CN201152850Y - Liquid concentration detecting device - Google Patents

Abstract

The liquid concentration detection device is characterized in that a closed container with a light-transmitting cover is provided, the light-transmitting or semi-transparent liquid fills the airtight container, and a reflective plate is fixedly installed in the airtight container to form a non-zero angle with the light-transmitting cover; The projection beam on the reflector comes from the projection light source outside the container, and the reflected beam on the reflector passes through the liquid in the container and the light-transmitting cover, and is detected by the optical receiver arranged outside the airtight container and on the optical path of the reflected beam. Receiving, taking the spot position signal on which the reflected light beam detected by the optical receiver is projected as the detection signal. The utility model has high detection precision and fast speed, has a wide detection range of the refractive index, and can be used for real-time and rapid detection of small changes in liquid concentration.

Description

Liquid Concentration Detection Device

technical field

The utility model relates to a device for detecting liquid concentration.

Background technique

Liquid concentration is a very important physical parameter of liquid substances. In the production of chemical industry, beverage, brewing, medicine and other industries, as well as in some scientific research, it is often necessary to measure the concentration of specific substances in liquid. Therefore, the accurate detection of liquid concentration Particularly important.

There are many methods to measure liquid concentration, the traditional methods are specific gravity method, optical rotation method, spectrophotometric method, ultrasonic method and refractive index method. Specific gravity refers to the mass ratio of the liquid mass to the same volume of distilled water under the same conditions. Although the specific gravity method has high precision, it is cumbersome and needs to be weighed several times with an analytical balance. Different components have different optical rotations, and the measurement accuracy is not high; spectrophotometry is used to detect light transmittance, and the sensitivity is not high enough; ultrasonic waves use the relationship between ultrasonic sound velocity and liquid density and viscosity to achieve the purpose of detection, which has the advantages of high precision. However, it is heavy and difficult to move; the existing refractive index method is typically the Abbe refractometer based on total reflection, which has a very high detection accuracy of the refractive index, which can reach 2×10 ^-4 , but the Abbe refractometer measures liquid The range of refractive index is relatively narrow, generally only 1.3-1.7.

Utility model content

The utility model is to avoid the shortcomings of the above-mentioned prior art, and provides a liquid concentration detection device based on the refractive index method with high measurement accuracy, fast and convenient measurement process, and a wide refractive index detection range.

The utility model solves the technical problem and adopts the following technical solutions:

The structural feature of the liquid concentration detection device of the utility model is that an airtight container with a light-transmitting cover plate is arranged, and the light-transmitting or semi-light-transmitting liquid is filled in the airtight container, and a reflective plate is fixedly installed in the airtight container; the projected light beam on the light-reflecting plate comes from the container The external projection light source, the reflected light beam on the reflector passes through the liquid in the container and the light-transmitting cover plate, and is received by the optical receiver arranged outside the airtight container on the optical path of the reflected light beam, and the reflection detected by the optical receiver The spot position signal on which the beam is projected is the detection signal.

The structural features of the liquid concentration detection device of the present utility model also lie in:

The projection light beam from the projection light source is perpendicular to the transparent cover plate.

The angle between the reflective plate and the light-transmitting cover plate is not zero.

The projection light source is a focused laser beam.

The optical receiver is a displacement sensor PSD or a one-dimensional linear array charge-coupled device CCD.

The airtight container is a constant temperature container.

The method for utilizing the utility model device to carry out liquid concentration detection is to carry out as follows:

a. Inject a reference liquid with known refractive index n ₁ into the airtight container, detect and record the position information of the reference spot projected on it by the optical receiver;

b. Replace the reference liquid in the airtight container with the measured liquid. Under the same conditions, the optical receiver detects and records the position information of the measured light spot projected on it;

c. Comparing the reference spot position information with the measured spot position information, and obtaining the offset Δd of the spot position due to the difference in refractive index between the reference liquid and the measured liquid, the offset Δd of the spot position is different from the reference The refractive index difference Δn ₁ of the liquid and the measured liquid has a one-to-one linear relationship, so the measured liquid refractive index n′ ₁ =n ₁ +Δn ₁ is obtained;

d. According to the one-to-one relationship between the refractive index _n'1 and the liquid concentration, the liquid concentration corresponding to the measured liquid refractive index _n'1 is obtained.

Compared with the prior art, the beneficial effects of the utility model are reflected in:

1. By adopting an optical receiver with micron or even submicron displacement resolution, the utility model can make the device achieve a refractive index detection accuracy of 0.5×10 ^-4 ; thus it can detect small changes in liquid concentration.

2. Although the displacement range of the optical receiver is limited, the utility model can achieve a wider detection range of the refractive index by properly selecting the reference liquid, that is, selecting a reference liquid whose refractive index is close to the measured liquid, and can also achieve a larger range of liquid concentration detection.

3. Since the airtight container can have a small capacity of tens of microliters, the reference liquid in the airtight container can be quickly replaced by the liquid to be tested through the peristaltic pump, which can achieve the purpose of quickly detecting the refractive index of the liquid.

Description of drawings

Fig. 1 is the structural representation of the utility model.

Fig. 2 is a schematic diagram of the detection principle of the utility model.

Fig. 3 is the test curve of the refractive index of the ethanol solution of different concentration that the utility model implements.

Fig. 4 is the refractive index test curve of another ethanol solution with different concentrations implemented by the utility model.

FIG. 5 is a graph showing the relationship between the minimum detectable Δn ₁ of the system and the incident angle α.

Labels in the figure: 1 projection light source, 2 light-transmitting cover plate, 3 airtight container, 4 reflector, 5 sealing ring, 6 peristaltic pump, 7 constant temperature system, 8 optical receiver, 9 signal processing device, 10 projection beam, 11 reflection beam.

The utility model will be further described below in conjunction with the accompanying drawings through specific embodiments.

Detailed ways

Referring to Fig. 1 and Fig. 2, an airtight container 3 with a light-transmitting cover plate 2 and a sealing ring 5 sealing the light-transmitting cover plate 2 is provided, and the light-transmitting or semi-light-transmitting liquid is filled with the airtight container 3 and fixed in the airtight container 3 The reflector 4 is set; the projected light beam 10 on the reflector 4 comes from the projection light source 1 outside the container, and the reflected light beam 11 on the reflector 4 passes through the liquid in the container and the light-transmitting cover plate 2, and is arranged on the outside of the airtight container 3 1. Received by the optical receiver 8 located on the optical path of the reflected beam 11 , the spot position signal projected on the reflected beam 11 detected by the optical receiver 8 is used as a detection signal.

In specific implementation, setting the projection light beam 10 from the projection light source 1 to be perpendicular to the light-transmitting cover plate 2, the angle between the reflective plate 4 and the light-transmitting cover plate 2 to be non-zero, and the projection light source 1 adopting a focused laser beam can all obtain better High measurement accuracy.

The optical receiver 8 adopts a displacement sensor PSD or a one-dimensional linear array charge-coupled device CCD, and the airtight container 3 is set as a constant temperature container controlled by a constant temperature system 7 to ensure that the temperature in the airtight container 3 is constant at ±0.01K.

The detection method is carried out as follows:

a. Inject a reference liquid with a known refractive index _n1 into the airtight container 3, detect and record the position information of the reference spot projected on it by the optical receiver 8;

b. Driven by the peristaltic pump 6, replace the reference liquid in the airtight container 3 with the measured liquid, and under the same conditions, detect and record the position information of the measured light spot projected on it by the optical receiver 8;

c. The signal processing device 9 compares the reference spot position information with the measured spot position information, and obtains the offset Δd of the spot position due to the difference in refractive index between the reference liquid and the measured liquid, and the offset Δd of the spot position There is a one-to-one linear relationship with the refractive index difference Δn ₁ of the reference liquid and the measured liquid, so the measured liquid refractive index n′ ₁ =n ₁ +Δn ₁ is obtained.

d. For a specific binary mixed liquid, the refractive index _n'1 has a one-to-one correspondence with the concentration of the liquid to be measured. Therefore, according to the one-to-one correspondence between the refractive index _n'1 and the liquid concentration, the measured The obtained liquid refractive index n' ₁ corresponds to the liquid concentration.

Fig. 2 shows that the utility model measurement principle is as follows:

According to the refractive index formula: n ₁ ·sinα=n ₂ ·sinβ=n ₃ ·sinγ, when the measured liquid replaces the reference liquid, the refractive index n ₁ of the liquid in the closed container changes, and at the same time, the refractive index of the liquid outside the closed container The air refractive index _n2 and the refractive index _n3 of the light-transmitting cover remain unchanged, and the projection beam 10 is incident perpendicular to the light-transmitting cover, so the incident angle α of the reflected light beam 11 from the liquid to the light-transmitting cover 2 remains unchanged, According to the refractive index formula, it can be seen that the exit angle γ will change, and the exit angle β from the transparent cover plate 2 to the air will also change accordingly. Therefore, the spot position of the projected beam received on the optical receiver 8 will move. The amount corresponds to the difference between the refractive index of the supplementary measurement liquid and the reference liquid. At the same time, the refractive index of the reference liquid is known, so that the refractive index of the measured liquid can be obtained. For a specific binary mixed liquid, the refractive index n' ₁ has a one-to-one correspondence with the concentration, so the concentration of the measured liquid is also obtained.

When the refractive index of the measured liquid is not much different from that of the reference liquid, that is $\frac{\mathrm{\&Delta;}{\mathrm{no}}_1}{{\mathrm{no}}_1}<5\%$ , assuming that the distance of the reflected light beam 11 from the transparent cover 2 to the optical receiver 8 is L, and the thickness of the transparent cover 2 is h, because $\frac{L}{h}>50,$ Then there are:

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;d</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; ctg</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; arcsin</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula: Δn ₁ is the difference in refractive index between the measured solution and the reference solution

Δd is the distance that the spot of the reflected beam moves on the optical receiver 8 .

Obviously when α≠0, Δn ₁ ≠0

Suppose the refractive index of the measured liquid is n′ ₁ , assuming that Δd in Figure 2 is positive, then:

n′ ₁ =n ₁ +Δn ₁ (2)

It can be known from the formula (1): when L, n ₁ , n ₂ , and α are constant, Δn ₁ has a linear relationship with Δd. When Δd takes the minimum displacement resolution value of the optical receiver 8, the obtained Δn ₁ is the minimum change value of the liquid refractive index that the system can detect. Since the optical receiver 8 adopted has a displacement resolution of micron or even submicron, the system has high detection accuracy.

Referring to Fig. 5 , under the condition of constant L, n ₁ , and n ₂ , when Δd is taken as the minimum displacement resolution value of the optical receiver 8, the functional relationship between the incident angle α (α is smaller than Brewster's angle) and Δn ₁ . Obviously, the larger the incident angle α is, the smaller Δn ₁ is, that is, the higher the detection sensitivity. In order to improve the detection accuracy, it can be achieved by increasing α, but due to the existence of the background noise of the system, when α reaches a certain value, the detection sensitivity will not be improved.

It can be seen from formula (2) that although the displacement range of the optical receiver 8 is limited, a wider detection range of the refractive index can be achieved by properly selecting the reference liquid, that is, selecting a reference liquid whose refractive index is close to that of the liquid to be measured.

In the following embodiment 1 and embodiment 2, projection light source 1 adopts the focused laser beam of λ=635nm; Optical receiver 8 adopts displacement sensor PSD, and minimum displacement resolution is 0.1 micron; Constant temperature system 7 controls the temperature of airtight container 3 At 20±0.01°C; the ethanol used is absolute ethanol (≥99.7%).

Example 1:

Referring to Figure 3, the reference liquid is distilled water, and the detection solvent is distilled water for the refractive index of different concentrations of ethanol, and the volume ratio concentration is 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% in sequence , 90%, 100% ethanol refractive index.

Example 2:

Referring to Fig. 4, the reference liquid is distilled water, and the detection solvent is the refractive index of ethanol with different concentrations of distilled water, and the refractive index of ethanol whose volume ratio concentration is 1%, 2%, 3%, 4% and 5% is detected successively.

In embodiments 1 and 2, the volume of the airtight container 3 used is about 800 microliters, and the replacement time is about 20 minutes, which is the time for detecting the refractive index of the liquid to be measured, that is, the time for curve equilibrium in Fig. 3 and Fig. 4 Roughly equivalent, if the volume of the airtight container 3 is 40 microliters, the reference liquid can be replaced by the liquid to be tested within 2 minutes, that is to say, the refractive index of the liquid to be tested can be detected within 2 minutes. In addition, as can be seen from Fig. 3 and Fig. 4, the solvent is distilled water and the refractive index n ' ₁ of different concentrations of ethanol has a one-to-one relationship with its concentration, but it is not a linear relationship. In embodiment 1, the concentration is from 0%-50 %, the refractive index change value is larger, and when its concentration is from 90% to 100%, the refractive index change value is smaller. Therefore, for the ethanol solution whose solvent is distilled water, the optimal detection concentration range is 0%-50%, and the concentration change of 0.2% or even lower can be detected.

Claims (6)

1, liquid concentration detection device is characterized in that the closed container (3) with euphotic cover plate (2) is set, and printing opacity or semi-transparent liquid are full of closed container (3), fixedly install reflector (4) in described closed container (3); Projecting beam (10) on the reflector (4) comes from the projection source (1) of external container, folded light beam (11) on the reflector (4) is passed liquid in container and euphotic cover plate (2), received by the outside that is arranged on closed container (3), the optical receiver (8) that is positioned on the light path of folded light beam (11), folded light beam (11) the projection light spot position signal thereon that detects with described optical receiver (8) is a detection signal.

2, liquid concentration detection device according to claim 1 is characterized in that the described projecting beam (10) of projection source (1) that comes from is perpendicular to euphotic cover plate (2).

3, liquid concentration detection device according to claim 1 is characterized in that described reflector (4) and euphotic cover plate (2) are non-vanishing angle

4, liquid concentration detection device according to claim 1 and 2 is characterized in that described projection source (1) is focussed laser beam.

5, liquid concentration detection device according to claim 1 is characterized in that described optical receiver (8) is displacement transducer PSD or one dimensional linear array Charge Coupled Device (CCD) CCD.

6, liquid concentration detection device according to claim 1 is characterized in that described closed container (3) is a thermostatic container.

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