RU2654316C2 - Device for the liquid media specific electrical conductivity measurement - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: device is designed to measure the seawater specific electrical conductivity directly in the medium and can be used for measurement in other liquids. Summary of invention is in that the liquid media specific electrical conductivity measuring device contains a current source, voltage meter, sensor with a solid dielectric casing in the form of a cup and two current electrodes, at that, the sensor frame includes a controlled current source, voltage and resistance meters, a power supply source for electromagnets and a microprocessor, the liquid specific conductivity

is determined by the formula

where I is the current through the current electrodes known value, U is the voltage between the potential electrodes measured value, α is the cup linear expansion temperature coefficient with the temperature increase for θ from zero one, γ is the cup measuring base linear compression coefficient with external pressure increase for P from zero one, K is the sensor cell "geometric constant" at zero temperature and pressure.

EFFECT: technical result is the improvement in the measurement accuracy in the medium particular point.

1 cl, 2 dwg

Description

The invention relates to measuring technique and is intended for use in oceanography to measure the electrical conductivity of sea water directly in the environment. It can be used in other areas.

Conductometers with contact sensors are widely used for high-precision measurement of the electrical conductivity of sea water in oceanography, the number of electrodes in which depends on how polarization effects on the electrodes can be eliminated on the measurement result and the formation of a closed electric field inside the measuring cell [A Guide to Conductivity measurement theory and practice of Conductivity Applications. www.tau.ac.il/XXchemlada/Fills/Conductivity_quick_EN%20(2).pdc]. [Lopatin B.A. Conductometry. - Novosibirsk: Publishing House of the Academy of Sciences of the USSR Academy of Sciences, 1964. - 279 s].

The use of only two current electrodes in the sensor does not eliminate the effect of polarization effects on the measurement result and does not ensure the achievement of high accuracy.

The use of four electrodes, two current (supply) and two potential (measuring), and the operating mode with a current source allows to eliminate the effect of polarization effects on current electrodes. However, to form a closed electric field inside the measuring cell, the sensors are made of a tube with five (three current and two potential) or seven (three current and four potential) electrodes forming an electronic tube at the ends of the tube [Stepanyuk I.A. Oceanological measuring transducers. - L .: Gidrometizdat, 1986. - 272 s]. The design of the sensor and the meter is complicated and the natural washability of the sensor is significantly deteriorated, which affects the representativeness and, therefore, the measurement accuracy at a particular point in the marine environment.

The simplest problem is the closure of the electric field inside the measuring cell is solved when performing the sensor in the form of a glass as proposed, for example, in the patent [RF Patent No. 2046361, 20.10.1995. Device for measuring the electrical conductivity of liquid media. Authors: Verevkin V.I., Bystrov V.A., Polyakov S.E.].

This device comprises a “dielectric tube with disk and ring electrodes located therein, a dielectric gasket located close to the disk electrode and forming a cup together with a dielectric tube, current and voltage recorders and a power source”.

This device is adopted as a prototype. Its disadvantages for achieving high accuracy are: the effect of polarization effects on the electrodes on the measurement result, poor natural flushing when stationary in a stationary medium, lack of correction of the dependence of the geometric dimensions of the sensor on its temperature and external hydrostatic pressure.

The aim of the invention is to increase the measurement accuracy by eliminating the influence of polarizing effects on the electrodes on the measurement result, correcting the influence of the temperature of the sensor housing and external hydrostatic pressure on the geometric dimensions of the sensor, improving the flushed ™ internal volume of the sensor.

This goal is achieved by the fact that in the liquid conductivity meter containing a current source, voltage meter, a sensor with a solid dielectric body in the form of a glass and two current electrodes, the sensor design is changed by installing a wedge-shaped 45 ° dielectric insert at the bottom of the glass and the first current electrode in the form of a half-disk at the bottom of the glass and the second current electrode in the form of a half ring along the edge of the glass, which are installed in opposite sectors of the circumference of the cross section st Akan, and it additionally introduced two potential point electrodes mounted on the generatrix of the inner wall of the glass at distances from current electrodes not less than the diameter of the glass, a distributed resistor temperature sensor, built into the glass body, magnetohydrodynamic fluid mover from two U-shaped magnetic circuits with magnetization coils, the first of which is installed by opening in the cross section of the cup from the outside between the first current electrode and the first potential electrode, the second The first magnetic circuit is installed by opening in the cross section of the cup outside between the second potential electrode and the second current electrode, a resistance meter connected to the outputs of the distributed temperature sensor, an electromagnet power source, the outputs of which are fed to the inputs of the magnetization coils, a microprocessor connected to the meter by inputs / outputs voltage, a resistance meter, a power source of electromagnets, an external output and with a current source that is made controllable; moreover, the specific conductivity of the liquid is determined by the formula

where I is the known value of the current through the current electrodes, U is the measured voltage value between the potential electrodes, α is the temperature coefficient of linear expansion of the cup with increasing temperature by θ from zero, γ is the coefficient of linear compression of the measuring base of the cup with increasing external pressure by P from zero , K is the "geometric constant" of the measuring cell of the sensor at zero temperature and pressure.

The invention is illustrated by drawings. In FIG. 1 shows the structural-functional diagram of the meter. In FIG. 2 shows a diagram of the formation of a cell-washing flow by a magnetohydrodynamic propulsion device (MHD).

Consider the essence of the proposed invention.

определяется формулойFor a measuring cell in the form of a cylinder with an inner diameter d and a length h forming the value of specific conductivity

defined by the formula

where I is the current through the cell, U is the voltage at its boundaries,

- "geometric constant" at the initial temperature (zero) of the sensor housing and external pressure (zero).

With an increase in temperature by θ and pressure on P, h and d and therefore K.

If we assume that these changes are independent and linear with the known coefficients α and γ, then we can write

Then, for the value of the "geometric constant" at specific temperature and pressure, when substituting expressions (3-6) into expression (2), we obtain

Typically, in oceanography, a conductivity meter is part of the STD complexes, which provide information on the water temperature and hydrostatic pressure P at the measurement point, for example, when probing in depth. Due to the thermal inertia of the body of the conductivity sensor (cup), its temperature will not necessarily be equal to the temperature of the water if the latter changes. Therefore, the temperature of the cup θ, it is advisable to control the built-in distributed resistor temperature sensor as proposed in this device. It is advisable to borrow information on hydrostatic pressure from the outside, from the data of the STD complex.

Thus, for known α, γ and measured values of θ, P, I, and U, the current “geometric constant” K _{θ, P} is determined by formula (6) and the electrical conductivity of the liquid by the formula

where G is the electrical conductivity of the measuring cell.

The structural and functional diagram of the meter of conductivity of liquid media is presented in FIG. 1. The meter includes an electric conductivity sensor (DE) 1, presented in 2 projections, a controlled current source (UIT) 2, a voltage meter (IN) 3, a resistance meter (IC) 4, an electromagnet power supply (IPEM) 5, microprocessor (MP) 6.

DE1 is used to establish quantitative relations between current and voltage in the measuring cell in accordance with Ohm's law.

DE1 consists of a solid-state dielectric cup 1 ₁ , at the bottom of which there is a wedge-shaped dielectric insert 1 ₂ and the first disk current electrode 1 ₃ (with output T ₁ ) in the lower sector, the second semi-ring current electrode 1 ₄ (with output T ₂ ) installed along the edge of the neck of the glass in the upper sector, along the generatrix of the cylinder on the inner wall of the glass at a distance h from each other and at least d (to form a uniform electric field) from the current electrodes, point potential electrodes are installed 1 ₅ and 1 ₆ with outputs P ₁ and P ₂ . A distributed resistor temperature sensor 1 ₇ with outputs C ₁ and C ₂ is built into the cup body. The shoes of the U-shaped magnetic circuits 1 ₈ and 1 ₉ with magnetization coils 1 ₁₀ and 1 ₁₁ , having electrical outputs M ₁ , M ₂ and M ₃ , M _{4, are} connected to the outer surface of the glass along the vertical axis. U-shaped magnetic cores are designed to form, together with the working current I, through current electrodes 1 ₃ and 1 _{4 of a} magnetohydrodynamic propulsion device (MHD), due to the Lorentz force providing water movement inside the glass for forced washing. The dielectric insert 1 ₂ , the implementation of the current electrodes in the form of a half disk (first) and a half ring (second) and their installation in different sectors of the circumference of the glass section are necessary to form the direction of the electric current lines needed for the MHD mover. The outputs of the current electrodes T ₁ and T _{2 are} connected to the outputs of the controlled current source 2, the outputs of the potential electrodes T ₁ and T _{2 are} fed to the inputs of the voltage meter 3, the outputs C ₁ and C _{2 of the} distributed temperature sensor 1 _{6 are} fed to the inputs of the resistance meter 4, the outputs windings of electromagnets M ₁ , M ₂ , M ₃ and M _{4 are} connected to the outputs of IPEM 5. Microprocessor 6 is used to control measurements and primary data processing and is connected via digital inputs and outputs to UIT 2, IN 3, IS 4 and IPEM 5 and external meter output 7.

The above structural and functional diagram and composition of the meter are valid when it is operated on direct, alternating and alternating current. However, to facilitate the fight against the polarization of current electrodes, the possibility of manufacturing electrodes other than precious metals, the exclusion of the influence of capacitive components in the complex resistance of the measuring cell, it is advisable to use such a scheme for switching on a 4-electrode measuring cell with alternating current with automatic adjustment to the active component of the resistance, which proposed in the patent [Gaysky V.A., Klimenko A.V. Conductometer // RF Patent No. 2312331, 06/30/2005. Publ. 12/10/2007. Bull. 34]. A description of the implementation of this device is given in [Gaysky V.A., Klimenko A.V., Grekov A.N., Vasiliev D.M. Liquid conductivity meter // Environmental monitoring systems / Means and monitoring. Sat scientific tr MGI NASU. - Sevastopol. 2005, - S. 81-84].

To avoid the occurrence of interelectrode potential, all electrodes are made of one material resistant to corrosion in sea water (platinum, gold, stainless steel, tantalum, etc.). Potential spot electrodes 1 ₄ and 1 ₅ with a possibly smaller diameter (such as a needle tip) are mounted flush with the inner surface of the beaker.

When using alternating current in the operation of the meter, the controlled current generator 2 includes a polarity switch at the output, the voltage meter 3 contains an input polarity switch in phase with the current generator, the power supply of electromagnets 5 also has a switch at the magnetization current output in phase with the current source for maintaining the constancy of the direction of the Lorentz force in the magnetohydrodynamic mover (MHD), and, consequently, the direction of the forced fluid motion [General physicist but. Electrical and magnetic phenomena // Reference manual / A.I. Akhiezer. - Kiev: Naukova Dumka, 1981. - S. 358]. [https.//en.wikipedia.org/wiki//magnetohydrodynamics].

In all cases, the voltage meter 3 should have a maximum input resistance so as not to bypass the measuring base between potential electrodes. A distributed temperature sensor built into the glass 1 _{6 is} made of metals with good heat sensitivity (platinum, copper or nickel) and provides temperature control by its resistance, measured using IP 4.

When measuring directly in the medium from a moving carrier of the meter (probe or tug), the sensor cup is well washed with a stream of flow around it with an appropriate orientation relative to the stream. In positional settings in a stationary environment, the flushing of the sensor cup to ensure representativeness (and accuracy) of measurements is carried out using an MHD mover.

и

, возникающие за счет силы Лоренца, направление которой определяется по правилу «правой руки».In FIG. 1, the poles of N, S electromagnets are conventionally marked, the lines of the working current and the directions of the flow vectors are shown

and

arising due to the Lorentz force, the direction of which is determined by the rule of the "right hand".

A more detailed diagram of the formation of a washing flow in a glass by an MHD mover is shown in FIG. 2, where the electric field with the necessary deviations of the current direction from the cylinder axis is formed by the installation of a wedge-shaped 45 ° degree insert on the bottom of the cup and the location of the current electrodes in opposite sectors of the circumference of the cup section. 2a, a pattern of overlapping traces of magnetic fields with a direction on the streamline is shown in FIG. 2b, a diagram of the formation of fluid flows under the influence of the Lorentz force in the MHD mover is shown in FIG. 2c.

Thus, the sensor implemented in the glass due to a specially formed electric field and streamlines between the current electrodes and the added electromagnets, the double MHD mover generates a longitudinal vortex inside the glass, washing the measuring cell of the sensor.

The magnitude of the Lorentz force (and the flow velocity V) is proportional to the current strength and the magnitude of the magnetic induction, the necessary values of which must be provided.

The device operates as follows. In the measurement medium, the sensor cup is filled with an updated fluid. Through current electrodes at the inputs T ₁ and T ₂ , a controlled current I enters the measuring cell, and voltage U appears at the outputs P ₁ and P _{2 of the} potential electrodes.

When measuring on a bipolar current with a secondary measuring transducer, which is formed by a current source 2 and a voltage meter 3 under the control of microprocessors, the common-mode components of current I and voltage U are selected, which determines the active component of the electrical conductivity G of the measuring cell between potential electrodes by the formula

Further, to determine the specific electrical conductivity of the liquid, calibration values of K and coefficients α and γ for the “geometric constant” K _{θ, P} , which are included in expression (8), are required.

образцового раствора, известных θ₀ и P₀, измеренных I₀ и U₀ из выражения (8) получимGiven

sample solution, known θ ₀ and P ₀ measured I ₀ and U ₀ from the expression (8) we obtain

К - «геометрическая константа» при начальной (нулевой) температуре и начальном (нулевом) давлении, зависящая только от параметров h и d измерительной ячейки.Where

K is the "geometric constant" at the initial (zero) temperature and initial (zero) pressure, depending only on the parameters h and d of the measuring cell.

The grading task is to determine the unknowns K, α, and γ.

, для которых в дополнение к выражению (10) справедливы выраженияTo simplify the procedure, it is not necessary to specifically stabilize the temperature and pressure, which can be measured by taking readings from four sample fluid samples

for which, in addition to expression (10), the expressions

We divide expression (10) in pairs into expressions (11) and obtain

We introduce the notation

We write

After the transformations, we obtain a system of linear algebraic equations of the form

with unknown α, γ, and αγ.

When solving system (15) according to Cramer’s rule, we obtain the determinant of the system

For unknowns of interest, we obtain

- The value of K is determined from equations (11) as the average

In the operating mode, the current G, θ and P are measured and the specific electrical conductivity of the liquid is calculated by the formula (8), where K _{θ, P} from the formula (7).

Thus, the goal is to increase accuracy by eliminating the influence on the measurement result of polarization effects on current electrodes, ensuring the closure of the electric field of the measuring cell, ensuring the representativeness of measurements at a specific point in space and time, correcting changes in the geometric dimensions of the measuring cell from changes in temperature and external pressure, achieved.

Claims (3)

A device for measuring the electrical conductivity of a liquid medium containing a current source, a voltage meter, a sensor with a solid dielectric body in the form of a cup and two current electrodes, characterized in that the sensor has a wedge-shaped 45-degree dielectric insert at the bottom of the cup and the first current electrode is made in a half disk at the bottom of the glass and the second current electrode is made in the form of a half ring along the edge of the glass and they are installed in opposite sectors of the circumference of the cross section of the glass, in Two potential point electrodes are additionally introduced; they are mounted on the generatrix of the inner wall of the glass at distances from the current electrodes not smaller than the diameter of the glass, a distributed resistive temperature sensor for the glass integrated in the glass body, magnetohydrodynamic propulsors from two U-shaped magnetic circuits with magnetizing coils, the first of which is installed by opening in the cross section of the cup outside between the first current electrode and the first potential electrode; the second magnetic circuit is installed by opening in the cross section of the cup outside between the second potential electrode and the second current electrode; resistance meter connected at the input to the outputs of the distributed temperature sensor; a power source of electromagnets, the outputs of which are fed to the inputs of the magnetization coils; a microprocessor connected by inputs and outputs with a voltage meter, a resistance meter, an electromagnet power source, an external output and a current source that is controllable; moreover, the electrical conductivity

fluid is determined by the formula

, where I is the known value of the current through the current electrodes, U is the measured voltage value between the potential electrodes, α is the temperature coefficient of linear expansion of the glass, θ is the temperature increase of the glass from zero, γ is the linear compression coefficient of the measuring base of the glass on the measuring base with increasing pressure, P is the increase in external pressure from zero, K is the "geometric constant" of the measuring cell of the sensor at zero temperature and pressure.

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