RU2757542C1 - Method for measuring the level of a dielectric liquid in a container - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to measuring technology and can be used for high-precision determination of the level of a dielectric liquid located in a container, regardless of the dielectric constant of the liquid. In the method, electromagnetic pulse signals are excited in the first segment of a long line and filled with a liquid in accordance with its level z in the container, signals reflected from the lower end of the segment of a long line are received, the total time t₁ of forward and reverse propagation of electromagnetic pulse signals is measured. In the second dimension, in the second segment of the long line located vertically in a container with a controlled liquid and filled with liquid in accordance with its level in the container, electromagnetic pulse signals propagating at a speed different from the propagation speed of electromagnetic pulse signals in the first segment of the long line are excited, electromagnetic pulse signals reflected from the lower end of the segment of the long line are received, the total time t₂ of the forward and reverse propagation of electromagnetic pulse signals is measured and a joint functional transformation of the measured values t₁ and t₂ is performed, the result of which is judged based the liquid level.

EFFECT: increase in the accuracy of measurements.

1 cl, 2 dwg

Description

The invention relates to measuring equipment and can be used for high-precision determination of the level of a dielectric liquid in any container, regardless of the dielectric constant of the liquid.

Known methods and devices for measuring the level of liquids in containers, based on the use of segments of long lines (coaxial line, two-wire line, etc.) as sensitive elements (Viktorov VA Resonant level measurement method. M .: Energy. 1969. 192 with.). This length of line is placed vertically in a container of controlled fluid. By measuring any of its informative parameter, in particular, the resonant frequency of electromagnetic oscillations, it is possible to determine the level of the liquid. The disadvantage of such measurement methods and devices implementing them is the low measurement accuracy due to the dependence of the level measurement results on the electrophysical parameters of the liquid.

There is also known a technical solution (SU 460447, 04/10/1973), which contains a description of a measurement method and a two-channel device - a level gauge, in which electromagnetic oscillations of the TEM type are excited in two independent sections of long lines with different loads on them at the ends forming its measuring channels at the fundamental (1st) harmonic. Their other ends are connected to the inputs of the corresponding secondary converters, the outputs of which are connected to the input of the information processing unit, the output of which is connected to the indicator. Along these segments of the long line, there is a different distribution of the energy of the electromagnetic field of a standing wave, required to obtain information about the level of a dielectric liquid, regardless of its dielectric constant. By measuring their resonance frequencies f ₁ and f _{2 of} electromagnetic oscillations (which are functions of the level z of the liquid and its dielectric constant ε), one can find the level z from the relation

и

- начальные (при z=0) значения f ₁ и f ₂ соответственно. Данное соотношение обладает свойством инвариантности к величине £ и ее возможным изменениям. Недостатком этих способа и устройства является невысокая точность измерения, главным образом, в области малых значений уровня, близких к нулевому значению. В этом случае при нулевом значении уровня (z=0) имеется неопределенность типа "0/0", а вблизи значения z=0 погрешность измерения резко возрастает, поскольку результат совместного преобразования резонансных частот может принимать разные значения из-за возможных, даже малых, девиаций значений резонансных частот (вышеприведенное преобразование неустойчиво относительно возможных флуктуаций значений

и

).where

and

- initial (at z = 0) values f ₁ and f _2, respectively. This relationship has the property of invariance to the value of £ and its possible changes. The disadvantage of this method and device is the low measurement accuracy, mainly in the region of low level values close to zero. In this case, at a zero value of the level (z = 0), there is an uncertainty of the type "0/0", and near the value z = 0, the measurement error sharply increases, since the result of the joint transformation of resonant frequencies can take different values due to possible, even small, deviations of the values of the resonant frequencies (the above transformation is unstable with respect to possible fluctuations of the values

and

).

A technical solution is also known (RU 2473056 C1, 01/20/2013), in which a segment of a long line with a terminal horizontal section is used, a vertically positioned segment of a long line, and filled with liquid in accordance with its level in the container. The horizontal section of a segment of a long line is abruptly filled with liquid and emptied when the liquid enters and is removed from it, respectively. Exciting electromagnetic oscillations in a segment of a long line at two different resonant frequencies, which correspond to different distributions of the energy of the electromagnetic field along a given segment of a long line, measuring these resonant frequencies and performing their joint functional processing according to the relationship corresponding to this particular measurement method, it is possible to determine the values of the liquid level regardless of the dielectric constant of the liquid. The disadvantage of this method is the presence of certain difficulties in the excitation and isolation of the harmonic of a segment of a long line of a higher order than the fundamental harmonic, which complicates its implementation.

Also known is a technical solution, in terms of the technical nature of the closest to the proposed method and adopted as a prototype (RU 2125245 C1, 20.01.1999). According to this method, electromagnetic oscillations are excited in a vertically positioned segment of a long line and filled with liquid in accordance with its level in a container, the natural (resonant) frequency f of a segment of a long line is measured and the measurement results are processed. In this case, electromagnetic pulse signals are additionally excited in a segment of a long line, signals reflected from the lower end of a segment of a long line are received, the total time t of forward and backward propagation of pulse signals is measured and taken into account when processing the measurement results. The disadvantage of this method is the low measurement accuracy in the region of low level values close to zero. In this case, at a zero value of the level (z = 0), there is an uncertainty of the type "0/0", and near the value z = 0, the measurement error sharply increases, since in this case the result of the combined transformation of f and t can take different values due to possible, even small deviations of f and t values.

The technical result of the present invention is to improve the measurement accuracy.

The technical result is achieved by the fact that in the method for measuring the level of a dielectric liquid in a container, in which, in the first measurement, in the first segment of a long line placed vertically in a container with a controlled liquid and filled with liquid in accordance with its level z in the container, electromagnetic pulse signals are excited, receive signals reflected from the lower end of a segment of a long line, measure the total time t _{1 of} forward and backward propagation of electromagnetic pulse signals, additionally, in the second dimension, in a second segment of a long line placed vertically in a container with a controlled liquid and filled with liquid in accordance with its level in the container, excite electromagnetic pulse signals that propagate at a speed different from the propagation speed of electromagnetic pulse signals in the first segment of a long line, receive electromagnetic pulse signals reflected from the lower end of a segment of a long line, measure The total time t _{2 of the} forward and backward propagation of electromagnetic pulse signals is taken, and a joint functional transformation of the measured values of t ₁ and t _{2 is} performed, the result of which is used to judge the level of the liquid in the container.

The proposed method is illustrated by drawings. FIG. 1 shows a functional diagram of a measuring device for implementing this method. FIG. 2. shows a cross-section of two lengths of a coaxial long line.

Shown here are liquid 1, a segment of a long line 2, an electronic unit 3 a segment of a long line 4, an electronic unit 5, a functional converter 6, a recorder 7, dielectric shells 8 and 9.

The essence of the proposed method is as follows.

и заполняемом жидкостью в соответствии с ее уровнем z в емкости возбуждают электромагнитные импульсные сигналы, принимают сигналы, отраженные от нижнего конца отрезка длинной линии, измеряют суммарное время t₁ прямого и обратного распространения импульсных сигналов. Дополнительно, во втором измерении, в располагаемом вертикально в емкости с контролируемой жидкостью втором отрезке длинной линии длиной

и заполняемом жидкостью в соответствии с ее уровнем z в емкости, возбуждают электромагнитные импульсные сигналы, распространяющиеся со скоростью, отличной от скорости распространения электромагнитных импульсных сигналов в первом отрезке длинной линии, принимают электромагнитные импульсные сигналы, отраженные от нижнего конца отрезка длинной линии, измеряют суммарное время t₂ прямого и обратного распространения электромагнитных импульсных сигналов, и производят совместное функциональное преобразование суммарное время t₂ прямого и обратного распространения электромагнитных импульсных сигналов. Производят совместное функциональное преобразование измеренных значений t₁ и t₂, по результату которого судят об уровне жидкости в емкости.According to this method, in the first dimension, in the first segment of a long line with a length of

and filled with liquid in accordance with its level z in the container excite electromagnetic pulse signals, receive signals reflected from the lower end of the long line segment, measure the total time t _{1 of} forward and backward propagation of pulse signals. Additionally, in the second dimension, in a second segment of a long line of length vertically placed in a container with a controlled liquid

and filled with liquid in accordance with its level z in the container, excite electromagnetic pulse signals propagating at a speed different from the propagation speed of electromagnetic pulse signals in the first segment of a long line, receive electromagnetic pulse signals reflected from the lower end of a segment of a long line, measure the total time t ₂ forward and backward propagation of electromagnetic pulse signals, and produce a joint functional transformation of the total time t ₂ forward and backward propagation of electromagnetic pulse signals. A joint functional transformation of the measured values of t ₁ and t ₂ is carried out, according to the result of which the level of the liquid in the container is judged.

Since the informative parameters t ₁ and t ₂ are functions of both the level z of the liquid and its dielectric constant ε, then by carrying out joint transformations of t ₁ and t ₂ , it is possible to exclude the influence of e on the results of determining the level z.

To implement the measurement method, two lengths of a long line, in particular a coaxial line, are used here as measuring channels. As informative parameters, the total time t _{2 of} forward and backward propagation of electromagnetic pulse signals, t ₁ and t _2, respectively, in the first and second segments of the long line is used. Consideration of the dependences of t ₁ and t ₂ on the level z, each of which is expressed by the corresponding equation, as a system of equations for the level z and the dielectric constant ε of the liquid in the container, makes it possible to obtain, after its solution, the required information about the level z, regardless of the value of e.

и отмечен уровень z диэлектрической жидкости; считается, что нижние концы отрезков длинной линии совмещены с дном емкости. У каждого отрезка коаксиальной длинной линии внутренний проводник покрыт по всей длине диэлектрической оболочкой определенной толщины. В первом измерении в емкости с контролируемой диэлектрической жидкостью 1 располагают вертикально первый отрезок длинной линии 2, пространство между проводниками которого заполняется жидкостью 1 в соответствии с ее уровнем в емкости. В отрезке длинной линии 2 возбуждают электромагнитные импульсные сигналы (видеоимпульсы), принимают сигналы, отраженные от нижнего конца отрезка длинной линии 2, измеряют, в электронном блоке 3, суммарное время t₁ прямого и обратного распространения импульсных сигналов. При этом сигналы, отраженные от поверхности жидкости, являются неинформативными (паразитными). Они могут быть достаточно легко отселектированы или за счет разной полярности сигналов, отраженных от поверхности жидкости и от нижнего конца отрезка длинной линии, который может быть выполнен, в частности, разомкнутым на этом конце, или за счет существенно разной амплитуды рассматриваемых сигналов (сигналы, отраженные от нижнего конца отрезка длинной линии, имеют значительно большую амплитуду). Дополнительно, во втором измерении, в емкости с контролируемой жидкостью 1 располагают вертикально второй отрезок длинной линии 4, пространство между проводниками которого заполняется жидкостью 1 в соответствии с ее уровнем в емкости. В отрезке длинной линии 4 возбуждают электромагнитные импульсные сигналы (видеоимпульсы), распространяющиеся со скоростью, отличной от скорости распространения электромагнитных импульсных сигналов в первом отрезке длинной линии 2. Принимают сигналы, отраженные от нижнего конца отрезка длинной линии 4, измеряют, в электронном блоке 5, суммарное время ₂ прямого и обратного распространения импульсных сигналов во втором отрезке длинной линии 4. Для возбуждения электромагнитных импульсных сигналов, распространяющихся с разной скоростью в первом и втором отрезках длинной линии используют для проведения измерений отрезки длинной линии 2 и 4, проводники каждого из которых покрыты по всей длине диэлектрическими оболочками разной толщины. Значения t₁ и t₂, измеряемые с помощью, соответственно, электронных блоков 3 и 5, поступают в функциональный преобразователь 6. В нем осуществляют совместное преобразование t₁ и t₂, результат которого, несущий информацию об уровне z жидкости 1 в емкости независимо от диэлектрической проницаемости ε жидкости, поступает на индикатор 7, подсоединенный к выходу функционального преобразователя 6.Consider a measuring device that implements this method of measuring the liquid level. FIG. 1 shows two segments of a uniform coaxial long line of the same length placed vertically in a container with a controlled dielectric liquid

and the level z of the dielectric fluid is marked; it is believed that the lower ends of the long line segments are aligned with the bottom of the container. For each segment of the coaxial long line, the inner conductor is covered along its entire length with a dielectric sheath of a certain thickness. In the first measurement, in a container with a controlled dielectric liquid 1, the first segment of a long line 2 is placed vertically, the space between the conductors of which is filled with liquid 1 in accordance with its level in the container. In the segment of the long line 2, electromagnetic pulse signals (video pulses) are excited, the signals reflected from the lower end of the segment of the long line 2 are received, and the total time t _{1 of the} forward and reverse propagation of the pulse signals is measured in the electronic unit 3. In this case, the signals reflected from the surface of the liquid are uninformative (parasitic). They can be quite easily selected either due to the different polarity of signals reflected from the liquid surface and from the lower end of a segment of a long line, which can be made, in particular, open at this end, or due to significantly different amplitudes of the signals under consideration (signals reflected from the lower end of a segment of a long line, have a significantly greater amplitude). Additionally, in the second dimension, a second segment of a long line 4 is placed vertically in a container with a controlled liquid 1, the space between the conductors of which is filled with liquid 1 in accordance with its level in the container. In a segment of a long line 4, electromagnetic pulse signals (video pulses) are excited, propagating at a speed different from the propagation speed of electromagnetic pulse signals in the first segment of a long line 2. Signals reflected from the lower end of a segment of a long line 4 are received, measured in the electronic unit 5, total time _{2 of} forward and backward propagation of pulse signals in the second segment of a long line 4. To excite electromagnetic pulse signals propagating at different speeds in the first and second segments of a long line, segments of a long line 2 and 4 are used for measurements, the conductors of each of which are covered with the entire length with dielectric shells of different thicknesses. The values of t ₁ and t ₂ , measured with the help of electronic units 3 and 5, respectively, enter the functional converter 6. In it, t ₁ and t ₂ are jointly converted, the result of which, which carries information about the level z of the liquid 1 in the container, regardless of dielectric constant ε of the liquid, is fed to the indicator 7, connected to the output of the functional converter 6.

In a coaxial long line, its inner conductor can be covered with a dielectric sheath. FIG. 2 shows a cross-section of two segments of a coaxial long line 2 and 4, on the basis of which this measurement method is implemented. These segments of the long line 2 and 4 have the same diameters of the inner and outer conductors, but their inner conductors are covered along their entire length with dielectric shells 8 and 9, respectively, of different thicknesses. Since this measurement method is designed to measure the level of a dielectric liquid, then in one of the two segments of the coaxial long line, the dielectric shell on its inner conductor may be absent (its thickness is zero).

Let us consider how the time characteristics of impulse signals (video signals), characterized, ultimately, by the values of t ₁ and t _{2 of the} total time of their direct (to the lower end of a segment of a long lines) and backward (to the input of a segment of a long line) propagation in the first and second segments of a long line, respectively.

распространения электромагнитных сигналов в каждом отрезке коаксиальной длинной линии в его верхней части, незаполненной контролируемой жидкостью, естьSpeed

propagation of electromagnetic signals in each segment of the coaxial long line in its upper part, not filled with the controlled liquid, is

- относительная эффективная диэлектрическая проницаемость двухслойной диэлектрической среды, образованной воздухом и диэлектрической оболочкой; а ₁, r, а ₂ - диаметры, соответственно, внутреннего проводника, оболочки и внешнего проводника отрезка длинной линии; ε_n - относительная диэлектрическая проницаемость материала оболочки.where c is the speed of light,

- the relative effective dielectric constant of a two-layer dielectric medium formed by air and a dielectric shell; a ₁ , r, and ₂ are the diameters, respectively, of the inner conductor, the shell and the outer conductor of a segment of a long line; ε _n is the relative dielectric constant of the shell material.

In the lower part of a segment of a coaxial long line filled with a controlled liquid with a dielectric constant ε, the propagation velocity of electromagnetic signals is

where

Since the temporal characteristics of the propagation of electromagnetic signals are ultimately characterized by the time t of their propagation, let us consider what this time is equal to when electromagnetic signals travel along a segment of a long line, partially, to the level z, filled with a controlled liquid, to the lower end of this segment of a long line and its reception at the upper end after passing twice (with forward and backward propagation) along a segment of a long line. This time t is obviously

From this we get

(и, следовательно, также и ε_эфф) отличны друг от друга, можно, путем совместного функционального преобразования значений времени распространения электромагнитных сигналов в каждом из этих отрезков длинной линии, получить информацию об уровне z при обеспечении инвариантности результата такого совместного преобразования к величине s контролируемой среды.Applying two long line segments with values

(and, therefore, also ε _eff ) differ from each other, it is possible, by joint functional transformation of the values of the propagation time of electromagnetic signals in each of these segments of a long line, to obtain information about the level z while ensuring the invariance of the result of such a joint transformation to the value s controlled Wednesday.

и ε_эфф, относящиеся к первому отрезку длинной линии, символами

и

, соответственно, а ко второму отрезку длинной линии - символами

и

, соответственно. В первом и втором измерениях, суммарное время t₁ и t₂, соответственно, прямого и обратного распространения импульсных сигналов вдоль первого и второго отрезков длинной линии выражается следующими формулами:By designating the values

and ε _eff , related to the first segment of a long line, by symbols

and

, respectively, and to the second segment of the long line - by symbols

and

, respectively. In the first and second dimensions, the total time t ₁ and t ₂ , respectively, of forward and backward propagation of pulse signals along the first and second segments of a long line is expressed by the following formulas:

- длина каждого отрезка длинной линии, с - скорость света.where

is the length of each segment of a long line, c is the speed of light.

следует, чтоFrom the ratio

follows that

Substituting into (7) the value of ε _eff from (4), we will have

а ко второму отрезку длинной линии - символами t₂,

и приравняв правые части соотношения (8), записанного для обоих отрезков длинной линии, получимDenoting the quantities related to the first segment of a long line by symbols t ₁ ,

and to the second segment of the long line - symbols t ₂ ,

and equating the right-hand sides of relation (8) written for both segments of the long line, we obtain

This ratio is invariant to the value of ε of the controlled environment.

С учетом этого выражения для

и

можно записать так:Let's make the following notation:

Given this expression for

and

can be written like this:

Then, taking into account (10) and (11), relation (9) for determining z, in which the value of z is contained in an implicit form, can be written as follows:

In relation (12), the quantity ε is absent, i.e. this ratio is invariant to the value of ε and its changes. Thus, carrying out in the functional converter 6 of the measuring device containing the computing device that implements this measurement method, the joint functional transformation of the values t ₁ and t ₂ determined in the first and second measurements, respectively, according to relation (12), it is possible to determine the value of the level z of the controlled liquid regardless of the value of ε. Finding the value of z from (12) in a computing device is possible when solving specific problems with known numerical values of the quantities included in relation (3). Relation (12) makes it possible to determine the level z at any of its values, including zero. This method of measurement provides high measurement accuracy at any values of the z coordinate, including its small, near zero, values.

Thus, this method makes it possible to measure the level of a dielectric liquid in a container, regardless of the value of its dielectric constant. This method is quite simple to implement, which is feasible on the basis of two segments of a long line located in a container with a controlled liquid.

Claims (1)

A method for measuring the level of a dielectric liquid in a container, in which, in the first measurement, in the first segment of a long line placed vertically in a container with a controlled liquid and filled with liquid in accordance with its level z in the container, electromagnetic pulse signals are excited, signals reflected from the lower end are received a segment of a long line, the total time t _{1 of the} forward and backward propagation of electromagnetic pulse signals is measured, characterized in that, additionally, in the second dimension, in the second segment of the long line placed vertically in a container with a controlled liquid and filled with liquid in accordance with its level in the container, excite electromagnetic pulse signals propagating at a speed different from the propagation speed of electromagnetic pulse signals in the first segment of a long line, receive electromagnetic pulse signals reflected from the lower end of a segment of a long line, measure the total time t ₂ forward and backward propagation of electromagnetic pulse signals, and perform a joint functional transformation of the measured values of t ₁ and f ₂ , the result of which is used to judge the level of the liquid in the container.

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