RU2087903C1 - Automatic concentration metering device - Google Patents

Abstract

FIELD: optical material composition analyzers. SUBSTANCE: device has radiation source, optical system for shaping two light beams, working and reference trays, and light detectors connected into differential circuit, as well as amplifier and control unit. Introduced in device is deflector whose electrodes are connected to control unit output. Inclined side wall of reference tray is made as 180 deg. segment of collecting lens and working surface of tray is shaped to obey law ensuring linearity of device transformation equation. Electric signal in deflector electrode circuit is directly proportional to concentration being measured. EFFECT: improved measurement accuracy. 3 dwg

Description

 The invention relates to measuring equipment, namely to optical analyzers of the composition of substances, is intended to automatically determine the optical density and concentration of components of various mixtures and solutions and can be used in chemical, food and other industries.

 A device for automatic concentration measurement [1] containing a radiation source, an optical system for forming the measuring and comparative channels and located respectively in these channels, working, reference cuvettes and radiation receivers, connected by differential circuit and electrically connected to an amplifier, the output of which is connected to the control unit .

 The disadvantages of the described device are the lack of speed and design complexity due to the presence of kinematic gears and movable elements.

 Closest to the proposed technical solution is an automatic refractometer of the type AR-1 [2] containing a radiation source, an optical system for generating the light flux, a working and reference cell, a two-lens lens, radiation receivers connected by a differential circuit and connected to an amplifier.

 The disadvantages of the described device are the complexity and unreliability of the design and low speed.

 The objective of the invention is to increase the reliability and speed of the device.

 In FIG. 1 shows a functional diagram of the device, FIG. 2 shows the course of the rays in the reference cuvette, in FIG. 3 view of a reference cell in axonometric projection.

 The device (Fig. 1) is constructed according to a two-beam scheme and contains a radiation source 1, mirrors 2 and 3 (mirror 2 translucent), a working 4 and a reference 5 cell, radiation receivers 6 and 7, connected by a bridge circuit, the shoulders of which are resistors 8, 9 and 10, an amplifier 11, a control unit 12, a deflector 13 with electrodes 14, a polarizer 15, a lens 16 and load resistors (voltage divider) 17. The output of the amplifier 11 is connected to the input of the control unit 12, the output of which is electrically connected to the electrodes 14 of the deflector 13 .

 The deflector provides continuous control of the direction of propagation of the beam in space under the influence of an electric signal. The diagram shows an electro-optical deflector in which the deflection angle α of the polarized light beam is determined by the magnitude of the electric field applied to its electrodes. When using an electro-optical deflector, a polarizer is installed in front of the deflector.

 The control unit 12 is designed to generate under the action of an amplified signal a mismatch in the voltage supplied to the deflecting electrodes of the deflector, in order to obtain the necessary beam deflection angle a. In the General case, the control unit 12 is an electronic controller, implemented, for example, on operational amplifiers, it also includes the necessary matching and amplifying elements for docking with the deflector. In particular, a digital astatic controller can be used as a control unit.

The device operates as follows (Fig. 1). The working cell 4 is filled with the analyzed solution with a concentration of C _x , and the reference cell 5 is filled with a reference solution of the same substance with a concentration of C _et .

At the initial moment of time, due to the unequal optical density of the analyzed and reference solutions in cuvettes 4 and 5, radiation detectors 6 and 7 are illuminated differently. Due to the inequality of their photocurrents, an unbalance voltage DU arises on the measuring diagonal of the bridge, which is amplified by the amplifier 11 and supplied to the input of the control unit 12, which, depending on the ΔU value, generates the voltage supplied to the electrodes 14 of the deflector 13. In accordance with the magnitude of the voltage supplied to the electrodes of the deflector, the angle α of the deviation of the light beam at the exit of the deflector changes, and therefore the length of the optical path of the beam in the reference cell 5. This changes (decreases or increases) the thickness other l _et photometric layer of the reference solution until the intensities of the light fluxes at the exits from the working 4 and reference 5 ditches are equal to each other. Then the radiation detectors 6 and 7 are equally illuminated, their photocurrents are equal, and the bridge unbalance voltage DU becomes equal to zero.

In equilibrium, each value of the optical density and concentration C _{x of the} analyzed solution corresponds to a certain angle α of the beam deflection and a certain amount of voltage supplied to the electrodes of the deflector. The output signal U _o is removed from the resistor 17 included in the control electrode circuit of the deflector.

One of the faces (EG) of the reference cell is installed parallel to the optical axis of the device. The inclined wall (AE) of the reference cell is made in the form of the 180 ^o -th segment of a plano-convex lens, which is part of the lens. The deflector must be installed in the focal plane of this lens on the optical axis of the device, that is, the distance d from the deflector to the reference cell should be equal to the focal length of the lens, which is determined by the curvature of its surface and the material from which it is made. This lens directs all rays incident on it from the deflector at various angles parallel to the optical axis of the device. The second lens of the lens is also made in the form of the 180 ^o -th segment of a plano-convex lens and is located parallel to the first lens (the inclined wall of the reference cell), but is offset relative to it by a distance Z along the optical axis. This lens focuses parallel rays incident on it from the first lens and collects them in its side focus, located on the optical axis of the device, where the corresponding radiation receiver 7 is located. As shown in the drawing, the path of the rays in the cuvette and lens is determined by the laws of geometric optics. By changing the distance Z between the reference cuvette 5 and the second lens of the lens when setting up the device, they achieve focusing of the rays on the radiation receiver mounted at a particular distance from the deflector. The design may provide for a rigid connection between two lenses of the lens and the reference cell with the possibility of a smooth change in the distance between the lenses when aligning the device. In particular, at Z = 0, both lenses can be turned from the inclined wall of the reference cell, that is, the inclined wall of the reference cell will be made in the form of a lens of two 180 ^o segments of collecting lenses with centers displaced relative to each other.

For linear static characteristic of the device over the entire operating range of the measurement, i.e. to the output U _O devices was directly proportional to the measured concentration C _x and optical density D _x, working surface should otprofilirovat reference cuvette. The profile of the working surface of the reference cell is determined by the set of points on its surface located at a distance r (α) from the point O of the deflector. Point O is the center of the polar coordinate system. The following is the conclusion of the formula for calculating the profile of the working surface of the reference cell, which provides a linear static characteristic of the device.

For a known angle θ of inclination of the lateral face (AE) of the reference cell to the base (EG) and for a fixed value of the current beam deflection angle a, we can determine the distance r from the deflector to the surface of the collecting lens
inclined wall of the cell. As can be seen from FIG. 2, angle
b = θ-α.

The value of r = r ₁ + r ₂ .

где b высота DOAB.From DAOD

where b is the DOAB height.

From dabd
r ₂ = b ctgβ = d sinα ctg (θ-α).

Then the quantity
r = r ₁ + r ₂ = d cosα + d sinα ctg (θ-α).

On the other hand, as can be seen from FIG. 2:
r = ρ (α) + l _et (1)
where ρ (α) is the profile of the working surface of the reference cuvette, defined as the distance from the point O of the deflector to the working surface of the reference cuvette,
l _{et is the} thickness of the photometric layer of the reference cuvette, that is, the length of the optical path of the beam in the reference cuvette.

где K коэффициент преобразования кюветы;
F функция, обратная функции f и содержащая те же параметры, то есть для нее выполняется равенство F[f(x)]X (x аргумент функции).From equation (1) we obtain
l _et = r-ρ (α) = d cosα + d sinα ctg (θ-α) -ρ (α) (2)
If the continuous deflector transformation equation has the form
α = f (U, b ₁ , b ₂ ... b _n ), (3)
where U is the voltage applied to the electrodes of the deflector;
b ₁ , b ₂ b _n deflector parameters,
then to obtain a linear static characteristic of the device, you should have a reference cell with the equation of transformation of the form

where K is the cell conversion coefficient;
F is a function that is the inverse of f and contains the same parameters, that is, it satisfies the equality F [f (x)] X (x is the argument of the function).

 It was experimentally established that K = 0.25 is optimal.

Из этого уравнения (5) получим формулу для расчета профиля рабочей поверхности эталонной кюветы в полярных координатах относительно точки O:

или

При таком профиле рабочей поверхности эталонной кюветы получим линейное уравнение преобразования устройства.Substituting in equation (4) the value of the thickness l _et photometric layer of the reference cell in accordance with expression (2), we obtain

From this equation (5) we obtain the formula for calculating the profile of the working surface of the reference cell in polar coordinates relative to point O:

or

With this profile of the working surface of the reference cell, we obtain a linear equation for the conversion of the device.

то есть получим уравнение (4). Тогда, подставив в это уравнение выражение (3) для угла α и учитывая математическое свойство обратных функций, получим

Отсюда
U=Kl_эт.Indeed, when substituting expression (6) into equation (2), we have

that is, we obtain equation (4). Then, substituting expression (3) for the angle α into this equation and taking into account the mathematical property of the inverse functions, we obtain

From here
U = Kl _et .

Device output
U _o = K _d U = K _d Kl _et = kl _et , (7)
where K _d the conversion factor of the voltage divider 17.

, (8)
то после подстановки (8) в (7) получим уравнение преобразования устройства:

где

коэффициент преобразования устройства.Since from equality
C _x l _p = C _et l _et
follows that

, (8)
then, after substituting (8) in (7), we obtain the equation for the conversion of the device:

Where

device conversion factor.

Thus, if for the existing type of deflector with a given static characteristic, the profile of the working surface of the reference cell is calculated using formula (6), then the device will have a linear transformation equation of the form (9), that is, in the entire operating range, the output signal U of the _output device is directly proportional to the measured concentration of C _x .

где K коэффициент преобразования эталонной кюветы, выбираемый при расчете.In the particular case, if a deflector with a linear static characteristic of the form
α = K ₁ U,
where K ₁ the conversion coefficient of the deflector,
then, to obtain a linear equation for the conversion of the device, the profile of the working surface of the reference cell must be calculated by the formula

where K is the coefficient of conversion of the reference cell, selected in the calculation.

и

Геометрические размеры кюветы определяются диапазоном ΔC_x измеряемых концентраций, максимальным углом α_max отклонения дефлектора и расстоянием d между дефлектором и эталонной кюветой. Как видно из фиг. 2, высота h основания кюветы
h=dtgα_max.If we take the angle θ 90 ^o , that is, to exclude the walls of the cell, then from equations (6) and (10) we obtain, respectively, the equation

and

The geometric dimensions of the cell are determined by the range ΔC _{x of the} measured concentrations, the maximum deflector deflection angle α _max and the distance d between the deflector and the reference cell. As can be seen from FIG. 2, height h of the base of the cell
h = dtgα _max .

,
где C $\genfrac{}{}{0ex}{}{\text{max}}{\text{x}}$ верхняя граница диапазона измерения концентрации.For a linear deflector

,
where c $\genfrac{}{}{0ex}{}{\text{max}}{\text{x}}$ upper limit of the concentration measurement range.

.Then

.

 The proposed device due to the exclusion of all mechanical components and the use of a deflector controlled by an electric signal, has increased speed and high operational reliability, while optimizing the design of the reference cell provides increased measurement accuracy.

 The deflector assembly includes the deflector itself and the elements necessary to obtain the specified beam deflection parameters. To increase the angle of deflection of the beam with small control voltages on the electrodes, a multi-prism deflector or a multi-deflector, which consists of several deflectors connected in series, can be used. To increase the maximum deflection angle and expand the measuring range, special optical elements can also be used, which allow for small input deflection angles to obtain large deflection angles of the light beam at the output of the optical angle multipliers.

 Automatic adjustment of the device to zero can be provided using a two-dimensional deflector with horizontally and vertically deflecting electrodes with the corresponding design of the reference cell. In this case, the profiled wall of the reference cell 5 should be made of optically absorbing material with an optical density uniformly increasing along the height of the cell. Then, depending on the operating mode of the device, the output of the control unit is connected to vertically or horizontally deflecting electrodes of the deflector and the beam will deviate in two mutually perpendicular directions, respectively, in the horizontal measurement mode and in the automatic vertical adjustment mode (along the height of the cuvette) with fixation set beam position. Thus, compensation is achieved for the measurement error arising from the formation of various deposits and contaminants on the walls of the working and reference cells, as well as elements of the optical system of lenses and filters.

 As follows from the foregoing, the absence in the proposed device of any mechanical components and moving parts leads to a significant simplification of the design, increased reliability and speed, increased measurement accuracy.

Claims (1)

A device for automatic concentration measurement, containing a radiation source and an optical system for forming the measuring and comparative channels located along the radiation, working, reference cuvettes and radiation receivers located in these channels, connected by a differential circuit and electrically connected to an amplifier, the output of which is connected to the input of the unit control, and a lens of two lenses, characterized in that the deflector is located between the radiation source and the reference cell and is made in the form of an electric of the optical deflector, the electrodes of which are connected to the output of the control unit, the objective lenses are made in the form of collecting lens segments parallel to each other at an adjustable distance and located between the reference cell and the corresponding radiation receiver located at the focus of the lens, while the first collecting lens segment is the second wall of the reference cell along the radiation path, the profile of the working surface ρ (α) and the base height h of which are determined respectively by the formulas
ρ (α) = d cosα + d sinα ctg (θ-α) -

where d is the distance from the deflector to the reference cell, equal to the focal length of the lens;
α is the current beam deflection angle by the deflector;
α _max is the maximum deviation angle possible for this type of deflector;
θ is the angle of inclination of the side wall of the reference cell to the optical axis;
F (α, b ₁ , b ₂ ... b _n ) is the inverse of the deflector transform function;
l _{p the} thickness of the photometric layer of the working cell;
C _{e t the} concentration of the standard solution;
C $\genfrac{}{}{0ex}{}{\text{max}}{\text{x}}$ - the upper limit of the range of measurement of concentration;
K 0.25 cell conversion coefficient.

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