RO115913B1 - Capacitive level sensor - Google Patents

Abstract

According to the invention, the capacitive level sensor for measuring any kind of liquid, irrespective of nature or degree of soiling is made up of two metallic armatures (1, 2), where one armature (1) is insulated on both sides while the other armature (2) may be uninsulated electrically. Both armatures ( 1 and 2) are located on the walls of a container (3) having two compartments (a, b) separated by an electro-insulating partition wall (4). The second compartment (b) is sealed, while the first compartment (a) can be flooded since it is provided with holes (c) at the lower side, said holes allowing the access of the liquid to be measured. As a result of the use of suitable materials and optimum dimensions, the electrical capacity of the claimed sensor varies linearly with the level and does not depend on the relative electrical permitivity of the measured liquid and on temperatures.

Description

RO 115913 B

The invention relates to a capacitive level sensor, with general use intended for measuring the level of various liquids in containers (tanks, boilers, cisterns, etc.) for the purpose of measuring the level of a liquid in a tank, a method based on the measurement of an electrical capacity is also known with the value dependent on the liquid level [1 ]. The capacitance is realized between two probe electrodes. These sensors generally output a quantity dependent on the nature of the liquid. There are situations where the electrical permittivity of the liquid varies over time, which would lead to measurement errors. The described method has the disadvantage that, at the variation of the electrical permittivity of the liquid to be measured or at variations in its temperature, it leads to measurement errors. In addition, the device made on the basis of this method can only be made for a single type of liquid.

for the same purpose, a constructive variant of the sensor with horizontally positioned plane-parallel armatures is also known, whose output signal does not depend on the relative electrical permittivity of the fluid to be measured [2], but this constructive variant presents the disadvantage that it can only be used in case of very low liquid levels.

The capacitive level sensor, according to the invention, eliminates the disadvantages of the previously presented solutions, in that it is made of two metal reinforcements, between which two compartments are arranged side by side, one in which the liquid penetrates, the level of which is determined, and another, made in the sealed version , so non-floodable.

By applying the invention, the following advantages are obtained:

- the output value of the sensor does not depend on the degree of dirtiness of the liquid, i.e. on its nature,

- the output value of the sensor does not depend on the temperature of the fluid,

- with the help of the sensor, the liquid level can be measured in a wide range of values,

- the sensor has a linear characteristic,

- can be made in fixed or portable version.

Two examples of the invention are given next, in connection with fig. 1 ...3, which represent:

- fig. 1, view in vertical section of the sensor, in the case of the rectangular version;

- fig.2, top view of the sensor, in the case of the rectangular version;

- fig.3, vertical section view of the sensor in the case of the cylindrical version.

The sensor shown in fig. 1 and 2 is made of two metal armatures 1 and 2, where armature 1 is insulated on both sides, while armature 2 can be electrically non-insulated. The two reinforcements are placed on the walls of a container 3 which presents two compartments a and b, made by means of an electrically insulating partition wall 4. Compartment b is made in a sealed version, while compartment a is floodable due to the fact that at the bottom it is equipped with holes c that allow the penetration of the liquid whose level is measured.

The sensor can also be made in a cylindrical version (fig.3), where armature 1 has the shape of a wire mounted on the vertical axis of the cylinder, and armature 2 is cylindrical and mounted concentrically on the outer wall of the container 3. Partition wall electrical insulator 4 also has a cylindrical shape, being mounted in a concentric position with the other elements presented previously. Liquid penetration

Claims (2)

RO 115913 Β to be measured in compartment a is also achieved by means of holes c made on the bottom of this compartment. The sensor according to the invention works as follows: in compartment a the liquid rises to the level of the reservoir liquid. In this case, the sensor can be modeled by two multilayer capacitances grouped in parallel, one corresponding to the portion of 50 above the liquid and one corresponding to the portion with the fluid. The relationship that gives the sensor capacity is: C = C _r ϋ Where it was noted with: C _o - the capacity of the empty sensor, Λ - the filling coefficient (ratio between the height of the liquid at a given moment and the total height of the sensor), e _ri - the relative permittivity of the insulating material from which container 3 and wall 4 are made. - the relative electrical permittivity of the liquid to be measured, d^/2 - the thickness of the dividing wall 4, δ - the length of compartment a, d- the length of compartment b. It is observed that for ε„ of values as low as possible and for the ratio d/δ as high as possible, the terms containing ε _Η become insignificant within the sums of which they are a part, so they are neglected. From the last relationship presented, the role of compartment b can be deduced, which makes the term 1-1 /ε _Η as small as possible and the term d/δ as large as possible. The described sensor can be used in the case of any type of liquid, with various degrees of dirtiness, special results in terms of errors being obtained in the case of liquids with high electrical permittivity. Claim Capacitive level sensor, mainly composed of two metal armatures (1 and 2], characterized by the fact that, between the two reinforcements (1 and 2), a 80 container (3) made of electro-insulating material is placed, equipped with two compartments (a and b), made by means of an electro-insulating partition wall (4) , and where a compartment [a), placed near an armature (1), is provided at the bottom with some holes (c) that allow the penetration of the fluid whose level is measured, while the other compartment (b), placed in the vicinity of the other armature 85 (2], it is made in the sealed version, thus obtaining a capacitor assembly in which the capacity depends only on the level of the liquid and in which the influences related to the permittivity and temperature of the mentioned liquid are eliminated. The president of the examination committee: Eng. Cojocarii Lavinia Examiner: phys. Hi Robert