RU2550763C1 - Method of measurement of liquid level in vessel - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: method of measurement of liquid level in a vessel is offered according to which in a vessel with dielectric liquid the waveguide resonator is vertically placed liquid, the liquid level x in which is equal to its level in the vessel, inaide it electromagnetic oscillations are excited and their resonant frequency is measured. At the resonant frequency f_n(x) electromagnetic oscillations of the type, for which f_n(x) is higher than the critical frequency f_nkp for the wave of this excited type in the wave guide are excited in the whole volume of the resonator, at the value x, lower than some value x1 at which f_n(x₁) is higher than f_nkp, and f_n(x) is measured, and at the value x, higher than x₁ at which f_n(x₁) is lower than f_nkp, in the whole volume of the resonator at the resonant frequency f_k(x) electromagnetic oscillations are excited of the type for which f_k(x) is higher the critical frequency of f_kkp for the wave of this excited type in the wave guide, with change of f_n(x₁) value down to f_k(x₁) value at x=x₁, and f_k(x) is measured. Design data of the resonator can be selected from the condition f_n(x₁)=f_k(x₁).

EFFECT: higher accuracy.

2 cl, 6 dwg

Description

The invention relates to measuring technique and can be used for high-precision measurement of the level of a dielectric fluid in a container. In particular, it can be used to measure the level of oil products, liquefied gases, etc.

Known methods for measuring the level of liquids in various containers, which determine the liquid level in the tank using sensors in the form of segments of transmission lines of electromagnetic waves - segments of long lines, hollow waveguides, waveguide resonators located in containers with controlled liquids (V.A., Lunkin B.V., Sovlukov A.S. High-frequency method for measuring non-electric quantities (Moscow: Nauka, 1980, 280 p.). When measuring the level of dielectric liquids, the range of variation of the informative parameter, in particular the resonant frequency of the electromagnetic oscillations of the resonator in the form of a long line segment or a segment of a hollow waveguide (waveguide resonator), turns out to be small, which makes it difficult to carry out measurements with the necessary high values of the sensitivity of level sensors and the accuracy of level measurements. This is typical for level measurements of liquids with a low dielectric constant, in particular for cryogenic liquids (liquid oxygen, hydrogen, helium, etc.).

A technical solution is also known (Viktorov V.A., Lunkin B.V., Sovlukov A.S. Radio wave measurements of technological process parameters. M .: Energoatomizdat. 1989, 208 pp. 86-90), which is the most technical in nature close to the proposed method and adopted as a prototype. This prototype method consists in exciting electromagnetic waves in a metal hollow waveguide resonator placed vertically in a container with a controlled dielectric fluid. The liquid level in the tank corresponds to its level in a partially-filled waveguide resonator. By measuring the resonant (natural) frequency of the electromagnetic oscillations of the resonator, it is possible to determine the level of the dielectric fluid filling the cavity of this resonator. However, for liquids with a small dielectric constant (less than 2), the range of variation of the resonant frequency and, accordingly, the sensitivity of the level gauge with a sensitive element in the form of such a waveguide resonator is small, which makes it difficult to measure the level with high accuracy.

The technical result of the present invention is to increase the sensitivity and, as a result, the measurement accuracy by increasing the range of variation of the resonant frequency of the resonator and by making it possible to conduct measurements of the level of dielectric liquids due to the excitation of various types of electromagnetic waves in the waveguide resonator and the associated redistribution of the energy of the standing wave electromagnetic field in the volume of the waveguide resonator at dielectric fluid levels above and below n some of its meaning.

The technical result is achieved by the fact that in the proposed method for measuring the liquid level in a capacitance, in which a vertically waveguide resonator is placed in a capacitance with a dielectric fluid, the fluid level x in which is equal to its level in the capacitance, electromagnetic waves are excited in it and the resonant frequency thereof is measured at the resonant frequency f _n (x) is excited in the entire volume of the resonator electromagnetic waves type for which f _n (x) above the critical frequency f _ncurv for this wave excited in the waveguide type this reason ora, a value of x, the smaller a value of x _1, where f _n (x ₁₎ above f _ncurv and the measured f _n (x), and a value of x, high x _1, where f _n (x ₁₎ below f _ncr , excite electromagnetic waves of the type for which f _k (x) above the critical frequency f _kcr for a wave of a given type in the waveguide of this resonator in the entire volume of the resonator at a resonant frequency f _k (x), and f _kcr <f _ncr , s by changing f _n (x ₁ ) to the value of f _k (x ₁ ) at x = x ₁ , and measure f _k (x). The design parameters of the resonator can be selected based on the condition f _n (x ₁ ) = f _k (x ₁ ).

The method is illustrated by drawings.

Figure 1 shows an example of a measuring device for implementing the proposed measurement method.

Figure 2, figure 3, figure 4, figure 5 and 6 are graphs of the dependence of the resonant (natural) frequency f of the electromagnetic oscillations of the waveguide resonator on the level x of the liquid for examples explaining the essence of the method.

The device (figure 1) contains a waveguide resonator 1 with a controlled dielectric fluid 2, a coupling element 3, an electromagnetic oscillation generator 4, a coupling element 5, a recorder 6.

The method is implemented as follows.

According to this method, different types of electromagnetic waves are excited in series in the waveguide resonator, depending on the level of the dielectric fluid, which leads, as a result, to an increase in the range of the resonant (natural) frequency f of the resonator when the level x changes within the same range, in particular from its zero value (no liquid) to the maximum value (full) in the tank. Different types of vibrations correspond to different distributions of the electromagnetic field energy in the volume of the waveguide resonator, in particular along its longitudinal coordinate (the distribution of field energy along the transverse coordinates may remain unchanged).

In the device (Fig. 1) for implementing this measurement method in a waveguide resonator 1 with a controlled dielectric fluid 2, electromagnetic waves are excited at one of the selected higher (i.e., with a critical frequency f _cr greater than the main (lower) type of oscillation ), i.e., vibrations of one of the higher types E _mnp or H _mnp with different numerical values of the indices m, n and p; the subscript p corresponds to the number of half-waves stacked along the length of the waveguide resonator. In particular, in a cylindrical waveguide resonator it can be electromagnetic oscillations of one of the higher types H ₀₁₁ , H ₂₁₁ , H ₀₁₁ , E ₂₁₁ and others (the main type of oscillation is H ₁₁₁ ); in a rectangular resonator, these are electromagnetic oscillations of one of the higher types H ₁₁₁ , E ₀₁₁ , H ₁₁₂ , H ₂₁₁ , E ₀₁₂ and others; the main type of oscillation is H ₁₀₁ (Lebedev I.V. Technique and devices of the microwave. T.1. M .: Higher school. 1970. 440 p. S.337-369). Methods of excitation of various types of electromagnetic oscillations in resonators, including higher types, their isolation and measurement of characteristics are known (see, for example, Grossman Yu.S. Theoretical fundamentals of radio engineering. Waveguides and resonators. Minsk: MVIRTU edition. 1960. 442 p. .).

The excitation of electromagnetic waves is carried out using the coupling element 3 from the generator of electromagnetic waves 4. The reception of electromagnetic waves is carried out using the coupling element 5 connected via a communication line to the recorder 6, which serves to determine the resonant frequency of the waveguide resonator 1 and, therefore, the level of the dielectric liquid 2 in the tank.

The transverse dimensions (radius R of a cylindrical waveguide resonator, the width of the wide wall of a rectangular waveguide resonator, etc.) can be chosen so that in the absence of liquid in the entire volume of the resonator of length l, electromagnetic waves are excited on some higher type of oscillations with a longitudinal index n; the resonant frequency f of the oscillations is f _n0 .

The condition for the propagation of electromagnetic waves through any waveguide is the fulfillment of the inequality: f> f _cr , which must satisfy the working frequency f and the critical frequency f _cr for a wave of an excited type, including a lower type, for example, for wave H ₁₁ in a circular waveguide (I. Lebedev B. Microwave Engineering and Instruments, Vol. 1. Edited by ND Devyatkov, Moscow: Higher School, 1970, 440 pp. 49-94). So, for waves of type H ₁₁ in a circular waveguide f _cr = 8.7849 / R GHz, for waves of type E ₀₁ in a circular waveguide f _cr = 11.47 / R GHz, where the radius R is expressed in centimeters.

For f <f _cr, a transcendental regime takes place in which the propagation of waves of the corresponding type does not occur along the waveguide, but only a weakening reactive field exists, which decreases with distance from the exciting element.

When the dielectric fluid enters the capacitance (resonator) and its level increases, the resonance (intrinsic) frequency f of this type of oscillations decreases from the initial value f _n0 at x = 0 (Fig. 2). For a certain value x _{1 of} the liquid level, depending on the chosen parameters of the resonator, the waveguide of this resonator becomes transcendental (the resonant frequency f becomes lower than the critical frequency f _ncr for waves of this excited type in the waveguide of this resonator) for the current value of the frequency f _n (x ₁ ) of the considered higher (n-th) type of oscillation.

In this case, the working resonant (natural) frequency f of the resonator abruptly changes to a value of f _k (x ₁ ) and now corresponds to another (k-th) type of oscillation, characterized by a lower value of the critical frequency f _kcr for a wave of this excited type in the waveguide of this resonator. For the kth type of oscillation, the values of f _k (x) are higher than f _kcr , with f _kcr <f _ncr ; there is an abrupt change in f _n (x ₁ ) to the value of f _k (x ₁ ) at x = x ₁ . With a further increase in the level x of the dielectric liquid, a monotonic decrease in the resonance frequency f _k (x) of this now working type of oscillation occurs. Electromagnetic vibrations of types n and k can generally be any that can be excited in a waveguide resonator.

(f_k0 - начальная, при x=0, резонансная частота k-ого типа колебаний), которое меньше значения $$f_{n0}/\sqrt{\epsilon }$$

, соответствующего исходному n-ому типу колебаний. То есть диапазон изменения (перекрытие) резонансной частоты увеличился и составляет теперь $$f_{n0}-f_{k0}/\sqrt{\epsilon }>f_{n0}-f_{n0}/\sqrt{\epsilon }$$

. Следовательно, увеличилась и чувствительность измерительного устройства с чувствительным элементом в виде рассматриваемого волноводного резонатора.As a result, we will have that, when the cavity is completely filled (x = l) with a dielectric fluid with permittivity ε, the resonant frequency f takes the value $$f_k$$$$0_{}/\sqrt{\epsilon }$$

(f _k0 is the initial, at x = 0, resonant frequency of the kth type of oscillation), which is less than the value $$f_n$$$$0_{}/\sqrt{\epsilon }$$

corresponding to the initial n-th type of oscillation. That is, the range of variation (overlap) of the resonant frequency has increased and is now $$f_{n0}-{\mathrm{<figure-callout\; id="0"\; label="f\; k"\; filenames="00000006.png,00000007.png"\; state="\{\{state\}\}">f\; </figure-callout>}}_k/\sqrt{\epsilon }>f_{n0}-{\mathrm{<figure-callout\; id="0"\; label="f\; n"\; filenames="00000006.png,00000007.png"\; state="\{\{state\}\}">f\; </figure-callout>}}_n/\sqrt{\epsilon }$$

. Consequently, the sensitivity of the measuring device with a sensitive element in the form of the considered waveguide resonator has also increased.

In Fig. 3, Fig. 4, Fig. 5 and Fig. 6, examples of the implementation of the method for adjacent excited types of oscillations of a cylindrical waveguide resonator are shown: H ₂₁₁ and E ₀₁₁ in Fig. 3 and Fig. 4, E ₀₁₁ and H ₁₁₁ in Fig. .5 and Fig. 6.

Figure 3 shows a graph of the dependence f (x), explaining this measurement method, as an example of oscillations of types H ₂₁₁ and E ₀₁₁ in a cylindrical waveguide resonator. In this hollow resonator, electromagnetic waves of higher magnetic type H ₂₁₁ (n-th type of vibration) are excited. When a dielectric fluid enters a capacitance (resonator) and its level x increases, the resonance (natural) frequency f of this type of oscillation decreases. At a certain value x _{1 of the} level of the dielectric fluid, depending on the chosen parameters of the resonator, the waveguide of this resonator becomes transcendent (the resonant frequency f becomes lower than the critical frequency f _ncr for waves of this type of excitation N ₂₁ in the waveguide of this resonator) for the current value of the frequency f _n (x ₁ ) considered higher (n-th) type of oscillation.

In this case, the working resonant (natural) frequency f of the resonator abruptly changes to a value of f _k (x ₁ ) and now corresponds to another type of oscillation E ₀₁₁ (k-type oscillation), characterized by a lower value of the critical frequency f _kcr for a wave of this excited type in the waveguide of this resonator. For oscillations of type E ₀₁₁ (k-th oscillation type), the values of f _k (x) are higher than f _kcr , and f _kcr <f _ncr ; there is an abrupt change in f _n (x ₁ ) to the value of f _k (x ₁ ) at x = x ₁ . With a further increase in the liquid level x, a monotonous decrease in the resonant frequency f _k (x) of this now working type of oscillations E ₀₁₁ occurs. Given the different nature of the dependence of f on the level x of the dielectric fluid for magnetic oscillations of type H ₂₁₁ and electric vibrations of type E ₀₁₁ in the waveguide resonator, we will result in a plot of f (x), shown schematically in figure 2 in the form of a solid bold line. The non-working sections of the curves f _n (x) and f _k (x) are shown by dashed lines.

For adjacent types of oscillations n and k, by choosing the design parameters of the waveguide resonator (its diameter and, if any, other elements, if this resonator has a more complex structure), it is possible to provide for a specific dielectric fluid (with a certain permittivity ε) at x = x ₁ equality: f _ncr = f _n (x ₁ ) = f _k (x ₁ ). The graph of the dependence f (x) is characterized by the absence of an abrupt change in f _n (x ₁ ) to the value f _k (x ₁ ) at x = x ₁ and has a monotonic character with a kink at x = x ₁ (Fig. 4, solid bold line). At the same time, the range of variation of f and the sensitivity of the measuring device increased.

Figure 5 shows another graph of the dependence f (x), explaining this measurement method, as an example of oscillations of types E ₀₁₁ and H ₁₁₁ in a cylindrical waveguide resonator. In this resonator, electromagnetic oscillations of the highest electric type E ₀₁₁ (n-th oscillation type) are excited. At a certain value x _{1 of the} level of the dielectric fluid, depending on the chosen parameters of the resonator, the waveguide of this resonator becomes transcendental (the resonant frequency f becomes lower than the critical frequency f _ncr for waves of this type of excitation E ₀₁ in the waveguide of this resonator) for the current value of the frequency f _n (x ₁ ) considered higher (n-th) type of oscillation. In this case, the working resonant frequency f abruptly changes to a value of f _k (x ₁ ) and now corresponds to another type of oscillation H ₁₁₁ (the k-th type of oscillation), characterized by a lower value of the critical frequency f _kcr for a wave of this excited type in the waveguide of this resonator. For vibrations of type H ₁₁₁ (k-th type of vibrations), the values of f _k (x) are higher than f _kcr , with f _kcr <f _ncr ; there is an abrupt change in f _n (x ₁ ) to the value of f _k (x ₁ ) at x = x ₁ . With a further increase in the liquid level x, a monotonic decrease in the resonance frequency f _k (x) of a given, now working, type of H ₁₁₁ oscillation occurs. Given the different nature of the dependence of f on the level x of the dielectric fluid for electric type E ₀₁₁ oscillations and magnetic type H ₁₁₁ oscillations in the waveguide resonator, we will end up with a plot of f (x), shown schematically in Fig. 5 as a solid bold line. The non-working sections of the curves f _n (x) and f _k (x) are shown by dashed lines.

Here, also by choosing the design parameters of the waveguide resonator, it is possible to ensure for a particular dielectric fluid (with a certain dielectric constant ε) that the equality for x = x _{1 is} : f _ncr = f _n (x ₁ ) = f _k (x ₁ ); for a different value of ε, the design parameters of the resonator must be different. The graph of the dependence f (x) is characterized by the absence of an abrupt change in f _n (x ₁ ) to the value f _k (x ₁ ) at x = x ₁ and has a monotonic character with a kink at x = x ₁ (Fig. 6, solid bold line). At the same time, the range of variation of f and the sensitivity of the measuring device with a sensitive element in the form of the considered waveguide resonator also increased.

Thus, by changing the working type of electromagnetic oscillations and the associated redistribution of the energy of the electromagnetic field of the standing wave in the volume of the waveguide resonator with a change in the level of the dielectric liquid, an increase in the range of changes in the resonant frequency in the same range of changes in the level of the liquid, increasing the sensitivity and accuracy of its measurements.

Claims (2)

1. A method of measuring the liquid level in a capacitance, in which a vertically waveguide resonator is placed in a capacitance with a dielectric fluid, the level x of the fluid in which is equal to its level in the capacitance, electromagnetic waves are excited in it and their resonance frequency is measured, characterized in that at the resonant frequency f _n (x) in the entire volume of the resonator excite electromagnetic oscillations of the type for which f _n (x) is higher than the critical frequency f _ncr for a wave of a given type in the waveguide of this resonator, at a value x less than x value ₁ , at which f _n (x ₁ ) is higher than f _ncr , and f _n (x) is measured, and at a value x greater _than x ₁ , at which f _n (x ₁ ) below f _ncr , excite in the whole volume resonator at a resonant frequency f _k (x) electromagnetic oscillations of the type for which f _k (x) is higher than the critical frequency f _kkp for a wave of a given excited type in the waveguide of this resonator, and f _kкp <f _nкp , with the value of f _n (x ₁ ) to the value of f _k (x ₁ ) at x = x ₁ , and measure f _k (x). 2. The method of measuring the liquid level in the tank according to claim 1, characterized in that the design parameters of the resonator are selected based on the condition f _n (x ₁ ) = f _k (x ₁ ).

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