RU2491517C1 - Method to measure liquid level in case of reservoir position change and device for its realisation - Google Patents

Abstract

FIELD: measurement equipment.SUBSTANCE: method and device to measure liquid level in case of reservoir position change, standard capacitance level sensors are used, at least five in case of reservoir vibrations in two planes, suspended hingedly to maintain their vertical position in case of reservoir vibrations, arranged evenly along axes of its symmetry and forming together with external resistors a phasing RC - circuit of a generator of harmonic oscillations connected via a frequency meter of rated values and a controller, the program of which is equipped with a characteristic of frequency dependence on liquid mass and taking into account the shape of the reservoir inner cavity, and also with the possibility to correct values of dielectric permeabilities of different liquids, instrumental error in process of calibration after installation of capacitance level sensors in the reservoir by setting of the frequency value corresponding to the minimum mass of liquid in the reservoir, which, when achieved, triggers the additional indication mode, to the level indicator and liquid mass.EFFECT: continuous measurement of level and amount of liquid as reservoir position changes in space and development of a device for its realisation using single-type standard capacitance level sensors, which will ensure high reliability.5 cl, 4 dwg

Description

The invention relates to measuring equipment, and in particular to methods and means for measuring the level and mass of liquids in tanks, and can find application, in particular, in devices for measuring the fuel supply in the tanks of vehicles and the level of liquid products filled into tankers during unrest on sea.

A known method for determining the physical parameters of liquefied gas in a tank (RF patent No. 2262667 from 08.26.2002, publ. 10/20/2005, G01F 23/26), including the level, using three different types of vertically arranged, RF capacitive sensors or sensors on based on segments of long lines. When implementing this method, the measured informative parameter of each sensor is the resonant frequency of the oscillatory circuit containing such a sensor as a frequency-setting element.

To determine the current values of the level and mass of liquefied gas in the tank, a liquid level is measured by the electric capacitance of the first radio-frequency sensor, a second liquid level measurement in the range of its decrease or decrease below the measured value of the electric capacitance of the second radio-frequency sensor and the electric capacitance of the third radio-frequency sensor located in the gas phase of the upper part of the tank.

The functional processing unit of the signals coming from the radio frequency sensors to determine the desired physical parameters of the liquefied gas in the tank determines the level and density of the gas phase.

The disadvantages of the analogue are the need for three measurements, the complexity of the calculations, the applicability in stationary horizontally standing containers, as well as the use of special empirical or calculation tables characterizing the dependence of the volume of filling with liquid on its level with complex forms of the container.

A device for measuring the level of fuel in a tank is known (RF patent No. 2040779 dated 1992.03.04, publ. 1995.07.25, G01F 23/16) containing a vertically mounted capacitive sensor — a capacitor with profiled plates. When the fuel level changes, the float moving, carries away through the magnetic field a slider with a conductive jumper of the capacitor plates, changing the capacitance included in the generator circuit, the frequency of which is measured by displaying in units of fuel mass on the indicator.

The disadvantages of the known device include the complexity of the design of the sensor, not adapted to various forms of the tank, the presence of moving parts, which reduces reliability, and an unacceptable dependence of the level on the position of the fuel tank.

The closest in technical essence are the method of measuring the liquid level in the tank and the device for its implementation (RF patent No. 2301971 from 2005 08.22, publ. 2007.06.27, G01F 23/16). The method is implemented by measuring the frequency of the generator, depending on the capacitive pressure sensor located outside the tank, communicating with it by a hydraulic channel (tube). For more accurate measurements, it is recommended to additionally use a reference pressure sensor with a generator, a synthesizer and an appropriate processor. The device is mounted on the tank by means of a magnet, communicates with the liquid through a tube lowered into the neck and contains a housing with a capacitive sensor installed in a sealed cavity connected to a generator connected via a frequency meter with an indicator, as well as a processor in the measurement circuit, the program of which is configured to track the shape the inner cavity of the tank.

The main significant disadvantage of the method and device is the impossibility of measuring the liquid level at inclined positions of the tank (tank, tank, tanker, etc.) and registering the minimum level, the complexity of the design of non-standard sensors requiring the use of two types of non-wetting liquids and for thermal compensation, the use of additional reference sensor and generator, as well as a magnet for mounting the device.

The objective of the claimed invention is the continuous measurement of the level and amount of liquid when changing the position of the tank in space and the development of a device for its implementation using the same standard capacitive level sensors, which will provide high reliability.

The problem is solved by the implementation of the method of measuring the liquid level when changing the position of the tank by measuring the generator frequency, depending on the parameters of the capacitive level sensors, according to which the capacitive level sensors are uniformly symmetrical along the axis of symmetry of the tank and connected in pairs in parallel with the external resistances of the phasing RC-chain, forming together with an amplifier, a generator connected through a frequency meter and a controller, the program of which is supplied with a calibration characteristic Coy frequency vs. liquid mass and takes into account the shape of the inner cavity of the tank, after processing result is supplied to the controller level and weight indicator.

In addition, the controller program is performed with the ability to correct the values of the dielectric constant of various liquids.

In addition, the controller program is provided with the ability to correct the instrumental measurement error during calibration after the installation of capacitive level sensors in the tank.

In addition, the controller program is provided with a frequency value setting corresponding to the minimum liquid mass, upon reaching which an additional display mode is activated.

The problem is also solved by a device for measuring the liquid level in the tank when changing its position, containing capacitive sensors, a generator connected via a frequency meter and a controller to an indicator, in which, according to the invention, capacitive level sensors are pivotally suspended to maintain a vertical position in the liquid during vibrations reservoir and connected in pairs in parallel with respect to the axis of symmetry of the reservoir, constitute elements of the phasing RC with external resistances - chains forming joint but with an amplifier generator.

In addition, the essence of the technical solutions is illustrated by drawings, where:

- figure 1 shows the Converter chain structure;

- figure 2 is an exemplary arrangement of capacitive level sensors in the tank;

- figure 3 is a schematic diagram of a phasing chain;

- figure 4 is a measurement circuit using capacitive level sensors as elements of a phasing chain of an RC generator.

Essence: the method is implemented using standard capacitive level sensors, at least five, when the tank oscillates in two planes, pivotally suspended to maintain their vertical position when the tank oscillates, located uniformly along its symmetry axes and together with external resistors form a phasing RC phase harmonic oscillator whose frequency depends on the liquid level.

Known traditional research methods do not allow obtaining analytical expressions that relate the liquid level to the generation frequency, which depends on the simultaneous individual change in the parameters of several capacitive level sensors (more than four), and thereby solve the actual problem.

Using the method of transformation functions (FP) allowed to eliminate this gap (see Gulin A.I. Analysis of amplitude-phase-frequency criteria for resonances of inhomogeneous chain structures // Vestnik UGATU. 2011. V.15. No. 1 (41). S.123-125 )

FP K _n Converter chain structure (Figure 1) (formally,

reciprocal of the traditional transmission coefficient), which is the ratio of the input active quantity U ₀ to the output B _n (voltage U _n or current I _n ) is described by the expression (see Gulin A.I. Diagnostics of measuring transducers and communication devices with an inhomogeneous chain structure // Control Diagnostics. 2010. No. 11. P.69-72) with an even number of shoulders n

$$K_n=\mathrm{one}+{\displaystyle \sum _{\begin{array}{l}i=\mathrm{one}\\ k=i+\mathrm{one}\end{array}}^{\begin{array}{l}n\\ n-\mathrm{one}\end{array}}{Z}_i{Y}_k}+{\displaystyle \sum _{\begin{array}{l}i=\mathrm{one}\\ k=i+\mathrm{one}\end{array}}^{\begin{array}{l}n-2\\ n-3\end{array}}{\displaystyle \sum _{\begin{array}{l}p=k+\mathrm{one}\\ q=p+\mathrm{one}\end{array}}^{\begin{array}{l}n\\ n-\mathrm{one}\end{array}}{Z}_i{Y}_k{Z}_p{Y}_q+...,\left(\mathrm{one}\right)}}$$

where i = 2b-1;

b = 1, 2, 3, ..., 0.5n,

and for chain structures (CS) with an odd number of shoulders n

$$K_n={\displaystyle \sum _{i=\mathrm{one}}^n{Z}_i}+{\displaystyle \sum _{\begin{array}{l}i=\mathrm{one}\\ k=i+\mathrm{one}\end{array}}^{\begin{array}{l}n-\mathrm{one}\\ n-2\end{array}}{\displaystyle \sum _{p=k+\mathrm{one}}^n{Z}_i{Y}_k{Z}_p+...,\left(2\right)}}$$

where b = 1, 2, 3, ..., 0.5 (n + 1) for a CA with an odd number of shoulders n.

Relations (1) and (2) lead to a recurrence formula for calculating the phase transition

$$K_n=T_n{K}_n{}_{-\mathrm{one}}+K_{n-2},\left(3\right)$$

where T _{i is the} immitance of the ith arm (resistance Z for odd i and conductivity Y for even i).

The initial conditions of the calculation algorithm K _n are the values K ₀ = 1 for n = 0 and K ₁ = T ₁ for n = 1.

The recommended arrangement of the same type of capacitive level sensors, which are the elements of the RC phasing chain (FC), along the reservoir and its electrical circuit are presented in Fig.2 and Fig.3, respectively. Capacitive level sensors are positioned at the extreme points along the symmetry axes of the tank and connected in pairs, and one sensor is in the center. Therefore, the required minimum number of capacitive level sensors, when the tank oscillates in two planes, to create a FC must be at least five. When the tank is inclined in different planes, the total capacitance is C _2-1 + C _{2 = 2} = 2C ₂ , and C _6-1 + C _{6 = 2} = 2C ₆ . With complex forms of tanks, the number of capacitive sensors coupled in pairs is increased over its space.

The expression of the AF of the six-armed FC according to (1) will be

$$\begin{array}{l}{K}_6=\mathrm{one}{Z}_{\mathrm{one}}{\mathrm{<figure-callout\; id="2"\; label="Y"\; filenames="00000017.png"\; state="\{\{state\}\}">Y</figure-callout>}}_2+Z_{\mathrm{one}}{Y}_{\mathrm{four}}+Z_{\mathrm{one}}{Y}_6+Z_3{Y}_{\mathrm{four}}+Z_3{Y}_6+Z_5{Y}_6+Z_{\mathrm{one}}{Y}_2{Z}_3{Y}_{\mathrm{four}}+\\ +Z_{\mathrm{one}}{Y}_2{Z}_3{Y}_6+Z_{\mathrm{one}}{Y}_2{Z}_5{Y}_6+Z_{\mathrm{one}}{Y}_{\mathrm{four}}{Z}_{5}Y{}_6+Z_3{Y}_{\mathrm{four}}{Z}_5{Y}_6+Z_{\mathrm{one}}{Y}_2{Z}_3{Y}_{\mathrm{four}}{Z}_5{Y}_6.\left(\mathrm{four}\right)\end{array}$$

For FC (Figure 3), where Z ₁ = Z ₃ = Z ₅ = R; Y ₂ = Y ₆ = jω2C; Y ₄ = jωC, we write the phase transition in the components of the real and imaginary parts

K ₆ = ReK ₆ + ImK ₆ ,

The condition for oscillations when using FC is

$${\mathrm{TO}}_{\mathrm{BUT}P}\cdot {\mathrm{TO}}_{F\mathrm{Ts}}\le \mathrm{one},\left(5\right)$$

where K _AP - AF active converter (amplifier);

K _FC - FP phasing chain.

Because The amplifier phase is real, in order to fulfill condition (5), it is necessary that the phase-to-phase conjugation to the _{central oscillator} at the self-excitation frequency is also real. In this case, both phase transitions can simultaneously have either positive or negative values, i.e. FC, depending on the type of active converter, must carry out a phase shift by an even or odd number t radians, where i = 1, 2, 3 ... is a natural series of numbers.

Consider the question of determining the frequency of quasiresonance in a six-arm FC (Figure 3), composed of RC elements and performing a phase rotation of 180 °, which is most often used in the construction of generators on single-stage amplifiers. The frequency of quasi-resonance is determined from the imaginary part of the phase transition phasing quadripole when it vanishes, i.e.

$$Im\cdot {\mathrm{TO}}_{F\mathrm{Ts}}=0,\left(6\right)$$

Substituting in (4) the values of Z _i and Y _{i + 1} and equating to zero the imaginary part of the phase transition (quasi-resonance condition), we obtain the expression for the desired frequency _ω ω _{0 of the} six-arm FC

ImK ₆ = Z ₁ Y ₂ + Z ₁ Y ₄ + Z ₁ Y ₆ + Z ₃ Y ₄ + Z ₃ Y ₆ + Z ₅ Y ₆ + Z ₁ Y ₂ Z ₃ Y ₄ Z ₅ Y ₆

ImK ₆ = -J4ω ³ C ³ R ³ + J10ωCR;

; $$\omega {}_0{}^3\mathrm{four}{C}^3{R}^3-\mathrm{one}0{\omega }_{0}CR=0$$

;

, $${\omega }_0^2{C}^2{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="00000017.png"\; state="\{\{state\}\}">R</figure-callout>}}^2=5/2$$

,

where from $${\omega }_0=\frac{\mathrm{one}}{RC}\sqrt{\raisebox{1ex}{$5$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}.\left(7\right)$$

We determine the real part of the phase transition ReK ₆ FC at the frequency of quasi-resonance ω ₀ from the expression (4)

ReK ₆ = Z ₁ Y ₂ Z ₃ Y ₄ + Z ₁ Y ₂ Z ₃ Y ₆ + Z ₁ Y ₂ Z ₅ Y ₆ + Z ₁ + Y ₄ Z ₅ Y ₆ + Z ₃ Y ₄ Z ₅ Y ₆ ,

substituting the values of the elements in it, we obtain

, $$Re{K}_6=\mathrm{one}-\mathrm{one}\mathrm{four}{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="00000017.png"\; state="\{\{state\}\}">R</figure-callout>}}^2{\omega }_0^2{\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="00000017.png"\; state="\{\{state\}\}">C</figure-callout>}}^2$$

,

a, substituting the value of the frequency of quasi-resonance from (7), we define

ReK ₆ = -34.

FC attenuates the signal level by 34 times, and a minus sign confirms a phase rotation of 180 °. Therefore, K _AP - AF of the active transducer (gain) should exceed more than 34 times.

When using an even number of capacitive sensors connected in pairs, the calculations for calculating the frequencies of quasi-resonances are reduced, as it turned out, to determining the coefficient k _{n of the} expression

$${\omega }_0=\frac{k_n}{RC}$$

, $$$$

$${\omega }_0=\frac{k_n}{RC}$$

,

As a result of analytical analysis, a formula was first obtained that determines the coefficient k _n from equations of the form

$${\displaystyle \sum _{i=0,\mathrm{one}...}^P{\left(-\mathrm{one}\right)}^i{k}_n^{2i+\mathrm{one}}{C}_{0,5n+\mathrm{one}+2\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="00000017.png"\; state="\{\{state\}\}">i</figure-callout>}}^{2+\mathrm{four}i}=0,\begin{array}{ccc}& & \end{array}\left(8\right)}$$

where p = 0.25n-1 - for even 0.5n;

p = 0.25 (n + 2) -1 - for odd 0.5n.

For example, for ten-arm (five-link) FC equation (8) has the form 15k-28k ³ + k ⁵ = 0, the solution of which gives the following values of k:

k _1,2 = ± 23/32; k _3.4 = ± 167/32; k ₅ = 0.

), так как использование других значений, удовлетворяющих (8), приведет к сдвигу фаз на 2π радиан и более.Of all the real positive roots of equation (8), it is necessary to use the smallest value k = 23/32 (for six-armed - three-link FC it is $$\sqrt{6}$$

), since the use of other values satisfying (8) will lead to a phase shift of 2π radians or more.

To calculate more complex FCs, you can use the program (see Tulin A.I., Sukhinets Zh.A. et al. Calculation of the frequency of quasi-resonance and transmission coefficient of multi-link RC structures // Certificate of official registration of a computer program No. 2003611147 / 05.16.2003 Rospatent. Moscow. 2003).

.It should be noted that the phase transition K _n FC at the frequencies of quasi-resonance with an increase in the number of arms n from six to infinity decreases and tends from K ₆ = -29 to K _n = -11.6, i.e. $$\underset{n\to \infty }{lim}\left|K_n\right|=\mathrm{one}\mathrm{one},6$$

.

The findings fully apply to cases where this method is implemented using radio frequency sensors based on long line segments (see, for example, the monograph: Viktorov V.A., Lunkin B.V., Sovlukov A.S. Radio wave measurements of process parameters. M .: Nauka. 1989. P.84-117). Then, to maintain vertical position when the tank is tilted, weights must be attached from below.

A device for measuring the liquid level in the tank 1 contains capacitive level 2 sensors, pivotally suspended to maintain a vertical position in the liquid when the tank vibrates, and constituting elements of the phasing chain 3 with external resistances to form a master oscillator 5 connected with an amplifier 4, connected through a frequency meter of nominal values (measuring the frequency in a given range to increase speed) 6 through the controller 7 with a digital indicator 8.

The controller program is equipped with a calibration characteristic of the dependence of the frequency on the mass of the liquid, taking into account the shape of the internal cavity of the tank, as well as the possibility of correction: the values of the dielectric constant of various liquids; instrumental measurement error during calibration after installing capacitive level sensors in the tank; setting the value of the minimum amount of liquid mass, upon reaching which an additional display mode is activated, attracting the attention of the operator.

The measurement of the liquid level in the tank 1 is as follows. The same type of capacitive level 2 sensors are hung on hinges, to maintain a vertical position in the liquid during oscillations of the tank, uniformly along the axes of its symmetry, are paired in parallel with external resistances to form a phasing chain 3, and together with amplifier 4, a master oscillator 5, which is connected through frequency meter of nominal values (measuring the frequency in a predetermined range to increase speed) 6 through the controller 7 with a digital indicator 8. With changes and fluctuations in the liquid level in the capacitance of the level sensors changes, and the total capacities of the pairwise connected sensors are unchanged when the tank deviates and form a homogeneous phasing chain 3 of the generator 5. In accordance with the values of these capacities, the frequency of the generator 5 is set, which is measured by the frequency meter 6, and the measurement result is converted by the controller 7 into units level, volume or mass and is indicated on indicator 8 in these units. The controller software provides for setting the values of the mass of liquid, below which an additional display mode that attracts the attention of the operator is turned on, and the calibration characteristic of the frequency dependence on the amount of liquid and taking into account the shape of the internal cavity of the fuel tank (tank),

So, the claimed invention allows to continuously measure the level and mass of the liquid when changing the position of the tank in space using the same standard capacitive level sensors, which ensures high reliability of the method.

Claims (5)

1. The method of measuring the liquid level when changing the position of the tank by measuring the frequency of the generator, depending on the parameters of the capacitive level sensors, characterized in that the capacitive level sensors are uniformly symmetrical along the axis of symmetry of the tank and are paired in parallel with the external resistances of the phasing RC-chain, forming together with an amplifier, a generator connected through a frequency meter and a controller, the program of which is provided with a calibration characteristic of the dependence of the frequency on the mass of the liquid and taking into account the shape of the inner cavity of the tank, after processing result is supplied to the controller level and weight indicator. 2. The method according to claim 1, characterized in that the processor program is configured to correct the values of the dielectric constant of various liquids. 3. The method according to claim 1, characterized in that the processor program is provided with the ability to correct the instrumental measurement error during calibration after installing capacitive level sensors in the tank. 4. The method according to claim 1, characterized in that the processor program is provided with a frequency value setting corresponding to the minimum liquid mass, upon reaching which an additional indication mode is activated. 5. A device for measuring the liquid level in the tank when changing its position, containing capacitive sensors, a generator connected through a frequency meter and a controller with an indicator, characterized in that the capacitive level sensors are pivotally suspended to maintain a vertical position in the liquid when the tank vibrates and connected in pairs parallel to the axis of symmetry of the tank, with external resistances are elements of a phasing RC - chain, forming together with the amplifier a generator.

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