RU2563310C2 - Measuring method of average light dispersion and device for its implementation - Google Patents

Abstract

FIELD: instrumentation.

SUBSTANCE: invention relates to applied physics, to optic instrument building, and in particular, to refractometric instruments intended for measurement of a refraction and dispersion parameter of different substances. According to the method, to the inlet edge of the measuring prism of the refractometer there directed is a quasi-monochromatic light beam of the working wave length λ_D; a coordinate of position of the light and shadow boundary X_D is determined in the focal plane of the lens; structural coefficients A and B are found; light wave length is changed from λ_D to λ_1, which is considerably different from λ_D as to displacement of the light and shadow boundary ΔX_Dλ; total angular dispersion is determined, and then, the desired average dispersion is found. The device includes a lighting shell, a measuring prism with known refraction parameter n_Do and average dispersion (Δ_FC)_o, the primary source of quasi-monochromatic light with wave length λ_D and an auxiliary one with wave length λ₁, which are in-series connected to a power supply source through a switching device. The lighting shell includes a temperature sensor connected to a temperature control; a Peltier element is installed between the lighting shell and the metal radiator base and connected to a DC source through a contact of a switching relay of the temperature control so that through normally closed contacts of the relay there supplied to the Peltier element is for example a minus potential, and the lighting shell is cooled down, and after actuation of the relay, a plus potential is supplied for heating.

EFFECT: invention allows simplifying the device design and the measurement process.

3 cl, 8 dwg

Description

The invention relates to optical instrumentation, more specifically, to refractometric devices for measuring the refractive index and dispersion of various substances.

The refractive index of substances depends on the wavelength of light. The wavelength λ of light at which the refractive index was measured is indicated as the subscript n _λ . For example, the refractive index in yellow light of a sodium lamp (λ _D = 589 nm) is denoted by n _D , in red (λ _c = 589 nm) or in blue (λ _F = 486 nm) light of a hydrogen lamp is denoted, respectively, n _C or n _F. The difference in the measurement results n _λ1 -n _λ2 is called the refractive dispersion or simply the dispersion, and the difference n _F -n _C is called the average dispersion and denote Δ _FC . Information about the Δ _FC dispersion is especially important for scientific and technological studies of optical glass, petroleum products, vegetable oil products, etc. [1]. Usually, for measuring the refractive indices n _D , n _F , n _C and finding the average dispersion Δ _FC = n _F -n _{C of} optical glass according to GOST 3514-94, the prism method and high-precision goniometers equipped with spectral lamps filled with sodium and hydrogen vapors are used, and also mercury, cadmium.

A significant drawback of the goniometric method of measuring the refractive index n _λ and the average dispersion n _F -n _C is the requirement to manufacture a triangular prism of significant dimensions from the test glass. For example, the size of the polished faces should be approximately 50 × 50 mm, and the angle between them Ө≈60 °. This means that measuring n _D , n _F , n _C and finding Δ _{FC of} finished optical parts with a goniometer is difficult or impossible.

To work with liquids, the goniometer must be equipped with complex hollow prisms, to fill which a significant amount of the studied liquid is required, as well as careful temperature control of the prisms.

Typically, measurements of the refractive indices n _D , n _F , n _{C of} solid and liquid substances are performed by the method of limiting angle [1]. The essence of the method is that along the contact boundary of two transparent media, for example, the studied liquid and a glass prism with an outlet face angle Ө and a known refractive index n _oλ , a monochromatic light beam of wavelength λ is directed also in the focal plane of the lens onto which the refracted rays fall , observe the border of light and shadow. By the position of this boundary, the angle of exit of the limiting rays from the prism β _{λ is found} , the desired refractive index n _{xλ is calculated} by the formula [1]:

.

.

To implement the method of limiting angle using two types of refractometers Pulfrich and Abbe.

The well-known Pulfrich refractometers IRF-23, IRF-457, PR-2 [1] contain a illuminator 1 (Fig. 1) with light sources in the form of a set of spectral lamps powered by special high voltage sources, a measuring prism 2 made of glass with known refractive indices n _oD , n _oF , n _oC , in contact with the test substance 3 and a right angle between the input and output faces (Ө = 90 °), a movable spotting tube 4 with a lens 5, a crosshair 6 and an eyepiece 7, which is rigidly connected with the movable part of an optical angle measuring device 8.

Monochromatic light from source 1, for example, a hydrogen lamp whose emission spectrum contains red (λ _c = 650 nm), blue (λ _F = 476 nm) and violet (λ _{q ′} = 434 nm) lines, are directed to the contact boundary of the test substance 3 with the working face of the measuring prism n2. Light is refracted into prism 2 at limiting angles α _c = arcSin (n _xc / n _oc ); α _F = arcSin (n _XF / n _oQ ) and α _{q ′} = arcSin (n _{xq ′} / n _{oq ′} ). Then the light rays pass through the measuring prism 2, are refracted on the output face of the prism 2 for the second time, and exit at angles β _c , β _F , β _{q ′} relative to the normal to the output face.

и $$n_F=\sqrt{n^2{}_{oF}-{\sin }^2{\beta }_F}$$

, а затем вычисляют среднюю дисперсию Δ_FC=n_F-n_c.The methodology for measuring n _c and n _F and determining the average dispersion Δ _FC = n _F -n _c on a Pulfrich refractometer is as follows. Moving the telescope, the crosshair 6 observed in the eyepiece 7 is combined with the border of light and the shadow of red light λ _s , and then blue light λ _F. In this case, each time using the angle measuring device 8, the angles β _c , β _F are measured, the desired refractive indices are calculated by the formulas $$n_c=\sqrt{n^2{}_{oc}-{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="00000030.png,00000033.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2{\beta }_c}$$

and $$n_F=\sqrt{n^2{}_{oF}-{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="00000030.png,00000033.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2{\beta }_F}$$

and then calculate the average dispersion Δ _FC = n _F -n _c .

To measure the refractive index on a standard spectral line λ _D = 589 nm, the hydrogen lamp is replaced with a sodium lamp with the connection of a different power source.

Significant disadvantages of Pulfrich refractometers are:

- cumbersomeness and the need to replace the spectral lamps and their power sources during the measurement process;

- spectral lamps require time to enter the mode after they are turned on;

- the need for a significant amount of calculations by the operator;

- complex visual optical angle measuring devices;

- significant dimensions and weight, limiting their use outside specialized laboratories.

According to the principle of operation, similar to Pulfrich refractometers are the multi-wavelength DR-M2 and DR-M4 refractometers known by Abbe from ATAGO (Japan) [2]. The structural diagram of refractometers is shown in figure 2.

Instead of spectral lamps, the DR-M2 and DR-M4 refractometers contain a separate lighting unit with a light source in the form of an incandescent lamp 1, a set of interchangeable interference filters and a fiber bundle. The measuring prism 2 is in contact with the test substance 3, made of glass with high and known refractive indices n _oD , n _oC , n _oF . The working and output faces of prism 2 make an angle Ө <90 °.

The telescope 4 with a lens 5, a scale 6 and an eyepiece 7 is fixed on the refractometer body fixedly, and the refracted light beams are sent to the telescope 4 using the movable part of the angle measuring device 8, on which the mirror 9 is mechanically fixed.

The measurement technique using Abbe multi-wavelength refractometers DR-M2 and DR-M4 is as follows.

. Результаты измерений индицируются на цифровом табло.One interference filter is selected from the set, for example, one that transmits yellow light (Δ _max = 589 nm), and using the switch, it is introduced into the working beam of light coming from incandescent lamp 1. Quasimonochromatic light with a maximum spectral density of radiation µ (λ) _max = 589 nm is directed to the contact boundary of the working face of the measuring prism 2 with the test substance 3. Light passes through the test substance 3, is refracted into the prism 2, passes through it, and leaves the prism 2 at an angle β _D with respect to the normal to the output face. Next, use the hand wheel to The mirror is moved together with the moving part of the digital sensor of angular displacements 8 to the position when the border of light and shadow observed in the eyepiece 7 is aligned with the zero point. Using the angle β _D measured in this way and the known values of n and n _{Dо, the} microprocessor integrated in the refractometer calculates the required refractive index n _DX by the formula

. The measurement results are displayed on a digital display.

.To measure the refractive index n _CX or n _FX using a switch, instead of a yellow filter, red (τ _λmax = 656 nm) or blue (τ _λmax = 486 nm) interference filters are introduced into the working beam of the illuminator. Each time when switching the filters, it is required to manually bring the border of light and shadow to a zero point, and to add new initial data for calculations to the microprocessor program, namely n _oC or n _оF glass of measuring prism 2 and the measured angles β _C or β _F. Using the values of refractive indices n _CX , n _DX , n _FX measured in this way, microprocessors of the known refractometers DR-M2 and DR-M4 can calculate and display the value of the Abbe number v calculated using the formula $$v=\frac{n_D-\mathrm{one}}{n_F-n_C}$$

.

There is no separate function for calculating and indicating the average dispersion Δ _FC in the programs of the processors of these refractometers, however, the operator can calculate the average dispersion Δ _FC on the basis of the measured values of n _F and n _C.

The accuracy of refractive index measurements is ± 0.0002. Significant disadvantages of Abbe multi-wavelength refractometers DR-M2 and DR-M4 are:

- the need to perform measurements of angles β _C , β _F , β _{D with an} angle measuring device and additional operator calculations to determine the average dispersion;

- significant dimensions and weight, limiting their use outside specialized laboratories;

- high price (more than 500 thousand rubles).

Abbe's universal high-precision laboratory refractometers are known, for example, IRF-454 (Russia), Abbe Refractometer B (Zeiss-Opton) [1] NAR-1T (ATAGO) [2], the construction of which implements a method for compensating the total angular dispersion of the Abbe measuring prism limiting rays (Δβ) _FC using compensators in the form of direct prisms Amici [1].

The Abbe IRF-454 laboratory refractometer [1] contains a source of natural or artificial “white” light, for example, a white LED 1 (Fig. 3), a stationary measuring prism 2 made of TF4 glass with a known refractive index n _Do = 1.7398 and average dispersion (Δ _FC ) _o = 0.02628, the working polished face of which is in contact with the test substance 3 and makes an angle Ө = 62 ° with the output polished face of the fixed motionless visual channel 4 with lens 5, a crosshair 6 and an eyepiece 7. On the movable sector are fixed scale 8 and h rkalo 9. 8 Scale for convenience not endowed in rotation angles of the prism 2 onto rays β _D, and in units of the refractive index n _DX for the working wavelength. Between the measuring prism 2 and the lens 5 there are two direct prisms of Amici 10. They are fixed in frames in the form of bevel gears connected to each other by a third bevel gear with a drum 11. The peculiarity of the Amici prisms is that they transmit yellow rays (λ _D = 589 nm) without deviation, and the red and blue rays (λ _c = 656 nm and λ _F = 486 nm) in the main plane of the section are bred at an angle of 2k = 2 × 88 ′ = 176 ′.

The known method of measuring the average dispersion of light using a compensator is implemented in a laboratory refractometer Abba IRF-454 B2M as follows.

A beam of “white” light from source 1, for example, natural (solar) or artificial light (incandescent, fluorescent, white LED), is directed to the output (working) face of the measuring prism 2 (Fig. 3) in contact with the test substance 3 .

The light passes through the layer of the test substance 3, is refracted into prism 2, passes through it in the plane of incidence, and is secondly refracted on the output face of prism 2. The angle of exit from the prism 2 of the limiting rays relative to the normal to its output face depends on the wavelength of the rays that make up the “white” light according to the formula β _λ = arcSin {n _oλ Sin [Ө-arcSin (n _xλ / n _oλ )]}.

The difference between the limiting angles for blue and red light (Δβ) _FC = β _F- β _C is called the average angular dispersion and depends on the average dispersion of the material (Δ _FC ) _about prism 2, the angle Ө of prism 2, the average dispersion (Δ _FC ) _{x of the} investigated substances 3.

The rays spread out in the plane of incidence into the spectrum are reflected from the mirror 9 and pass the direct vision prisms 10. Each direct vision prism in its main section bends red (λ _s ) and blue (λ _F ) rays at an angle k = 0.02559816 radians. Using the digitized drum 11, the prisms 10 are turned in different directions at an angle γ (Fig. 4) and the angle of rotation γ of the prisms 10 is found such that their angular dispersion 2k Cosγ is equal in magnitude but opposite in sign of the average angular dispersion (Δβ) _FC , i.e. (Δβ) _FC -2kCosγ = 0 _о . Thus, the angular dispersion (Δβ) _FC is completely compensated, i.e. all limiting rays of different wavelengths in the focal plane of lens 5 come to the place where the yellow rays are located, are summed up and in eyepiece 7, in addition to the crosshairs, the operator observes a black and white (not colored) border of light and shadow.

The rotation angle γ of the Amici prisms 10 is determined by the number of divisions Z of the drum 11 using a vernier. The initial (zero) position of the prisms 10 is the position at which Z = 30 divisions, i.e. when γ = 30 · 3 ° = 90 °, since the price of one division of the Z scale is 3 °. The accuracy of reading the angle γ by the nonius is ± 0.3 °. Therefore, the error in determining the total angular dispersion (Δβ) _FC using two Amici prisms 10 in the best case is ± 2.68 · 10 ^-4 rad.

By turning the scale 8 together with the mirror 9, the light and shadow border observed in the eyepiece is combined with a crosshair, and then, according to the scale 8 observed in the eyepiece 7, the refractive index n _{D is} taken.

Using the refractive index n _D measured in this way, using the tables calculated in advance, constructive coefficients A and B are found, and then the average dispersion is determined by the formula [1]:

,

,

;Where

;

;

;

;

;

2k is the angular dispersion for the blue and red rays of two Amici prisms; σ = Cosγ;

γ is the angle of synchronous rotation of Amici prisms in different directions.

For example, if in the process of checking the grade of glass of optical parts using an Abbe IRF-454 refractometer, measurement results were obtained on a scale of 8 refractive index n _DX = 1.51690 and on a drum scale 11 the number of divisions Z = 42.4, then, using the accompanying Manual for the operation of the IRF-454 refractometer, the tables show the structural coefficients A = 0.02320, B = 0.025303 according to the measured refractive index n _D , and b = Cos (42.3 × 3 °) = according to the number of divisions Z = 42.3 0.60042025, and then find the average dispersion of the investigated optical part (Δ _FC ) _x = A + Bb = 0.0232-0.025303 · 0.60042025 = 0.008007.

According to GOST 3514-94, we determine that this optical part is made of a piece of glass K8, the batch of which has characteristics n _D = 1.51690 and (Δ _FC ) _x = 0.008007.

The main advantage of the known method of compensating the total angular dispersion of the limiting rays (Δβ) _FC coming out of the measuring prism 2 (FIG. 3) using Amici 10 direct prisms is that to illuminate the plane of contact of the test substance 3 with the working face of the measuring prism 2 instead monochromatic, you can apply "white" light natural (daylight) or artificial (from an incandescent lamp or LED).

Significant disadvantages of the IRF-454B2M, NAR-1T refractometers are:

- the high complexity of manufacturing prisms direct vision Amici;

- the need to install two prisms of direct vision Amici due to the large average dispersion (Δ _FC ) _o = 0.02628 TF4 glass measuring prism;

- the subjectivity of the operator’s perception of the presence or absence of discoloration of the border of light and shadow observed in the eyepiece;

- non-linear relationship between the introduced direct prism of Amici prism angular dispersion and their rotation angle γ;

- the presence of a movable scale endowed with refractive index values, and only for the working wavelength λ _D ;

- the need for recounting and manufacturing of a new scale every time a batch of glass melting is changed, from which a measuring prism is made;

- bulkiness and significant weight (~ 4 kg), which is an obstacle to rapid measurements.

A well-known group of Abbe refractometers with a fixed universal uniform scale and only one prism of direct vision of Amichi [1].

So, the prototype closest to the object of the application is an Abbe IRF-451 submersible refractometer [1], which contains a white light source 1 (Fig. 5), a measuring prism 2 of optical glass with a known refractive index n _Do in contact with the test substance 3.

The measuring prism 2 is mounted on the telescope 4, in which, after the prism 2, a lens 5, a uniform scale 6 and an eyepiece 7 are mounted in series. The refractometer is equipped with a glass illuminator 8 in which the test substance 3 and the working part of the measuring prism 2 are located.

To direct the light to the working face of the measuring prism 2, a mirror 9 is installed. Between the measuring prism 2 and the lens 5 there is a direct vision prism Amici 10, which is mounted on a movable inner pipe with a ring 11 fixed on this pipe. The glass-illuminator 8 is partially immersed in the bath fluid thermostat 12.

The known method of measuring the average dispersion using an IRF-451 refractometer is implemented as follows.

A beam of “white” light from a source 1 (daylight or artificial light) is directed by a mirror 9 through the bottom of a glass 8 to the boundary of contact of the measuring prism 2 with the test substance 3. Light passes through the layer of the test substance 3, is refracted into the prism 2, and is secondly refracted at the exit face prisms 2. The rays spread out in the plane of incidence into the spectrum pass through the prism 10, fall into the lens 5, which in the plane of the scale 6 builds an image of the border of light and shadow. Using the ring 11, the direct prism of Amici 10 is rotated by an angle γ at which the angular dispersion of the prism 10 is equal to the angular dispersion (Δβ) _FC , but with the opposite sign i.e. the angular dispersion compensation (Δβ) _FC- kCosγ = 0 will occur, where k = 0.01309 rad is the angle of dilution of the red and blue rays with the Amici prism 10. In this case, sharp images of the relative scale 6 and black and white (not colored) are observed in eyepiece 7 the boundaries of light and shadow (Fig.6).

Using scale 6, the coordinate of the position of the border of light and shadow X _D relative to the maximum value of X _Dmax for the working wavelength λ _{D is determined} , i.e. take readings of the number of divisions M = (X _D / X _Dmax ) 100 of scale 6, then use the table to translate the divisions of the scale M into the measured value of the refractive index n _DX . The rotation angle of the Amici prism 10 is counted by the number of divisions Z of the ring 11 using a vernier. The price of one division of the ring 11 is 3 °, the price of division of the nonius is 0.3 °.

, определяют среднюю дисперсию исследуемого веществаFurther, in the same way as in the IRF-454B2M refractometer described above, using the tables found n _Dx determine the design coefficients A ′ and B and the found number of divisions Z of the ring 11 characterizing the angular dispersion $$\Delta {\beta }_{F{C}^{-}}=kCos\gamma =kCos\left(Z\cdot 3°\right)$$

determine the average dispersion of the test substance

(Δ _FC ) _x = A ′ (Δ _FC ) _o + Bk Cosγ,

where (Δ _FC ) _o is the average dispersion of the material of the measuring prism;

k = 45 ′ = 0.01309 rad - the angle of dilution of red and blue rays with the Amichi prism;

γ = Z · 3 ° - the angle of rotation of the Amici prism in degrees.

The accuracy of reading the angle γ by the nonius is ± 0.3 °. Therefore, the error in determining the total angular dispersion (Δβ) _FC using a single Amici prism 10 is ± 1.34 · 10 ^-4 rad.

Significant disadvantages of the IRF-451 refractometer are:

- the high complexity of manufacturing a prism of direct vision Amichi;

- the subjectivity of the operator’s perception of the presence or absence of discoloration of the border of light and shadow observed in the eyepiece;

- non-linear relationship between the introduced prism of direct vision of Amici angular dispersion and its angle of rotation γ;

- the presence of a bulky liquid bath - thermostat.

A new method is proposed for measuring the average dispersion of light with an Abbe refractometer and a device for its implementation.

The essence of the proposed method is that the Abbe refractometer after determining the position coordinates of the boundaries of light and shadow X _D for working λ _D-wavelength of the working face of the measuring prism instead of the beam of the operating wavelength of light λ _D is directed quasi-monochromatic light beam, which has a maximum spectral density radiation μ (λ) _max corresponds to the wavelength of light λ ₁ , significantly different from the working wavelength λ _D , in the focal plane of the lens register the magnitude and sign of the relative displacement of the border of light and shadow ΔX = X _D - X _λ1 , find the total angular dispersion

Δβ _{D, λ1} = (ΔX / X _Dmax ) arctg (X _Dmax / F ¹ ),

(Δ_FC)_o=(В′+ΔВ·X_D/X_Dmax)) ΔX_D/X_Dmax·β_Dmax,·q,and then find the desired average dispersion of the test substance by the formula: $${\left({\Delta }_{FC}\right)}_x=\left(A_{\min }^{\text{'}\text{'}}+\Delta A\text{'}\text{'}\cdot X_D/X_{D\max }\right)$$

(Δ _FC ) _o = (В + ΔВ · X _D / X _Dmax )) ΔX _D / X _Dmax β _Dmax, q

и $$B_{\min }^{\text{'}}$$

- конструктивные коэффициенты, соответствующие началу диапазона измерения показателя преломления n_Dmin рефрактометра Аббе;Where: $$A_{\min }^{\text{'}\text{'}}$$

and $$B_{\min }^{\text{'}\text{'}}$$

- design coefficients corresponding to the beginning of the measuring range of the refractive index n _{Dmin of the} Abbe refractometer;

- величина изменения A′ в диапазоне измерения n_DX от n_Dmin до n_Dmax; $$\Delta A\text{'}\text{'}=A_{\max }^{\text{'}\text{'}}-A_{\min }^{\text{'}\text{'}}$$

- the magnitude of the change A ′ in the measurement range n _DX from n _Dmin to n _Dmax ;

- величина изменения B′ в диапазоне n_DХ от n_Dmin до n_Dmax; $$\Delta B\text{'}\text{'}=B_{\max }^{\text{'}\text{'}}-B_{\min }^{\text{'}\text{'}}$$

- the magnitude of the change in B ′ in the range of n _DX from n _Dmin to n _Dmax ;

(Δ _FC ) _o is the average dispersion of the material of the measuring prism;

M = X _D / X _Dmax is the relative coordinate of the border of light and shadow, corresponding to n _DX for the working wavelength λ _D ;

ΔM = ΔX / X _Dmax is the relative displacement of the border of light and shadow in the process of changing quasi-monochromatic light beams;

X _Dmax - the maximum possible shift of the recorded border of light and shadow in the focal plane of the lens for the working wavelength λ _D and for n _DX = n _Dmax ;

ΔX _{D, λ1} is the relative shift of the border of light and shadow in the process of changing the wavelength of the light incident on the measuring prism;

β _Dmax = _arctan (X _Dmax / f ¹ ) is the angular field, i.e. maximum beam deflection angle after the measuring prism;

f ¹ - the focal length of the lens of the refractometer;

- дисперсионный коэффициент. $$q=\frac{\mathrm{one}/{\lambda }_F^2-\mathrm{one}/{\mathrm{<figure-callout\; id="2"\; label="\lambda \; C"\; filenames="00000030.png,00000033.png"\; state="\{\{state\}\}">\lambda \; </figure-callout>}}_C^{}}{\mathrm{one}/{\lambda }_i^2-\mathrm{one}/{\mathrm{<figure-callout\; id="2"\; label="\lambda \; D"\; filenames="00000030.png,00000033.png"\; state="\{\{state\}\}">\lambda \; </figure-callout>}}_D^{}}=\frac{1.9097}{\mathrm{one}/{\lambda }_{\mathrm{one}}^2-2.88}$$

- dispersion coefficient.

A device is proposed for implementing a method for measuring the average dispersion of light by an Abbe refractometer, comprising a illuminator beaker, a measuring prism in the form of an obliquely cut cylinder made of a transparent material with a known refractive index n _оλ and average dispersion (Δ _FC ) _o , the output face of which is in contact with the test substance and makes an angle Ө with the output polished face, the lens in the focal plane of which there is a device for recording the location of the border of light and shadow, for example, extraordinary scale and eyepiece. The illuminator glass contains the main source of quasimonochromatic light, the maximum of the spectral radiation density of which μ (λ _o ) _max coincides with the working wavelength λ _o , and an auxiliary source of quasimonochromatic light, the maximum of the spectral radiation density of which μ (λ ₁ ) _max differs significantly from the working length waves λ _o . Each light source is connected to the power source in series through a switching device, providing alternating inclusion of light sources. In a glass-illuminator made of a material with high thermal conductivity, a temperature sensor is mounted, connected to a temperature regulator. Between the case of the illuminator cup and the metal base-radiator of the refractometer, a Peltier element is placed, which is connected sequentially through a switching device of the temperature regulator to a direct current source.

Figure 1 shows a structural diagram of a known refractometer Pulfrich IRF-23.

Figure 2 shows the structural diagram of the well-known Abbe refractometers multiwave DR-M2, DR-M4 company ATAGO.

Figure 3 shows the structural diagram of the Abbe IRF-454B2M refractometer.

Figure 4 shows the principle of addition of angular dispersions of two prisms of direct vision of Amici during their rotations.

Figure 5 shows a structural diagram of a known refractometer IRF-451.

Figure 6 shows the image of a uniform scale and the border of light and shadow observed by the operator when working with the IRF-451 refractometer.

7 shows a structural diagram of the proposed device.

On Fig shows a fragment of the scale of the proposed device with the image of the relative coordinate M of the border of light and shadow for the working wavelength of light λ _D and the relative displacement of the border of light and shadow by ΔM after turning on the auxiliary source of quasi-monochromatic light.

Possible embodiments of the proposed method for measuring the average dispersion of light by an Abbe refractometer will be considered using the example of the Abbe refractometer circuit shown in FIG. 7.

Proposed Abbe refractometer (7) comprises glass-illuminator 1, the measuring prism 2 as an obliquely truncated cylinder made of a transparent material such as glass BK10 with known refractive index n _DO = 1.5688 and an average dispersion (Δ _{FC) o} = 0.01015. The input face of the measuring prism 2 is in contact with the test substance 3 and makes an angle Ө = 66 ° with the output polished face. The measuring prism 2 is fixed in the lower part of the pipe 4. In the pipe 4, immediately after the measuring prism 2, a lens 5 is installed, in the focal plane of which there is a device for registering the location of the border of light and shadow, for example, a uniform scale 6. An eyepiece is installed behind the scale 6. illuminator 1 contains a sleeve 8 of a material with high thermal conductivity. In the lower part of the illuminator glass, a reflecting device 9 is installed, for example, in the form of prisms from a transparent material, and two light sources - the main 10 and auxiliary 11. The maximum spectral radiation density µ (λ _o ) _{max of the} main source of quasi-monochromatic light 10 coincides with the working length waves λ _about = λ _D = 589 nm, for example, a yellow LED HLMP-EL25SY00. To achieve even greater monochromaticity, immediately after the LED 10, an interference filter 12 is installed with a transmission maximum τ _max matching the operating wavelength λ _Dmax = 589 nm, having a transmission halfwidth Δλ≤5 nm.

The maximum spectral radiation density µ (λ ₁ ) _{max of the} auxiliary source of quasi-monochromatic light 11 differs significantly from the working wavelength λ _D , for example, µ (λ ₁ ) _max = 447 nm (blue-violet EL383UBCH ₂ ). Immediately after the LED 11, an interference filter 13 is installed with a maximum transmission τ _max ≈λ _i = 447 nm.

An illumination prism 14 of a transparent material, for example, polymethylmethacrylate, is fixed in the sleeve 8 in the form of an oblique cut cylinder. The cutting angle of the prism 14 is equal to the cutting angle of the cylinder of the measuring prism 2. The sleeve 8 is fixed to the base 15 of the illuminator glass 1 made of a material with high thermal conductivity, for example, aluminum alloy. At the base 15 is fixed a temperature sensor 16 of the temperature controller 17, which is located in the housing of the stand 18.

The illuminator glass 1 and the stand body 18 are mounted on a metal plate 19. In the lower part of the base 15 of the illuminator glass, a Peltier element 20 is installed so that one of its surfaces has good thermal contact with the base 15, and the other with the plate 19, which serves as a radiator . The Peltier element 20 is sequentially connected through a switching device 21 of the thermostat 17 to a constant current source 22 having two potentials - plus and minus with a midpoint.

The light sources 10 and 11 are connected to the power supply unit 22 in series through a switching device 25, which provides their alternate connection.

In the housing 18 of the stand there is a compartment for accessories 23 with a movable cover 25.

The proposed method for measuring the average dispersion of light with an Abbe refractometer is as follows.

The refractometer stand with a power source 22 and a temperature regulator 17 is connected to the network (220 ± 22) V, using the program menu of the temperature regulator 17 set the temperature value, for example 20 ° C, which must be maintained in the glass-illuminator 1, and withstand the time until the start of temperature control. The refractometer pipe 4 is removed from the illuminator glass, 0.3-0.5 ml of the test substance 3, for example motor fuel, is poured into the illuminator glass 1, and then the refractometer pipe 4 is inserted back into it. In this case, the test fuel 3 fills the gap between the measurement 2 and the lighting 14 with prisms, using the switch 23 they connect the LED 10 to the power supply 22. The light beam from the yellow LED 10 passes the interference filter 12, becomes quasi-monochromatic with a maximum spectral radiation density µ (λ _o ) _max = 589 nm and width spectrum Δλ <5 nm, is reflected from the reflector 9 and falls on the contact boundary of the working surface of the measuring prism 2 with the test substance 3.

Light rays moving along the contact boundary and close to them pass through the layer of the test substance 3, are refracted into the prism 2, pass through it, and are refracted on the output face of the prism 2 and fall into the pipe 4.

The limiting rays exit from prism 2 with respect to the normal to its exit face at an angle β _D = arcSin {n _Do Sin [θ-arcSin (n _Dx / n _Do )]} = arcSin {1,5688sin [66 ° -arcSin (n _DX / 1,5688)]},

where n _Do = 1,5688 - the refractive index of the glass BK10 prism 2 for a wavelength of λ _D = 589 nm;

Ө = 66 ° is the angle between the working and output faces of prism 2;

n _Dx is the refractive index of the investigated substance 3 for a wavelength of λ _D = 589 nm.

A lens 5 with a focal length f in its focal plane, where the scale 6 is located, builds an image of the border of light and shadow. Using the eyepiece 7 determine the coordinate of the border of light and shadow for yellow light X _D = f′tg β _D relative to the reference point X _o corresponding to the beginning of the measuring range n _Dxmin . For this refractometer example, in which scale 6 contains M _max = 100 divisions, it is convenient to express the coordinate of the border of light and shadow in relative units in the divisions of scale 6, i.e. M = (X _D / X _Dmax ) · 100, where X _Dmax is the maximum shift of the border of light and shadow at n _Dmax .

Then, if required, the divisions of the scale M are converted using tables into other quantities, for example, into the measured value of the refractive index n _Dx .

After determining the coordinates of the position of the border of light and shadow X _D , expressed in divisions M of a uniform scale 6, the yellow LED 10 is disconnected from the power supply unit 22 with the switch 25 and the auxiliary blue-violet LED 11 is connected. The light from the LED 11 passes the interference filter 13, becomes quasimonochromatic with the maximum spectral radiation density (μ _λi ) _max = 447 nm and the spectrum width Δλ <5, is reflected from the reflector 9 and falls on the contact boundary of the working surface of the measuring prism 2 with the test substance 3.

Rays of blue-violet light also refract into prism 2, pass through it, but exit prism 2 at a different angle β _λi , namely β _λi = arcSin {n _λio Sin [θ-arcSin (n _λix / n _λio )]} = arcSin {1,59417sin [66 ° -arcSin (n _{λix [} / 1,59417)]}, where n _λix = 159417 is the refractive index of the glass of prism 2 for wavelength λ _i = 447 nm;

n _λix is the refractive index of the analyte for the wavelength λ _i .

Moreover, the border of light and shadow observed in eyepiece 7 (Fig. 8) will shift by ΔX = X _D -X _λi / = f ′ (tgβ _D -tgβ _λ ), which corresponds to divisions of the scale 6 ΔМ = (ΔХ / X _Dmax ) ·one hundred. This shift of the border of light and shadow, expressed in divisions of the ΔM scale, is a measure of the angular dispersion of the rays Δβ _{D, λi} emerging from the prism 2 (Fig. 7) relative to the angular field of view of the pipe 4, i.e.

Δβ _{D, λi} = (ΔX / X _Dmax ) arctg (X _Dmax / f ′) 0.01 ΔM · β _Dmax ,

where β _Dmax = _arctan (X _Dmax / f ′) is the angular field of view of the pipe 4;

f ′ is the focal length of the lens 5.

Having the constructive coefficients A ′ and B calculated in advance, the coordinate of the border of light and shadow M = (X _D / X _Dmax ) · 100, measured in yellow light λ _D = 589 nm, and the coordinate offset ΔM = (ΔX / X _Dmax ) · 100 obtained by changing the wavelength of light, find the average dispersion of the test substance 3 by the formula

,

,

и B_min - конструктивные коэффициенты, соответствующие началу диапазона измерения n_Dхmin рефрактометра;Where $$A_{\min }^{\text{'}\text{'}}$$

and B _min are the design coefficients corresponding to the beginning of the measurement range n _{Dхmin of the} refractometer;

- величина изменения коэффициента А′ в диапазоне измерения n_DX от n_DXmin до n_DXmax; $$\Delta A\text{'}\text{'}=A_{\max }^{\text{'}\text{'}}-A_{\min }^{\text{'}\text{'}}$$

- the magnitude of the change in coefficient A ′ in the measurement range of n _DX from n _DXmin to n _DXmax ;

ΔB = B _max -B _min - the change in coefficient B in the range of n _DX from n _DXmin to n _DXmax ;

(Δ _FC ) _O is the known average dispersion of the material of the measuring prism 2;

X _Dmax - the maximum possible range of displacement of the recorded border of light and shadow in the focal plane of the lens 5;

β _Dmax = _arctan (X _Dmax / f ′) is the angular field of view of the pipe, i.e. the maximum range of the angle of deviation of the rays with a wavelength of λ _D = 589 nm at the output of prism 2;

f ′ is the focal length of the lens 5;

- дисперсионный коэффициент. $$q=\frac{\mathrm{one}/{\lambda }_F^2-\mathrm{one}/{\mathrm{<figure-callout\; id="2"\; label="\lambda \; C"\; filenames="00000030.png,00000033.png"\; state="\{\{state\}\}">\lambda \; </figure-callout>}}_C^{}}{\mathrm{one}/{\lambda }_i^2-\mathrm{one}/{\mathrm{<figure-callout\; id="2"\; label="\lambda \; D"\; filenames="00000030.png,00000033.png"\; state="\{\{state\}\}">\lambda \; </figure-callout>}}_D^{}}=\frac{4.2315-\mathrm{2,3218}}{\mathrm{5,0015}-\mathrm{2,8800}}=\mathrm{0,90016}$$

- dispersion coefficient.

M = (X _D / X _Dmax ) · 100 - coordinate of the border of light and shadow in the divisions of the scale 6, corresponding to the refractive index of the investigated substance n _DX ;

ΔM = (ΔX / X _Dmax ) · 100 - the relative shift of the border of light and shadow in the process of changing the wavelength of the light incident on the measuring prism 2.

, $$A_{\max }^{\text{'}}=\mathrm{0,916630}$$

, B_min=0,478996, B_max=0,328823, β_Dmax=0,26060238 рад и q=0,90016, среднюю дисперсию (Δ_FC)_x исследуемого вещества находят по упрощенной формуле: (Δ_FC)_x=0,916682·0,01015+(0,478996-0,150177·0,01M)0,01ΔM·0,2606024·0,90016=0,00930433+(0,478996-0,00150177М)ΔМ·0,00234584,For this example performance of an Abbe refractometer, in which n _{DO = 1,5688, (Δ FC) o} = 0,01015, Ө = 66 °, f '= 75 mm, the scale length of 20 mm (100 bars) and, respectively, $$A_{\min }^{\text{'}\text{'}}=0.916735$$

, $$A_{\max }^{\text{'}\text{'}}=0.916630$$

, B _min = 0.478996, B _max = 0.328823, β _Dmax = 0.26060238 rad and q = 0.90016, the average dispersion (Δ _FC ) _{x of the} test substance is found by the simplified formula: (Δ _FC ) _x = 0 916682 · 0.01015 + (0.478996-0.150177 · 0.01M) 0.01ΔM · 0.2606024 · 0.90016 = 0.00930433 + (0.478996-0.00150177M) ΔМ · 0.00234584 ,

where M and ΔM - the number of divisions of the scale 6.

It can be seen from the formula that this is a linear equation, and to measure the average dispersion (Δ _FC ) _{x of a} substance, it is enough to determine, on a scale of 6, the coordinate of the border of light and shadow in the divisions M, when the main light source is 10, and the amount of shift of the border of light and shadow ΔM after changing wavelength when the auxiliary light source 11 is turned on.

So, for example, in the process of researching motor fuel with the proposed Abbe refractometer, the results were obtained:

M = 35 divisions (which according to the conversion table corresponds to n _D = 1.4200) and ΔM = + 0.95 divisions. The desired average dispersion of this sample of motor fuel

(Δ _FC ) _x = 0.00930433 + (0.478996-0.0015017735) 0.9510.00234584 = 0.010254618.

In cases where the average dispersion (Δ _FC ) _{x of the} test substance 3 is 0.00930433, then when the light of the main source 10 is changed to the light of the auxiliary source 11, the shift of the border of light and shadow does not occur, i.e. ΔM = 0, and if (Δ _FC ) _x <0.00930433, then the shift of the border of light and shadow will be in the opposite direction compared to the considered example for motor fuel, i.e. ΔM will be with the opposite minus sign.

Suppose, as a test sample 3, an aqueous solution of ethylene glycol was poured into a glass-illuminator 1 and, using the proposed Abbe refractometer, the results of measurements of M = 3.1 divisions (n _D = 1.3815) and ΔM-2.4 divisions were obtained. In this case, the desired average dispersion (Δ _FC ) _x = 0.00930433 + (0.478996-0.00150177 · 3.1) (- 2.4) · 0.00234584 = 0.0066338.

From these two examples of the proposed method and device, it can be seen that the difference between the average dispersion of the investigated motor fuel (Δ _FC ) _x = 0.01025 and the average dispersion of an aqueous solution of ethylene glycol (Δ _FC ) _x = 0.0066338, equal to 0.00362, with changing wavelengths from λ _D to λ _i will lead to the total shift of the border of light and shadow by ΔM _Σ = 3.35 divisions of scale 6. Therefore, with the accuracy of visual fixation of the movement of the border of light and shadow ± 0.1 divisions, the measurement of the average dispersion is accurate substances ± 0.0001, which is a higher point compared with known methods and devices.

An even higher accuracy of measuring the average dispersion can be obtained if, instead of a scale 6 and an eyepiece 7, in the proposed Abbe refractometer, a multi-element photodetector L with N photo-sensitive elements is installed in the focal plane of lens 5, for example, in the form of a ruler 20 mm long and 3,000 elements per line and electronic signal processing circuitry.

In this case, the shift of the border of light and shadow is conveniently expressed in pixels.

The recorded coordinate of the border of light and shadow in pixels relative to the first photosensitive element of the photodetector will be P _D = (X _D / X _Dmax ) · N = (X _D / X _Dmax ) · 3000 pixels, and the calculation formula for measuring the average dispersion will be

,

,

where ΔP is the number of pixels corresponding to the shift of the border of light and shadow when changing wavelengths.

In addition, when photoelectric registration of the displacement of the border of light and shadow using a multi-element photodetector, it is possible to increase the accuracy of measuring the average dispersion due to an even greater increase in the difference between the operating wavelength λ _about and auxiliary λ ₁ , using the infrared range of light emission.

The proposed method for measuring the average dispersion of light has several advantages compared with the known.

Firstly, the implementation of the method does not require expensive dispersion compensators (Amici prisms).

Secondly, there is a linear relationship between the magnitude of the recorded shift of the border of light and shadow ΔM, when the wavelength of light is changed, and the desired average dispersion (Δ _FC ) _x , which simplifies the measurement process.

Thirdly, in cases when working with a group of specific substances for which the refractive indices n _Dx and, accordingly, the readings of the proposed refractometer M are in a narrow range, the formula for calculating the average dispersion (Δ _FC ) _{x is} significantly simplified.

If you use the proposed visual refractometer, then:

- for gasolines (M _cf ≈35 scale divisions 6)

(Δ _FC ) _x = 0.00930433 + ΔM · 10 ^-3 ;

- for jet fuels (M _cf ≈57 div.)

(Δ _FC ) _x = 0.00930433 + ΔM · 9.23 · 10 ^-4 ;

- for diesel fuels (M _cf ≈77 div.)

(Δ _FC ) _x = 0.00930433 + ΔM · 8.5 · 10 ^-3 ;

- for aqueous solutions (M _cf ≈15 div.)

(Δ _FC ) _x = 0.00930433 + ΔM · 1.07 · 10 ^-3 .

Fourth, the proposed method for measuring the average dispersion allows you to build the simplest portable spectrorefractometers to perform rapid analyzes of the quality of oils, motor fuels, drugs and other products.

The proposed method and device will be used to create a number of portable spectrorefractometers that will be used in the food industry (analysis of animal and vegetable oils), in the petrochemical industry (control of motor fuels, oils), in pharmacy for drug control, in chemistry and biology.

Sources of irformation

1. Ioffe B.V. Refractometric chemistry methods. 3rd ed., Revised., L .: Chemistry, 1983.

2. ATAGO Refractometers and polarimeters, WWW / atago.ru / av @ labdepot, ru.

3. RF patent No. 2296981 dated 04/10/2007, Bull. No. 10, 2007 (Refractometer).

Claims (3)

1. The method of measuring the average dispersion of light, in which a beam of light in the focal plane installed after the measurement is directed to the input face of the measuring prism of a refractometer made of a material with a known refractive index n _Do and an average dispersion (Δ _FC ) _x in contact with the test substance lens prisms with a focal length f ′ register the position of the border of light and shadow X _D for the limiting rays of the working wavelength λ _D = 589 nm, leaving the measuring prism at an angle β _D , find the refractive index saponification of the test substance n _Dx , from it and from the known values of the angle of inclination of the output face of the measuring prism θ and refractive index n _Do determine the design coefficients A ′ and B, find the total angular dispersion of the limiting rays (Δβ) _FC coming out of the measuring prism, then determine the average the dispersion of the test substance (Δ _FC ) _x = A ′ (Δ _FC ) _x + B (Δβ) _FC ,
characterized in that in order to simplify the measurement process and increasing the accuracy, after determining the position coordinates of the boundaries of light and shadow X _D relative to the maximum possible value X _Dmax for working λ _D-wavelength of the working face of the measuring prism instead of the beam of the operating wavelength of light λ _D is directed quasimonochromatic a light beam with a maximum spectral density of radiation µ (λ) _max corresponding to a wavelength λ ₁ substantially different from the working wavelength λ _D , in the focal plane of the lens register the value and the sign of the relative displacement of the border of light and shadow ΔX = X _D -X _λ1 , it is used to find the total angular dispersion
$$\Delta {\beta }_{D,{\lambda }_{\mathrm{one}}}=\left(\Delta X_D/X_{D\max }\right)\cdot arctg\left(X_{D\max }/f^{\text{'}\text{'}}\right)$$

, and then find the desired average dispersion of the test substance by the formula $${\left({\Delta }_{FC}\right)}_x=\left(A_{\min }^{\text{'}\text{'}}+\Delta A^{\text{'}\text{'}}\cdot X_D/X_{D\max }\right){\left({\Delta }_{FC}\right)}_o+\left(B_{\min }+\Delta B\cdot X_D/X_{D\max }\right)\Delta X_{D,\lambda \mathrm{one}}/X_{D\max }\cdot {\beta }_{D\max }\cdot q$$

,
Where $$A_{\min }^{\text{'}\text{'}}$$

and B _min are the design coefficients corresponding to the beginning of the measurement range of the refractive index n _{Dmin of the} refractometer;
$$\Delta A^{\text{'}\text{'}}=A_{\max }^{\text{'}\text{'}}-A_{\min }^{\text{'}\text{'}}$$

- the magnitude of the change in the coefficient A ′ in the measurement range n _Dх from n _Dхmin to n _Dxmax ;
ΔB = B _max -B _min - the change in the coefficient B in the range of n _Dх from n _Dхmin to n _Dxmax ;
(Δ _FC ) _o is the known average dispersion of the material of the measuring prism;
X _Dmax is the maximum possible displacement of the recorded border of light and shadow in the focal plane of the lens;
ΔX _D , _λi is the relative displacement of the border of light and shadow in the process of changing the wavelength of the light incident on the measuring prism;
β _Dmax = _arctan (X _Dmax / f ′) is the angular field, i.e. the maximum range of the angle of deviation of the limiting rays with a wavelength of λ _D at the output of the measuring prism;
f ′ is the focal length of the refractometer lens;
$$q=\frac{\mathrm{one}/{\lambda }_F^2-\mathrm{one}/{\lambda }_C^2}{\mathrm{one}/{\lambda }_i^2-\mathrm{one}/{\lambda }_D^2}=\frac{1.9097}{\mathrm{one}/{\lambda }_{\mathrm{one}}^2-\mathrm{2,880}}$$

- dispersion coefficient. 2. A device for measuring the average dispersion, containing a glass-illuminator, a measuring prism in the form of an obliquely cut cylinder made of a transparent material with a known refractive index n _Oλ and average dispersion (Δ _FC ) _o , the input face of which is in contact with the test substance and makes an angle θ with an output polished face, a lens in the focal plane of which there is a device for recording the location of the border of light and shadow, characterized in that to increase the accuracy and simplify the measurement process Ia average dispersion of the test substance, Glass illuminator comprises a main source of quasi-monochromatic light, the maximum of the spectral radiation density which μ (λ _{o) max} coincides with the working length of λ _o wave, and an auxiliary source of quasi-monochromatic light, the maximum spectral which μ radiation density (λ _{1) max} significantly differs from the operating wavelength λ _о , each light source is connected to the power source in series through a switching device, providing alternating switching on of the source of light, in a glass-illuminator made of a material with high thermal conductivity, a temperature sensor is mounted connected to a thermostat, and a Peltier element is placed between the body of the glass of the illuminator and the metal base-radiator, one contact of which is connected to the zero point of the regulated power source, and the other - with the middle contact of the thermostat switching relay so that through the normally closed contacts of the thermostat relay the Peltier element is connected, for example, to the negative potential for cooling of the glass-illuminator, and after the thermoregulator relay is activated, the Peltier element is connected to the plus potential for heating the glass-illuminator. 3. The device for measuring the average dispersion according to claim 2, characterized in that as a device for recording the location of the border of light and shadow in the focal plane of the lens is a multi-element photodetector, for example, in the form of a line of photosensitive elements.

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