SU1749783A1 - Polarimeter for measuring sugar concentration in urine - Google Patents

Abstract

Usage: the invention relates to an optical instrument. SUMMARY OF THE INVENTION: A polarimeter comprises a light source, a diaphragm, a collimator, a light filter, a polarization filter, a cuvette, a Wollaston birefringent prism, behind which a movable mask modulator is installed with windows arranged displaced by the window size along the direction of movement. The plane of the mask is aligned with the plane of the image of the diaphragm, with the bifurcation plane perpendicular to the direction of movement of the mask. A photodetector is connected to the input of an amplifier with an adjustable gain factor, the output of which is connected to a digital voltmeter, and is directly connected to the first input of the comparison device. A reference voltage source is connected to the second input of the comparator, and the output of the comparator is connected to an adjustable element of the current source that supplies the light source. 3 sludge. SO with

Description

The invention relates to optical instrumentation, namely, to polarimetric measurements of the concentration of sugar in solutions.

The field meter allows for rapid mass screening of patients in clinics, first-aid posts, in everyday life for the early diagnosis and treatment of diabetes mellitus.

The well-known portable polarimeters of the P-161 type and circular polarimeters of the SM type contain movable and stationary polarization filters, between which a cuvette with the test medium is installed. A movable polarization filter is associated with a limb for visual reference of the angle of rotation of this filter. Still

the filter is made of several parts, the transmission planes of which differ from each other by a small angle (5-8 °), constituted the so-called penumbral device.

The drawbacks of visual instruments are low measurement accuracy (± 0.1 in angle and ± 0.2% in sugar concentration), rapid operator fatigue, and the resulting additional subjective measurement errors caused by this.

Famous photoelectric polarimeters are constructed using a single-beam compensation scheme. Some of them are constructed according to the compensation scheme for the angle of rotation of the polarization plane by rotating one of the polarization filters, and some by

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circuit with fixed polarization filters, but with the use of wedge, magneto-optical or electro-optical compensators.

The closest to the proposed is a polarimeter with non-EASY polarization filters containing a light source, a condenser, a diaphragm, a collimator, two polarization filters fixed so that their transmission planes are mutually orthogonal and a cuvette with the medium under study and a modulator are installed between them. compensator, working: using the Farad effect.

However, active substance, such as TF5 glass, a modulator-compensator located between polarization filters, inevitably distorts the state of polarization of the light passing through it due to natural or thermally induced anisotropy of glass, which introduces significant errors in measuring the angle of rotation of the polarization plane and, therefore, the concentration of sugar.

In addition, taking into account the law of Malus, describing the dependence of the intensity of the transmitted light J on the angle of rotation of the polarization plane

I I0cos2 (a + A a),

the strong influence of the anisotropy of the semitransparent layer of the divider on the state of polarization of light, the difference in the transmission of light of the semitransparent layer and polarizers,

differences in sensitivity and other characteristics of photodetectors,

The purpose of the invention is to improve the measurement accuracy and simplify the design. The goal is achieved by the fact that

in a polarimeter containing a light source, a diaphragm of diameter d, a collimator with a focus of f, a limiting aperture, a light filter, two polarization filters, a cell filled with the medium under study, a modulator and a photodetector, the modulator is mounted behind the polarization filters, is designed as a mobile masks with windows of dimensions a x B, arranged offset by the width of the window B

along the direction of movement, the mask plane is aligned with the image plane of the collimator diaphragm by the projection system with magnification M, one of the polarization filters is high

in the form of a two-beam polarization prism, the polarization planes of the p- and s-components of which are angles of ± 45 ° with respect to the transmission plane of the other polarization filter; the bifurcation angle of the rays with a two-beam prism satisfies the condition

where 1o is the intensity of the light falling on the first polarization filter;

Before; - increment of the angle after the cuvette, with mutually orthogonal polarization filters (a 90 °) and at small angles Yes (compensation zone) the increment cll / d and always the smallest, which is not optimal for obtaining the greatest sensitivity and accuracy.

Precise metering devices (accuracy within thousand fractions of a degree) or exact magneto-optical (electro-optical) compensators are structurally complex and expensive.

Known devices, for example, a balancing scheme for polarimetric measurements, Kotor contains a light divider in the form of a glass cube with a translucent layer, two polarizers with transmission planes ± 45 ° with respect to the azimuth of the linearly polarized light beam incident on the divider, two The photo receivers included in the bridge circuit cannot provide even the accuracy of measurements of the angle of rotation of the polarization plane, which is provided by the known polarimeters described. The reasons for this are

arctg- - / 3 arctg

A-Md 2f

moreover, the bifurcation plane is perpendicular to the direction of movement of the mask, the photodetector is connected via capacitance to the input of the amplifier with an adjustable coefficient of amplifier, the output of which is connected to the digital voltmeter, and directly connected to the first input of the comparator, to the second input of which the reference voltage source is connected and the output of the comparator is connected to an adjustable element of the current source feeding the light source.

FIG. Figure 1 shows a structural diagram of a polarimeter for measuring the concentration of sugar in the urine: in Fig. 2 — the mask of the modulator from the side of the light incident on it (section A-A in Fig. 1); in fig. 3 shows the dependence of the light intensity on the angle of rotation of the plane of polarization of light, illustrating the operation of the polarimeter.

A field meter for measuring the concentration of sugar in the urine contains a source of light 1, a condenser 2 installed along the beam, a diaphragm 3 with a diameter d, a collimator 4 with a focus f, a limiting aperture 5,

a light filter 6, for example, transmissive yellow light (line D of the spectrum, i.e., A 589 nm), polarization filters 7 and 8, between which a cuvette 9 of length L with protective isotropic glasses 10 and the test medium 11 is installed. One of the polarization filters, for example, filter 8, is made in the form of a double-beam polarization prism, for example, in the form of Volaston's prism, the polarization plane of the p- and s-component of which are angles of ± 45 ° relative to the transmission plane of another fixed stationary polarization filter 7. Behind Wollaston's prism 8 getting lens 12 which together with the collimator lens 4 is a projection system with increasing M. bifurcation angle rays ft Wollaston prism 8 satisfies a condition

W 2f

arctg --- fi arctg

A -Md 2f

For the polarization filters 7 and 8 in the focal plane of the lens 12 there is installed a modulator in the form of a movable mask 13 fixed on flexible elements 14, for example, in the form of flat springs cantilever mounted on the case body. The mask 13 is in the focal plane of the projection system with magnification M, consisting of lenses 4 and 12, and is made in the form of an opaque plate with transparent rectangular windows of size AxB (Fig. 2), which are offset by the width B of the window along the direction moving the mask, which is perpendicular to the bifurcation plane by the Wollaston prism. i.e., the windows are shifted so that the edges of the transparent adjacent windows lie on a line coinciding with the direction of the bifurcation of the ray by the prism 8, DL. oscillation to the frame 15 of the mask 13 is attached a plate 16 of a magnetic material that plays the role of a moving core of the electromagnet 17, which is connected to an AC network through a diode 18. A lens 19 and a photodetector 20 are mounted to the modulator mask 13 21 is connected to the input of amplifier 22. whose gain is adjusted during tuning. The output of amplifier 22 is connected to a digital voltmeter 23, which has a digital display and an output for connecting a digital printing device. At the same time, the photodetector 20 is directly connected to the first input of the comparator 24, to the second input of which the reference voltage source U0 is connected, and the output of the comparator 24 is connected to the regulating element 25 of the current source 26 supplying the light source 1.

5 Polimeter for measuring urine sugar concentration works as follows.

The light body of the light source 1 (Fig. 1) is transferred by condenser 2 to the plane

0 of the diaphragm 3, which is in the focus of the collimator 4. The rays of light that pass through the diaphragm 3, after the collimator 4, become collimated, some of them go through the limiting aperture 5 and the narrowband filter 6. Next, the collimated monochromatic beam of light passes the polarization filter 7, becomes linearly polarized with an azimuth of polarization, for example, 45 ° to the horizon.

0 passes through the cuvette 9 with the test medium 11, the two-beam prism of Wollaston 8 and is divided into two linearly polarized beams, the p- and s-components of which make angles of ± 45 ° with respect to the plane of transmission5 of the polarized filter 7, and beams depend on the angle of rotation of the plane of polarization of light a, the medium under study 11. A projection system consisting of lenses 4 and

0 12, transfer the image of the diaphragm 3 to the plane of the mask 13 in the form of two separated images with increasing M. At an azimuth of the polarization filter of 7 ± 45 ° to the horizon, the beam separation plane

5 with a Wollaston 8 prism can be positioned vertically or horizontally (in FIG. 1, a vertical version of this plane is shown). The mask 13 (Fig. 2) under the influence of an electromagnet 17,

0 ac power supplied through the diode 18, on a magnetically soft measles 16, oscillates with a frequency sy in the direction perpendicular to this plane, i.e., in this embodiment, horizontally. Since the angle

5 bifurcated rays with a two-beam prism 8 satisfies the condition

arctg -MA yg arctg-A-Md

50

2f

2f

while the transparent windows of the mask 13 are displaced along the direction of its oscillation by the value B of the window, during the oscillation of the mask 13 forked by the Wollaston 8 double beam prism, the light beams periodically alternately pass the upper beam when the mask 13 (Fig. 2) is shifted to the left, then the lower the beam, when the mask 13 is displaced to the right, and then the transmitted light beams of the lens 19 (FIG. 1) are collected and the photosensitive layer of the photodetector 20. Moreover, since the lens 19 from the plane of the receiver 20 builds an image of the plane in front of the lens 12, where the beam is not yet split n, in the process of modulation of beams in the plane of mask 13 past the light beams enter the same position of the photosensitive layer of the photodetector 20, thereby eliminating the occurrence of spurious signals

If the test medium 11 (Fig. 1) does not possess optical activity, for example, distilled water, then monochromatic linearly polarized light with an azimuth of 45 ° passes through the cell 9 without changes and the Wollaston 8 two-beam prism divides into two beams absolutely identical as in shape and the intensity of light (Fig. 3, points 1, 2 on the Maluse curve, showing the dependence of the intensity of light t passing through the polarized gri filter and changing the angle of the polarization plane of the light incident on it) In this case, the photodetector 20 receives a time-unchanged light I equal to half the intensity of the light Jo incident on the Wollaston 8 prism, i.e. I 0.5f0.

If the test medium 11 has optical activity due to its sugar content, then, depending on the concentration of sugar c at the exit of the cuvette 10, the azimuth of the linear polarization changes by

, 01,

where a about 52.6 ° is the specific rotation of the sugar polarization plane for the working wavelength A 589 nm.

In this case (Fig. 3), the equality of the beam intensities after the Wollaston prism is violated, for example, one of them increases D1 I0sin2 Yes (Fig. 3, Vol. 3), and the other decreases by the same amount (Fig. 3, t. 4). As a result, in the signal spectrum of the photoreceiver 20, in addition to the constant component proportional to the light intensity I 0.5 10 (FIG. 3, Vol. 5), there is a variable component of the SU frequency, which is proportional to the intensity D1 (FIG. 3, curve 6). The variable component of the signal is filtered by the capacitor 21 (Fig. 1) and its amplitude is measured by a digital voltmeter 22, which can operate in two modes. In the mode of measuring the angle of rotation of the polarization plane Yes O, 5 arcsinl / I0 at small Yes, the measurement is carried out taking into account the assumption Yes D1 / 21 ° In the mode of measuring concentration

100 yes

is taken into account a D -L

Lenna cuvette length, for example when L - - 100 mm with 2 Yes. The measurement results are displayed on the display panel of the digital voltmeter 23 and, at the request of the operator, can be recorded by the printing device.

The amplitude of the variable component of the light flux DI depends on both the angle of rotation Do and the magnitude of the absorption of the test medium 11, and the amplitude of the constant component 0 depends only on the absorption of g. Therefore, to eliminate the influence of the absorption g on the results of measuring the angle of rotation polarization plane Yes and, therefore, the concentration C constant component of the signal of the photodetector 20 is fed to one input of the comparison device 24, and the reference (reference) potential to the second input of the device 24. The difference of these potentials The regulating element 25, which regulates the current value of the lamp 1 from the source 26 and thereby controls the intensity of the radiation of the lamp 1 so that the constant component of the signal of the photoreceiver 20 does not depend on the absorption of the medium Ne, always equal to the value set in advance when calibrating for a unit. Such automatic adjustment of a single DC value ensures proportionality DI 2 Yes c. high accuracy and ease of measuring the concentration of sugar in solutions and, above all, in the urine

The sensitivity and accuracy of measurements of the proposed polarimeter depends mainly on the detecting ability of the photodetector 20, on the sensitivity and dynamic range of the digital voltmeter 23 and reach values of ± 0.001 ° and ± 0.0015 °, respectively.

Such high measurement accuracy is ensured by the presence of new distinctive features of the proposed polarimeter.

So, in contrast to the known devices built according to the compensation scheme, in the proposed polarimeter both polarization filters are fixed and, therefore, angular measuring devices are not required, which are sources of significant and sometimes basic measurement errors. In addition, the known photoelectric polarimeters with fixed polarization filters are single-beam and the moment of compensation for the angle of rotation of the polarization plane when one of the polarization filters is rotated is determined by the maximum light quenching, when the curve I f (a) ) has the lowest toughness. In the proposed polarimeter, a two-beam scheme is used and the entire measurement process is carried out (Fig. 3) on a section of curve 1 - f (a) with a maximum slope. Therefore, with the same deviations from the zero position of the linear polarization azimuth, the increment of the light flux А I / D and in the proposed polarimeter is higher and, consequently, the sensitivity is also higher.

The proposed polarimeter is much simpler than the existing known photovoltaic polarimeters in that it does not contain complex angle-measuring devices, does not contain compensators, and does not require technologically sophisticated elements and assemblies. The bifurcation angle ft with a Wollaston 8 prism is sufficient within a little more than 0.5 °, so this prism can be made not of Iceland spar, as usual, but of cheaper material, such as crystalline quartz. The absence of complicated measuring devices allows reducing the size and weight of the proposed field meter.

Thus, when using the proposed polarimeter, the measurement accuracy (± 0.0015 °) increases while the construction is simplified, the cost and laboriousness of the polarimeter are reduced to the limits when it can be used both in clinics and in everyday life, and moreover in service, the proposed polarimeter is simple (it is required to fill the cell, turn on the polarimeter in the network and read the measurement results on a digital indicator).

Claims (1)

Invention Formula A field meter for measuring the concentration of sugar in the urine, containing a radiation source and installed along the path of radiation and an optically coupled condenser, a diaphragm of diameter d, a collimator with a focal distance f, a limiting aperture, a light filter, two polarization filters mounted between them with the medium under study, a modulator, a focusing lens and a photodetector, as well as an amplifier, characterized in that, in order to increase the accuracy and simplify the design, a polarization filter is placed behind the second polarization filter during the course of the radiation The modulator is installed behind the lens during radiation and is designed as a movable mask located in a plane perpendicular to the optical axis, with windows of size AxB located offset by an amount B along the direction of displacement , perpendicular to the optical axis, while the mask is installed so that the plane is aligned with the plane of the image of the diaphragm of the projection system, one of the polarization filters is made in the form of a two-beam polarization isms, the plane of polarization P 'and the S-component which are inclined at ± 45 ° to a plane passing the second polarization filter, the angle / bifurcation ray-beam prism satisfies a condition arctg p arctg A -Md 2f and the bifurcation plane is perpendicular to the direction of movement of the mask, a capacitor, a digital voltmeter, a comparison device, a regulating element and a current source are inserted into the polarimeter, the first output of the photoreceiver is connected via a capacitor to the amplifier input, the output of which is connected to the digital voltmeter, the second output of the photoreceiver connected to the first input of the comparison device, to the second input of which the reference voltage source is connected, and the output of the comparison device is connected to the regulating element of the source and current. 5A. I 4 {w ;; u, 8 x 1 // 20 I i i I - .... / / i Ј ± sup -40 five