped convex surface of the compound lens facing away from the solution to be tested; the laser light emitted by the laser diode passes through the plano-convex lens, the sample cell and the compound lens in sequence, and is imaged as two light spots on the image sensor, and the solution concentration is inverted by the distance between the two light spots on the image sensor; a temperature sensor and a pressure sensor are provided at the bottom of the sample cell; the temperature sensor and the pressure sensor are used to detect the temperature and pressure of the solution to be tested, respectively, and the temperature sensor and the pressure sensor are used to monitor environmental parameters in real time and compensate for the influence of temperature and pressure on the measurement through an algorithm.

[0053] This solution concentration measurement device measures concentration by detecting changes in the distance between two light spots. A temperature sensor and a pressure sensor detect temperature and pressure, respectively, and an algorithm compensates for their effects on the measurement. In this embodiment, the composite lens is a combination of a prism and two cylindrical lenses. The two cylindrical lenses are positioned on one side of the prism facing away from the solution being measured, with an angle δ of 180° - 2α. This angle δ is related to the concentration detection range. The image sensor is a linear array CMOS image sensor.

[0054] The detection method comprises the following steps:

[0055] Step A: The laser light emitted by the laser diode is collimated into parallel light by a plano-convex lens. The parallel light is incident on the sample cell through a glass window and then emitted by a compound lens to form an image on the image sensor.

[0056] Step B: Parallel light passes through a compound lens and is imaged as two light spots on an image sensor. Since changes in solution concentration will cause changes in the refractive index, the change in refractive index will affect the size of the light spots and thus the distance between the two light spots. The distance s between the two light spots on the image sensor is recorded, and the solution concentration is inverted by the distance s between the two light spots.

[0057] Step C: detecting the temperature and pressure of the solution to be measured by a temperature sensor and a pressure sensor, respectively, and compensating for the effects of temperature and pressure on the measurement by an algorithm;

[0058] The relationship between alcohol concentration and refractive index (such as Figure 3 ) as an example, the calculation steps for inverting the solution concentration are as follows:

[0059] like Figure 2 , let the parameters of the compound lens be: the base angle of the compound lens is α, the curvature radius of the compound lens is R; initial state: let the concentration of the test solution be c0, the refractive index of the test solution be n0, when propagating in the compound lens, the angle between the light passing through the center of the compound lens and the horizontal direction is γ0, and the distance between the two light spots is D0;

[0060] When the laser passes through the solution to be tested and is incident on the inclined incident point A in the compound lens, the geometric relationship shows that the incident angle is the base angle α of the compound lens, and the refraction angle in the compound lens is β;

[0061] According to the law of refraction: nsinα=n L sinβ; where n is the refractive index of the solution to be measured, n L is the refractive index of the compound lens; when the angle is small, sinα≈α;

[0062] The internal refraction angle β of the compound lens is calculated as: When the small angle approximation is used,

[0063]

[0064] The angle γ between the light passing through the center of the compound lens and the horizontal direction is:

[0065] When the laser passes through the solution to be tested and is incident on the compound lens from the inclined incident point A, it forms a light spot at point B of the image sensor through the compound lens. Let the distance from point B to the optical axis be s.

[0066] Let the straight-line distance from the image sensor to the center of the compound lens be L; let the distance between the two light spots be D. According to symmetry, D = 2s; the calculation formula is:

[0067]

[0068] The relationship between the distance ΔD between the two light spots on the image sensor and the refractive index of alcohol (such as Figure 4 ), based on the above calculation, the relationship between alcohol concentration and the distance ΔD between the two light spots can be derived, as shown in Figure 5 .

[0069] In this embodiment, temperature compensation is to add a temperature compensation element, such as a temperature sensor, to the solution concentration measuring instrument. Figure 6 The resistance value of the temperature sensor changes with temperature. By measuring the change in the resistance value of the temperature sensor, the temperature change can be known. Then, according to the pre-established temperature compensation model, the measured value of the refractive index of the solution is compensated in real time. The calculation formula is as follows:

[0070] n temperature (λ,T)=(b1+b2λ 2 +b3λ 4 )(TT b )+(b4+b5λ 2 +b6λ 4 )(TT b ) 2 +(b7+b8λ 2 +b9λ 4 )(TT b ) 3 ;

[0071] Where b1-b9 is the temperature-wavelength coupling coefficient, T b is the reference temperature and T is the temperature.

[0072] In this embodiment, pressure compensation is to add a pressure balancing device, such as installing a gas pressure regulating valve or a liquid pressure stabilizer, so that the pressure in the measurement environment remains relatively stable, reducing the impact of pressure changes on the solution refractive index measurement. Figure 7 , based on the pressure change of the pressure sensor, the measured value of the refractive index of the solution is compensated in real time; the calculation formula is as follows:

[0073] n pressure (λ,T,p)=[c1+c2λ 2 +(c3+c4λ 2 )T](pp b )+(c5+c6λ 2 )(p-

[0074] p b ) 2 ;

[0075] Where c1-c6 are correction coefficients, p b is the reference pressure, p is the pressure;

[0076]

[0077] Among them, a1-a5 is the compensation coefficient, λ a is the characteristic wavelength, and λ is the wavelength of incident light.

[0078] The above is only a preferred specific embodiment of the present invention, but the design concept of the present invention is not limited to this. Any technician familiar with this technical field who uses this concept to make non-substantial changes to the present invention within the technical scope disclosed by the present invention shall be deemed to infringe the scope of protection of the present invention.

Claims

1. A method for real-time detection of solution concentration based on composite lens focus offset, characterized by: The detection method also includes a solution concentration measuring device, which includes a laser diode, a plano-convex lens, a sample cell, a compound lens, and an image sensor arranged in sequence along the light path; The sample cell includes a test solution channel containing a test solution; a glass window is provided on one side of the test solution channel facing the plano-convex lens; the composite lens is provided on one side of the test solution channel facing the image sensor, with the curved convex surface of the composite lens facing away from the test solution; The laser light emitted by the laser diode passes through the plano-convex lens, the sample cell, and the compound lens in sequence, and is imaged as two light spots on the image sensor; A temperature sensor and a pressure sensor are provided at the bottom of the sample pool; the temperature sensor and the pressure sensor are used to detect the temperature and pressure of the solution to be tested respectively; The composite lens is a combination of a prism and two cylindrical lenses, and the two cylindrical lenses are combined at an angle δ on a surface of the prism facing away from the solution to be tested, and δ=180°-2α, where α is the base angle of the composite lens; The detection method comprises the following steps: Step A: The laser light emitted by the laser diode is collimated into parallel light by a plano-convex lens. The parallel light is incident on the sample cell through a glass window and then emitted by a compound lens to form an image on the image sensor. Step B: Parallel light is projected onto the image sensor through a compound lens to form two light spots, and the distance s between the two light spots on the image sensor is recorded. The concentration of the solution is inverted by the distance s between the two light spots; Step C: Detect the temperature and pressure of the solution to be measured by a temperature sensor and a pressure sensor respectively, and compensate for the influence of temperature and pressure on the measurement by an algorithm.

2. The method for real-time detection of solution concentration based on composite lens focus offset according to claim 1, characterized in that: In step B, the calculation steps for the inverse solution concentration are as follows: Assume that the parameters of the composite lens are: the base angle of the composite lens is α, the radius of curvature of the composite lens is R; the refractive index of the solution when the solution concentration is c0 is n0, when the light passing through the center of the composite lens propagates in the composite lens, the angle between the light and the horizontal direction is γ0, and the distance between the two light spots is D0; When the laser passes through the solution to be tested and is incident on the inclined incident point A in the compound lens, the geometric relationship shows that the incident angle is the base angle α of the compound lens, and the refraction angle in the compound lens is β; According to the law of refraction: nsinα=n L sinβ; where n is the refractive index of the solution to be measured, n L is the refractive index of the compound lens; when the angle is small, sinα≈α; The internal refraction angle β of the compound lens is calculated as: When the small angle approximation is used, The angle γ between the light passing through the center of the compound lens and the horizontal direction is: When the laser passes through the solution to be tested and is incident on the compound lens from the inclined incident point A, it forms a light spot at point B of the image sensor through the compound lens. Let the distance from point B to the optical axis be s. Let the straight-line distance from the image sensor to the center of the compound lens be L; let the distance between the two light spots be D. According to symmetry, D = 2s; the calculation formula is:

3. The method for real-time detection of solution concentration based on composite lens focus offset according to claim 1, characterized in that: The image sensor is a linear array CMOS image sensor.

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