RU175647U1 - DEVICE FOR MEASURING LIQUID LEVEL, BASED ON THE ELECTRO-OPTICAL EFFECT IN NEMATIC LIQUID CRYSTALS - Google Patents

Abstract

The utility model relates to the field of instrumentation and can be used to measure the level of liquids in the oil and gas industry and the chemical industry. The objective of the utility model is to increase the speed. The stated problem is solved by the fact that in a liquid level measurement system based on the electro-optical effect in nematic liquid crystals, containing a coaxial capacitor with isolated from each other electrodes connected in series with the measuring circuit. Unlike the prototype, the measuring circuit is made in the form of a cell, which is a multilayer structure consisting of a plate of conductive glass, a homeotropically oriented nematic liquid crystal, a plate of a cadmium sulfide crystal CdS, and tin dioxide electrodes SnO. Cadmium sulfide CdS is a photoconductor, the conductivity of which depends on the intensity of the light passing through it. The nematic liquid crystal is made in the form of a mixture: n-n-butyl-n'-heptanoyl-hydroxybenzene + n-methoxybenzylidene-n-butylaniline. 3 ill.

Description

The utility model relates to the field of instrumentation and can be used to measure the level of liquids in the oil and gas industry and the chemical industry.

Known:

1) a liquid level meter (ed. St. RF No. 2150088, class G01F 23/26, publ. 12.10.1998), consisting of capacitive cylindrical level sensors, including coaxial cylindrical electrodes.

The disadvantages of this design are the lack of reliability and low noise immunity to the effects of random interference.

2) Electro-optical information-measuring system for monitoring the liquid level (ed. St. RF No. 161789, class G01F 23/26, published May 10, 2016), containing a coaxial capacitor with a central electrode in the form of a round rod and a hollow cylindrical electrode, which are insulated apart from each other using an electrical insulating cover. An optical radiation source in the form of a laser diode emits a coherent beam of light, which after passing through the polarizer becomes plane-polarized. The capacitor is connected in series with a measuring circuit made in the form of a Pockels cell, the electrodes of which form a series circuit with the electrodes of a coaxial capacitor. The change in voltage at the electrodes of the Pockels cell contributes to the conversion of the refractive index of a plane-polarized light beam. At the exit from the crystal, the result of the summation of the oscillations over the components will be elliptical polarized light. Part of the energy coming out of the device through the analyzer is the energy of oscillations having a plane of polarization parallel to the given analyzer. A photodiode converts a light beam incident on its photosensitive region into an electric voltage, which is processed by a microcontroller containing an amplifier, an analog-to-digital converter, and a microprocessor, and the obtained data are displayed on a liquid crystal indicator.

The disadvantage of this design is the low speed.

The objective of the utility model is to create a new device for measuring the liquid level with the achievement of the following technical result: increased performance.

This problem is solved in that in a device for measuring the liquid level, based on the electro-optical effect in nematic liquid crystals (NLC), containing a coaxial capacitor with insulated electrodes from each other, connected in series with the measuring circuit, according to a utility model, the measuring circuit is made in the form of a liquid crystal cell, which is a multilayer structure of a plate of conductive glass and a plate of a crystal-photoconductor of cadmium sulfide CdS, on which epleny tin dioxide SnO ₂ electrodes, the mixture was placed between the plates of a nematic liquid crystal, n-butyl-n-n'-heptanoyl-oksibenzol + n-methoxybenzylidene-n-butylaniline.

In FIG. 1 is a structural diagram of a device for measuring a liquid level based on an electro-optical effect in nematic liquid crystals; FIG. 2 shows an experimental electro-optical liquid crystal (LC) cell; FIG. Figure 3 shows the dependences of: a) the optical signal versus voltage for various illumination values of the photoconductor wafer; b) phase delay from voltage, the amount of illumination of the plate of the photoconductor (in percent).

In this block diagram (Fig. 1), a coaxial capacitor is used, the electrodes of which are connected to the LCD cell. It is made in the form of a hollow cylindrical electrode 1 and a central electrode-rod 2, connected to the electrodes of the electro-optical LCD cell. The LCD cell is illuminated by a laser 3, the beam of which first passes through the polarizer 4. Next, the light transmitted through the LCD cell 5 and the analyzer with a photodetector 6 is processed by a microcontroller 7, which includes an amplifier, an analog-to-digital converter, and a microprocessor. Data from the microcontroller goes to the operator’s workstation, where it is displayed on the screen 8 of the monitor in any convenient form.

The principle of operation of the electro-optical system on nematic liquid crystals is as follows: a change in the level of the dielectric liquid located between the electrodes 1 and 2 of the coaxial measuring capacitor causes a change in the capacitance of this capacitor in proportion to the change in the liquid level. This, in turn, leads to a change in the reactance of the capacitor and leads to a change in the voltage drop across it.

The LCD cell (Fig. 2) is a structure of a plate of conductive glass 9 and a plate of a crystal-photoconductor CdS 10. Electrodes 11 of tin dioxide SnO ₂ are attached to the plates. The use of CdS is due to the fact that it is a photoconductor, and its conductivity can be changed using light of various intensities. A mixture of 12 nematic liquid crystals of n-n-butyl-n'-heptanoyl-hydroxybenzene + n-methoxybenzylidene-n-butylaniline was placed between the plates.

The use of an LCD cell in the proposed system gives an increase in speed and accuracy of measurements, which was made possible thanks to a pronounced orientational effect in liquid crystals, the relaxation time of which is 10 ^-6 s.

Since the nematic has a dielectric constant ε _α ≈ 0, it can be considered semi-infinite provided that, with the thickness of the liquid crystal z → ∞, the angle of inclination of the LC molecules is θ → 0.

Given the long-range order parameter

, т.е. распределение дипольного момента p уменьшается от электрода вглубь жидкого кристалла, как

, b=-1/δ, δ~λ^-1 - эффективная глубина существования поверхностной поляризации,

и

- константы, где

, k - коэффициент упругости, E - напряженность электрического поля.where S ₁₀ is the order parameter near the surface in the absence of a field, h is the thickness of the liquid crystal,

, i.e. the distribution of the dipole moment p decreases from the electrode deeper into the liquid crystal, as

, b = -1 / δ, δ ~ λ ^-1 is the effective depth of existence of surface polarization,

and

are constants where

, k is the coefficient of elasticity, E is the electric field strength.

The equation of state of a nematic liquid crystal will have the form:

We introduce the notation y = η (ξ), ξ = e ^-λz , and we obtain the equation:

,

,

his decision

.

.

,

,

,

,

further for a << 1, we obtain for changing the refractive index

(1)

(one)

those. a change in the refractive index of an LC depends on the applied electric field voltage in direct proportion.

Using the experimental results of the dependence of the intensity of light transmitted through the LCD cell (wavelength 550 nm) on the applied voltage (Fig. 3a), we obtained the dependences of the phase delay and the magnitude of the illumination of the photoconductor wafer on the voltage (Fig. 3b), which demonstrate the linear nature of the change in the double refraction of the cell according to the formula (1). It is this detected linear electro-optical effect that underlies the proposed device for measuring liquid level.

Claims (1)

A device for measuring the liquid level, based on the electro-optical effect in nematic liquid crystals, containing a coaxial capacitor with electrodes isolated from each other, connected in series with the measuring circuit, characterized in that the measuring circuit is made in the form of a liquid crystal cell, which is a multi-layer structure of a plate of conductive glass and cadmium sulfide CdS crystal-photoconductor wafer onto which SnO ₂ tin dioxide electrodes are attached, etc. and a nematic liquid crystal mixture of n-n-butyl-n'-heptanoyl-hydroxybenzene + n-methoxybenzylidene-n-butylaniline was placed between the plates.

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