RU2792263C2 - Liquid density meter and its variants - Google Patents

Abstract

FIELD: liquid density meters.

SUBSTANCE: group of inventions (versions) relates to liquid density meters in a medium with high external pressure, for example, for deep-sea oceanographic instruments. The liquid density meter has a vertical tube with a side hole and a nozzle at the middle of its height, connecting the internal area of the tube to the tank made of elastic material, a reference liquid that fills the inside of the tube and the cylinder, the first and second differential pressure sensors, respectively, in the lower and upper ends of the tube, installed inside the tube of the sensor of average temperature and average pressure of the reference liquid, four secondary measuring converters connected at the outputs of the sensors, a commutator of measuring signals, connected at the outputs of the secondary measuring converters, an analog-to-digital converter at the output of the switch and a processor at the output of the analog-to-digital converter.

EFFECT: enabling the use of a liquid density meter in deep-sea instruments and improving the accuracy of measuring the local density of a medium.

4 cl, 1 dwg, 1 tbl

Description

The invention relates to measuring technology and is intended for measuring the local density of sea water in deep-sea (probing and stationary) oceanographic instruments. It can be used in other areas where there is a need for accurate measurements of the local density of a liquid in the presence of high external pressures.

Known hydrostatic liquid density meters containing pressure sensors at the ends of a vertical column of liquid and using the difference between these pressures, the height of the column and the acceleration of gravity to calculate the density of the liquid in the column [Zhemkov E.I. Method and device for hydrostatic measurement of sea water density. Proceedings of the 12th International scientific. - tech. conf. «Modern methods and means of oceanological research. Ch. 1. M., 2011. S. 95-97], [Fedotov G.A. A new modification of the hydrostatic method for determining the density of sea water. Fundamental problems of modern hydrodynamics. 2013. V. 6, No. 1. S. 58-65].

At high external pressures (for example, at depths in the sea), such meters cannot provide the necessary high accuracy in measuring the density of water (to determine which, a pressure difference at two different depths is needed) due to excessive and unattainable requirements for the accuracy of measuring direct pressures.

Known hydrostatic densitometers of liquid media used in the oil refining industry and containing, for example, a vertical measuring column in the form of a U-shaped pipe of two parallel pipes of different diameters, impulse tubes with a reference liquid, temperature and pressure transducers, pressure taps, contact transducers of the pressure difference between column of the reference liquid and columns of the measured liquid in the ascending and descending branches, the information processing unit [RF Patent for utility model No. 15787. Published 11/10/2000. Bull. No. 31. Varlamov V.P., Bortasevich B.C., Churinov M.I. Density meter for liquid media]. This device according to the principle of operation and composition is the closest to the claimed liquid density meter. However, by design, it is not suitable for use in deep-sea and probing instruments, and its composition is insufficient to ensure high accuracy in measuring the local density of a liquid. In addition, it does not disclose the mechanism for the selection and transmission of pressures to contact pressure difference transducers. The idea of building a differential density meter is given in the source [Application for invention No. 2013125104 A. Publ. 12/10/2014. Bull. No. 34. Skopintsev S.P. Differential density meter: method and device]. However, the application materials do not sufficiently disclose its feasibility.

The purpose of the invention is to provide the possibility of using the meter in deep-sea instruments and improve the accuracy of measurements of the local density of the medium. This goal is achieved by the fact that, unlike the prototype containing a vertical column, a reference liquid, pressure and temperature sensors, an information processing unit, in the claimed liquid density meter, the vertical column is made in the form of a tube with a side hole and a branch pipe in the middle of the tube connecting the inner area of the tube with a cylinder having a body made of elastic material, wherein the reference liquid fills the inner area of the tube and the cylinder, the first and second differential pressure sensors in the lower and upper ends of the tube, respectively, the average pressure and average temperature sensors of the reference liquid installed inside the tube, four secondary measuring transducers, switched on at the outputs of the sensors, a switch of measuring signals switched on at the outputs of the secondary measuring transducers, an analog-to-digital converter at the output of the switch, a processor at the output of the analog-to-digital converter, while the measured density of the liquid in the geo graphic point at latitude ϕ and at depth z in the sea is determined by the formula:

- плотность эталонной жидкости [кг/м³];Where

- density of the reference liquid [kg/m ³ ];

- средняя температура [°С] и

- среднее давление [Па];

- average temperature [°С] and

- average pressure [Pa];

ΔP ₁ - indication of the lower differential sensor [Pa];

ΔР ₂ - indication of the upper differential sensor [Pa];

g(ϕ, z) - free fall acceleration [m/s ² ];

h - vertical dimension of the tube [m].

The second version of the device contains two structurally identical liquid density meters with different densities of reference liquids, each of which contains a vertical column made in the form of a tube with a side hole and a branch pipe in the middle of the tube connecting the inner area of the tube with a cylinder having a body made of an elastic material, and the reference the liquid fills the inner area of the tube and the cylinder, the first and second differential pressure sensors in the lower and upper ends of the tube, respectively, sensors of average pressure and average temperature of the reference liquid installed inside the tube, four secondary measuring transducers connected at the outputs of the sensors, a switch of measuring signals connected to outputs of the secondary measuring transducers, an analog-to-digital converter at the output of the switch, a processor at the output of the analog-to-digital converter, and the measured density of the liquid is determined by the formula:

и

- плотности эталонных жидкостей [кг/м³] в первом и втором измерителях при температурах

[°С] в первом и

[°С] во втором измерителях и общем давлении

[Па];Where

And

- density of reference liquids [kg / m ³ ] in the first and second meters at temperatures

[°C] in the first and

[°C] in the second gauge and total pressure

[Pa];

ΔР ₁₁ and ΔP ₂₁ - differential pressures in the lower ends of the tubes of the first and second meters [Pa];

ΔР ₁₂ and ΔР ₂₂ - differential pressures in the upper ends of the tubes of the first and second meters, respectively [Pa].

The third version of the device contains n structurally identical liquid density meters with different densities of reference liquids distributed in the range of measured density variability, each of which contains a vertical column made in the form of a tube with a side hole and a branch pipe in the middle of the tube connecting the inner area of the tube with a cylinder having case made of elastic material, wherein the reference liquid fills the inner area of the tube and cylinder, the first and second differential pressure sensors in the lower and upper ends of the tube, respectively, sensors of average pressure and average temperature of the reference liquid installed inside the tube, four secondary measuring transducers connected at the outputs of the sensors , a switch of measuring signals connected at the outputs of the secondary measuring converters, an analog-to-digital converter at the output of the switch, a processor at the output of the analog-to-digital converter, and the measured liquid density viscosity is determined by the formula:

и

[°С] и общем среднем давлении

[Па];where ρ _0i , ρ _0j are the densities i and j of reference liquids [kg/m ³ ] at medium temperatures

And

[°C] and total mean pressure

[Pa];

ΔP _i1 and ΔP _j1 - differential pressures at the lower end of the tube of the i-th and j-th meters [Pa];

ΔP _i2 and ΔPj ₂ [Pa] - differential pressures at the upper end of the tubes of the i-th and j-th meters.

The fourth version of the device contains several structurally identical liquid density meters, each of which contains a vertical column made in the form of a tube with a side hole and a branch pipe in the middle of the tube, connecting the inner area of the tube with a cylinder having a body made of an elastic material, and the reference liquid fills the inner area of the tube and a cylinder, the first and second differential pressure sensors, respectively, in the lower and upper ends of the tube, sensors installed inside the tube for average pressure and average temperature of the reference liquid, four secondary measuring transducers connected at the outputs of the sensors, a commutator of measuring signals connected at the outputs of the secondary measuring transducers, an analog-to-digital converter at the output of the switch, a processor at the output of the analog-to-digital converter, moreover, a thermoelectric heater-cooler of the reference liquid installed inside the tube is additionally introduced, into not a tube connected to a heating-cooling balancing signal generator connected at the input to the processor output, and the measured density of the liquid is determined by the formula:

[кг/м³] - цифровой отсчет кода плотности эталонной жидкости при средней температуре

[°С] и среднем давлении

[Па], уравновешиваемой измеряемую плотность внешней среды в момент времени t.Where

[kg / m ³ ] - digital reading of the density code of the reference liquid at an average temperature

[°С] and average pressure

[Pa], balanced by the measured density of the external environment at time t.

The structural-functional diagram of the liquid density meter is shown in Fig. 1.

которая меньше или больше измеряемой плотности ρ и зависит от средней температуры

и среднего давления

. Торцы трубки герметично закрыты крышками 5 (нижняя) и 6 (верхняя). В крышке 6 имеется отверстие 7 с пробкой для заливки эталонной жидкости. Общий объем эталонной жидкости выполняется таким, чтобы при сжатии внешним давлением на максимальных глубинах уменьшение ее объема происходило за счет стягивания эластичного баллона 3, сохраняя трубку заполненной. Поскольку в рабочем диапазоне температур и давлений коэффициент сжимаемости жидкостей не превышает 10^-4 атм^-1 (10^-9 Па^-1), то при работах на больших глубинах в несколько сотен атмосфер (n⋅10⁷ Па) изменение объема эталонной жидкости составит на более 1%. В крышках установлены дифференциальные датчики давления 8₁ - в нижней крышке и 8₂ - в верхней крышке. Внутри трубки установлены распределенный датчик 9 средней температуры

эталонной жидкости и датчик 10 среднего давления

на середине по высоте трубки. Выходы датчиков поданы на входы вторичных измерительных преобразователей 11₁-11₄, выходы которых через коммутатор 12 соединены со входом аналого-цифрового преобразователя 13 и далее со входом процессора 14.Consider the composition and operation of the meter. The device includes a tube 1 with a branch pipe 2 in the middle of the tube in height, which unites the internal volume of the tube with an elastic balloon 3. The tube 1 and the balloon 3 are filled with a reference liquid 4 with a known density

which is less or greater than the measured density ρ and depends on the average temperature

and medium pressure

. The ends of the tube are hermetically sealed with covers 5 (lower) and 6 (upper). The cover 6 has an opening 7 with a plug for filling the reference liquid. The total volume of the reference liquid is made in such a way that, when compressed by external pressure at maximum depths, its volume decreases due to the contraction of the elastic balloon 3, keeping the tube filled. Since in the operating range of temperatures and pressures the compressibility coefficient of liquids does not exceed 10 ^-4 atm ^-1 (10 ^-9 Pa ^-1 ), then when working at great depths of several hundred atmospheres (n⋅10 ⁷ Pa), the change in the volume of the reference liquid will be more than 1%. The covers are equipped with differential pressure sensors 8 ₁ - in the bottom cover and 8 ₂ - in the top cover. A distributed sensor 9 of the average temperature is installed inside the tube

reference fluid and medium pressure sensor 10

midway down the tube. The outputs of the sensors are fed to the inputs of the secondary measuring transducers 11 ₁ -11 ₄ , the outputs of which are connected through the switch 12 to the input of the analog-to-digital converter 13 and further to the input of the processor 14.

In the fourth version of the device, a heater-cooler generator 15 (outside the tube) and a heater-cooler 16 (inside the tube) are additionally introduced into it. The processor 14 output is connected to the heating-cooling signal generator 15, loaded on the Peltier thermoelectric heater-cooler 16, placed at one end inside the tube, the other end outside the tube. When a tube is placed in a medium, the pressure of the external environment acts on the tube; P ₁ - on the bottom cover, P ₂ - on the top cover, P ₃ - on an elastic balloon and a reference liquid in the middle of the tube.

In this case, the hydrostatic equation is valid

и измеряемой плотности ρ(ϕ, z).The tube must have sufficient rigidity to retain its shape at a pressure P ₁ -P ₂ =ΔP, regardless of the magnitude of the pressures P ₁ and P ₂ . The tube material must have low thermal conductivity and a low thermal expansion coefficient in order to maintain h. The differential sensor 8 ₁ serves to measure the difference between the external pressure P ₁ and the internal pressure at the lower end of the tube. The differential sensor 8 ₂ serves to measure the difference between the internal pressure at the upper end of the tube and the external pressure P ₂ . The pressure at the ends inside the tube depends on the density ratio of the reference liquid

and measured density ρ(ϕ, z).

внутреннее давление на нижнем входе дифференциального датчика 8₁ состоит из суммы давления Р₃, передаваемого из эталонного баллона 3, воспринимающего это давление из внешней среды, и давления вертикального столба эталонной жидкости высотой h₁, т.е.At

the internal pressure at the lower inlet of the differential sensor 8 ₁ consists of the sum of the pressure P ₃ transmitted from the reference cylinder 3, which perceives this pressure from the external environment, and the pressure of the vertical column of the reference liquid with height h ₁ , i.e.

In this case, the internal pressure at the inlet of the upper differential sensor 8 ₂ consists of the pressure difference P ₃ and the pressure of the vertical column of the reference liquid with height h ₂ , i.e.

The signals at the output of differential sensors will be equal to

Adding the last two expressions, we get

where h=(h ₁ +h ₂ ).

Equating the right parts of equations (1) and (6), we obtain

как видно из выражений (4) и (5), выходные сигналы дифференциальных датчиков будут отрицательными и выражение (4) примет видAt

as can be seen from expressions (4) and (5), the output signals of differential sensors will be negative and expression (4) will take the form

. Для измерения локальной плотности морской воды в качестве эталонной жидкости возможно использовать морскую воду с фиксированной соленостью, плотность которой можно контролировать по известному уравнению состояния морской воды, измеряя среднюю температуру

и среднее давление

образца с высокой реализуемой точностью.Thus, in the device, the task of measuring the density of a liquid is reduced to controlling the density of a reference liquid and measuring small pressure deviations of vertical columns of liquid with a measured density and a reference liquid. The rational choice of the reference fluid depends on the specific conditions of use of the meter. To ensure high accuracy of the density of the reference liquid, it is necessary to know

. To measure the local density of sea water, it is possible to use sea water with a fixed salinity as a reference liquid, the density of which can be controlled by the well-known equation of state of sea water by measuring the average temperature

and mean pressure

sample with high realizable accuracy.

In the first version of the liquid (sea water) density meter for the probe, a liquid (for example, sea water with a given salinity) is taken as a reference liquid, the density of which, for example, is equal to the density in the middle of the range of possible liquid densities (sea water in the environment of the study region). The measurement accuracy of differential pressures ΔР ₁ and ΔР ₂ should be sufficient to obtain corrections with the required accuracy to determine the desired density of the medium in single measurements on the probing trajectory.

In addition, in accordance with expression (7), it is necessary to know g(ϕ, z)h, i.e., have the acceleration of gravity tied to the geographic latitude ϕ and depth z of the measurement point, as well as the vertical height h of the reference liquid column. In general, when using a local seawater density meter in large oceanographic probes, obtaining these data is possible from the outside. However, this complicates the use of the proposed local density meter. It is desirable to exclude this information when determining the density, since the density of the reference liquid is already available for the measuring point. To do this, two density meters with different densities of reference liquids ρ ₀₁ and ρ ₀₂ are introduced into the device, structurally made so that the axes of the tubes are parallel and the lengths h are equal. This is the second version of the device. For a pair of meters, we obtain the following expressions

which we transform to the form

the solution of the system of equations (11) and (12) with respect to the measured density ρ will be

и

- плотности эталонных жидкостей при температурах

и

и давлении

в первом и втором измерителях; ΔР₁₁ и ΔР₂₁ - дифференциальные давления в нижних торцах трубок, а ΔР₁₂ и ΔР₂₂ - дифференциальные давления в верхних торцах трубок первого и второго измерителей соответственно.Where

And

- density of reference liquids at temperatures

And

and pressure

in the first and second meters; ΔР ₁₁ and ΔР ₂₁ - differential pressures at the lower ends of the tubes, and ΔР ₁₂ and ΔР ₂₂ - differential pressures at the upper ends of the tubes of the first and second meters, respectively.

Expression (13) does not contain the term g(ϕ, z)h and, therefore, it is not required to bind g to the latitude ϕ and depth z, as well as the projection of h onto the vertical.

Thus, the second version of the device is invariant to the magnitude of the acceleration of gravity (natural or artificial), a small deviation from the vertical, since with significant deviations from the vertical, the signals of differential pressure sensors decrease, which is undesirable.

We investigate questions of accuracy. According to the TEOS-10 thermodynamic equation of state for seawater [IOC, SCOR and IAPSO, 2010. The international thermodynamic equation of seawater 2010: Calculation and use of thermodynamic properties. International Oceanographic Commission, Manuals and Guides. no. 56. UNESCO (English). 196p. (Available from http://www.TEOS-10.org)], for example, a density measurement accuracy of 0.000004 g/cm ³ is required in the range 1.010000-1.030000 g/cm ³ or in relative units 2* ^{10 -4} %.

Modern differential sensors have a basic error of at least 0.1% and to ensure the required accuracy in the full range of seawater density variability, at least 5 subranges with ± 2 Pa small subranges of differential pressure variability, set by different densities of the reference liquid in 5 meters, will be required, similar to standard density measurements by a group of hydrometers.

Such a standard solution at the present level of technology seems difficult to implement.

эталонной жидкости. При попарной обработке данных n измерителей по выражению (13) формируется

результатов измерений. При этом суммы систематических и случайных погрешностей парных измерений становятся случайными на множестве результатов измерений и уменьшаются при осреднении по формулеThis problem is solved in the third version of the device, which uses n meters in parallel with the same hg values and different densities.

reference liquid. When pairwise processing of data n meters according to the expression (13) is formed

measurement results. In this case, the sums of systematic and random errors of paired measurements become random on the set of measurement results and decrease when averaging according to the formula

where ρ _0i , ρ _0j - densities i and j of reference liquids; ΔP _i1 and ΔP _j1 - differential pressures at the lower end of the tube of the i-th and j-th meters; ΔP _i2 and ΔP _i2 - differential pressures at the upper end of the tubes of the i-th and j-th meters.

раз. Это меньше, чем разбиение на n поддиапазонов. Однако, при этом диапазоны изменчивости давления для всех дифференциальных датчиков будут в n раз больше и, следовательно, проще и дешевле реализуемыми.One can expect a decrease in the root-mean-square error of the measurement result and calculations according to formula (14) in

once. This is less than splitting into n subranges. However, in this case, the ranges of pressure variability for all differential sensors will be n times larger and, therefore, easier and cheaper to implement.

можно не только контролировать, но и изменять в определенных пределах, регулируя ее среднюю температуру

, учитывая, что среднее давление

задается внешней средой.Density

can not only be controlled, but also changed within certain limits by adjusting its average temperature

, given that the average pressure

set by the external environment.

For example, the dependence of the density of normal water on temperature is shown in Table 1 from [Water. Density at atmospheric pressure and temperatures from 0 to 100°C. GSSSD 2-89. Properties of materials and substances. Water and water vapor. Issue 1. Tables of reference data. M.: Publishing house of standards. 1990].

Table 1 shows that the sensitivity to temperature of the density of normal water increases with increasing temperature, and when the temperature changes from 4 to 44°C, the density of water changes by 0.009341 kg/m ³ . Since the actual range of density variability, for example, sea water is more than twice as wide, it is necessary to use two or three tuning sub-ranges, therefore, two or three meters with different adjustable densities of the reference liquid.

It seems that the use of normal water and its standard hydrothermodynamic characteristics as a reference liquid is possible at the first stage. In what follows, apparently, it would be expedient to choose such a liquid as the reference one, the definition of which would be less conditional.

To change the temperature inside the tube, a thermoelectric heater-cooler 15 is installed, which is switched on for heating or cooling by changing the direction of the current, and the level of heating or cooling is set by the current strength of the signal generator 16, controlled from the output of the processor 14. Using the sum of the signals at the outputs of the differential sensors, positive , if the density of the reference liquid is less than the measured density and negative, if the density of the reference liquid is greater than the measured density, it is possible to adjust the density ρ ₀ of the reference liquid to the measured density by adjusting the level of its average temperature by heating-cooling. In fact, this is a tracking converter of the measured density, which includes a heater-cooler 16 and a control signal generator 15 connected to the output of the processor 14. This is the fourth version of the liquid density meter.

_Here , the mode of bitwise binary balancing of the unknown density given by the density of the reference liquid is possible, in which instead of the second term _of Eq. In this case, there are no requirements for measurement accuracy and knowledge of the values of the quantities included in the expression for the correction. However, it is required to specify the weighted small values of temperature corresponding to the binary weighted small values of the density of the reference liquid.

выполняется последовательно, то такой режим из-за снижения быстродействия целесообразно использовать в стационарных приборах.Since the implementation of several new densities

is performed sequentially, it is advisable to use this mode in stationary devices due to a decrease in performance.

Liquid density meters with bit-by-bit balancing of the density of the reference liquid also belong to the fourth version of the device with the replacement of follow-up balancing with a bit-by-bit one.

At the same time, the requirements for the accuracy of setting the density of reference liquids are preserved and the requirements for the accuracy of the product g(ϕ, z)h and the need to bind the base to the vertical are removed.

Claims (21)

1. A liquid density meter containing a vertical column, a reference liquid, pressure and temperature sensors, an information processing unit, characterized in that the vertical column is made in the form of a tube with a side hole and a branch pipe in the middle of the tube connecting the inner area of the tube with a cylinder having a body of elastic material, wherein the reference liquid fills the inner area of the tube and the cylinder, the first and second differential pressure sensors in the lower and upper ends of the tube, respectively, sensors of average pressure and average temperature of the reference liquid installed inside the tube, four secondary measuring transducers connected at the outputs of the sensors, a commutator measuring signals connected at the outputs of the secondary measuring transducers, an analog-to-digital converter at the output of the switch, a processor at the output of the analog-to-digital converter, while the measured density of the liquid at a geographical point at latitude ϕ and at depth z at sea is determined by the formula

Where

- density of the reference liquid [kg/m ³ ];

- average temperature [°С] and

- average pressure [Pa]; ΔР ₁ - indication of the lower differential sensor [Pa]; ΔP ₂ - indication of the upper differential sensor [Pa]; g(ϕ, z) - free fall acceleration [m/s ² ]; h - vertical dimension of the tube [m]. 2. Liquid density meter, characterized in that it contains two structurally identical liquid density meters with different densities of reference liquids, each of which contains a vertical column made in the form of a tube with a side hole and a branch pipe in the middle of the tube connecting the inner area of the tube with a cylinder, having a body made of elastic material, and the reference liquid fills the inner area of the tube and the cylinder, the first and second differential pressure sensors, respectively, in the lower and upper ends of the tube, the average pressure and average temperature sensors of the reference liquid installed inside the tube, four secondary measuring transducers connected at the outputs sensors, a commutator of measuring signals connected at the outputs of secondary measuring transducers, an analog-to-digital converter at the output of the switch, a processor at the output of the analog-to-digital converter, and the measured density of the liquid is determined by the formula e

Where

And

- density of reference liquids [kg / m ³ ] in the first and second meters at temperatures

[°C] in the first and

[°C] in the second gauge and total pressure

[Pa]; ΔP ₁₁ and ΔР ₂₁ - differential pressure at the lower ends of the tubes of the first and second meters [Pa]; ΔР ₁₁ and ΔР ₂₂ - differential pressures in the upper ends of the tubes of the first and second meters, respectively [Pa]. 3. Liquid density meter, characterized in that it contains n structurally identical liquid density meters with different densities of reference liquids distributed in the range of measured density variability, each of which contains a vertical column made in the form of a tube with a side hole and a pipe in the middle of the tube, connecting the inner area of the tube with a cylinder having a body made of an elastic material, and the reference liquid fills the inner area of the tube and the cylinder, the first and second differential pressure sensors, respectively, in the lower and upper ends of the tube, the sensors of average pressure and average temperature of the reference liquid installed inside the tube, four secondary measuring transducers connected at the outputs of the sensors, a commutator of measuring signals connected at the outputs of the secondary measuring transducers, an analog-to-digital converter at the output of the switch, a processor at the output of the analog-to-digital converter vatel, and the measured density of the liquid is determined by the formula

where ρ _0i , ρ _0j are the densities i and j of reference liquids [kg/m ³ ] at medium temperatures

And

[°C] and total mean pressure

[Pa]; ΔP _i1 and ΔP _j1 - differential pressures at the lower end of the tube of the i-th and j-th meters [Pa]; ΔP _i2 and ΔP _j2 [Pa] - differential pressures at the upper end of the tubes of the i-th and j-th meters. 4. A liquid density meter, characterized in that it contains several structurally identical liquid density meters, each of which contains a vertical column made in the form of a tube with a side hole and a branch pipe in the middle of the tube connecting the inner area of the tube with a cylinder having a body made of elastic material, moreover, the reference liquid fills the internal area of the tube and the cylinder, the first and second differential pressure sensors, respectively, in the lower and upper ends of the tube, the sensors of average pressure and average temperature of the reference liquid installed inside the tube, four secondary measuring transducers connected at the outputs of the sensors, a commutator of measuring signals, included at the outputs of the secondary measuring transducers, an analog-to-digital converter at the output of the switch, a processor at the output of the analog-to-digital converter, and a thermoelectric heater-cooler installed inside the tube is additionally introduced The reference fluid is connected outside the tube to the generator of the balancing heating-cooling signal, connected at the input to the output of the processor, and the measured density of the liquid is determined by the formula

Where

[kg / m ³ ] - digital reading of the density code of the reference liquid at an average temperature

[°С] and average pressure

[Pa], balanced by the measured density of the external environment at time t.

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