RU2008625C1 - Resistor level gauge - Google Patents

Abstract

FIELD: measuring devices. SUBSTANCE: device has four electrodes, four switch elements, power supply unit, measuring unit, information processing unit, control unit. Capacitance of first and second electrodes is equal and is not equal to capacitance of third and fourth electrodes. EFFECT: increased functional capabilities. 7 dwg

Description

 The invention relates to instrumentation and can be used in various industries for measuring liquid level.

 Known ohmic level gauges containing a power source, electrodes and a measuring device (see, for example, US patent N 3089337, CL 73-295, 1963; US patent N 3119266, CL 73-304, 1964; French patent N 2115093, CL G 01 F 28/00, Ageikin D. I. et al. Sensors of control and regulation. M.: Engineering, 1965, p. 401, etc.). The disadvantages of these level gauges are limited accuracy, due to the influence of a previously unknown ohmic resistance of the liquid, especially in real operating conditions. For example, the ohmic resistance of water when measuring its level in the locks of hydraulic structures is significantly affected by impurities (soluble and insoluble).

 Known ohmic level gauge containing a sensor made in the form of a steel pipe, immersed in an electrically conductive material and connected by ends to a power source (see A. S. of the USSR N 777453, class G 01 F 23/24, 1974). The disadvantage of this level gauge is the presence of a signal at a zero value of the material level.

 The closest in technical essence to the proposed and selected authors for the prototype is an ohmic level gauge by a. with. USSR N 535462, class G 01 F 23/24, 1976, containing a power source, low-resistance resistors coated with a layer of a substance whose electrical resistance is greater than the electrical resistance of the liquid being controlled, a measuring device, and the electrodes are made in the form of a double cylindrical spiral with a uniform pitch and opposite direction of turns, the longitudinal axial line of which perpendicular to the surface of the liquid.

 The disadvantages of this level gauge are the limited accuracy of measuring the liquid level, the complexity of manufacturing and limited functionality. Low measurement accuracy is determined by the influence of a previously unknown specific resistivity of the liquid on the readings. It requires the selection of material for the manufacture of a layer whose resistance is greater than the resistance of the liquid, which limits the functionality. The complexity of manufacturing is due to the need to apply a layer of substance on top of the electrodes.

 The aim of the invention is to improve the accuracy of level measurement by eliminating the influence on the measurement result of a previously unknown value of the contact resistance of the liquid between the electrodes of the ohmic level gauge.

 The goal is achieved by the fact that the third and fourth electrodes, the control unit, the information processing unit, the first, second, third and fourth key elements are additionally introduced into the ohmic level gauge containing the first and second electrodes, the power supply and the measuring device connected in series, while the resistance the third and fourth electrodes are not equal to the resistance of the first and second electrodes, the upper leads of the first and third electrodes are connected to the outputs of the first and second key elements, respectively The findings of the second and fourth electrodes are combined and connected to the free output of the measuring device, the output of which is connected to the combined inputs of the third and fourth key elements, the outputs of which are connected respectively to the first and second inputs of the information processing unit, the free bus of the power source is connected to the combined inputs of the first and the second key elements, the control inputs of the first and third key elements are combined and connected to the first output of the control unit, the second output of which By connecting to the combined control inputs of the second and fourth key elements.

The essence of the proposed invention is as follows. In an ohmic level gauge, the accuracy of measuring the liquid level substantially depends on the resistance of the liquid R _to between the immersion parts of the electrodes of length l _x .

In real operating conditions, for example, when measuring the water level in the locks of hydraulic structures, soluble and insoluble impurities significantly affect the P value. To eliminate the influence of a previously unknown factor R _k on the measurement result, it is proposed to use information redundancy - to measure the value of the level l _x in two cycles.

In the first cycle, either the equivalent resistance R _{1 of the} entire measuring circuit, including the first and second electrodes, is measured, or the current I ₁ flowing through the measuring circuit (I ₁ = E / R ₁ , where E is the EMF value of the power source). Resistance R ₁ = R _x + R _n1 + R _K1 , where R _x is the resistance of the surface part of the length (ll _x ) of the first and second electrodes; R _n1 is the resistance of the wires and blocks of the measuring circuit of the level gauge in the first measurement cycle; R _K1 is the fluid resistance between the immersion parts of the first and second electrodes.

In the second cycle, either the equivalent resistance R _{2 of the} measuring circuit, including the third and fourth electrodes, is measured, or the current I ₂ = E / R ₂ flowing along the measuring circuit. Resistance R ₂ = KR _x + R _n2 + R _K1 , where KR _x is the resistance of the surface part of the length ll _{x of the} third and fourth electrodes (according to the condition of resistance of the third and fourth electrodes they are not equal to the resistance of the first and second electrodes); k is the coefficient of proportionality between the resistances of the electrodes (K> 0, K ≠ 1); R _n2 is the resistance of the wires and blocks of the measuring circuit of the level gauge in the second measurement cycle; R _K2 is the fluid resistance between the immersion parts of the third and fourth electrodes.

(R₁-R₂). (1)
или
R_x=

-

. (2)
Зная R_x, можно определить текущее значение уровня жидкости.If R = R _K2 , R _n1 ≈ R _n2 , then
R _x =

(R ₁ -R ₂ ). (1)
or
R _x =

-

. (2)
Knowing R _x , you can determine the current value of the liquid level.

 Distinctive features of the proposed technical solution are: the introduction of the third and fourth electrodes; introduction of a control unit; introduction of an information processing unit; the introduction of four key elements; the resistance of the third and fourth electrodes are not equal to the resistance of the first and second electrodes; the relationship between known and newly introduced elements.

 Signs - the introduction of four key elements and the connection of their control inputs with the corresponding outputs of the control unit are known (see, for example, Martyashin A.I. et al. Converters of electrical parameters for monitoring and measurement systems. M.: Energy. 1976, p. 127, Fig. 2-43) and are used for their intended purpose.

 The sign - the introduction of a control unit that serves to issue control pulses at certain points in time - is known (see, for example, Martyashin A.I. et al. Converters of electrical parameters for control and measurement systems. M.: Energy, 1976, p. 129 , Fig. 2-45) and is used for its intended purpose.

 The authors did not find technical solutions for level gauges that would use such signs as the use of the third and fourth electrodes, the resistances of which are not equal to the resistance of the first and second electrodes; use of information redundancy to improve measurement accuracy.

 According to the authors, these signs are significant, the use of which allows to increase the accuracy of the measurement by eliminating the influence of difficult factors.

 In FIG. 1 shows a block diagram of an ohmic level gauge; in FIG. 2 - a variant of the technical implementation of the control unit; in FIG. 3 is an embodiment of a technical implementation of an information processing unit; in FIG. 4 is a variant of the location of the electrodes in the tank to ensure equality of the resistance of the liquid between the first and second, as well as between the third and fourth electrodes; in FIG. 5 is an embodiment of a technical implementation of an information processing unit when using an ammeter as a measuring device; in FIG. 6 is a diagram of a memory element; in FIG. 7 is a diagram of a connection of electrodes.

In FIG. 1-5 accepted notation:
l is the length of the electrodes 1.1,. . , 1.4;
l _x is the current value of the liquid level;
ll _x is the surface of the electrodes (the length of the electrodes located above the liquid level); h is the distance from the lower end of the electrodes 1.1,. . . 1.4 to the bottom of the tank; Δ is the distance between the electrode 1.1 (1.3) and the electrode 1.2 (1.4).

 The ohmic level gauge (Fig. 1) contains four electrodes 1.1, 1.2, 1.3, 1.4, four key elements 2.1,. . . . , 2.4 a power source (EMF source) 3, a measuring device 4, an information processing unit 5, a control unit 6, while the electrodes 1.1,. . . . 1.4 are made of the same length l and are placed vertically at the same distance h from the bottom of the tank 7, the values of the resistances of the electrodes are 1.3, 1.4 are K times (K> 0, K ≠ 1) greater than the values of the resistances of the electrodes 1.1, 1.2, the upper terminal the electrode 1.1 (1.3) is connected to the output of the key element 2.1 (2.2), the upper terminals of the electrodes 1.2, 1.4 are combined and connected to the first terminal of the measuring device 4, the second terminal of which is connected to the first (minus) bus of the power supply 3, the second (plus) bus which is connected to the integrated information inputs key elements 2.1, 2.2, the output of the measuring device 4 is connected to the combined information inputs of the key elements 2.3, 2.4, the outputs of which are connected respectively to the first and second inputs of the information processing unit 5, the control inputs of the key elements 2.1, 2.3 are combined and connected to the first output of the block 6 control, the second output of which is connected to the combined control inputs of the key elements 2.2, 2.4.

 The distances Δ between the electrodes 1.1 and 1.2, as well as between the electrodes 1.3 and 1.4 are equal to each other.

 The power source may be made in the form of an alternating current source.

 The electrodes 1.3, 1.4 can be made of the same material as the electrodes 1.1, 1.2. but of different cross-sectional areas, or from excellent material of the same configuration.

 Electrodes 1.1,. . . 1.4 to increase the sensitivity, they can be made in the form of a double cylindrical spiral with a uniform or uneven pitch and the opposite direction of the turns, similar to immersion electrodes along a. with. USSR N 535462, 974133.

 The key elements are well-known elements (see, for example, A. Sidorov. Diode and transistor switches. -M.: Communication, 1975; Analog signal switches on semiconductor elements. Edited by Ya. P. Belenky. M.: Energy, 1976; Arkhovsky V.F. Schemes of switching analog signals. M.: Communication, 1975; Ivanova O. N. Electronic switching. M.: Communication, 1971).

 As the control unit 6, a known programmable pulse generator can be used.

 The technical implementation of programmable pulse generators is known (see, for example, Programmable Pulse Generators for LSI Testing, Express Information (EI), Ser. PEA, 1972, N 41, ref. 163; "Programmable Synchronous Single-Pulse Generator", EI, ser. PEA and BT, 1979, N 28, ref. 162; "Tunable pulse generator", EI, ser. PEA and VT, 1977, N 37, ref. 210; "Pulse train generator", Swiss patent N 543835 , published on December 14, 73, etc.).

 In FIG. 2 shows a diagram of one of the options for the technical implementation of the control unit 6.

 The control unit 6 (Fig. 2) contains a pulse generator 8, a counter 9, a decoder 10, a zero-setting bus 11 and a Start bus 12, while the output of the pulse generator 8 is connected to the counter input of the counter 9, the generalized output of which is connected to the generalized input the decoder 10, the two outputs of which are connected respectively to the first and second outputs of the control unit 6, the zero setting bus 11 is connected to the zero input of the counter 9, the start bus 12 is connected to the start input of the pulse generator 8.

 Under the generalized output (input) refers to a multi-wire output (input). The zero-setting bus 11 and the "Start" bus 12 are connected via an reset button to an additional power supply (not shown in the diagram of Fig. 2).

 The information processing unit 5 (Fig. 3) contains a memory element 13, an adder 14, a scale amplifier 15, an indicator 16, while the output of the memory element is connected to the first (summing) input of the adder 14, the output of which is connected to the input of a scale amplifier 15, the output of which connected to the indicator input, the first input of the calculation unit 5 is the information input of the memory element 13, the second input is the combined control input of the memory element 13 and the second (subtracting) input of the adder 14.

 The memory element 13 (Fig. 3) can be implemented on the basis of a sampling-storage device (UVX). The function of the memory element is to store on the storage capacitor for some time the instantaneous value of the input voltage. In sampling mode, the UVX repeats the input signal, and then, upon command, remembers its instantaneous value and switches to storage mode.

 In FIG. 5 shows a second embodiment of the technical implementation of the information processing unit 5. In contrast to the block 5 shown in FIG. 3, the information processing unit 5 (Fig. 5) further comprises two blocks 17.1, 17.2, non-linearities realizing the function y = 1 / x, where x is the input signal; y is the day off. The output of the nonlinearity block 17.1 is connected to the input of the memory element 13, and the output of the nonlinearity block 17.2 is connected to the second input of the adder 14, the first input of the information processing unit 5 is the input of the nonlinearity block 17.1, and the second input is the combined input of the nonlinearity block 17.2 and the control input of the element 13 memories.

 Non-linearity blocks 17.1, 17.2 can be implemented on the basis of division blocks, the schemes of which are given in the book by W. Titze, K. Schenk "Semiconductor circuitry", M.: Mir, 1982, p. 163, fig. 11.42, p. 166, fig. 11.46. In this case, a single signal from an additional power source (not shown in FIG. 5) is supplied to the input of the divisible division unit, and the output signal of the measuring device 4 is fed to the input of the divider of the division unit.

 An ammeter (current sensor) or an ohmmeter can be used as a measuring device 4. The technical implementation of ammeters with an electrical output is given in the literature (see, for example, W. Titze, K. Schenk. Semiconductor circuitry. M.: Mir, 1982, p. 469, Fig. 25.6, 25.7).

 Ohmic level gauge (Fig. 1) when using an ohmmeter as a measuring device 4 operates as follows. In this case, the information processing unit 5 has the technical solution shown in FIG. 3.

 In the initial state, in the control unit 6 (Fig. 2), a signal is input to the zero-setting input of the counter 9 via the zero-setting bus 11 and its content is set to zero.

 Since the signals at the information and control inputs of the memory element 13 (Fig. 9) are equal to zero, its contents are also equal to zero.

Suppose that it is required at a certain point in time to determine the level l _x liquid in the tank 7 (Fig. 1).

In the control unit 6 (Fig. 2), a start signal 12 is applied to the start of the pulse generator 8 via the "Start" bus 12, which starts to issue pulses with a predetermined frequency. These pulses are fed to the counting input of the counter 9, which counts them. The signals from the outputs of the counter 9 are fed to the inputs of the decoder 10. At a certain point in time t ₁ , a signal appears at one of the outputs of the decoder 10, which is fed to the first output of the information processing unit 5. This signal is fed to the control inputs of the key elements 2.1, 2.3 (Fig. 1) by opening them.

In the circuit: positive bus of power supply 3 - key element 2.1 - electrode 1.1 - liquid in the capacitance 7 between electrodes 1.1, 1.2 - electrode 1,2 - measuring device 4 - negative bus of power supply 3 - current I ₁ will flow.

= R_x= R_k1+R_n1, (3) где R_x - сопротивление части электродов 1.1, 1.2, расположенной над уровнем жидкости, пропорциональное величине l-l_x; R_K1 - сопротивление жидкости между погружными частями электродов 1.1, 1.2;
R_n1 - сопротивление проводов и блоков измерительной схемы в первом цикле измерения (внутреннее сопротивление измерительного прибора 4, источника 3 питания, открытого ключевого элемента 2.1);
Е - значение ЭДС источника 3 питания (его выходное напряжение).Meter 4 measures equivalent resistance
R ₁ =

= R _x = R _k1 + R _n1 , (3) where R _x is the resistance of the part of the electrodes 1.1, 1.2 located above the liquid level, proportional to ll _x ; R _K1 is the resistance of the fluid between the submerged parts of the electrodes 1.1, 1.2;
R _n1 is the resistance of the wires and blocks of the measuring circuit in the first measurement cycle (internal resistance of the measuring device 4, power supply 3, open key element 2.1);
E is the EMF value of the power source 3 (its output voltage).

A voltage proportional to R ₁ from the output of the measuring device 4 through the open key element 2,3 is supplied to the first input of the information processing information processing unit 5. In block 5 (Fig. 3), this signal is supplied to the information input of the memory element 13, which stores it .

Then, at time t ₂ , a signal appears at the second output of the control unit 6, and the signal at the first output of the control unit 6 is zero. In this case, the key elements 2.1, 2.3 are closed and the key elements 2.2, 2.4 are opened;
In the circuit: positive bus of power supply 3 - open key element 2.2 - electrode 1.3 - liquid in capacitance 7 between electrodes 1.3, 1.4 - measuring device 4 - negative bus of power supply 3 - current I ₂ will flow.

= k·R_x+R_k2+R_n2, (4) где (K R_x) - сопротивление части электродов 1.3, 1.4 расположенной над уровнем жидкости, пропорциональное величине 1.3, 1.4;
R_K2 - сопротивление жидкости между погружными частями электродов 1.3, 1.4;
R_n2 - сопротивление проводов и блоков измерительной схемы во втором цикле измерения (внутренние сопротивления источника 3 питания, измерительного прибора 4, открытого ключевого элемента 2.2).The measuring device 4 will measure the equivalent circuit resistance equal to
R ₂ =

= k · R _x + R _k2 + R _n2 , (4) where (KR _x ) is the resistance of the part of the electrodes 1.3, 1.4 located above the liquid level, proportional to 1.3, 1.4;
R _K2 is the resistance of the fluid between the submerged parts of the electrodes 1.3, 1.4;
R _n2 is the resistance of the wires and blocks of the measuring circuit in the second measurement cycle (internal resistance of the power source 3, measuring device 4, open key element 2.2).

The output signal of the measuring device 4, proportional to R ₂ , is supplied through the open key element 2.4 to the second input of the information processing unit 5.

(R₁-R₂). При R_K1 ≈ R_K2. R

R_n2. y

(1-K) R_x. Выходной сигнал сумматора 14 y₁₄ подается на вход масштабного усилителя 15 с коэффициентом усиления | 1/(1-K)| . Выходной сигнал усилителя 15 будет пропорционален величине R_x, значение которого отобразится в индикаторе 16. Если шкалу индикатора 16 отградуировать соответствующим образом, то его показание будет соответствовать будет соответствовать текущему значению жидкости l_х в емкости 7.In the information processing unit 5 (Fig. 3), this signal is supplied to the control input of the memory element 13 and to the second (subtracting) input of the adder 14. At the output of the memory element 13, a signal proportional to R ₁ will appear, which is fed to the first (summing) input of the adder 14. The output signal of the adder 14 y

(R ₁ -R ₂ ). At R _K1 ≈ R _K2 . R

R _n2 . y

(1-K) R _x . The output signal of the adder 14 y ₁₄ is fed to the input of a scale amplifier 15 with a gain | 1 / (1-K) | . The output signal of the amplifier 15 will be proportional to the value of R _x , the value of which will be displayed in the indicator 16. If the scale of the indicator 16 is calibrated accordingly, then its reading will correspond to the current value of the liquid l _x in the tank 7.

 If an ammeter is used as the measuring device 4, the information processing unit 5 has the technical implementation shown in FIG. 5. In this case, the ohmic level gauge works as follows.

I₁=

, где Е - значение ЭДС источника 3 питания.In the first cycle, a signal appears at the output of the measuring device 4

I ₁ =

where E is the value of the EMF of power source 3.

The signal y ₄ is supplied in block 5 of the measurements to the input of the block of nonlinearity 17.1, the output signal of which y _17.1 = 1 / y ₄ = (R _x + R _K1 + R _n1 ) / E is stored in the memory element 13.

I₂=

, который в блоке обработки информации 5 (фиг. 5) подается на вход блока нелинейностей 17.2 и на вход элемента 13 памяти. Выходной сигнал блока нелинейностей y_17.2=

подается на вычитающий вход сумматора 14, на суммирующий вход которого с выхода элемента 13 памяти подается сигнал y_17.1. Выходной сигнал сумматора 14 при условии, что R

R_K2, R_n1

R_n2 равен величине y₁₄= R

. Сигнал _у14 подается на вход масштабного усилителя 15 с коэффициентом усиления

. Выходной сигнал масштабного усилителя 15 y₅, пропорциональный R_x, подается на вход индикатора 16. Показания индикатора 16 будут пропорциональны R_x и, соответственно, пропорциональны величине l_x (при соответствующей градуировке).In the second cycle of level measurement at the output of the measuring device 4, the signal y

I ₂ =

, which in the information processing unit 5 (Fig. 5) is fed to the input of the nonlinearity block 17.2 and to the input of the memory element 13. The output signal of the block of nonlinearities y _17.2 =

fed to the subtracting input of the adder 14, to the summing input of which the signal y _17.1 is supplied from the output of the memory element 13. The output signal of the adder 14, provided that R

R _K2 , R _n1

R _n2 is equal to y ₁₄ = R

. The signal _y14 is fed to the input of a scale amplifier 15 with a gain

. The output signal of the scale amplifier 15 y ₅ proportional to R _x is supplied to the input of the indicator 16. The readings of the indicator 16 will be proportional to R _x and, accordingly, proportional to the value of l _x (with the appropriate graduation).

To ensure equality, R _K1 = R _K2 electrodes 1.1,. . . , 1.4 perform the same geometric shape and are located on the sides of the square (Fig. 4), while the electrodes 1.1 (1.3) and 1.2 (1.4) are located on opposite sides of the square.

 In this case, to eliminate the influence of the electrodes on each other, it is possible to connect the upper terminals of the electrodes 1.2, 1.4 to the corresponding key elements (2.5, 2.6), the outputs of which are combined and connected to the corresponding terminal of the measuring device. The control inputs of the key elements 2.1 (2.2) and 2.5 (2.6) are combined (Fig. 7).

 To synchronize the work before the second input of the adder 14, you can put a delay element (delay line).

 Since the signal is equal to zero at the information input of memory element 13 (key element 2.3 is open), its contents will also be zero.

 This completes the liquid level measurement cycle. If necessary, the measurement cycle is repeated.

The liquid level can be measured with a periodicity of δ = t ₂ . In this case, the pulse generator 8 in the control unit 6 operates continuously. At the corresponding outputs of the control unit 6, signals will appear that control, as described above, the operation of the level gauge.

As a result of the application of the proposed level gauge, the accuracy of measuring the current liquid value is increased by eliminating the influence of a previously unknown value of contact resistance (liquid resistance) between the immersion parts of the electrodes; sensitivity increases due to the manufacture of electrodes in the form of a double helix with the opposite direction of the turns; reliability is increased by eliminating mechanical moving particles; operational reliability is increased by eliminating the influence of fouling of submersible electrodes in real operating conditions. The electrical resistance of the fouling is included in R _K , which in this technical solution does not affect the measurement result.

 (56) Copyright certificate of the USSR N 535462, cl. G 01 F 23/24, 1974.

Claims (1)

 OMIC LEVEL METER, containing the first and second electrodes with equal resistances and connected in series with a power source and a measuring device connected to the upper terminal of the second electrode, characterized in that the third and fourth electrodes are connected to the measuring device, the control unit, from the first the fourth key elements and an information processing unit, to the inputs of which the outputs of the third and fourth key elements are connected, the first and second inputs of which are connected to the outputs respectively the control unit and the measuring device, to the second input of which the first output of the power source is connected, the second output of which is connected to the first inputs of the first and second key elements, to the second inputs of which the outputs of the control unit are connected, while the first and third electrodes are connected respectively to the first and the third key elements, and the resistance of the third and fourth electrodes are equal to each other and not equal to the resistance of the first electrode.

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