RU2018116C1 - Method and device for determining light scattering (diffusion) coefficient in liquid media - Google Patents

Abstract

FIELD: optics; measuring optic characteristics of media. SUBSTANCE: method involves the steps of: directing rediation from a point-type isotropic light source and from directional light source, modulating light fluxes and irradiating them from which a light seattering coefficient is determined. EFFECT: enhanced accuracy. 2 cl, 2 dwg

Description

 The invention relates to measurements of the optical characteristics of liquid media both on samples and upon immersion of the measuring device directly in the studied liquid medium.

 The invention may find application for measuring optical characteristics in natural water bodies, for measuring turbidity of tap water, wastewater, gasoline, kerosene, other fuels, beer, suspensions and emulsions and other liquid media, in the chemical, food, pharmaceutical, metallurgical and other industries industry.

Known methods for measuring the scattering index (σ) by measuring the scattering index σ (θ) in a fixed direction θ, and then finding σ either using correlation dependencies or by numerically integrating the function σ (θ) in the range of angles θ 0.2-170 ^о . These methods have low accuracy and require complex devices for their implementation.

 The objective of the proposed technical solution is to increase the accuracy of determining the scattering index in liquid media while simplifying the device.

ln (F_n/F_н),, где R - расстояние в жидкой среде, которое проходит излучение от источников;
F_н - световой поток от изотропного источника, прошедший исследуемую среду;
F_н - световой поток от направленного источника, прошедший исследуемую среду.The technical problem is solved in a method for determining the scattering index in liquid media, including the direction of radiation of an isotropic source into a liquid medium, measuring the characteristics of the scattered light field and the subsequent calculation of the scattering index due to the fact that the radiation of a directed source is additionally directed into the liquid medium, and the light fluxes of isotropic and directional radiation change in time (modulate) according to various laws, measure the light flux from both sources, past the blown medium using a single photodetector, and the scattering index of the medium is calculated by
σ =

ln (F _n / F _n ), where R is the distance in the liquid medium, which passes radiation from sources;
F _n - the light flux from an isotropic source that has passed the medium under study;
F _n - the light flux from a directional source that has passed the medium under study.

 A device for determining the scattering index in a liquid medium, consisting of a power supply source, a sealed enclosure with protective glasses, inside which an isotropic light source, protective glasses and a photodetector connected to an amplification, calculation and recording unit are mounted on one optical axis, is equipped with an additional directional source light mounted on the optical axis in front of an isotropic source, a voltage modulation unit supplying the light sources, and a photodetector signal processing unit.

 The essence of the invention lies in the possibility of more accurately determining the scattering index, directing into the medium under study radiation from sources of isotropic and directed radiation. Due to the different modulation of the radiation of both sources, the change in the light flux passing through the medium under study can be measured using a single photodetector equipped with an appropriate processing unit that separates signals proportional to the two measured radiation fluxes. Due to the claimed features of the method and device, there is no need to combine the source image with the pinhole, as in the prototype, in the present invention, the image of the directional light source is formed directly behind the protective glass on the photodetector.

 Thus, the proposed technical solution allows you to get rid of the error associated with different changes in the sensitivity of the two photodetectors over time during operation, and simplifies the device, makes it easy and simple to carry out its adjustment in the reference environment.

 To do this, it is enough to combine the image of the directional source directly observed on the protective glass with the sensitive area of the photodetector, while in the prototype the adjustment requires placing an additional element (for example, frosted glass) in the plane of the diaphragm to visualize the image of the source, removing the photodetector located behind the diaphragm and a rather complicated procedure for combining a small image of a source with a pinhole using sensitive adjusting elements.

 Thus, the claimed distinctive features of the method and device for its implementation are essential for solving the task.

 Figure 1 shows a diagram of a device for determining the dispersion index of a liquid medium; figure 2 shows the voltage curves generated by the modulation unit for supplying isotropic and directional light sources (2, a), the curves of the time dependence of the flows perceived by the photodetector from isotropic and directional sources, and the corresponding signals generated in the processing unit (2, b)

 The device placed in a liquid medium 1 has protective glasses 2 and 3, an isotropic source 4 immediately in front of the protective glass 2, a directional source 5 (which can be either a laser, or consisting of a point emitter 6 and a lighting lens 7 projecting an image of the emitter 6 onto the photocathode of the photodetector 8), a photodetector 8, located directly behind the protective glass 3. The light sources are fed from a common power source through a modulation unit 9, which changes the luminous fluxes of the light sources in time nym laws. The photodetector 8 has an output to the signal processing unit 10, and the signal from the unit 10 enters the amplification, calculation and registration unit 11.

F_н(t)dt, F_n=

F_n(t)dt,, где Т_н и Т_и - периоды изменения потоков F_н(t) и F_и(t).The method is implemented using the device as follows. The voltages U _n (t) and U _and (t) supplying directional and isotropic light sources are generated by the same power source with modulation unit 9. This ensures that the ratio F _n / F _{and the} fluxes coming from both sources are constant over time . These flows passing through the scattering medium arrive at the photodetector 8 and create at its output a signal S (t) = S _n (t) + S _and (t) equal to the sum of the signals, each of which is proportional to the fluxes F _n (t) _and F _and (t). The signal S (t) enters the processing unit 10, which filters the signals S _n (t) and S _and (t) and generates voltages V _n and V _and proportional to the time-average values of the flows F _n (t) and F _and ( t):
V _n ~ F _n , V _n ~ F _n,,
F _n =

F _n (t) dt, F _n =

F _n (t) dt ,, where T _n and T _and are the periods of variation of the flows F _n (t) and F _and (t).

The possibility of filtering in the processing unit 10 of the signals S _n (t) and S _and (t) is provided by an appropriate choice of the laws of change in time of the voltages U _n (t) and U _and (t). For example, U _n (t) and U _and (t) can be sinusoidal signals with different frequencies ω _{n and} ω _and (Fig. 2, a). Then the values of V _n and V _and can be determined by highlighting the harmonic components of the signal S (t) with frequencies 2ω _{n and} 2ω and measuring their amplitudes, which are linearly related to the average values of the flows F _n and F _and (Fig.2, b), those.

V _n / V _and = F _n / F _and .

There are other possible ways of isolating signals V _n and V _and .

ln (V_n/V_н), равна показателю рассеяния исследуемой среды.From the processing unit, these signals are sent to the amplification, calculation and registration unit 11, where the ratio of the signals V _n and V _and : V _n / V _and = F _n / F _{and is} generated, as well as calculated and recorded at the "output" of the device (for example, on the display) σ =

ln (V _n / V _n ) is equal to the dispersion index of the medium under study.

The device is pre-regulated in a reference medium (air or distilled water, in which the absorption coefficients κ and scattering σ are equal to zero). Adjustment is that by changing the supply voltage U _n (t) and U _{and a} (t) at the modulation unit 9, achieve signal equality V _H and V _and in the processing unit, and consequently the flow F _n and F _and reference environment. Because the
F _n = C _n exp [- (κ + σ) R],
F _and = C _and exp [-κR], the equality F _n = F _and for κ = 0 and σ = 0 means that C _n = C _and = C.

ln (V_н/V_n) будет, очевидно, равенσ . На выходе блока 11 демонстрируется либо величина показателя рассеяния исследуемой среды σ, либо при соответствующей градуировке устройства пропорциональная σвеличина концентрации взвешенных частиц в жидкой среде.When installing the adjusted device in the studied liquid medium with absorption and scattering κ and σ, the ratio of signals V _and / V _n generated in block 11 will be equal to
V _and / V _n = F _and / F _n = Cexp [-κR] /
/ Cexp [- (κ + σ) R] = e ^σR , and

ln (V _n / V _n ) will obviously be equal to σ. At the output of block 11, either the value of the scattering index σ of the test medium is demonstrated, or with an appropriate graduation of the device, proportional to σ is the concentration of suspended particles in a liquid medium.

 The claimed device can be implemented on a known element base, for example, using LEDs AL-336K or FD-226.

 An important advantage of the proposed method and device over the prototype is the use of a single photodetector, which in the adopted measurement method significantly increases the accuracy of measurements by eliminating the error associated with the departure of the sensitivity of different photodetectors over time (due to temperature and other influences). In addition, the device is simplified, since when aligning it there is no need for a complex process of combining the source image with a point aperture. In the proposed device, the light spot is focused directly on the photodetector located immediately behind the protective glass, i.e. a light spot is directly observed on the protective glass 3.

 If it is necessary to measure the scattering index or suspension concentration not in situ, but on the sample, the cuvette with the test medium is placed between the protective glasses 2 and 3. In this case, the length of the cuvette must be equal to the "base" of the device R, and its diameter D must be greater than or equal to R.

Claims (2)

1. The method of determining the indicator of light scattering in liquid media, during the implementation of which direct radiation of a point isotropic light source into the test medium, measure the light flux transmitted through the test medium and determine the scattering index, characterized in that the directed light flux is additionally sent to the test medium, modulate luminous fluxes, measure the additional luminous flux passing through the test medium, and the scattering index is determined by the formula
σ =

ln (F _n / F _n ),
where R is the distance in the liquid medium, which both light fluxes pass;
F _p and F _n - the measured light flux from isotropic and additional sources, respectively.  2. A device for determining the indicator of light scattering in liquid media, containing a point isotropic light source, protective glasses installed along the radiation, a photodetector connected to an amplification, processing and recording unit, characterized in that a directional radiation source mounted on it is additionally inserted the optical axis between the point isotropic light source and the first protective glass of the device for placing the medium under study, and a modulation unit connected to radiation sources.

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