RU2296981C1 - Refractometer - Google Patents

Abstract

FIELD: technical physics, in particular, refractometer devices, meant for measuring refraction coefficient and other related parameters of solid and liquid substances.

SUBSTANCE: refractometer contains measuring prism, reflecting device, diaphragm, and objective, mounted in focal plane of which is device for determining shifting of light and shadow limit. Located between measuring prism and substance being studied is wedge of transparent substance, refraction coefficient of which exceeds maximal refraction coefficient of substance being studied and exceeds refraction coefficient of measuring prism material, its main cross-section coincides with light fall plane, thick edge is positioned on the side of light fall, and wedge angle satisfies a certain condition. Measuring prism may be made of liquid, which is held by means of glass plate and amounts to angle of 90 deg. with plane of contact of wedge and liquid of measuring prism.

EFFECT: increased precision of measurements and lower requirements to temperature control.

2 cl, 7 dwg

Description

The invention relates to optical instrumentation, and more specifically to a large class of refractometric devices designed to measure the refractive index of various solid, liquid and gaseous substances.

Abbe simple visual or photoelectric refractometers are widely used in the world [1]. Among them, the most accurate are Zeiss submersible refractometers [1], which in many countries were reproduced under various names. For example, in the USSR IRF-1, IRF-451 refractometers (Kazan), RPL-2 (Kiev) were manufactured [1].

Close to the object of the application, the refractometer is a precision laboratory RPL-2 refractometer [1], which contains an illuminator 1 in the form of an incandescent bulb (Fig. 1), a measuring prism 2 made of a transparent substance in the form of optical glass K8 with a known refractive index n _o , the input face which is horizontal, in contact with the test substance 3, the refractive index of which is n _x <n _o , and the output face of the glass of the measuring prism 2 makes an angle Θ <90 ° with its input face. The refractometer is equipped with an illuminating prism 4. Further along the light beam, a reflecting device 5 in the form of a prism, aperture 6, a dispersion compensator 7 in the form of an Amici prism, a lens 8 with a focal length f = 223.8 mm, a uniform scale in the focal plane, are installed 9 with a length of 20 mm, containing 100 divisions, with the help of which the displacement of the limiting beam is determined, i.e. the amount of displacement ΔX of the image observed in the eyepiece 10 of the border of light and shadow.

To count the tenths of the scale division 9 between the lens 8 and the scale 9, an inclined plane-parallel plate 11 is placed, rotated by the device 12 with ten divisions, each of which corresponds to 0.1 divisions of the scale 9. Counting accuracy is 0.1 divisions of the scale (1 division of the circular dial ) corresponds to the accuracy of measuring the refractive index ± 5 · 10 ^-5 .

To correct the correct readings, the refractometer has a screw 13, during rotation of which the reflecting device 5 is tilted and the image of the border of light and shadow is shifted relative to the scale 9. Amici prism 7 is fixed in a pipe with a ring 14, during the rotation of which compensation of dispersion effects occurs when refracting nonmonochromatic light from source 1. The refractometer is mounted on a massive metal stand 15.

The RPL-2 refractometer, like other well-known Abbe refractometers, has a number of significant drawbacks.

Firstly, an Abbe RPL-2 refractometer uses a K8 type optical glass (GOST 13659-78) with a temperature dependence of the refractive index (∂n / ∂t) in the temperature range from -60 to + as a measuring prism 120 ° C does not exceed the value of 0.0028 · 10 ^-4 1 / deg.

And the dependence of the refractive index on the temperature of the studied liquids, even under normal conditions (from +10 to + 40 ° C), is hundreds of times greater.

For example, in water at t = (20 ± 2) ° C (∂n / ∂t) ≈1 · 10 ^-4 1 / deg, in vodka (∂n / ∂t) _in ≈3 · 10 ^-4 1 / deg , for alcohol (∂n / ∂t) _with ≈4 · 10 ^-4 1 / deg, for gasoline (∂n / ∂t) _b ≈6 · 10 ^-4 1 / deg. Therefore, mutual compensation of thermal effects does not occur, in order to ensure precision measurements of the refractive index of liquids with an accuracy of ± 5 · 10 ^-5, it is necessary to carry out temperature control with an accuracy of ± 0.1 ° C and make corrections to the measurement result. In practice, this is a difficult task, requiring precision thermometers, special rooms and operator skills.

Secondly, there are a number of problems for the solution of which the accuracy of the measurement of the refractive index of ± 5 · 10 ^-5 is insufficient.

For example, to determine the strength of alcohol and vodka according to GOST 12712-80 or to determine the autolytic activity of flour according to GOST 27495-87, the accuracy of measuring the refractive index is no worse than ± 2 · 10 ^-5 .

A significant increase in the accuracy of measurements of RPL-2 refractometers is practically impossible, since the focal length f of the lens is already large (f = 223.8 mm) and its further increase will lead to an even greater increase in the length of the device, which is unacceptable from an ergonomic point of view.

Thirdly, the average dispersion of K8 glass of the measuring prism of the RPL-2 refractometer n _F -n _C = 0.00806 is significantly larger than the studied aqueous solutions (n _F -n _C ≈0.0059). Therefore, the Abbe RPL-2 refractometer cannot work without a dispersion compensator, the role of which is performed by the Amici prism.

Fourth, the RPL-2 refractometer contains one measuring prism made of K8 glass, which provides a measurement range from 1.33330 to 1.3810 (Δn = 0.048). To measure the refractive index of a liquid with a higher refractive index, for example, alkyl benzenes, in the same range Δn = 1.5280-1.4800 = 0.048, interchangeable measuring prisms from other grades of glass with a higher refractive index are required. But in this case, the disadvantages discussed above are exacerbated. For example, the average dispersion of TF4 glass (often used in refractometers) is five times larger than the average dispersion of K8 glass. This means that compensation of dispersion effects requires the installation of two Amici prisms.

Fifth, the RPL-2 refractometer contains a massive metal stand, which has good thermal contact with the frame of the measuring prism. Therefore, reliable measurements of the refractive index can be made only in the steady-state thermal regime, i.e. only at the temperature of the device equal to the ambient temperature.

Known methods for increasing the sensitivity and accuracy of Abbe refractometers.

For example, a slight increase in sensitivity can be achieved by increasing the angle Θ between the working and output faces of the measuring prism. Figure 2 shows a curve 16 of the dependence of the displacement of the limiting beam ΔX on the refractive index n _x for the case when the measuring prism is made of K8 glass and the angle Θ = 60 °. If the angle Θ = 90 °, then the sensitivity and accuracy of the refractometer increases, which is shown in figure 2 by curve 17.

The sensitivity of the refractometer increases even more significantly if the measuring prism is made of a material with a lower refractive index than that of K8 glass, i.e. if the ratio n _x / n _o approaches unity. Curves 18 and 19 in figure 2 show the dependence of the displacement of the limiting ray ΔX on the refractive index n _x at Θ = 90 ° and, respectively, at n _o = 1.4704 (glass LK6) and n _o = 1.3760 (solution of glycerol in water).

Closest to the object of the application is proposed in 1893 by Galvax device [1], which is shown in figure 3.

The Galvax device contains two mutually perpendicular plane-parallel glass plates 20 and 21 (Figure 3), which together with the window 22 and side glasses 23 and 24 form a cuvette with two cavities for a reference liquid 25 with a refractive index n _о and for the test liquid 3 with a refractive index from n _{x min} to n _{x max} .

In the Galvax device, the cuvette is installed on the platform 26 of the goniometer, and the telescope 27 with the lens is located on the alidade 28 of the goniometer.

The cavity of the cell with the studied liquid 3, for which the refractive index n _x > n _o , plays the role of a measuring prism with an angle Θ = 90 °.

The angle of exit of the limit beam β is measured by a goniometer by moving the telescope 27 relative to the platform 26 with the cuvette.

The accuracy of measuring the difference in refractive indices n _x -n _o for the Galvax device can be estimated using the formula

where β is the exit angle of the limiting ray;

Δβ is the accuracy of measuring angle β with a goniometer;

n _o is the refractive index of the reference fluid.

So, for example, if the angle β is ~ 5 ° (similar to the RPL-2 refractometer), n _о = 1.3330 (water at t = 20 ° C), and Δβ = 0.0051 ° = 8.9 · 10 ^-5 radian (as in RPL-2), then according to the formula Δn = 5.8 · 10 ^-6 . This means that a Galvax device with a liquid measuring prism allows measurements of the difference in the refractive index with higher accuracy than usual with an Abbe type RPL-2 refractometer with a glass prism.

The Galvax device can be attributed to differential refractometers, since the difference in refractive indices is measured n _x -n _o , and the temperature coefficients of the refractive indices of the reference and studied liquids can be close and mutually compensated at a temperature t ≠ 20 ° C.

The dispersion of the reference and studied liquids practically coincides, the angle β is small, therefore, the Galvax device does not contain a dispersion compensator.

However, the Galvax refractometer also has a number of significant drawbacks.

Firstly, in a Galvax device, light first enters the reference liquid 25 (figure 3) with a refractive index n _o <n _x , passes a plane-parallel plate 20, and then a significant layer of the studied liquid 3 passes through, which must be absolutely transparent. If the test liquid 3 has turbidity and scatters light, then the border of light and shadow 29 observed in the focal plane of the telescope objective 27 will not be sharp, which will lead to significant measurement errors or to a complete disruption of the device.

Secondly, in a Galvax device, as in conventional Abbe refractometers, the first medium (liquid) into which the light enters must have a refractive index lower than the refractive index of the measuring prism, the role of which is the test fluid. Otherwise, the principle of operation of this device is violated. Therefore, in a Galvax device, the same liquid as the test liquid with the same refractive index and the same temperature coefficient of refractive index (∂n / ∂t) cannot be used as a reference liquid. This is the main significant drawback of the differential circuit of the Galvax device compared to the known differential circuits with adjacent prisms of industrial flow refractometers [1], such as, for example, in the circuit described in the patent of the Russian Federation [2].

становится больше 85°, наблюдаемая граница света и тени становится менее контрастной.Thirdly, as n _x approaches n _o , when the limiting (critical) angle

becomes more than 85 °, the observed border of light and shadow becomes less contrast.

A refractometer is proposed, which has all the advantages of an Abbe refractometer and a Galvax refractometer, but free from the above disadvantages.

The refractometer contains a illuminator, a measuring prism made of a transparent substance with a known refractive index n _о , which contains a horizontal input face and an output face making an angle Θ with the input face, as well as a series-mounted reflecting device, a diaphragm, a lens, in the focal plane of which there is a device for determine the magnitude of the shift ΔX image of the border of light and shadow, which determine the desired refractive index of the test substance.

The refractive index n _{of the} measuring prism is equal to one of the values of the measuring range of the refractometer from n _{x min} to n _{x max} , the temperature coefficients of the refractive indices of the material of the measuring prism and the test substance are close, their difference does not exceed ± 5 · 10 ^-5 1 / deg, and between a wedge of a transparent substance is placed by a measuring prism and an analyte. The wedge refractive index n _{k is} greater than the refractive index of the test substance n _{x max} , more than the refractive index of the measuring prism n _o . The wedge is fixed in such a way that its main section coincides with the plane of incidence of light, its thick edge is located on the side of incidence of light. The polished edges of the wedge are in contact with the test substance and with the measuring prism, respectively. The wedge angle γ satisfies the condition:

where γ is the wedge angle;

n _{x max} - the maximum value of the refractive index of the investigated substance;

n _o is the refractive index of the material of the measuring prism;

n _k is the refractive index of the wedge material;

С≈0.5 ° - a constant value that takes into account guaranteed good contrast between the border of light and shadow and the required measurement range.

As an embodiment, a refractometer is proposed in which the measuring prism is made of liquid. To hold the liquid in the frame, a plane-parallel glass plate is installed at the exit of the light beam, its plane is perpendicular to the plane of incidence of light and makes an angle Θ with the plane of contact of the wedge with the liquid of the measuring prism, the frame of the measuring prism is made of material with high thermal conductivity, mounted on a heat-insulating gasket. A horizontal cylindrical cap with a bottom made of a material with low thermal conductivity is fixed to the frame of the measuring prism using a union nut. A glass window is fixed on the upper part of the bottom to illuminate the working surface of the measuring prism, and in the lower part of the bottom, an inlet fitting for supplying the test liquid is fixed. Inside the cap, in its upper part, a temperature equalizer is installed in the form of a segmented part of a cylinder made of a material with high thermal conductivity, the flat surface of which is parallel to the working surface of the wedge of the measuring prism and makes a gap of 1 to 2 mm with it. The outlet fitting for the withdrawal of the test fluid is fixed in the upper part of the cap opposite the through hole in the temperature equalizer, the axial line of which is perpendicular to its flat surface.

The figure 1 shows a structural diagram of a well-known Abbe RPL-2 refractometer.

Figure 2 shows the dependence curves of the magnitude of the displacement of the border of light and shadow (limit beam) in the focal plane of the lens of the Abbe refractometer depending on the refractive index at various angles Θ and refractive indices of the measuring prism n _o .

Figure 3 shows a structural diagram of a known Galvax device.

The figure 4 shows a structural diagram of the proposed refractometer, operating in the mode of measurement of the refractive index of optical glass.

The figure 5 shows a structural diagram of the proposed refractometer, operating in the measurement mode of the refractive index of liquids.

The figure 6 shows the dependence of the measured refractive index of vodka on the number of divisions of the relative scale of the proposed refractometer.

The figure 7 shows the dependence of the strength of vodka on the number of divisions of the relative scale of the proposed refractometer.

A refractometer is proposed, for example, for precision measurements of the refractive index of glass, containing a illuminator 1 (Fig. 4), for example, in the form of an HLMP-DL25 LED emitting quasi-monochromatic yellow light with a maximum spectral density of radiation μ (λ) _max = 589 nm, measuring prism 2 from a transparent substance, for example, K8 glass with a known refractive index n _o for yellow light λ _D = 589 nm.

Measuring prism 2 contains a horizontal inlet face and an outlet face making an angle Θ = 90 ° with the inlet face. The test substance (test glass) 3 may have a refractive index for yellow light of about n _{x min} = 1.5100 to n _{x max} = 1.5200. The refractometer also contains a sequentially reflecting device 5, an aperture 6, a dispersion compensator 7 in the form of an Amici prism, a lens 8, in the focal plane of which there is a device for determining the magnitude of the displacement of the image of the border of light and shadow, for example, in the form of a uniform scale 9 with a length of 20 mm, containing 100 divisions. The refractive index n _{o of the} measuring prism 2 is equal to one of the possible measurement ranges of the desired glass refractive index from n _{x min} = 1.5100 to n _{x max} = 1.5200, for example, n _o = 1.516300.

The temperature coefficients of the refractive indices of the material of the measuring prism 2 (K8 glass) and the test substance 3 (also K8 glass) are practically equal to each other. A wedge 30 of a transparent substance is placed between the measuring prism and the test substance. The refractive index n _{k of the} wedge 30 is greater than the refractive index of the test substance (glass) n _{x max} , more than the refractive index of the measuring prism n _o . The wedge is made, for example, of leucosapphire (Al ₂ O ₃ ), which has a high hardness and high refractive index n _k = 1.7688. The wedge 30 is fixed in such a way that its main cross section coincides with the plane of incidence of light, its thick edge is located on the side of incidence of light. The polished faces of the wedge 30 are in contact respectively with the test substance (glass) 3 using immersion liquid (α-bromonaphthalene with kerosene) and with measuring prism 2 using optical glue.

The wedge angle γ satisfies the condition:

где γ - угол клина;

where γ is the wedge angle;

n _{x max} = 1,5200 - the maximum value of the refractive index of the investigated substance (glass);

n _o = 1.5163 is the refractive index of the material of the measuring prism (glass K8);

n _k = 1.7688 is the refractive index of the wedge (sapphire) material.

C = 0.5 ° is a constant value.

To count the tenths of a division of the scale 9, the refractometer is equipped with a device for moving the scale 9 by the value of one division with the drum 12 with ten divisions corresponding to 0.1 divisions of the scale 9.

The refractometer is equipped with a stand 15, on which a case 31 with accessories 32 is mounted, a power supply unit and an electronic thermometer containing an indicator 33, which is mounted on the upper part of the case 31, and a temperature sensor 34, mounted in the frame of the measuring prism 2.

As an embodiment, figure 5 shows a structural diagram of the proposed refractometer operating in the mode of measurement of the refractive index of liquids, for example, to determine the strength of vodka and alcohol. The refractometer contains a light source in the form of an HLMP-DL25 LED (Fig. 5), a measuring prism 2 from a transparent liquid, for example, vodka with a strength А _о = 40% with a known refractive index n _о = 1.355104 (for t = 20 ° C) .

Between the liquid of the measuring prism 2 (vodka with a strength of A _o = 40%, n _o = 1.355104) and the test liquid 3 (vodka with a strength of A _o = 31%, n _{x min} = 1.3510114 to A _o = 59%, n _{x max =} 1.361342) a wedge 30 of a transparent substance is placed. The refractive index n _{k of the} wedge 30 is greater than the refractive index of the test substance (vodka, n _{x max} = 1.361342), more than the refractive index of the liquid of the measuring prism (n _o ²⁰ = 1.355104) and is made, for example, of K8 glass having a refractive index n _o ²⁰ = 1.5163. The wedge angle γ satisfies the condition

To hold liquid (vodka) in the frame 35, a plane-parallel glass plate 36, for example, of K8 glass (n _cn ²⁰ = 1.5163), is installed at the output of the light beam, its plane is perpendicular to the plane of incidence of light and makes an angle Θ = 90 ° with the plane of contact wedge 30 with a liquid measuring prism 2. Angle Θ = 90 ° satisfies the condition

where n _cn = 1,5163 is the refractive index of the glass plate 36;

Θ = 90 ° - the angle between the plane of the plate and the plane of contact of the wedge 30 with the liquid of the measuring prism 2;

n _o is the refractive index of the liquid of the measuring prism 2;

n _{x min} = 1,350785 - the minimum value of the refractive index of the investigated liquid (vodka with a strength of 31%).

The frame 35 of the measuring prism of the liquid 2 is made of a material with high thermal conductivity, for example, of brass, mounted on a heat-insulating gasket 37. A horizontal cylindrical cap 39 with a bottom 40 made of a material with low thermal conductivity is fastened to the frame 35 of the measuring prism with a cap nut 38, for example made of plastic. A glass window 41 is fixed on the upper part of the bottom 40 to illuminate the working surface of the contact of the wedge 30 with the test substance 3 (test vodka), and in the lower part of the bottom 40 there is an inlet fitting 42 for supplying the test liquid 3. Inside the cap 39, an equalizer is installed in its upper part temperature 43 in the form of a segmented part of a cylinder made of a material with high thermal conductivity, the flat surface of which is parallel to the working surface of the wedge 30 of the measuring prism and makes a gap from 1 to 2 mm with it.

In the upper part of the cap 39, opposite the hole 45 in the temperature equalizer 43, an output nozzle 44 is fixed so that its axial line is perpendicular to the flat surface of the temperature equalizer 43. Next, in the direction of the light rays, a reflecting device 5, aperture 6, lens 8, in the focal plane of which a device is installed for determining the magnitude of the image shift of the border of light and shadow, for example, in the form of a uniform scale 9. To observe the scale 9 and the border of light and shadow, an eyepiece 10 is installed. For counting ten x the division of the scale 9, the refractometer is equipped with a device 12 for moving the scale 9 by the value of one division. One division of the drum 12 corresponds to the movement of the scale 9 by the value of 0.1 division of the scale 9.

The refractometer is equipped with a stand 15, on which a case 31 with accessories 32 is mounted, a power supply unit and an electronic thermometer with an indicator 33. A temperature sensor 34 is mounted in the lower part of the cap 39. A dividing cube 46 is installed between the lens 8 and the scale 9, and in the focal plane reflected from cube 46 of the light beam has a multi-element photodetector 47 connected to a microprocessor (not shown in the drawing).

The proposed refractometer in the mode of measuring the refractive index of the glass works as follows.

Quasimonochromatic light with a maximum spectral radiation density μ (λ) _max = 589 nm from light source 1 (Fig. 4) falls on the contact boundary of the test substance 3 (glass) having a refractive index from n _{x min} = 1.51007 to n _{x max} = 1.52129, with a wedge 30 having a refractive index of n _k = 1.7688. Since n _x <n _k , the incident rays are refracted and enter the wedge 30. Next, the refracted light rays pass through the wedge 30, are refracted at the interface between the wedge 30 and the measuring prism 2, pass the measuring prism 2, are refracted at the output of the prism 2, and pass through a reflective device 5, aperture 6, Amici prism 7 and lens 8. In the focal plane of lens 8, where the scale 9 is located, an image is constructed in the form of light and dark fields with a sharp boundary between them. The scale 9 and the location of the image of the border of light and shadow relative to the scale 9 are observed with the eyepiece 10. The rays of light corresponding to the border of light and shadow are called limiting and correspond to incoming rays that glide along the contact boundary of the test substance 3 and the wedge 30, i.e. their angle of incidence is α≈90 °.

Let us consider an example when the refractive index of the test glass 3 is equal to the refractive index of the measuring prism 2, i.e. n _x = n _o = 1.5163 (glass of one batch of cooking). In this case, the limiting rays are refracted into the wedge 30 at a critical angle

Wedge angle 30 γ = 0.8 °. Therefore, unlike a plane-parallel plate at the exit of the wedge 30, the limiting rays will not slip along the boundary of the contact of the wedge 30 with the measuring prism 2, as at the input (α = 90), but will exit into the measuring prism 2 at an angle

This means that if there were no wedge 30, then the limiting rays from the test glass 3 into the measuring prism would be refracted at the same angle α _cr.eff , when the refractive index of the measuring prism 2 would be equal to the effective refractive index

After refraction, at the exit face of the measuring prism 2, the limiting rays exit at an angle

β _cf = arcsin [n _o · sm (α _cr.sr -90] = arcsin [1.5163 · sin (82.531386-90 °)] = - 11.367035 °.

In the process of adjusting the refractometer using a screw 13, the reflecting device 5 is installed in such a position that the border of light and shadow observed in the eyepiece 10 coincides with the middle of the scale 9, i.e. combined with the 50th division of scale 9, which corresponds to a refractive index n _x = n _o = 1.5163 and an angle β _cf = -11.367035 °.

The required refractive index of glass 3 is found using the table and the programmable device, in which the dependence is used:

where n _k is the refractive index of the wedge material 30;

γ is the angle of the wedge 30;

n _o is the refractive index of the measuring prism 2;

Θ is the angle of the output face of the measuring prism 2;

M - the number of divisions of the scale 9, located in the light zone of the image of the border of light and shadow;

- цена деления шкалы 9 (в градусах);

- the price of the division of the scale 9 (in degrees);

ΔX is the length of the scale 9 between the first and hundredth divisions;

f 'is the focal length of the lens 8.

So, for the considered example, when n _x = n _o = 1.5163, M-50 and β _cf = -11.367035 °, after substituting into the formula we find n _{x cp} = 1.5163.

If the test glass is another brew, i.e. n _x ≠ n _o , then, for example, at M = 0, after substituting into the formula (taking into account ΔX = 20 mm and f '= 223.8 mm), we find n _{x min} = 1.510068, and at M = 100 we find n _{x max} = 1.5212952.

Thus, due to the presence of a wedge 30, we can measure the refractive index of the glass from n _{x min} = 1.510068 to n _{x max} = 1.5212952 relative to the glass of prism 2 with a known refractive index, for example, n _o = 1.5163 even when n _{x max} = 1.5212952> n _o = 1.5163, which is not possible with conventional Abbe refractometers. Moreover, the measurement accuracy of the proposed refractometer is higher than that of conventional Abbe refractometers, namely

- диапазон изменения углов предельных лучей при длине шкалы ΔX=20 мм и фокусном расстоянии объектива f'=223,8 мм,Where

- the range of angles of the limiting rays with a scale length ΔX = 20 mm and a focal length of the lens f '= 223.8 mm,

Δα = 8.9 · 10 ^-3 is the accuracy of counting the displacement of the border of light and shadow on a scale of 9 (in radians).

In the measurement mode of the refractive index of liquids, for example, vodka according to GOST 12712-80, the proposed refractometer works as follows.

Quasimonochromatic light with a maximum spectral radiation density μ (λ) _max = 589 nm from light source 1 (Fig. 5) passes through window 41 and falls on the contact boundary of the substance under study 3 (vodka), which has a refractive index of, for example, from n _x = 1 , 3507853 to n _{x max} = 1.3613452 with a wedge 30 having a refractive index of n _k = 1.5163 (glass K8). Since n _x <n _k , the incident rays are refracted and enter the wedge 30, are refracted at the interface between the wedge 30 and the liquid of the measuring prism 2, the liquid of the measuring prism 2 passes, and the liquid of the prism 2 is refracted twice - the protective glass 36 and the glass 36 - air. Then pass the reflecting device 5, the aperture 6, the lens 8, the dividing cube 46 and fall on the scale 9. In the focal plane of the lens 8, where the scale 9 is located, an image of the border of light and shadow is built.

The scale 9 and the image of the border of light and shadow are observed using an eyepiece 10. At the same time, a part of the light flux of the dividing cube 46 reflects on a multi-element photodetector 47, for photoelectric recording of the location of the border of light and shadow.

Initially, for adjustment inside the prism 2 and through the fitting 42 inside the cap 39, the same liquid is poured (vodka with the strength A _o = 40%, n _o ²⁰ = 1.355104), i.e. n _x = n _o ²⁰ = 1.355104. In this case, the limiting rays are refracted into the wedge 30 at a critical angle

Plane-parallel glass plate 36 does not change the considered direction of the rays, therefore, the limiting rays exit the measuring prism 2 at an angle

β _cf = arcsin [n _o · sin (α _red. -90 °)] = arcsin [1.355104 · sin (82.343921-90 °)] = - 10.40096 °

During the initial adjustment, when assembling the refractometer with a screw 13, the reflecting device 5 is installed in a position in which the border of light and shadow observed in the eyepiece 10 coincides with the 35th division of the scale 9. This is necessary in order to take into account the difference between n _o -n _{x min} and the difference between n _{x max} -n _o , i.e. to provide a measuring range from n _{x min} = 1,35078 to n _{x max} = 1,361345.

The required refractive index and, accordingly, the strength of vodka are found using tables, a graph shown in Fig.6, or a programmable device that obtains information about the location of the border of light and shadow from a multi-element photodetector 47. The same dependence n _x = f ( γ, Θ, n _o , β _cf , M, n _k , Δβ) above.

So, for example, if n _x = n _o = 1.355104, Θ = 90 °, γ = 1 °, β _cf = -10.400913 °, Δβ = 0.05106 °, then at M = 35 after substitutions in the formula or according to the tables, schedule (Fig.6) we find n _{x cp} = 1.355104, which corresponds to the strength of vodka And _about = 40%.

If the strength of the investigated vodka differs from 40%, then its refractive index is n _x ≠ n _о . Suppose the observed border of light and shadow is shifted to the beginning of scale 9, i.e. M = 0, then n _{x min} = 1,3507853, which corresponds to the strength A _o = 31.15% (see Fig. 7), and if M = 100 (end of scale 9), then n _{x max} = 1.3613452 , which corresponds to the strength And _about = 58.72%, (Fig.7).

Thus, if vodka with a strength of A _o = 40% (n _o = 1.355104) is poured into the frame 35 (Fig. 5), then the measurement of the refractive index of the analyzed vodka is ensured from n _{x min} = 1,3507853 to n _{x max} = 1 , 3613452 with an accuracy of ± 1 · 10 ^-5 , which corresponds to the range of vodka strength from A _{o min} = 31.15% to A _{o max} = 58.70% with an accuracy of ± 0.02%.

This fully meets the requirements of GOST 12712-80, according to which it is required to measure the strength of vodka in the range from 38 to 56% with an accuracy of ± 0.2%.

With such high measurement accuracy, the temperature regime under which measurements of the refractive index, especially liquids, is very important.

The temperature equalization of the reference fluid measuring cell 2 and the test fluid 3 in the proposed refractometer is as follows.

The investigated liquid (vodka) enters the cap 39 (Fig. 5) through the lower fitting 42, washes the frame 35 with the liquid of the measuring prism 2, enters the gap between the wedge 30 and the temperature equalizer 43, and leaves the refractometer through the fitting 44. Due to the presence of a heat-insulating gasket 37, high thermal conductivity of the frame 35 and a temperature equalizer 43 inside the cap 39, a temperature is quickly established equal to the temperature of the flowing test liquid (vodka).

If the test liquid is supplied in portions, then after the supply of the next portion for a short time inside the cap, the temperature is equal between the test 3 and the reference 2 liquids.

If the temperature coefficients of the refractive index (∂п / ∂t) _{x of the} test fluid and (∂n / ∂t) _{o of the} test fluid are equal, for example, test fluid 3 and test fluid 2 are vodka of the same strength A _о = 40%, then regardless the value of the same temperature established inside the cap 39, there is a mutual compensation of the influence of temperature on the refractive index of the investigated 3 and reference 2 liquids.

If the temperature coefficients of the refractive index of the investigated 3 and reference 2 liquids are close, but not the same, then there is an incomplete compensation of the influence of temperature. For example, if vodka A _o = 40% is poured into the measuring prism 2, for which (∂n / ∂t) _o = 2.7 · 10 ^-4 1 / deg, and inside the cap 39 there is vodka with the strength A _o = 56%, for which (∂n / ∂t) _x = 3.2 · 10 ^-4 1 / deg, then when the temperature t ≠ 20 ° C is established inside the cap 39, the error Δn 'is introduced into the measurements of the refractive index n _k according to the formula:

Δn '= [(∂n / ∂t) _x - (∂n / ∂t) _o ] · (t-20 °) = (3.2-2.7) · 10 ^-4 1 / deg · (t- 20 °) = 5 · 10 ^-5 1 / degree · (t-20 °)

At t-20 °> 1 ° C, the error Δn 'is taken into account using tables, graphs or special processor programs. To do this, use a temperature sensor 34 and an electronic thermometer with a temperature indicator 33. At a temperature of (20 ± 1) ° C, no corrections are required, therefore, the accuracy of temperature control inside the cap 39 may be low (± 1 ° C).

The proposed refractometer can be used to measure the refractive index of any other clear liquids, for example, petroleum products (motor fuels, jet fuels, etc.), food products (juices, water, beer, wine, syrups), concentration of drugs, chemical products, etc. .d. For this, another liquid is poured into the frame of the measuring prism 35 through a special neck, previously having vented the cork. For example, when measuring the salinity of seawater, water of normal (average) salinity is poured, when measuring the quality of tonics, beer, champagne, a solution of glycerol with water is poured (n _o ≈1.3400), to control diesel fuel, kerosene is poured (n _o ≈1.4400 ), and to control the frost resistance of antifreeze, a solution of ethylene glycol in water is poured (n _o ≈1.3600), etc. Accordingly, for each product, tables are calculated or programs for microprocessors are compiled.

The proposed refractometer has a number of significant advantages over existing refractometers.

The main advantage is that due to the presence of a wedge, a substance having a refractive index and a temperature coefficient of refractive index that is close to or equal to the same parameters of the medium under study, as, for example, for differential refractometers [2] operating by the prism method, is used as a measuring prism. . But unlike the prism method, the proposed refractometer works well even when the test medium has turbidity or scatters light (serum, epuret, tonics, beer, milk, patient urine).

The proposed refractometer allows to increase the accuracy of measurements and at the same time reduce the requirements for temperature control during the measurement.

The average dispersion of the materials of the measuring prism and the studied substances are almost identical, and the light source emits quasimonochromatic light. Therefore, to work with liquids, the proposed refractometer does not require dispersion compensators (Amici prisms), which are the most time-consuming optical element in conventional Abbe refractometers. And to work with highly refracting glasses, although compensators are required, they are simple, with a small dispersion coefficient. In the case of a transition from work from one fluid to another, it is not necessary to change the measuring prism, as in conventional Abbe refractometers, but it is enough to drain the sample fluid from the frame of the measuring prism and fill in another.

Since the scale in the proposed device is uniform and expressed in relative units, when working with other products, the design of the device remains the same. It is enough to take other tables or switch to the processor using another program. The proposed refractometer contains a heat-insulating sheath (for example, a cap) around the measuring prism of heat-insulating material, which facilitates thermal stabilization and equalization of the temperature of the test and reference substances (liquid or glass).

In the proposed refractometer, light first enters the test substance, and then spreads in completely transparent substances, which are optical glass and pure liquids. This means that scattering in a turbid test substance will practically not affect the image quality of the border of light and shadow built by the lens, which everyone who worked with refractometers knows. But if it were the other way around, as in the Galvax device, i.e. if, after refraction, there was a transparent substance at the interface between the investigated medium and the wedge, and the turbid substance under study was the measuring prism, then the observed border of light and shadow would either be blurred (with weak scattering) or be absent altogether.

Structurally, the refractometer is designed so that during operation there can be no mechanical effects on the cuvette part or other elements of the optics that could interfere with the operation of the refractometer. The refractometer rests on a stand and can be stacked separately from the stand.

The stand is mounted a place for accessories (accessories).

The refractometer meets all the requirements of ergonomics and aesthetics.

The proposed refractometer will find wide application in the optical, food, chemical industries.

It should be emphasized the particular relevance of the proposed refractometer in the laboratories of the alcohol industry, distilleries, and winemaking enterprises in connection with the state monopoly on the production of alcohol and alcoholic beverages.

INFORMATION SOURCES

1. Ioffe B.V. Refractometric chemistry methods. 2nd ed., Rev. and add. L., "Chemistry", 1974

2. RF patent No. 2241220 dated December 13, 2001, Bull. No. 33, 2004

Claims (2)

1. A refractometer containing a illuminator, a measuring prism made of a transparent substance with a known refractive index n ₀ , which contains a horizontal input face and an output face making an angle of 90 ° with the input face, as well as a series-mounted reflective device, aperture, lens, in the focal plane which has a device for determining the amount of displacement ΔX of the image of the border of light and shadow, which determines the desired refractive index of the test substance, characterized in that while the refractive index of the material of the measuring prism n ₀ is equal to one of the values of the measuring range of the refractometer from n _{x min} to n _{x max} , the temperature coefficients of the refractive indices of the material of the measuring prism and the test substance are close, their difference does not exceed ± 5 · 10 ^-5 1 / deg, and between the prism and the measurement target substance is placed a wedge of a transparent substance whose refractive index n is larger than _a maximum refractive index of the substance n _{x max} greater refractive index of the material of the measuring etc. zmy n _0, and fixed in such a manner that its principal section coincides with the plane of incidence of the light, its thick edge located on the side of light incidence, the polished face of the wedge in contact with the test substance and the material of the measuring prism wedge angle γ satisfies the condition

where γ is the wedge angle; n _{x max} - the maximum value of the refractive index of the investigated substance; n ₀ is the refractive index of the material of the measuring prism; n _k is the refractive index of the wedge material; C = 0.5 ° - a constant value that guarantees high contrast images of the border of light and shadow. 2. The refractometer according to claim 1, characterized in that the measuring prism is made of liquid, for holding which a plane-parallel glass plate is installed in the frame at the exit of the light beam, its plane is perpendicular to the plane of incidence of light and makes an angle of 90 ° with the plane of contact of the wedge with the measuring liquid prisms, the frame of the measuring prism is made of a material with high thermal conductivity, mounted on a heat-insulating gasket, on the frame of the measuring prism with the help of a union nut, a horizontal a cylindrical cap made of a material with low thermal conductivity, a glass window is fixed on the top of the cap bottom to illuminate the working surface of the wedge contact with the test substance, and an inlet is fixed at the bottom of the cap bottom, a temperature equalizer in the form of a segment part is installed inside the cap at the top of the cap cylinder of a material with high thermal conductivity, the flat surface of which is parallel to the working surface of the wedge and makes a gap of 1 to 2 mm with it, and the outlet fitting is fixed in the upper part of the cap opposite the through hole in the temperature equalizer.

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