Capacitive method of measuring level of liquids and device for realising said method

FIELD: physics.

SUBSTANCE: method if based on measuring capacitance of a double-electrode capacitive liquid level sensor, which in turn in any sequence measures capacitance of the double-electrode capacitive liquid level sensor and capacitance of the same sensor is measured after connecting a capacitive sensor of dielectric properties to it, after which the level h from the upper end of the double-electrode capacitive liquid level sensor is calculated using the formula:

, where h is the level of the liquid in the reservior; CA is capacitance of the double-electrode capacitive liquid level sensor; CB is overall capacitance of the double-electrode capacitive liquid level sensor connected in parallel to the capacitive sensor of dielectric properties; A, B and D are structural parametres of the double-electrode capacitive liquid level sensor and capacitive sensor of dielectric properties. The device for measuring liquid level has a double-electrode capacitive liquid level sensor made in form of a coaxial capacitor, and two cylindrical electrodes. The lower end of the inner electrode of the double-electrode capacitive liquid level sensor is connected to one of the electrodes of the capacitive sensor of dielectric properties through the closing contact of a reed relay, and the lower end of the outer electrode of the double-electrode liquid level sensor is connected to the second electrode of the capacitive sensor of dielectric properties.

EFFECT: high accuracy of measuring the level of different liquids, as well as elimination of measurement errors caused by change in dielectric permittivity of the measured liquid.

2 cl, 1 dwg

 

The technical field to which the invention relates.

The invention relates to the field of measuring and control technology and can be used for level measurement of dielectric and conductive liquids, for example in tanks with oil or petroleum products.

The level of technology

A known method of measuring the liquid level in the tank by using connected to the generator, connected through the frequency indicator, a capacitive sensor mounted in the tank with the measured liquid. The sensor is equipped with a movable slide provided with a conductive coating and is located in magnetoresitive the tube, which can move has a circular float with permanent magnet. When changing the fuel level float is moved synchronously him move and slide, locking changes in the capacitance (see the description of the invention to the patent of Russian Federation №2040779, C01P 23/16, publ. 1995.07.25).

The disadvantage of this method is the low accuracy of the measurement and the difficulty of its implementation, with significant differences in height, reaching 10-20 meters.

Known capacitive method for measuring liquid level by using a capacitive liquid level sensor and a compensation capacitor sensor whose readings introduce the correction of the measuring circuit (see Sensors Handbook / Sharapov V.M., Mi the AEB I.G. etc. / Cherkassy: Brahma-Ukraine, 2008, Chapter 8, str-287).

The disadvantage of this method is the need for its implementation extra line compensation of the sensor with the measuring device. The measured capacitance of the compensation sensor is increased by the capacitance value of the communication line, the properties of which depend on its length, and change over time (a phenomenon of aging) and under the influence of temperature. This reduces the accuracy of measurement and complicates the installation of the device.

Known capacitive sensor dielectric properties of gaseous and liquid media containing electrodes connected to the output terminals. The electrodes are made of flexible metal solid or stranded wire covered with insulation and randomly placed into a ball (see A.S. USSR 1125530 And 23.11.1983, Igumenov, Overbroad).

This sensor can serve as an indicator of the level of liquid media at the interface liquid-air or liquid-liquid". In the second case, the liquid should be immiscible and have different dielectric constant.

The disadvantage of this sensor is the lack of continuous monitoring of liquid level, especially when large changes.

The closest in technical essence and the achieved positive effect (and ninety authors for the prototype) is a method of measuring the level of the dielectric liquid, by deep in the capacitive sensor in the form of a number of vertically one above the other and are numbered in ascending order from the bottom up identical unit capacitors in the interelectrode space which freely enters the dielectric fluid. Consistently measure the capacitance of a single capacitor, starting from the bottom. According to the results of the measurements determine the desired sequence number of the first unit capacitors, whose interelectrode space is filled with a dielectric fluid is less than its length. Measure the total capacitance of a single capacitor with the desired sequence number and connected in parallel at the time of measurement, adjacent the bottom of the unit capacitor. Determine the length of the fill interelectrode space of the dielectric fluid of these two parallel-connected unit capacitors in the corresponding formula. Then determine the level of the dielectric liquid according to the appropriate formula (see the description of the invention to the patent of Russian Federation №2242727 C2, G01F 23/26, publ. 2004.12.20).

The disadvantages of this method are the high cost of time for measurement, and the inability to compensate for the measurement error caused by the change in dielectric permittivity of the counter is controlled fluid. The dielectric constant may change in case of replacement of the brand or grade of the controlled fluid, and the change of its temperature.

The closest in technical essence and the achieved positive effect (and adopted by the authors for the prototype) is a capacitive level sensor containing elektroizolyatsionnye apart cylindrical coaxial electrodes located on the screen, made in the form of United pipe sleeves. The pipe is held in the cavity of the inner electrode and elektrosokirani from him. On one sleeve electrodes are fastened with screws and nuts and elektrosokirani, and the other sleeve is located on the opposite ends of the electrodes (see the description of the invention to the patent of Russian Federation №2112931, C1, G01F 23/26, publ. 1998.06.10).

The disadvantage of the sensor is a cumbersome and material design.

Disclosure of inventions

The technical result that can be achieved using the present invention is to improve the accuracy of the level measurement of liquids, but also to eliminate measurement errors caused by changes in dielectric properties of the controlled environment.

The technical result is achieved by a capacitive method of measurement of liquids is based on measuring the electrical capacitance electrode of the capacitor level sensor LM is bone, alternately, in any order to measure the capacity of the two-electrode capacitor of the liquid level sensor and measure the capacitance of the sensor after connecting the condenser sensor dielectric properties, and then calculate the level h from the upper end of the two-electrode capacitor of the liquid level sensor according to the formula:

,

where h is the level of the controlled fluid in the reservoir;

CA- the electric capacity of the capacitor electrode of the liquid level sensor;

CB- the total capacity of the two-electrode capacitor of the liquid level sensor connected in parallel with capacitor sensor dielectric properties;

A, b, and D are the design parameters of the two-electrode capacitor of the liquid level sensor and a condenser sensor dielectric properties.

The technical result is achieved in that the device for measuring liquid level contains a two-electrode capacitive liquid level sensor, made in the form of a coaxial capacitor, and contains two cylindrical electrode, the lower end of the internal electrode electrode condenser liquid level sensor connected to one of electrodes of the capacitor dielectric sensor properties through closing to the beat of reed relays, and the lower end of the outer electrode of the capacitor electrode of the liquid level sensor is connected with the second electrode of the capacitor sensor dielectric properties.

The essence of the capacitive method of measurement of liquids, based on the measurement of electrical capacitance electrode of the capacitor sensor 2 liquid level, is that serially in any order to measure the capacity of the CAtwo-electrode capacitor of the sensor 2 fluid level and after the parallel connection of the capacitor sensor 4 dielectric properties through the normally open contact reed relays 7, measure the total capacity of CBtwo-electrode capacitor of the sensor 2 fluid level and condenser sensor 4 dielectric properties, and then calculate the level h from the upper end electrode of the capacitor sensor 2 liquid level according to the formula:

,

where h is the level of the controlled fluid in the reservoir;

A, b, and D are the design parameters of the two-electrode capacitor of the sensor 2 fluid level and condenser sensor 4 dielectric properties.

Brief description of drawings

The drawing shows a diagram of the device for measuring liquid level, implementing capacitive method for level measurement of liquids./p>

The implementation of the invention

Capacitive method for level measurement of liquids is performed by the device 1 for measuring the electrical capacitance connected to the capacitor electrode sensor 2 liquid level, set vertically in the tank 3 with a controlled fluid by alternately measuring capacitance CAthe two-electrode capacitor of the sensor 2 fluid level and after the parallel connection of the capacitor sensor 4 dielectric properties, the cavity of which is constantly filled with the controlled fluid, and measure the total capacity of CBtwo-electrode capacitor of the sensor 2 fluid level and parallel connected capacitor sensor 4 dielectric properties, and then calculate the level h from the top of the glass electrode of the capacitor sensor 2 level of liquids according to the formula:

,

where h is the level of the controlled fluid in the reservoir;

A, b, and D are the design parameters of the two-electrode capacitor of the sensor 2 fluid level and condenser sensor 4 dielectric properties of the controlled fluid.

Device for measuring the liquid level in the tank 3 contains a two-electrode capacitor sensor 2 liquid level, connected in parallel with capacitor dates the ICOM 4 dielectric properties, installed at the bottom of the device for measuring liquid level. Two-electrode capacitor sensor 2 liquid level is made in the form of a coaxial capacitor with a cylindrical electrodes 5, internal and 6 external. The lower end of the internal electrode 5 electrode of the capacitor sensor 2 liquid level is connected to one of electrodes of the capacitor sensor 4 dielectric properties through the normally open contact reed relay 7. The lower end of the outer electrode 6 electrode of the capacitor sensor 2 liquid level is connected with the second electrode of the capacitor sensor 4 dielectric properties. Condenser sensor 4 dielectric properties made in the form of randomly laid wire electrodes are covered with insulation, the interelectrode space which is constantly filled with the controlled fluid. Two-electrode capacitor sensor 2 liquid level is connected to the device 1 for measuring the electrical capacitance. Device for measuring the liquid level can be used as dielectric fluids, and for conductive liquids. In this case, at least one of the electrodes of the electrode of the capacitor sensor 2 fluid level and condenser sensor 4 dielectric properties must have an insulating coating of a single the e of the dielectric.

Measurement of liquid level in the reservoir occur as a capacitive method of measurement of liquids. Vertically mounted device for measuring the liquid level in the tank 3. Measure the capacitance CAtwo-electrode capacitor of the sensor 2 of the liquid level.

The capacity of the two-electrode capacitor of the sensor 2, the liquid level in the General case, when the level of the controlled fluid is located between the flanking markers is determined by the expression:

where C1- capacity unfilled liquid part of the two-electrode capacitor of the sensor 2 liquid level;

With2- capacity immersed in the liquid of the sensor.

Then through the normally open contact reed relay 7 is connected to the device 1 for measuring the electrical capacitance of the capacitor sensor 4 dielectric properties of parallel connected with the capacitor electrode sensor 2 liquid level. Measure the total capacity of CBtwo-electrode capacitor of the sensor 2 liquid level connected in parallel with capacitor sensor 4 dielectric properties.

The total capacity of CBunder these same conditions will be determined by the expression:

where C3- capacity capacitor dielectric sensor 4 SV is ist, constantly immersed in the controlled fluid.

The value of C1and C2changes together with changes in the level of the controlled fluid in the tank 3, and accordingly CA.

However, With3does not depend on changes in the liquid level, and is a function of only the dielectric constant of the controlled fluid.

The capacity C1depends on the level change of the controlled fluid in the reservoir 3, i.e. the length of the non-immersed part of the electrode of the capacitor sensor 2 liquid level, and respectively from the specific capacity of the empty sensor. The relative permittivity of air or gas environment on the change of the capacity to influence will not be, as the dielectric constant of air and various gases is approximately equal to the unit.

Report level readings can be conducted from any vertical point of the tank 3. For example: from the bottom of the tank 3, from the lower or upper end electrode of the capacitor sensor 2 liquid level. Simple geometric calculations easily these systems report to bind to any convenient point. However, the report of the level h of the liquid easier to lead from the upper end electrode of the capacitor sensor 2 liquid level, especially for buried in the ground tanks, and also in those cases where the technology is to whom the regulations of the measurement of liquid level in the upper part of the tank 3, and the length L of two-electrode capacitor of the sensor 2, the liquid level can be choose less than the height of the reservoir 3. In this case, the calculation formula for measuring the liquid level on the basis of obvious geometric constructions should introduce a correction equal to the difference between the vertical marks the upper end electrode of the capacitor sensor 2 fluid level and adopted a new point of reference.

Introduce the concept of specific capacity γ two-electrode capacitor of the sensor 2, the liquid level in the unfilled state per unit of its length. The value of γ for the coaxial probe is determined by known methods by calculation (see j. Friden. Modern sensors. The Handbook. M: Technosphere, 2006, Chapter 3, p.66-68)or determined experimentally in the manufacture of the sensor. Then, the capacitance C1:

where:

ε1the relative permittivity of air or gas environment above the surface of the controlled fluid (ε1≈1).

γ is the specific capacity of the electrode of the capacitor sensor 2 liquid level [pF/m];

h is the length of the non-immersed part of the electrode of the capacitor sensor 2 liquid level [m].

Capacity2in this case, will be:

where:

ε2- relative is the dielectric constant of the controlled fluid;

L - length two-electrode capacitor of the sensor 2 liquid level [m].

In this capacity two-electrode capacitor of the sensor 2, the liquid level will be less than the total capacity of the condenser sensor 4 dielectric properties in C3that is determined by the expression:

where:

With0- the initial capacity of the condenser sensor 4 dielectric properties in the air, i.e. to dive into the controlled fluid. The value of0determined by known methods by calculation (see Grayden. Modern sensors. The Handbook. M: Technosphere, 2006, Chapter 3, p.66-68)or determined experimentally in the manufacture of the sensor.

Output calculation expression, allowing the measurement results CAand CBto determine the level of h:

Here are the dielectric constant of the controlled fluid:

Substituted in the expression (1) expression (3) and (4) and get:

Here are h:

Substitute in (9) the expression (7) and find the design formula for determining h:

To simplify impose a constructive constants:

Then the calculation formula (10) is met compact form:

According to the proposed capacitive method of measurement of liquids conducted a series of demonstration experiments with transformer oil, diesel oil, waste engine oil, tap water.

Technical parameters of the two-electrode capacitor of the liquid level sensor (for dielectric liquids)

The total length of the sensor, m0,975
The inner diameter of the outer electrode, mm18
The outer diameter of the inner electrode, mm10
Specific capacity per unit length of the sensor, γ (pF/m)13,8
The capacity of the compensation sensor, With0(pF)30

Structural constants of the gauge: A=3,794[m-1];

In=113,8 [dimensionless quantity]; D=3,699 [pF/m].

Examples of specific implementation capacitive method of measurement of liquids

Example 1

Transformer oil with ε2=2,16

The actual level, mCA, pF CB, pFThe estimated level, mAbsolute error, m
02302950,007-0,007
0,31200,42265,70,3060,004
0,6163228,40,5870,013
0,87125,7191,10,8650,005

Example 2

Diesel fuel with ε2=2,21

The actual level, mCA, pFCB, pFThe estimated level, mAbsolute error, m
0234300,40,008-0,008
0,31KZT 205.7273,60,316 -0,006
0,6KZT 166.5237,10,61-0,001
0,87126197,50,879-0,009

Example 3

Waste engine oil with ε2=2,36

The actual level, mCA, pFCB, pFThe estimated level, mAbsolute error, m
02983690,0740,074
0,312663380,311-0,001
0,6reach 232.5306,20,63-0,003
0,87202,4273,20,8690,001

Technical parameters of the two-electrode capacitor is of Attica liquid level (for conductive liquids)

The total length of the sensor, m1
The inner diameter of the outer electrode, mm6
The diameter of the conductors, mm1
Specific capacity per unit long sensor, γ (pF/m)45
The capacity of the compensation sensor, With0(pF)37
The radial thickness of insulation (polyethylene), mm0,25

Structural constants of the gauge: A=1,21[m-1];

In=45 [dimensionless quantity]; D=1,21 [pF/m].

Example 4

Tap water with ε2=4,91

The actual level, mCA, pFCB, pFThe estimated level, mAbsolute error, m
0226408-0,030,03
0,4161,3350,6 0,360,04
0,893,9285,60,730,07
0,971,7266,30,850,05

The proposed capacitive method for level measurement of liquids and device for its implementation compared with the prototype and other known technical solution has the following advantages:

- has a high accuracy of measurement.

- can be used for different variations of the measured fluid level in the reservoir;

- allows simultaneous measurement of liquid level in the tank to compensate for the measurement error caused by the change in the dielectric constant of the controlled fluid;

the design of the device for measuring liquid level eliminates the need for strip-line connection of the capacitor sensor dielectric properties of the instrument for measuring electrical capacitance, as these functions are performed directly electrode condenser liquid level sensor.

1. Capacitive method for level measurement of liquids, based on the measurement of electrical capacitance electrode of the capacitor is Attica liquid level, wherein the serially in any order to measure the capacity of the two-electrode capacitor of the liquid level sensor and measure the capacitance of the sensor after connecting the condenser sensor dielectric properties, and then calculate the level h from the upper end of the two-electrode capacitor of the liquid level sensor according to the formula:
,
where h is the level of the controlled fluid in the reservoir;
WithAnd- the electric capacity of the capacitor electrode of the liquid level sensor;
WithIn- the total capacity of the two-electrode capacitor of the liquid level sensor connected in parallel with capacitor sensor dielectric properties;
A, b, and D are the design parameters of the two-electrode capacitor of the liquid level sensor and a condenser sensor dielectric properties.

2. Device for measuring liquid level, containing two-electrode capacitive liquid level sensor, which is made in the form of a coaxial capacitor and contains two cylindrical electrode, characterized in that the lower end of the inner electrode of the capacitor electrode of the liquid level sensor connected to one of electrodes of the capacitor sensor dielectric properties through the normally open contact Herc is a new relay, and the lower end of the outer electrode of the capacitor electrode of the liquid level sensor is connected with the second electrode of the capacitor sensor dielectric properties.



 

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1 dwg

FIELD: measuring engineering.

SUBSTANCE: device comprises fuel level indicator and rheostat pickup made of an analogue-digital converter with the balance input. The three-position switch is connected with the lever indicator. The device additionally has three resistive dividers, voltage stabilizer, and shunting resistor made of a 0.003-0.006-Om resistor. The rheostat level pickup is mounted inside the fuel tank vertically, and its linear horizontal size at this level is directly proportional to the area of the tank section in the horizontal plane at this level.

EFFECT: expanded functional capabilities.

1 dwg

The invention relates to the measuring of the level of the melt and can be used in the metallurgical industry, in particular in installations engaged in the welding of the metal surface layer on a cylindrical part

The invention relates to the field of measurement technology, in particular to the manufacture of devices level control of conductive liquid and bulk materials

FIELD: measuring engineering.

SUBSTANCE: device comprises fuel level indicator and rheostat pickup made of an analogue-digital converter with the balance input. The three-position switch is connected with the lever indicator. The device additionally has three resistive dividers, voltage stabilizer, and shunting resistor made of a 0.003-0.006-Om resistor. The rheostat level pickup is mounted inside the fuel tank vertically, and its linear horizontal size at this level is directly proportional to the area of the tank section in the horizontal plane at this level.

EFFECT: expanded functional capabilities.

1 dwg

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