RU78929U1 - CAPACITIVE TWO-ELECTRODE LIQUID SENSOR - Google Patents

Abstract

A capacitive two-electrode liquid level sensor containing a protective shield made in the form of a metal pipe, mainly of circular cross section and with a length not less than the difference in the measured level, and electrodes made of single-core or multi-strand insulated conductors, characterized in that the wire electrodes laid in the form of single or multi-turn loops installed in the inner cavity of the protective shield along its axis and secured with two studs mounted across the protective shield at its ends, while the distance between the studs should be not less than the range of the measured level, moreover, one of the studs is mounted on a rotary sleeve mounted on a sliding fit coaxially with a protective screen at one of its ends.

Description

The technical field to which the utility model relates.

The utility model relates to the field of electrical engineering and is intended to measure the level of dielectric and conductive liquids, and can be used in control systems and technological processes.

State of the art

Known capacitive sensor of the dielectric properties of gaseous and liquid media, containing electrodes connected to the output terminals. The electrodes are made of flexible metal single-core or stranded wires coated with insulation and randomly laid in a ball (A.S. USSR 1125530 A, 11.23.83., I.G. Minaev, O.V. Rebrova).

This sensor can serve as a signaling device for the level of liquid media at the interface “liquid-air” or “liquid-liquid”. In the second case, the liquids must be immiscible and differ in the value of permittivity.

The disadvantage of this sensor is the inability to continuously monitor the liquid level, especially with large changes.

The closest in technical essence and the achieved positive effect and adopted by the authors for the prototype is a liquid level meter containing a two-electrode capacitive sensor with external and internal electrodes that are electrically connected to the electronic circuit. According to the first embodiment, the known capacitive sensor is made in the form of a coaxial capacitor. Inner electrode

the sensor is made tubular and mounted inside the fluoroplastic probe. According to a second embodiment, the inner electrode of the coaxial capacitor is tubular and additionally provided with a protective shield. The screen is made in the form of a spiral spring made of bronze and is electrically connected to an external electrode - the housing of a coaxial capacitor (RU 2300742 C2, 2007.06.10).

The disadvantages of the sensor are: the complexity in the manufacture of the sensor for measuring large differences in liquid levels, a small specific electric capacity per unit length of the sensor; the complexity of manufacturing a universal sensor for various changes in the measured level with the ability to maintain the same electrical capacitance; the inability to adjust the sensor capacitance to eliminate technological variation in its manufacture.

Utility Model Disclosure

The technical result that can be achieved using the proposed utility model is to significantly increase the specific capacitance per unit length of the sensor and to obtain the possibility of manufacturing sensors for various drops of the measured level, while maintaining the initial sensor capacity.

The technical result is achieved by the fact that a capacitive two-electrode liquid level sensor containing a metal protective shield made in the form of a hollow pipe, mainly of circular cross-section, two studs installed across the protective shield at its ends at a distance of not less than the level difference, two coated with insulation of wire electrodes folded together and forming at least one turn, laid in the cavity of the protective screen along its axis and secured with two studs. One of the studs is mounted on a rotary sleeve coaxially mounted at one end of the shield. Each of the wire electrodes at least

one end connected to the measuring device. The other ends of the wire electrodes are in the upper part of the sensor, i.e. above the surface of the measured level, which simplifies the task of isolating them from contact with a conductive fluid. For dielectric liquids, this problem does not occur. In addition, the ends of the respective electrodes can be connected in pairs and connected to the input terminals of the measuring device. In this case, the principle of operation of the sensor does not change. Measuring the capacitance of the sensor is possible in one of many known ways. For example: (A.S. USSR 1057880 A, 11.30.83., I.G. Minaev, A.V. Ivashina).

Brief Description of the Drawings

In FIG. shows a section of the proposed capacitive two-electrode liquid level sensor installed in a tank with a level-controlled liquid and connected to a measuring device.

Utility Model Implementation

Capacitive two-electrode liquid level sensor contains a metal protective screen 1, made in the form of a hollow pipe mainly of circular cross section. The metal shield 1 is simultaneously the body of a capacitive two-electrode liquid level sensor and is mounted vertically in a tank 2 filled with liquid, the level of which is to be measured.

A stud 3 is fixed at one end of the metal shield 1 across its geometric axis. At the other end of the metal shield 1 is aligned with it in a sliding fit, as shown in FIG. the rotary sleeve 4 is installed. The rotary sleeve 4 can also be mounted on the end of the metal shield 1 with

threaded connections (not shown in FIG.). In the rotary sleeve 4 across its geometric axis mounted stud 5.

The length of the metal protective shield 1 together with the rotary sleeve 4 fixed at its end and, accordingly, the distance between the studs 3 and 5 should be not less than the range of the measured level.

Studs 3 and 5 serve as clamps for turns of wire electrodes 6 made of coated single-core or multicore wires.

To center the turns of the wire electrodes 6 relative to the geometric axis of the metal protective shield 1 on the studs 3 and 5 between the inner walls of the metal protective shield 1 and the turns of the wire electrodes 6 are installed dielectric washers 7.

The ends of single-core or stranded wires of wire electrodes 6 are connected to the measuring device 8.

A capacitive two-electrode liquid level sensor operates as follows.

A capacitive two-electrode liquid level sensor is installed in the tank 2 with the liquid, the level of which must be measured.

The wire electrodes 6 form an electric capacitor, which is a sensitive element of a capacitive two-electrode liquid level sensor.

It is known that, ceteris paribus, the capacitance of the capacitor is proportional to the relative permittivity ε of the substance filling the interelectrode space. For ε, the air is practically equal to 1, and for various liquids the values of e lie in the range from 2 to 30. Water has an even greater value ε = 80. The proposed capacitive two-electrode liquid level sensor is an electric capacitor with a multilayer, more precisely a two-layer dielectric.

One layer of interelectrode space is occupied by an insulating coating of wire electrodes, which has a constant value of e. The other is either air (at a minimum level value) or liquid (when the capacitive two-electrode liquid level sensor is completely immersed).

Therefore, when the level changes from minimum to maximum, the total capacity of the capacitive two-electrode liquid level sensor will also change.

The measuring device 8, made according to any known scheme for measuring capacitance, can be calibrated in units of level for specific liquids. According to the testimony of the measuring device 8 judge the value of the level in the tank 2.

In the manufacture of the proposed capacitive two-electrode liquid level sensor, technological variation in the initial values of the capacitance is possible. This disadvantage can be eliminated by turning the rotary sleeve 4 in one direction or another, and thereby changing the relative position of the wire electrodes 6 and the electric capacitance of the capacitive two-electrode liquid level sensor.

The proposed design of a capacitive two-electrode liquid level sensor makes it possible to approximately preserve the initial capacitance for the case of measuring both small level differences (fractions of a meter) and significant (meters). For this, it is enough, keeping the initial length of the wire electrodes 6 and installing the studs 3 and 5 at the required distance, lay the electrodes in the cavity of the metal protective shield 1. In this case, the number of turns between the studs 3 and 5 will change from the minimum (in the case of a maximum level difference) to maximum (in case of a minimum level difference). In the second case, the specific capacity of the capacitive two-electrode liquid level sensor per unit of differential, the level will also be maximum.

In cases where it is necessary to obtain the largest specific capacity of a capacitive two-electrode liquid level sensor, it is possible to increase the initial length of the wire electrodes 6. With the same arrangement of studs 3 and 5, in this case the number of turns will increase, which will lead to an increase in the capacitance of a capacitive two-electrode liquid level sensor .

Wire electrodes 6 should preferably be used in fluoroplastic insulation, as having minimal wettability and high chemical resistance.

A demonstration experiment was conducted. A metal protective shield made of a round hollow metal pipe with an inner diameter of 25 mm and a length of 0.2 m, a distance between the studs of 0.18 m, the length of each of the wire electrodes is 1 m. The electrodes are made of single-core wire with fluoroplastic insulation (cross section 0.35 mm ² , TU 160-505185-71), which amounted to two full turns laid in the cavity of the protective screen along its axis. The initial capacitance of the sensor in a water-free state was 31 pF. By turning the rotary sleeve in any direction, the capacitance gradually increased and, when rotated 360 °, reached its maximum value of 43 pF. When turning the sleeve in the opposite direction, the sensor took on the value of its original capacitance. Therefore, the proposed design of the sensor with a rotary sleeve allows you to adjust the initial capacity within 30%.

When the sensor was immersed in a tank of water, the capacitance increased, and when completely immersed, it reached its maximum value of 67 pF. In this case, the specific capacitance of the sensor per unit length of its immersion was 370 pF / m.

They placed longer wire electrodes (2 m each) in the same screen. The initial sensor capacitance was 74 pF. When fully immersed in water, the capacitance increased to 147 pF. Specific capacity at

this reached a value of 815 pF / m. As a device for measuring capacitance, the RLC Meter E7-22 was used.

The proposed capacitive two-electrode liquid level sensor in comparison with the prototype and other known technical solutions has the following advantages:

- allows you to eliminate technological variation in the initial values of the capacity;

- the design of a capacitive two-electrode liquid level sensor allows you to approximately maintain the initial capacity for the case of measuring both small level drops (fractions of a meter) and significant (meters);

- This capacitive two-electrode sensor can significantly increase the specific capacitance per unit length of the sensor.

Claims (1)

A capacitive two-electrode liquid level sensor containing a protective shield made in the form of a metal pipe, mainly of circular cross section and with a length not less than the difference in the measured level, and electrodes made of single-core or multi-strand insulated conductors, characterized in that the wire electrodes laid in the form of single or multi-turn loops installed in the inner cavity of the protective screen along its axis and secured with two studs mounted across the protective screen at its ends, while the distance between the studs should be not less than the range of the measured level, moreover, one of the studs is mounted on a rotary sleeve mounted on a sliding fit coaxially with a protective screen at one of its ends.