CN104198436B - A light-transmitting liquid concentration detection system and detection method - Google Patents

Abstract

The invention discloses a kind of light-transmissive fluid concentration detection system, it is characterized in that: tested light-transmissive fluid is enclosed in settling vessel；It is positioned on the inwall of container side and the second illuminator is set, the first illuminator and the 3rd illuminator it is respectively arranged with on the inwall of the container opposite side relative with the second illuminator, the laser beam that the laser instrument of external container sends is projected to the first illuminator, injection conduct detection light after the refraction of the second illuminator and the 3rd illuminator the most successively, photodetector receives detection light light spot position signal, obtains tested light-transmissive fluid concentration through signal processing.Accuracy of detection of the present invention is high, speed is fast, simple in construction, it is easy to operation, and has wider refractive index detection range, can be used for the minor variations of detection strength of fluid real-time, quick.

Description

A light-transmitting liquid concentration detection system and detection method

technical field

The invention relates to a light-transmitting liquid concentration detection system and a detection method, belonging to the detection field.

Background technique

Concentration is a very important index to measure the quality of industrial products and an important physical parameter of liquid substances. Therefore, in the production of chemical, pharmaceutical, food and other industries, as well as in some scientific research, it is often necessary to accurately and quantitatively measure the concentration of specific substances in liquids. Traditional methods for measuring liquid concentration mainly include specific gravity method, chemical analysis method, ultrasonic method, optical method and so on. Although the specific gravity method has high precision, it needs to be weighed many times with an analytical balance, and can only detect the concentration of the upper surface solution; the chemical analysis method has high detection precision, but many chemical reagents consumed during its use are very expensive , the cost is high, and it requires a long analysis cycle, which cannot meet the requirements of real-time online detection; although the ultrasonic method has high precision, the equipment used is heavy and difficult to move, and the concentration of the liquid to be measured must be appropriate, neither too high nor too high Low; although the optical method is convenient, fast, cheap and non-polluting, it is easily affected by optical rotation, sensitivity, equipment or environment, resulting in low accuracy. These techniques require complex and expensive experimental setups, and cannot be used for real-time detection of the concentration of flowing liquids. At the same time, sampling is time-consuming and cumbersome, with large lag and inaccurate analysis results, which cannot meet the actual requirements of current industrial production.

In the patent "liquid concentration detection device and detection method" of publication number 101216422, a device and detection method for detecting liquid concentration are disclosed. It uses light reflection and refraction in a tight container with a light-transmitting cover to measure the refractive index and concentration of an unknown liquid, which can achieve the purpose of quickly detecting the liquid’s refractive index. However, in this device, the number of refractions in the optical path is small, and the spot displacement Δd is small , the sensitivity is not high.

In the patent "a liquid concentration detection device" with publication number 102590098A, a photoelectric element is used to detect the intensity of refracted light on the exit surface, which is costly, and the system is complicated and difficult to build.

In the paper (Research on Optical Salinity Detection Technology Based on Position Sensitive Devices[J]. The method of changing the salinity of the measured brine is used to obtain the relationship between the salinity and the position of the light point on the photosensitive detector to stabilize the salinity of the brine, but the process takes a long time, which is not conducive to real-time online detection.

In the paper (Performance Analysis of Photoelectric Detection System for Solution Mass Fraction [J]. Sensors and Microsystems, 2013, 31(11): 8-10.), scholars proposed to optimize the optical path and increase the light through multiple reflections. The process can effectively overcome the above defects, but the spot displacement caused by the change of unit concentration is small, and the sensitivity cannot meet the requirements.

Contents of the invention

In order to avoid the disadvantages of the above-mentioned prior art, the present invention provides a light-transmitting liquid concentration detection system and detection method, in order to effectively improve the sensitivity of photoelectric detection of the concentration of transparent liquid, and realize the miniaturization of equipment. When the refractive index of the reference solution is known, the system can quickly and accurately measure the concentration of the transparent solution and the refractive index of the solution.

The technical solution adopted by the present invention to solve its technical problems is:

The structural features of the light-transmitting liquid concentration detection system of the present invention are as follows: a static container is arranged, and the light-transmitting liquid to be measured is sealed in the static container; in the container, a second A reflective mirror, a first reflective mirror and a third reflective mirror are respectively arranged on the inner wall of the container on the other side opposite to the second reflective mirror, the mirror surfaces of the first reflective mirror and the third reflective mirror are parallel to each other and The second reflector is at an inclination angle; on the side wall of the container, an upper light-transmitting window is arranged above the second reflector, and a lower light-transmitting window is arranged below the second reflector;

The laser beam emitted by the laser installed outside the container is projected from the upper light-transmitting window to the first reflector, and the refracted light of the first reflector is refracted by the second reflector and the third reflector in turn. , emitted from the lower light-transmitting window and used as detection light;

A photodetector is set to receive the light spot position signal of the detection light, and the concentration of the light-transmitting liquid to be measured is obtained through signal processing.

The structural features of the light-transmitting liquid concentration detection system of the present invention also lie in:

The laser is a semiconductor laser with good linearity at λ=635nm.

The photodetector is a position sensitive sensor PSD or a one-dimensional linear charge-coupled device CCD.

The characteristics of the method for utilizing the detection system of the present invention to carry out the concentration of light-transmitting liquid are to carry out as follows:

Step a, inject a reference light-transmitting liquid with a known refractive index n1 into the container, set the angle at which the laser beam emitted by the laser enters the container from the upper window, so that the incident light passes through the first reflector, the second reflector and the After the refraction of the third mirror, it is emitted from the lower light-transmitting window, and the reference spot position information is obtained in the photodetector; the detection state is set with the detection state of the laser and the photodetector;

Step b, replacing the reference light-transmitting liquid in the container with a standard salt ion solution, keeping the laser and the photodetector in a set detection state, and obtaining the spot position information of the standard salt ion solution in the photodetector;

Step c, repeat step b for standard salt ion solutions of different concentrations, correspondingly obtain the spot position information of standard salt ion solutions of different concentrations, and thus obtain the relationship diagram between the concentration and the spot position information in the photodetector;

Step d, for the measured transparent liquid, obtain the position information of the light spot of the measured transparent liquid on the photodetector according to step b, and obtain the concentration value of the measured transparent liquid by comparing with the relationship diagram.

Compared with the prior art, the beneficial effects of the present invention are reflected in:

1. The laser beam of the present invention is reflected multiple times in the mirror group, increasing the optical path, enlarging the spot displacement Δd, effectively improving the detection sensitivity of the transparent solution, reducing the height required by the detection instrument, and having a compact structure.

2. The invention belongs to non-contact measurement, which is safer for the measurement of toxic liquids;

3. The system of the present invention is simple in structure and good in stability. It can conveniently and accurately realize the real-time online detection of liquid concentration by using the position-sensitive detector PSD or one-dimensional linear charge-coupled device CCD to collect information, and can be widely used in teaching use.

Description of drawings

Fig. 1 is a structural schematic diagram of the present invention.

Fig. 2 is a schematic diagram of the optical path detection principle of the present invention.

Figure 3 shows the result after multiple reflections.

Labels in the figure: 1 laser, 2 upper light-transmitting window, 3 container, 4 first reflector, 5 second reflector, 6 third reflector, 7 lower light-transmitting window, 8 photoelectric detector, 9 data acquisition card, 10 computer, 11 bottom rubber plug, 12 solution outlet, 13 outlet valve, 14 top rubber plug, 15 solution inlet, 16 inlet valve.

detailed description

Referring to Fig. 1, the structural form of the light-transmitting liquid concentration detection system in the present embodiment is: a static container 3 is set, the bottom of the container 3 is sealed by a bottom rubber stopper 11, and a solution outlet 12 is provided in the bottom rubber stopper 11, And outlet valve 13 is set on solution outlet 12, is used for discharging liquid; The top of container 3 is provided with top rubber stopper 14, offers solution inlet 15 on top rubber stopper 14, is provided with inlet valve 16 on solution inlet 15, Used to inject light-transmitting liquid into the container 3.

The light-transmitting liquid to be tested is sealed in a static container 3; in the container 3, a second mirror 5 is arranged on the inner wall on one side of the container, and the inner wall on the other side of the container opposite to the second mirror 5 The first reflector 4 and the third reflector 6 are respectively arranged on the top, the mirror surfaces of the first reflector 4 and the third reflector 6 are parallel to each other and form an inclination angle with the second reflector 5; on the side of the container On the wall, an upper light-transmitting window 2 is arranged above the second reflector 5, and a lower light-transmitting window 7 is arranged below the second reflector 5;

The laser beam emitted by the laser 1 arranged outside the container is projected from the upper light-transmitting window 2 to the first reflective mirror 4, and the refracted light of the first reflective mirror 4 passes through the second reflective mirror 5 and the third reflective mirror in turn. After the refraction of the reflector 6, it is emitted from the lower light-transmitting window 7 and used as detection light;

The photodetector 8 is set to receive the light spot position signal of the detection light, which is collected by the data acquisition card 9 and processed by the computer 10 to obtain the concentration of the light-transmitting liquid to be measured.

In a specific implementation, the laser 1 is a semiconductor laser with good linearity of λ=635nm; the photodetector 8 is a position sensitive sensor PSD or a one-dimensional linear charge-coupled device CCD.

The method for carrying out the concentration of the light-transmitting liquid with the detection system in this embodiment is to proceed as follows:

Step 1. Inject a reference light-transmitting liquid with a known refractive index n1 into the container, and set the angle at which the laser beam emitted by the laser 1 enters the container from the upper window 2, so that the incident light passes through the first mirror 4 and the second mirror in sequence. After the refraction of reflective mirror 5 and the 3rd reflective mirror 6, emit from lower light-transmitting window 7, and obtain reference spot position information in photodetector 8; Determine the detection status;

Step 2, replacing the reference light-transmitting liquid in the container with a standard salt ion solution, keeping the laser and the photodetector in a set detection state, and obtaining the spot position information of the standard salt ion solution in the photodetector 8;

Step 3, repeat step 2 for standard salt ion solutions of different concentrations, correspondingly obtain the spot position information of standard salt ion solutions of different concentrations, and thus obtain the relationship diagram between the concentration and the spot position information in the photodetector 8;

Step 4. For the transparent liquid under test, according to step 2, obtain the spot position information of the transparent liquid under test on the photodetector 8, and obtain the concentration value of the transparent liquid under test by comparing with the relationship diagram.

Fig. 2 has shown the measuring principle of the present invention as follows:

The schematic diagram of the optical path based on the reflective detection concentration is shown in Figure 2. In a closed container filled with light-transmitting or semi-transparent liquid, there are two reflectors at an angle of α with the inner wall of the container, which are respectively the first reflector 4 and the third reflector. mirror 6, the distance between the two reflectors is l; the light emitted by the laser enters the solvent pool at an angle of θ ₁ and then shoots to the first reflector 4 at a refraction angle of θ ₂ , and after being reflected by the first reflector 4, the light Refract to the second reflector 5 with θ ₃ reflection angle, enter the 3rd reflector 6 with θ ₄ reflection on the 2nd reflector 5, after the reflection of the 3rd reflector 6, the light turns to glass with reflection angle θ ₅ , again After passing through the glass at an incident angle θ ₆ , it irradiates the PSD surface at a refraction angle θ ₇ . In the early stage of light path adjustment, let the light shine vertically on the PSD. According to the law of optical refraction, the relationship between the angle of incidence and the angle of reflection can be obtained as follows:

n ₁ sinθ ₁ ＝n ₂ sinθ ₂ (1)

θ ₃ = θ ₂ +α (2)

θ ₄ = θ ₂ + 2α (3)

n ₁ sinθ ₇ = n ₂ sinθ ₆ (4)

As shown in Figure 3, suppose the vertical distance from the incident point of the light on the glass to the first mirror 4 is h ₁ , and the distance from the point where the light is first incident on the first mirror 4 to the glass surface is h ₂ , and so on, get h ₃ , h ₄ , the reflected light beam is refracted by the liquid-air interface to the PSD detection target surface, and the optical distance is L, and the distance between the incident point and the outgoing point of the light on the glass is w, then according to Trigonometric functions can be obtained:

${\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

h ₄ ＝h ₃ sin(90+α)sin(90-θ ₄ )/sin(90-θ ₄ -α) (6)

l＝h ₂ tanθ ₂ +h ₂ tan(θ ₃ +α) (7)

${\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; l</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

w=h ₂ tanθ ₂ +h ₂ tan(θ ₃ +α)+h ₄ tanθ ₄ +h ₄ tan(θ ₅ +α) (10)

When the refractive index of the solution in the container changes, the reflected beam is deflected accordingly, and the PSD outputs the offset of the beam in the form of voltage. When the concentration of the solution changes, the changed optical path is shown by the dotted line in the figure, the refractive index n ₂ becomes n' ₂ , and the angles θ ₂ , θ ₃ , θ ₄ , θ ₅ , θ ₆ , and θ ₇ change to θ' respectively ₂ , θ′ ₃ , θ′ ₄ , θ′ ₅ , θ′ ₆ , θ′ ₇ , and the vertical distance from the point where the light first incident on the first mirror 4 to the glass surface changes from h ₂ to h' ₂ , the distance w between the incident point and the exit point of the light on the glass becomes w'. _A similar result to w can also be obtained by using the changed angle and h2. The Δd offset obtained on the PSD has a one-to-one correspondence with the difference in the refractive index of the measured liquid, and the liquid concentration when the refractive index of the liquid is _n'2 is obtained. Then the final displacement Δd of the spot on the PSD due to the change of the refractive index of the solution is:

Δd=(w-w')cosθ ₇ +[L+(w-w')sinθ ₇ ]tan(θ ₇ -θ′ ₇ )

The above derivation process is the calculation result of one reflection of light in the solution. It can be known that the deflection signal of the microbeam due to the change of the refractive index of the solution is mainly caused by two factors, one is caused by the change in the multiple refraction effect; The other is the part that increases due to increasing the height of the solvent pool. Theoretical analysis shows that increasing the height of the solvent pool to an appropriate value, and at a larger incident angle, the PSD signal responds better. However, due to the influence of the equipment itself and the experiment itself, on the one hand, increasing the height of the solvent pool will increase the solution replacement time, and at the same time have a great impact on the actual response signal of the PSD; on the other hand, it will also increase the space occupied by the instrument itself. , so that the instrument is not easy to miniaturize. When designing the experimental optical path, the number of light reflections in the solvent pool should be increased as much as possible, which can make the structure of the instrument space more compact and obtain better resolution. For this reason, continue to calculate the calculation results after the second reflection and the third reflection of the mirror.

Fig. 3 is the relationship diagram of the angle of incidence θ ₁ and the spot displacement Δd obtained by simulating and calculating different incident angles and the first reflection, the second reflection, and the third reflection respectively through the first reflector 4 and the third reflector 6. It can be seen from Figure 3 that the sensitivity of the detection system can be greatly improved after multiple reflections.

The structural form given in this embodiment is that the first reflector and the third reflector are respectively arranged on the left side. If the number of reflectors continues to increase on the left side, the displacement of the light spot will be effectively increased and the sensitivity of the detection system will be improved. When the number of mirrors reaches a certain number, the sensitivity of the detection system will reach the desired effect.

The present invention is described through a specific implementation process, and without departing from the scope of the present invention, various transformations and equivalent substitutions can be made to the invention. Therefore, the present invention is not limited to the specific implementations disclosed, but rather falls within the scope of all embodiments of the claimed invention.

Claims (4)

1. a light-transmissive fluid concentration detection system, is characterized in that: arrange the container of a standing, and tested light-transmissive fluid is enclosed in institute State in settling vessel；In the above-described container, it is positioned on the inwall of container side and the second illuminator (5) is set, second anti-with described The first illuminator (4) and the 3rd illuminator (6) it is respectively arranged with on the inwall of the container opposite side that light microscopic (5) is relative, described One illuminator (4) is parallel to each other with the minute surface of the 3rd illuminator (6) and becomes an inclination angle with described second illuminator (5)；Described On container side wall, be in described second illuminator (5) is provided above printing opacity form (2), is in described second illuminator (5) lower section arranges lower printing opacity form (7)；

The laser beam sent by the laser instrument (1) being arranged on external container is projected to described from described upper printing opacity form (2) One illuminator (4), the reflection light of described first illuminator (4) is successively through the second illuminator (5) and the reflection of the 3rd illuminator (6) After, by the injection of lower printing opacity form (7) and as detection light；

Photodetector (8) is set and is used for receiving the light spot position signal of described detection light, obtain tested printing opacity through signal processing Strength of fluid.

Light-transmissive fluid concentration detection system the most according to claim 1, is characterized in that: described laser instrument (1) be λ= The semiconductor laser of 635nm.

Light-transmissive fluid concentration detection system the most according to claim 1, is characterized in that: described photodetector (8) is position Put sensitive sensor PSD or one dimensional linear array Charge Coupled Device (CCD) CCD.

4. the method utilizing detecting system described in claim 1 to carry out light-transmissive fluid Concentration Testing, is characterized in that: as follows Carry out:

Step a, in container, inject the benchmark light-transmissive fluid that known refractive index is n1, the laser light that laser instrument (1) sends is set Restraint the angle entering in container from upper printing opacity form (2) so that incident ray is sequentially passing through the first illuminator (4), second anti- After the reflection of light microscopic (5) and the 3rd illuminator (6), injection in lower printing opacity form (7), and obtain in photodetector (8) Obtain benchmark hot spot positional information；With this detection state of described laser instrument and photodetector for setting detection state；

Step b, the benchmark light-transmissive fluid in container is replaced by standard salt solion, keeps described laser instrument and photodetection Device, for setting detection state, obtains the facula position information of standard salt solion in photodetector (8)；

Step c, standard salt solion for variable concentrations repeat step b, the corresponding standard salt ion obtaining variable concentrations The facula position information of solution, and thus obtain the graph of a relation of facula position information in concentration and photodetector (8)；

Step d, for tested transparency liquid, obtain tested transparency liquid at photodetector (8) upper facula position letter by step b Breath, by the comparison with described graph of a relation, obtains the concentration value of tested transparency liquid.