RU2083955C1 - Method of measurement of level of liquid - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: resistance R₁ is measured in circuit between submerged electrodes, depth of submersion of electrodes is changed by Δ, resistance R₂ in circuit between submerged electrodes after change of depth of their submersion is measured and level of liquid is determined, Description gives mathematical expressions to calculate level of liquid. EFFECT: enhanced accuracy of method. 7 dwg

Description

 The invention relates to instrumentation and can be used to measure the level of conductive fluids using submersible electrodes.

 Known electrothermal method of measuring the liquid level (see Germany patent N 3423802, CL G 01 F 32/24, 1986), based on the measurement of the resistance of the immersion electrode, made in the form of a heated resistor with a positive temperature coefficient.

 The disadvantage of this method is the limited accuracy due to the influence of ambient temperature.

 A known method of measuring the liquid level, based on measuring the active resistance between the immersion electrodes (see N. A. Mozhegov. Automatic measuring instruments for the volume, level and porosity of materials. M. Energoatomizdat, 1990, p. 27).

 The disadvantage of this method is the limited accuracy of the level measurement.

,
где
S площадь поперечного сечения электрода;
ρ удельное сопротивление электродов (к>0, к≠1).A prototype of the invention is a level measurement method according to US Pat. RF N 2008625, class G 01 F 23/24, 1994), consisting in the fact that they measure the resistance R ₁ in the circuit between the first and second electrodes, change the resistance of the electrodes "k" times, measure the resistance R ₂ in the circuit, and the liquid level l _x is determined by the formula:

,
Where
S is the cross-sectional area of the electrode;
ρ specific resistance of the electrodes (k> 0, k ≠ 1).

 The disadvantage of this method is the limited scope due to the need to change the resistivity of the electrodes, which requires the use of either atypical electrodes or additional electrodes connected in parallel with the first.

 The technical result of using the invention is to expand the scope of the method by providing the possibility of using standard electrodes.

,
где
R₀= ρ•l₀/S_э сопротивление электродов;
ρ удельное сопротивление электродов;
S_э площадь поперечного сечения электродов;
l₀ длина электродов;

при опускании электродов

.This result is achieved due to the fact that in the method of measuring the liquid level, which consists in measuring the resistance R ₁ in the circuit between the first and second electrodes, by which the level value is found, the immersion depth is additionally measured on D, the resistance R ₂ in the circuit is measured, and the level liquids l _{x are} determined by the formula:
when lifting electrodes

,
Where
R ₀ = ρ • l ₀ / S _{e the} resistance of the electrodes;
ρ resistivity of the electrodes;
S _e the cross-sectional area of the electrodes;
l _{0 is the} length of the electrodes;

when lowering the electrodes

.

The invention consists in the following. The accuracy of the ohmic level gauges is significantly affected by the previously unknown or difficult to account contact resistance of the fluid R _k between the immersion parts of the electrodes. This situation occurs, for example, when the water level in the locks changes, when the value of R _k depends on weather conditions (moisture, temperature), various impurities of organic and (or) inorganic origin.

To eliminate the influence of R _k on the measurement result l _x , information redundancy is used. The measurement is carried out at two values of the electrode immersion depth.

 A distinctive feature of the proposed measurement method is the change in the immersion depth of the electrodes in the second measurement cycle.

 Figure 1 presents a diagram of a device that implements the proposed method of measurement, with one pair of electrodes; figure 2 diagram of the device shown in figure 1, the electrodes of which are shifted vertically relative to the starting position; figure 3 diagram of a device that implements the proposed method of measuring the level having two pairs of electrodes, shifted vertically relative to each other by Δ> 0 in figure 4 diagram of an automatic level gauge; in FIG. 5 version of the technical implementation of the block computing automatic level gauge; in FIG. 6 is a second embodiment of a technical implementation of a computing unit; 7, a third embodiment of a technical implementation of a computing unit.

 The device for measuring the level (figure 1) contains two electrodes 1, 2 and a measuring device 3, while the electrodes 1, 2 are placed in a container 4 with a measured liquid.

In the device (Fig. 2), the electrodes 1, 2 are installed with an increase in height by Δ> 0 compared to the electrodes in the device shown in Fig. 1 ((Δ <l _x )).

The device (figure 3) contains an additional pair of electrodes 5, 6 and a switch 7 in comparison with the device, a diagram of which is shown in figure 1 or figure 2. In this case, the electrodes 5, 6, made similarly to the electrodes 1, 2, are shifted vertically relative to the electrodes 1, 2 (for example, up) by the value Δ> 0 (Δ <l _x ). The upper leads of the electrodes 1, 2 are connected to the disconnecting contacts of the switch 7 and the upper terminals of the electrodes 5, 6 to the closing contacts of the switch 7, the movable contacts of which are connected to the inputs of the measuring device 3.

The electrodes can be made in the form of rectangular plates of length l ₀ , width d, plan area S _e , and located at a distance δ from each other. An ohmmeter can be used as a measuring device.

 The level gauge (Fig. 4) contains four electrodes 1, 2, 5, 6, two power supplies 8, 9, two measuring devices 3, 10, a calculation unit 11. In this case, the electrodes 1, 2, 5, 6 are placed in a container 4, liquid level in which it is necessary to measure. The upper terminal of the electrode 2 (6) is connected to the first terminal of the measuring device 3 (10), the second terminal of which is connected to one of the terminals of the power supply 8 (9), the other terminal of which is connected to the upper terminal of the electrode 1 (5). The outputs of the measuring devices 3 and 10 are connected to the first and second inputs of the calculation unit, respectively.

 The electrodes 5, 6 are shifted in height by D> 0 with respect to the electrodes 1, 2. In FIG. 4 shows that the electrodes 5, 6 are raised relative to the electrodes 1, 2.

 The resistance of the electrodes are equal and the electrodes are made of the same type.

 The calculation unit 11 (Fig. 5) contains direct voltage sources 12, 13 generally adjustable, adders 14, 15, dividing element 16, indicator 17, while the output of source 12 is connected to the summing input of adder 14, the output of source 13 is connected to the first the summing input of the adder 15. The outputs of the adders 14, 15 are connected respectively to the first and second inputs of the division element 16, the output of which is connected to an indicator 17, the first input of the computing unit 11 is the second summing input of the adder 15, the second input combined subtracting inputs The adders 14, 15.

 In the computing unit 11 (Fig. 6), the source 12 output is connected to the subtracting input of the adder 14, the source 13 output to the first subtracting input of the adder 15. The outputs of the adders 14, 15 are connected responsibly to the first and second inputs of the division element 16, the output of which is connected to the input indicator 17, the first input of the computing unit 11 is the summing input of the adder 15, the second input is the combined summing input of the adder 14 and the second subtracting input of the adder 15.

 The calculation unit (Fig. 7) contains two analog-to-digital converters / ADC / 18, 19, a microprocessor / personal computer or microcomputer / 20 and an indicator 17, while the outputs of the ADC 18, 19 are connected to the first and second inputs of the microprocessor 20, respectively the output of which is connected to the input of the indicator 17, while the first and second inputs of the calculation unit are respectively the inputs of the ADC 18, 19.

 The process of measuring the liquid level is carried out in two cycles.

 In the first cycle, the resistance in the circuit between the immersion electrodes 1, 2 is measured (Fig. 1).

Moreover, R ₁ = R _e1 + R _k1
Where
R _e1 = ρ ₀ (l ₀ -l _x ) S _e = (R ₀ -ρ ₀ l _x / S _e ) resistance of a part of electrodes 1, 2 with a length (l ₀ -l _x ) located above the liquid;
ρ ₀ specific resistance of the electrodes 1, 2;
S _e the cross-sectional area of the electrodes;
R ₀ = ρ ₀ l ₀ / S _e ohmic resistance of the electrodes;
R _k1 = ρ _x • δ / l _x • d contact resistance of the liquid;
ρ _{x a} previously unknown specific resistivity of the liquid between the electrodes 1, 2;
l _{0 is the} length of the electrodes;
δ distance between the electrodes 1, 2;
d is the width of the electrodes;
l _x current fluid level.

Во втором цикле измеряют сопротивление R₂ при уменьшении глубины погружения электродов 1,2 на величину Δ<l_x(Δ>0) /при их поднятии/.Then

In the second cycle, the resistance R _{2 is} measured with a decrease in the immersion depth of the electrodes 1.2 by Δ <l _x (Δ> 0) / when they are raised /.

где R $\genfrac{}{}{0ex}{}{\text{′}}{\text{о}}$ = ρ_о•Δ/S_э
Из (4) и (5) следует, что

На фиг.3 показано использование двух пар электродов, при этом электроды 1,2 опущены вниз по сравнению с электродами 5,6, на Δ>0(Δ<l_x)
В первом цикле измерения переключатель 7 находится в положении 1. Измерительный прибор 3 измеряет сопротивление R₁ /см. формулу (4)/. Во втором цикле измерения переключатель 7 находится в положении 11. Измерительный прибор измеряет сопротивление R₂ /см. формулу (5)/. Уровень жидкости определяется по формуле (6).Wherein

where r $\genfrac{}{}{0ex}{}{\text{′}}{\text{about}}$ = ρ _about • Δ / S _e
It follows from (4) and (5) that

Figure 3 shows the use of two pairs of electrodes, while the electrodes 1.2 are lowered down compared to the electrodes 5.6, at Δ> 0 (Δ <l _x )
In the first measurement cycle, the switch 7 is in position 1. The measuring device 3 measures the resistance R ₁ / cm. formula (4) /. In the second measurement cycle, the switch 7 is in position 11. The measuring device measures the resistance R ₂ / cm. formula (5) /. The liquid level is determined by the formula (6).

Из (4) и (7) следует

Анализ (6), (8) показывает, что результат измерения l_x не зависит от заранее неизвестного значения ρ_x Величины R₀ и

рассчитываются заранее
Автоматический уровнемер /фиг. 4/ при использовании в качестве измерительного прибора омметра работает следующим образом. В данном случае блок вычислений имеет техническую реализацию, приведенную на фиг.5. При этом, в блоке вычислений 11 выходной сигнал источника напряжений 12 устанавливается равным

а источника

Измерительный прибор 3 измеряет эквивалентное сопротивление
R₁ R_э1 + R_к1
При условии, что электроды 1,2,5,6 выполнены в виде прямоугольных пластин длиной l₀, шириной d и площадью в плане S_э, то

Сопротивление R_э1 представляет собой сопротивление части электрода 1,2, расположенной над уровнем жидкости, пропорциональное длине (l₀-l_x). Сопротивление R_к1 сопротивление жидкости между погружными частями электродов 1, 2.With an increase in the immersion of the electrodes 1.2 by the value (Δ <(l ₀ -l _x )) in the second measurement cycle, the resistance value R ₂ has the form / cm. Appendix/:

From (4) and (7) it follows

Analysis (6), (8) shows that the measurement result l _x does not depend on a previously unknown value ρ _x Values R ₀ and

calculated in advance
Automatic level gauge / FIG. 4 / when used as a measuring device, an ohmmeter works as follows. In this case, the calculation unit has a technical implementation, shown in Fig.5. Moreover, in the computing unit 11, the output signal of the voltage source 12 is set equal to

and the source

Measuring instrument 3 measures equivalent resistance
R ₁ R _e1 + R _k1
Provided that the electrodes 1,2,5,6 are made in the form of rectangular plates of length l ₀ , width d and plan area S _e , then

Resistance R _e1 is the resistance of the part of the electrode 1,2 located above the liquid level, proportional to the length (l ₀ -l _x ). Resistance R _k1 fluid resistance between the immersion parts of the electrodes 1, 2.

Выходные сигналы измерительных приборов 8, 10, пропорциональные соответственно R₁, R₂, подаются соответственно на первый и второй входы блока вычислений 19 (фиг.5).The measuring device 10 measures the equivalent circuit resistance equal to R ₂ R _e2 + R _k2 ,
Where
R _e2 resistance of a portion of the electrodes 5.6 located above the liquid level length (l ₀ -l _x );
R _k2 fluid resistance between the immersion parts of the electrodes 5, 6;

The output signals of the measuring instruments 8, 10, proportional to R ₁ , R ₂ , respectively, are supplied respectively to the first and second inputs of the computing unit 19 (Fig. 5).

Сигнал, пропорциональный R₂, подается на вычитающий вход сумматора 15 и на вычитающий вход сумматора 14, на суммирующий вход которого подается сигнал

с выхода источника 12.In the computing unit 11 (Fig. 5), a signal proportional to R ₁ is supplied to the second summing input of the adder 15, to the first summing input of which the output signal of the source 13

A signal proportional to R ₂ is supplied to the subtracting input of the adder 15 and to the subtracting input of the adder 14, to the summing input of which a signal is supplied

from the output of the source 12.

Выходной сигнал сумматора 15

Выходные сигналы сумматоров 14, 15 подаются на соответствующие входы элемента деления 16, выходной сигнал которого

подается на вход индикатора 17, показание которого может быть отградуировано в единицах длины.The output signal of the adder 14

The output signal of the adder 15

The output signals of the adders 14, 15 are fed to the corresponding inputs of the division element 16, the output signal of which

fed to the input of the indicator 17, the reading of which can be calibrated in units of length.

 Consider the operation of the level gauge in the case when the electrodes 5,6 are located at a value of D> 0 below the electrodes 1,2.

. Данный сигнал подается на вычитающий вход сумматора 14. Выходное напряжение источника 13

подается на первый вычитающий вход сумматора 15, ко второму входу блока 11 подключен суммирующий вход сумматора 14.In this case, in the computing unit 11 (Fig.6), the output signal of the source 12 is set equal

. This signal is fed to the subtracting input of the adder 14. The output voltage of the source 13

fed to the first subtracting input of the adder 15, the summing input of the adder 14 is connected to the second input of the block 11.

где

Тогда

Выходные сигналы измерительных приборов 3, 10, равные соответственно R₁ и

подаются на первый и второй входы блока вычислений 11. В блоке вычислений 11 сигнал, пропорциональный R₁, подается на суммирующий вход сумматора 15, на первый и второй вычитающий входы которого подаются сигналы с выхода измерительного прибора 3, пропорциональные R₁, и с выхода источника

. Выходной сигнал измерительного прибора 10, пропорциональный

, подается на суммирующий вход сумматора 14, на вычитающий вход которого подается выходной сигнал источника 12
Выходной сигнал сумматора 14

Выходной сигнал сумматора 15

.When the level gauge is operating, the output signal of the measuring device 10 is equal to

Where

Then

The output signals of the measuring instruments 3, 10, respectively equal to R ₁ and

are fed to the first and second inputs of the computation unit 11. In the computation unit 11, a signal proportional to R ₁ is supplied to the summing input of the adder 15, to the first and second subtracting inputs of which signals from the output of the measuring device 3, proportional to R ₁ , and from the source

. The output signal of the measuring device 10 is proportional

is fed to the summing input of the adder 14, the subtracting input of which the output signal of the source 12
The output signal of the adder 14

The output signal of the adder 15

.

, подаются на входы элемента деления 16, выходной сигнал которого

подается на вход индикатора 17.The output signals of the adders 14, 15, respectively

are fed to the inputs of the division element 16, the output signal of which

fed to the input of the indicator 17.

 Block computing 11 (Fig.7) works as follows.

The output signals of measuring instruments 3, 10, respectively equal to R ₁ , R ₂ , in the calculation unit 11 are fed to the inputs of the ADC 18, 19, in which signals proportional to R ₁ , R _{2 are} converted into encoded signals / codes / Y ₁₈ , Y ₁₉ . The output signals of the ADC 18, 19 are fed to the inputs of the microprocessor / microcomputer / 20, which, using formulas (1) or (2), calculates the value of the level l _x which is displayed in indicator 17.

Claims (1)

The method of measuring the liquid level, namely, that they measure the resistance R ₁ in the circuit between the first and second electrodes, by which they find the level values, characterized in that they further change the immersion depth of the electrodes by Δ, measure the resistance R ₂ in the circuit, and the liquid level l _x is determined by the formula:
when lifting electrodes

where R ₀ = ρ ₀ l ₀ / S _e is the resistance of the electrodes;
ρ ₀ is the specific resistance of the electrodes;
S _e the cross-sectional area of the electrodes;
l _{0 is the} length of the electrodes;

0 <Δ <l _x ,
when lowering the electrodes

0 <Δ <(l ₀ -l _x ) .x

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