EP3977065A1

EP3977065A1 - Device for capacitive measurement of a height of a fluid in a tank

Info

Publication number: EP3977065A1
Application number: EP20740361.9A
Authority: EP
Inventors: Pierre Thibault; Alexandre Delorme; Alix DUCLOS
Original assignee: Kapflex
Current assignee: Kapflex
Priority date: 2019-05-27
Filing date: 2020-05-25
Publication date: 2022-04-06
Also published as: WO2020240127A1; FR3096775B1; FR3096775A1; US20220170775A1

Abstract

The invention relates to a device for capacitive measurement of a height of a fluid in a tank, comprising at least one pair of capacitors (C_i ^L, C_i ^R), extending in a longitudinal direction (Z'-Z), and comprising: - a first capacitor (C_i ^L), forming first geometric patterns (C_i ^LB, C_i ^LT) defining a first line capacitance; - a second capacitor (C_i ^R), opposite the first capacitor (C_i ^L), and forming second geometric patterns (C_i ^RB, C_i ^RT) defining a second line capacitance; the first and second geometric patterns (C_i ^LB, C_i ^LT; C_i ^RB, C_i ^RT) being arranged so that: - the first and second line capacitances, integrated in the longitudinal direction (Z'-Z), have a sum that depends on the position of the fluid in the longitudinal direction (Z'-Z); - the first and second line capacitances, integrated in the longitudinal direction (Z'-Z), have a difference which is a constant for reference positions of the fluid in the longitudinal direction (Z'-Z).

Description

DEVICE FOR CAPACITIVE MEASUREMENTS OF A FLUID HEIGHT

IN A TANK

Technical area

The invention relates to the technical field of devices for capacitive measurement of a height of fluid in a reservoir. More specifically, the invention relates to so-called compensation devices, making it possible to measure the height of the fluid without knowing precisely the dielectric permittivity of the fluid.

The invention finds its application in particular in the measurement of a height of fluid in a mobile tank belonging to a mobile transport device (e.g. automobile, aircraft, boat), or in a fixed tank used in an industrial process.

Measuring the height of the fluid in a tank is an important issue in terms of safety and economically, for example to prevent breakdowns due to a lack of fuel supply or to anticipate the need to replenish the tank for commissioning. implementation of an industrial process.

State of the art

A device known from the state of the art, in particular from document WO 99/10714 (hereinafter Dl), is a device for capacitive measurements of a height of a fluid in a reservoir, the fluid having a free surface, the device comprising a pair of capacitors extending in a longitudinal direction, intended to be parallel to the normal to the free surface of the fluid; the pair of capacitors comprising:

- a first capacitor, comprising a first pair of electrodes forming first geometric patterns defining a first linear electric capacitance varying in the longitudinal direction;

- a second capacitor, opposite the first capacitor, and comprising a second pair of electrodes forming second geometric patterns defining a second linear electric capacitance varying in the longitudinal direction.

In D1 (p.14, 1.3; p.15, 1.16), the first and second geometric patterns are arranged so that the first and second linear electrical capacities, integrated along the longitudinal direction, have a ratio which depends on the position of the fluid in the longitudinal direction and which is independent of the dielectric constant of the fluid.

Such a device of the state of the art is not entirely satisfactory insofar as it does not allow precise measurement of the height of the fluid when the reservoir is almost full or almost empty. Indeed, such configurations require an almost infinite precision on the measurement to obtain a reliable compensation of the measurement in the presence of small variations in dielectric permittivity of the fluid.

Disclosure of the invention

The invention aims to remedy all or part of the aforementioned drawbacks. To this end, the invention relates to a device for capacitive measurements of a height of a fluid in a reservoir, the fluid having a free surface, the device comprising at least one pair of capacitors extending in a longitudinal direction. , intended to be parallel to the normal to the free surface of the fluid; the or each pair of capacitors comprising:

- a second capacitor, opposite the first capacitor, and comprising a second pair of electrodes forming second geometric patterns defining a second linear electric capacitance varying in the longitudinal direction;

the device being remarkable in that the first and second geometric patterns are arranged so that:

the first and second linear electrical capacities, integrated along the longitudinal direction, have a sum which depends on the position of the fluid in the longitudinal direction;

- The first and second linear electric capacitors, integrated along the longitudinal direction, have a difference which is a constant for reference positions of the fluid along the longitudinal direction.

Thus, such a device according to the invention makes it possible, thanks to such an arrangement of the first and second geometric patterns, to improve the precision of the measurement of the height of the fluid when the reservoir is almost full or almost empty. Indeed, the combination of the information of the sum and of the difference of the first and second linear electrical capacities, integrated along the longitudinal direction, gives better measurement accuracy over the spatial extent of the reservoir (along the longitudinal direction), by choosing suitable reference positions, while maintaining a compensation device that does not require precise knowledge of the dielectric permittivity of the fluid. Moreover, the sum and the difference of the first and second linear electric capacities, integrated along the longitudinal direction, can be easily measured, for example via an electronic circuit comprising a two-channel measuring system, with a differential mode.

Definitions

- By "opposite" is meant that the first and second capacitors face each other in a direction perpendicular to the longitudinal direction.

- By "fluid reference position" is meant a position of interest (which one wishes to identify) of the fluid in the reservoir in the longitudinal direction, corresponding to a position located on a pair of capacitors in the longitudinal direction. By way of non-limiting examples, a position of interest may correspond to a fluid level indicating that the reserve has started, a fluid level indicating that the reservoir is full or half full, etc. A reference position of the fluid can be predetermined geometrically, by arranging the first and second geometric patterns of the pair of capacitors so that the first and second linear electric capacitances, integrated in the longitudinal direction, have a difference which is a constant (preferably zero) for a predetermined position in the longitudinal direction. Said predetermined position defines the reference position.

The term “constant” is understood to mean that the difference between the first and second linear electrical capacities, integrated in the longitudinal direction, is independent of the position of the fluid in the longitudinal direction. In other words, the difference between the first and second linear electrical capacities, integrated along the longitudinal direction, does not vary for the reference positions, whatever the position of the fluid in the reservoir, whether the fluid is present or absent. of the tank. The first and second geometric patterns are advantageously arranged so that the first and second linear electric capacitors, integrated along the longitudinal direction, have a difference which is zero for the reference positions of the fluid, whatever the position of the fluid in the reservoir. , whether the fluid is present or absent from the reservoir. Thus, it is easier to design the first and second geometric patterns independently of the nature of the fluid.

The device according to the invention may include one or more of the following characteristics. According to one characteristic of the invention, the or each pair of capacitors comprises a median axis extending in a direction perpendicular to the longitudinal direction.

According to a characteristic of the invention, the first geometric patterns are arranged on either side of the median axis so as to form an axial symmetry along the median axis; and the second geometric patterns are arranged on either side of the median axis so as to form an axial symmetry along the median axis.

Thus, an advantage obtained is that the first and second linear electrical capacities, integrated along the longitudinal direction, have a difference which is zero for:

- a first reference position of the fluid corresponding to a median position in the longitudinal direction (ie position on the median axis if the fluid is in contact with the device or position parallel to the median axis if the fluid is at a distance from the device) ,

a second reference position of the fluid corresponding to an upper distal position in the longitudinal direction. The term “distal” is understood to mean the longitudinal position furthest from the center of the pair of capacitors. In the presence of a single pair of capacitors, the upper distal position corresponds to a fully filled reservoir.

According to a characteristic of the invention, the first geometric patterns and the second geometric patterns are arranged above the median axis so as to form a central symmetry; the first geometric patterns and the second geometric patterns are arranged below the median axis so as to form a central symmetry.

Thus, an advantage provided is that the first and second linear electrical capacities, integrated along the longitudinal direction, have a sum which is proportional to the position of the fluid in the longitudinal direction on either side of the median axis.

According to one characteristic of the invention, the first geometric patterns and the second geometric patterns are arranged above the median axis so that the first and second linear electric capacitors, integrated above the median axis along the direction longitudinal, have a difference which is a constant preferably zero; the first geometric patterns and the second geometric patterns are arranged below the median axis so that the first and second linear electric capacitors, integrated below the median axis in the longitudinal direction, have a difference which is a constant of zero preference. Thus, an advantage obtained is that the first and second linear electrical capacities, integrated along the longitudinal direction, have a difference which is constant (possibly zero) for:

According to one characteristic of the invention, the first and second geometric patterns are arranged so that the first and second linear electric capacitors, integrated along the longitudinal direction, have a difference which changes sign on either side of the axis. median.

Thus, an advantage obtained is to overcome ambiguities about the longitudinal position of the fluid relative to the median axis.

According to one characteristic of the invention, the first and second geometric patterns are arranged so that the first and second linear electric capacitors, integrated in the longitudinal direction, have a zero difference for at least two reference positions of the fluid in the longitudinal direction. .

According to a characteristic of the invention, the first and second geometric patterns are arranged so that the first and second linear electrical capacitors, integrated along the longitudinal direction, have a sum proportional to the position of the fluid along the longitudinal direction.

By "proportional" is meant that there is a linear relationship between the sum of the first and second linear electrical capacities, integrated along the longitudinal direction, and the position of the fluid along the longitudinal direction.

Thus, an advantage obtained is that it simplifies obtaining the measurement of the height of the fluid. According to one characteristic of the invention, the first and second capacitors are capacitors with interdigitated electrodes.

Thus, an advantage obtained is to be able to determine the dielectric permittivity of the fluid.

According to one characteristic of the invention, the device comprises a set of pairs of capacitors, each pair of capacitors having a length in the longitudinal direction; the set of pairs of capacitors being distributed along the longitudinal direction so that their length follows a geometric series.

Thus, an advantage obtained is to accumulate:

- continuous measurements for each given pair of capacitors;

- discrete measurements between each pair of capacitors.

The fact of distributing the set of pairs of capacitors along the longitudinal direction so that their length follows a geometric series makes it possible to spatially modulate the precision of the measurement of the height of the fluid in the longitudinal direction, at equal electrical capacity for each pair of capacitors. The pairs of capacitors with the shortest lengths locally have better accuracy in measuring the height of the fluid than the pairs of capacitors with the longer lengths. This type of configuration can be chosen, for example, if the targeted application seeks better precision when the tank is almost empty in order to predict the moment of replenishment.

According to one characteristic of the invention, the device comprises a set of pairs of capacitors distributed in the longitudinal direction periodically.

By "periodically" is meant that the first and second geometric patterns are repeated identically at a regular spatial interval in the longitudinal direction.

Thus, an advantage obtained is to accumulate:

- continuous measurements for each given pair of capacitors;

- discrete measurements between each pair of capacitors.

In addition, such a periodic distribution makes it possible to facilitate the industrial production of the device, and to be able to adapt easily to different sizes of tank.

According to one characteristic of the invention, the device comprises a set of pairs of capacitors distributed in the longitudinal direction; the first and second geometric patterns of two adjacent pairs of capacitors are arranged so that: the sum of the first and second linear electrical capacities, integrated along the longitudinal direction, is a monotonic function along the longitudinal direction;

- The difference of the first and second linear electrical capacities, integrated along the longitudinal direction, is constant in the longitudinal direction, preferably zero, for the reference positions of the fluid in the longitudinal direction.

Thus, an advantage obtained is to accumulate:

- continuous measurements for each given pair of capacitors;

- discrete measurements between each pair of capacitors.

In addition, it is made possible to spatially modulate the measurement precision of the height of the fluid in the longitudinal direction. The sensitivity of the pair of capacitors will be greater than the sum of the first and second linear electrical capacities, integrated in the longitudinal direction, is high. This type of configuration can be chosen, for example, if the targeted application seeks better precision when the tank is almost empty in order to predict the moment of replenishment.

According to one characteristic of the invention, the device comprises a protective layer made of a dielectric material, preferably a plastic material, and arranged to cover the or each pair of capacitors.

Thus, an advantage obtained is to be able in particular to protect the electronic part of the device from the fluid.

According to one characteristic of the invention, the device comprises:

- a printed circuit board,

- Electrically conductive tracks, arranged on the printed circuit board, and forming the or each pair of capacitors.

Thus, an advantage obtained is to easily produce the device on an industrial scale.

Another subject of the invention is a reservoir, comprising at least one device according to the invention, the or each pair of capacitors being arranged so as to generate an electric field inside the reservoir.

According to one characteristic of the invention, the reservoir contains a fluid, and comprises a side wall made of a dielectric material; the device is arranged inside the side wall, away from the fluid. Thus, an advantage obtained is to do away with direct contact between the fluid and the device liable to cause damage. The device according to the invention remains functional and reliable insofar as it does not require precise knowledge of the dielectric permittivity of the medium comprising the side wall and the fluid. In addition, the device is mechanically protected from the outside environment thanks to the side wall.

According to one characteristic of the invention, the reservoir comprises a heating device, arranged in the reservoir for heating the fluid, the heating device comprising a metal part forming a mass; and the or each pair of capacitors is electrically connected to ground.

Thus, an advantage obtained is to simplify the earthing of the device.

According to one characteristic of the invention, the device is arranged at a distance from the fluid of between 0.05 mm and 25 mm, preferably between 4 mm and 6 mm.

Thus, an advantage obtained is to maintain satisfactory precision in the measurement of the height of the fluid.

Brief description of the drawings

Other features and advantages will become apparent from the detailed description of various embodiments of the invention, the disclosure being accompanied by examples and references to the accompanying drawings.

Figure 1 is a partial schematic view, in exploded perspective, of a device according to the invention, illustrating a first embodiment of the device in a wall of a tank.

Figure 2 is a partial schematic view, in exploded perspective, of a device according to the invention, illustrating a second embodiment of the device in a wall of a tank.

Figure 3 is a schematic perspective view of a tank equipped with a device according to the invention.

Figure 4 is a schematic longitudinal sectional view of a first embodiment of a set of pairs of capacitors of a device according to the invention.

Figure 5 is a schematic longitudinal sectional view of a second embodiment of a set of pairs of capacitors of a device according to the invention.

Figure 6 is a schematic longitudinal sectional view, on an enlarged scale, of a pair of capacitors according to the first embodiment illustrated in Figure 4. Figure 7 is a schematic view in longitudinal section, on an enlarged scale, of a pair of capacitors according to the second embodiment illustrated in Figure 5.

Figure 8 is a schematic view, in longitudinal section, of a set of pairs of capacitors distributed in the longitudinal direction periodically.

Figure 9 is a schematic view, in longitudinal section, of a set of pairs of capacitors distributed in the longitudinal direction so that their length follows a geometric series.

Figure 10 is a schematic view, in longitudinal section, of a set of pairs of capacitors of which the sum of the first and second linear electrical capacitances, integrated in the longitudinal direction, is a monotonic function in the longitudinal direction; the set of pairs of capacitors being arranged on either side of a separator.

Figure 11 is a view similar to Figure 10, in the absence of a separator.

Figure 12 is a partial schematic sectional view of a wall of a reservoir, illustrating a first embodiment of the device according to the invention.

Figure 13 is a partial schematic sectional view of a wall of a reservoir, illustrating a second embodiment of the device according to the invention.

Figure 14 is a graph representing on the abscissa the number of periods of a set of pairs of capacitors, and on the ordinate the electrical capacity (in pF) for the left capacitors (C ^L ) and for the right capacitors (C ^R ) .

Figure 15 is a graph showing on the x-axis the number of periods of a set of pairs of capacitors, and on the y-axis the difference in electrical capacity (in pF) between the left capacitors and the right capacitors.

Detailed description of the embodiments

The elements which are identical or perform the same function will bear the same references for the various embodiments, for the sake of simplification.

An object of the invention is a device 1 for capacitive measurements of a height of a fluid in a reservoir 2, the fluid having a free surface, the device 1 comprising at least one pair of capacitors C _i ^L , C _i ^R extending in a longitudinal direction Z'- Z, intended to be parallel to the normal to the free surface of the fluid; the or each pair of capacitors C _i ^L , C _i ^R comprising: - a first capacitor C _i ^L , (i corresponding to the i-th pair) comprising a first pair of electrodes forming first geometric patterns C _i ^LB C _i ^LT defining a first linear electric capacitance varying in the longitudinal direction Z'-Z ;

- a second capacitor C _i ^R , (i corresponding to the i-th pair), opposite the first capacitor C _i ^L , and comprising a second pair of electrodes forming second geometric patterns C _i ^RB , C _i ^RT defining a second capacitor linear electric varying in the longitudinal direction Z'-Z.

The first and second geometric patterns C _i ^LB , C _i ^LT ; C _i ^RB , C _i ^RT are arranged so that:

- the first and second linear electrical capacities, integrated along the longitudinal direction Z'-Z, have a sum (denoted Si, i corresponding to the i-th pair) which depends on the position of the fluid in the longitudinal direction Z'-Z;

- the first and second linear electric capacitors, integrated along the longitudinal direction Z'-Z, have a difference (denoted D ;, i corresponding to the i-th couple) which is a constant (denoted K) for reference positions of the fluid along the longitudinal direction Z'-Z.

If one notes z the position of the fluid according to the longitudinal direction Z'-Z and z _ref the reference positions, one has:

S _i ( _Z ) = C _i ^LB (z) + C _i ^LT (z) + C _i ^RB (z) + C _i ^RT (z)

D ( _Z ) = C _i ^LB (z) + C _i ^LT (z) + C _i ^RB (z) + C _i ^RT (z)

D _i (Z _ref ) = K

Couple (s) of capacitors

The or each pair of capacitors C _i ^L , C _i ^R advantageously comprises a median axis X'-X extending in a direction perpendicular to the longitudinal direction Z'-Z.

The first and second capacitors C _i ^L , C _i ^R are advantageously capacitors with interdigitated electrodes.

The device 1 advantageously comprises a set of pairs of capacitors G ^L , C _i ^R , each pair of capacitors C _i ^L , C _i ^R having a length (denoted L) in the longitudinal direction Z'-Z.

According to a first embodiment (illustrated in FIG. 9), the set of pairs of capacitors C _i ^L , C _i ^R is distributed along the longitudinal direction Z'-Z so that their length L; follows a geometric series:

L _i a ^i-1 * d; a>1; i Î [1; NOT] where a is the reason for the geometric sequence, d is the length of the first pair of capacitors C ₁ ^L , C ₁ ^R , N is the number of pairs of capacitors C _i ^L , C _i ^R , i is the i-th pair of capacitors C _i ^L , C _i ^R. The pairs of capacitors with the shortest lengths (lower levels) locally have better precision in measuring the height of the fluid than the pairs of capacitors with the longer lengths (upper levels). This spatial modulation of the measurement accuracy is useful for both:

- accurately estimate the level remaining in a tank 2 and,

- predict with good precision the date needed for a replenishment, under the assumption of constant or predictable fluid consumption over time.

This has an economic advantage thanks to better management of replenishment, since, by extrapolation of the quantity (h _{i + 1 -} h _i ) / (t _{i + 1-} t _i ) or h _{i + 1} (respectively h _i ), are the remaining heights of fluid at times t _{i + 1} (respectively t _i ), it is possible - with less uncertainty than a method based on human experience alone - to know the date of exhaustion of the fluid in the reservoir 2. From a mathematical point of view, such measurement points allow a person skilled in the art to qualify models which he will have been able to develop, and to update his forecasts.

According to a second embodiment (in particular illustrated in FIGS. 4, 5 and 8), the set of pairs of capacitors C _i ^L , C _i ^R is distributed in the longitudinal direction Z'-Z periodically. The length L; of each pair of capacitors C _i ^L , C _i ^R is therefore constant in the longitudinal direction Z'-Z.

L _i = 1; i Î [1; NOT]

where l is the spatial period of the pairs of capacitors C _i ^L , C _i ^R.

The device 1 advantageously comprises:

- a printed circuit board 3,

- Electrically conductive tracks, arranged on the printed circuit board, and forming the or each pair of capacitors C _i ^L , C _i ^R.

The printed circuit board 3 can be made from a material chosen from polyimide, FR-4 epoxy resin, cellulose paper. The electrically conductive tracks can be made from a material chosen from Cu, Al, graphite, graphene. The term “electrically conductive” is understood to mean that the tracks are made of a material having an electrical conductivity at 300 K greater than or equal to 1 S. cm ⁴ .

The device 1 advantageously comprises a protective layer 4 made of a dielectric material, preferably a plastic material, and arranged to cover the or each pair of capacitors C _i ^L , C _i ^R. By "dielectric" is meant that the material has an electrical conductivity at 300 K of less than or equal to 10 ⁶ S. cm ^-1 By way of nonlimiting examples, the dielectric material in which the protective layer 4 is made can be an epoxy resin or a silicone paste.

The device 1 advantageously comprises a GND ground plane. The term “ground plane” is understood to mean any means of obtaining a reference potential for the pair or pairs of capacitors C _i ^L , C _i ^R.

The device 1 advantageously comprises control electronics 10, configured to control the or each pair of capacitors C _i ^L , C _i ^R. The control electronics 10 are electrically connected to the GND ground plane. The control electronics 10 advantageously comprise a microcontroller. The control electronics 10 advantageously comprises an electronic circuit configured to measure:

By way of non-limiting example, such measurements can be performed using the AD7746 component from the manufacturer "Analog Devices", which is a Sigma-Delta capacitive digital converter with a differential mode.

The device 1 advantageously comprises a connector 11, arranged to communicate the measurements carried out by the device 1. The connector 11 may be a CAN (“Controller Area Network”) data bus. According to one alternative, the control electronics 10 include a wireless communication module, preferably chosen from Bluetooth, low-energy Bluetooth, RFID, Wifi, LoRa, SigFox technologies.

First and second geometric patterns

By way of nonlimiting examples, the electrodes of each pair of capacitors C _i ^L , C _i ^R may have a longitudinal section of rectangular shape or of chevron shape.

The first geometric patterns C _i ^LB , C _i ^LT are advantageously arranged on either side of the median axis X'-X so as to form an axial symmetry along the median axis X'-X. The second geometric patterns C _i ^RB , C _i ^RT are advantageously arranged on either side of the median axis X'-X so as to form an axial symmetry along the median axis X'- X. The first geometric patterns C _i ^LT and the second geometric patterns C _i ^RT are advantageously arranged above the median axis X'-X so as to form a central symmetry. The first geometric patterns C _i ^LB and the second geometric patterns C _i ^RB are advantageously arranged below the median axis X'-X so as to form a central symmetry.

It follows that :

The first geometric patterns C _i ^LT and the second geometric patterns C _i ^RT are advantageously arranged above the median axis X'-X so that the first and second linear electric capacitors, integrated above the median axis X'-X along the longitudinal direction Z'-Z, have a difference which is a constant preferably zero. The first geometric patterns C _i ^LB and the second geometric patterns C _i ^RB are advantageously arranged below the median axis X'-X so that the first and second linear electric capacitors, integrated below the median axis X'-X along the longitudinal direction Z'-Z, have a difference which is a constant preferably zero.

The first and second geometric patterns C _i ^LB , C _i ^LT ; C _i ^RB , C _i ^RT are advantageously arranged so that the first and second linear electrical capacitors, integrated along the longitudinal direction Z'-Z, have a difference which changes sign on either side of the median axis X '-X. In the case where the set of pairs of capacitors C _i ^L , C _i ^R is distributed along the longitudinal direction Z'-Z periodically with a spatial period l, the measurement uncertainty on the height of the fluid is reduced to l / 2. It is possible to carry out an inventory of the quantity of fluid according to an accuracy of the total height of the

device 1, where N is the number of pairs of capacitors C _i ^L , C _i ^R.

The first and second geometric patterns C _i ^LB , C _i ^LT ; C _i ^RB , C _i ^RT are advantageously arranged so that the first and second linear electrical capacitors, integrated along the longitudinal direction Z'-Z, have a zero difference for at least two reference positions of the fluid along the longitudinal direction Z ' -Z.

The first and second geometric patterns C _i ^LB , C _i ^LT ; C _i ^RB , C _i ^RT are advantageously arranged so that the first and second linear electrical capacitors, integrated along the longitudinal direction Z'-Z, have a sum proportional to the position of the fluid along the longitudinal direction Z'-Z.

According to one embodiment (illustrated in Figures 10 and 11), the device 1 comprises a set of pairs of capacitors C _i ^L , C _i ^R distributed along the longitudinal direction Z'-Z; the first and second geometric patterns C _i ^LB , C _i ^LT ; C _i ^RB , C _i ^RT of two adjacent pairs of capacitors C _i ^L , C _i ^R are advantageously arranged so that:

- the sum of the first and second linear electrical capacities, integrated along the longitudinal direction Z'-Z, is a monotonic function along the longitudinal direction Z'-

Z;

- The difference of the first and second linear electrical capacities, integrated along the longitudinal direction Z'-Z, is constant along the longitudinal direction Z'-Z, preferably zero, for the reference positions of the fluid along the longitudinal direction Z'- Z.

Thus, it is possible to carry out a coding of the information of a sub-sector (ie corresponding to the spatial extent of a pair of capacitors C _i ^L , C _i ^R ) with respect to an adjacent sub-sector, differentiated. The monotonic function can be a linear function so that a first sub-sector can contain an electrical capacity, denoted C ₀ , for a given spatial extension, then the second (higher) sub-sector can contain a higher electrical capacity (equal at b C ₀ , b> 1) for the same given spatial extension.

Tank

One object of the invention is a reservoir 2 comprising at least one device 1 according to the invention, the or each pair of capacitors C _i ^L , C _i ^R being arranged so as to generate an electric field inside the reservoir 2.

The reservoir 2 can contain a fluid. The reservoir 2 may include a side wall 20 made of a dielectric material. The dielectric material is preferably a plastic material or a composite material. The plastic material can be polyethylene. The composite material can be a prepreg material comprising a matrix (or resin) impregnating a reinforcement. The resin can be a thermosetting resin or a thermoplastic resin.

The device 1 is advantageously arranged inside the side wall 20, away from the fluid. The side wall 20 separates the fluid from an external medium. Where appropriate, the side wall 20 is hollow and comprises two parts P1, P2 forming a closed cavity. Such a hollow side wall 20 makes it possible to protect the device 1 from the external environment and from the fluid. The device 1 advantageously comprises an energy recovery system, arranged inside the closed cavity, and configured to recover energy from an external source located in the external environment. The energy recovery system is electrically connected to the microcontroller of the control electronics 10. The energy is advantageously chosen from electromagnetic energy, mechanical energy and thermal energy. By way of nonlimiting examples, the external source can be a generator induction, a thermoelectric generator, a piezoelectric system. The external source may emit radio waves. Where appropriate, the external source is advantageously selected from:

- a smartphone equipped with a near-field communication module (NFC for "Near Field Communication" in English),

- an antenna emitting a low energy Bluetooth type signal (BLE for “Bluetooth Low Energy” in English), or a Wifi signal at 2.4 GHz or 5 GHz.

The device 1 advantageously comprises storage means, arranged inside the closed cavity to store the energy recovered by the energy recovery system 4. By way of nonlimiting examples, the storage means may include a battery or a supercapacitor (e.g. carbon-based).

According to an alternative illustrated in Figure 12, the device 1 can be arranged outside the side wall 20. The attachment of the device 1 to the outside of the side wall can be achieved by gluing or by thermoforming.

The reservoir 2 may include a heating device 5, arranged in the reservoir 2 to heat the fluid. The heating device 5 may comprise a metallic part (for example made of stainless steel) forming a mass. The or each torque condensateursC _i ^L, _i C ^R is preferably electrically grounded. The setting to a common potential of the fluid and the control electronics 10 makes it possible to obtain measurements of the height of the fluid through a thick side wall 20, by measuring the electrical capacities by a three-wire method.

The capacitive measurement device 1 is advantageously arranged at a distance from the fluid of between 0.05 mm and 25 mm, preferably between 4 mm and 6 mm.

It is possible, from the measurements of S and D by the electronic circuit of the control electronics 10, to calculate an effective dielectric constant including the side wall 20 and the fluid facing the corresponding sub-sector (ie the range of the pair of capacitors C _i ^L , C _i ^R facing the fluid), so that each sub-sector has its own calibration law. Thus, it is possible to:

- correct the thickness variations of the wall 20 of the tank 2 for a given fluid,

- to adapt the sensitivity of each sub-sector to variations in the properties of the fluid.

Such self-calibration will in particular be made possible insofar as the level of the fluid can vary, and that the various values associated with fixed points can be deduced and recorded. Such values constitute calibration points for dynamically calibrating the device 1, for example using a Levenberg-Marcquardt type algorithm in order to model according to a simple law the relationship between the height of the fluid and the measured electrical capacity. An artificial intelligence algorithm, based on a learning system, could usefully complement this first approach.

Manufacturing process

When the dielectric material of the side wall 20 of the tank 2 is a thermoplastic type plastic material, the side wall 20 can be formed by an extrusion blow molding process. The device 1 is added to the mold (insert) before the blowing phase. The addition of inserts to the blow mold can be done by robots at a rate that does not slow down the molding cycle of tank 2.

According to an alternative, the side wall 20 of the reservoir 2 can be formed by an injection and blow molding process. It is possible to use a stake (the outer part P2 of the wall) to hold the device 1 in the blow mold.

According to another alternative, the side wall 20 of the tank 2 can be formed by a rotational molding process where the device 1 is held in the mold using a support such as a canvas or a grid, the support being of preferably metallic.

Results

An example of a measurement result is illustrated in FIGS. 14 and 15. The device 1 is integrated inside a side wall 20 of the tank 2, with a thickness of the order of 5 mm. The fluid is Adblue® liquid. It can be seen that the electrical capacities of the first and second capacitors (left capacitance C ^L and right capacitance C ^R ) decrease with the height of the liquid, according to a total decrease of the order of 8 pF of dynamics over 29 pF, which is largely sufficient for an accurate measurement, while the magnitude of the difference | C ^L -C ^R | maximum is of the order of 0.45 pF, and may be adapted by the geometry of the electrodes. It can be seen in FIG. 15 that is indeed zero for the half-periods. The zeros of

D being multiple, it is advantageous to know at least approximately the dielectric properties of the fluid. As an indication, if the height of the device 1 consists of N sub-periods of the same length, the device 1 will have around 2N + 1 zeros, and the dielectric properties will be advantageously known to typically better than

to remove any indeterminacy on each discrete level.

The invention is not limited to the embodiments disclosed. Those skilled in the art are able to consider their technically operative combinations, and to substitute equivalents for them.

Claims

1. Device (1) for capacitive measurements of a height of a fluid in a reservoir (2), the fluid having a free surface, the device (1) comprising at least one pair of capacitors (C _i ^L , C _i ^R ) extending in a longitudinal direction (Z'-Z), intended to be parallel to the normal to the free surface of the fluid; the or each pair of capacitors (C _i ^L , G ^R ) comprising:

- a first capacitor (C _i ^L ), comprising a first pair of electrodes forming first geometric patterns (C _i ^LB , C _i ^LT ) defining a first linear electric capacitance varying in the longitudinal direction (Z'-Z);

- a second capacitor (C _i ^R ), opposite to the first capacitor (C _i ^L ), and comprising a second pair of electrodes forming second geometric patterns (C _i ^RB , C _i ^RT ) defining a second linear electric capacitance varying according to the longitudinal direction (Z'-Z); the device being characterized in that the first and second geometric patterns (C _i ^LB , C _i ^LT ; C _i ^RB , C _i ^RT ) are arranged so that:

- the first and second linear electrical capacities, integrated along the longitudinal direction (Z'-Z), have a sum which depends on the position of the fluid in the longitudinal direction (Z'-Z);

- the first and second linear electrical capacities, integrated along the longitudinal direction (Z'-Z), have a difference which is a constant for reference positions of the fluid along the longitudinal direction (Z'-Z).

2. Device (1) according to claim 1, wherein the or each pair of capacitors (C _i ^L , C _i ^R ) comprises a median axis (X'-X) extending in a direction perpendicular to the longitudinal direction ( Z'-Z).

3. Device (1) according to claim 2, wherein the first geometric patterns (C _i ^LB , C _i ^LT ) are arranged on either side of the median axis (X'-X) so as to form a axial symmetry along the median axis (X'-X); and the second geometric patterns (C _i ^RB , C _i ^RT ) are arranged on either side of the median axis (X'-X) so as to form an axial symmetry along the median axis (X'-X ).

4. Device (1) according to claim 2 or 3, wherein the first geometric patterns (C _i ^LT ) and the second geometric patterns (C _i ^RT ) are arranged above the median axis (X'-X) so as to form a central symmetry; the first geometric patterns (C _i ^LB ) and the second geometric patterns (C _i ^RB ) are arranged below the median axis (X'-X) so as to form a central symmetry.

5. Device (1) according to one of claims 2 to 4, wherein the first geometric patterns (C _i ^LT ) and the second geometric patterns (C _i ^RT ) are arranged above the median axis (X ' -X) so that the first and second linear electric capacities, integrated above the median axis (X'-X) along the longitudinal direction (Z'-Z), have a difference which is a constant preferably zero ; the first geometric patterns (C _i ^LB ) and the second geometric patterns (C _i ^RB ) are arranged below the median axis (X'-X) so that the first and second linear electric capacitors, integrated below of the median axis (X'-X) in the longitudinal direction, (Z'-Z) have a difference which is a constant preferably zero.

6. Device (1) according to one of claims 2 to 5, wherein the first and second geometric patterns (C _i ^LB , C _i ^LT ; C _i ^RB , C _i ^RT ) are arranged so that the first and second Linear electrical capacities, integrated along the longitudinal direction (Z'-Z), have a difference which changes sign on either side of the median axis (X'-X).

7. Device (1) according to one of claims 1 to 6, wherein the first and second geometric patterns (C _i ^LB , C _i ^LT ; C _i ^RB , C _i ^RT ) are arranged so that the first and second Linear electrical capacities, integrated along the longitudinal direction (Z'-Z), have a zero difference for at least two reference positions of the fluid along the longitudinal direction (Z'-Z).

8. Device (1) according to one of claims 1 to 7, wherein the first and second geometric patterns (C _i ^LB , C _i ^LT ; C _i ^RB , C _i ^RT ) are arranged so that the first and second Linear electrical capacities, integrated along the longitudinal direction (Z'-Z), have a sum proportional to the position of the fluid along the longitudinal direction (Z'-Z).

9. Device (1) according to one of claims 1 to 8, wherein the first and second capacitors (C _i ^L , C _i ^R ) are capacitors with interdigitated electrodes.

10. Device (1) according to one of claims 1 to 9, comprising a set of pairs of capacitors (C _i ^L , C _i ^R ), each pair of capacitors (C _i ^L , C _i ^R ) having a length ( Li) in the longitudinal direction (Z'-Z); the set of couples of capacitors (C _i ^L , C _i ^R ) being distributed along the longitudinal direction (Z'-Z) so that their length (D) follows a geometric series.

11. Device (1) according to one of claims 1 to 9, comprising a set of pairs of capacitors (C _i ^L , C _i ^R ) distributed in the longitudinal direction (Z'-Z) periodically.

12. Device (1) according to one of claims 1 to 9, comprising a set of pairs of capacitors (C _i ^L , C _i ^R ) distributed in the longitudinal direction (Z'-Z); the first and second geometric patterns (C _i ^LB , C _i ^LT ; C _i ^RB , C _i ^RT ) of two adjacent pairs of capacitors (C _i ^L , C _i ^R ) are arranged so that:

- the sum of the first and second linear electrical capacities, integrated along the longitudinal direction (Z'-Z), is a monotonic function along the longitudinal direction (Z'-

Z);

- the difference of the first and second linear electrical capacities, integrated along the longitudinal direction (Z'-Z), is constant along the longitudinal direction (Z'-Z), preferably zero, for the reference positions of the fluid along the direction longitudinal (Z'-Z).

13. Device (1) according to one of claims 1 to 12, comprising a protective layer (4) made of a dielectric material, preferably a plastic material, and arranged to cover the or each pair of capacitors (C _i ^L , C _i ^R ).

14. Device (1) according to one of claims 1 to 13, comprising:

- a printed circuit board (3),

- Electrically conductive tracks, arranged on the printed circuit board (3), and forming the or each pair of capacitors (C _i ^L , C _i ^R ).

15. Reservoir (2), comprising at least one device (1) according to one of claims 1 to 14, the or each pair of capacitors (C _i ^L , C _i ^R ) being arranged so as to generate an electric field at inside the tank (2).

16. Tank (2) according to claim 15, containing a fluid, and comprising a side wall (20) made of a dielectric material; the device (1) is arranged inside the side wall (20), away from the fluid.

17. Tank (2) according to claim 16, comprising a heating device (5), arranged in the tank (2) for heating the fluid, the heating device (5) comprising a metal part forming a mass; and the or each pair of capacitors (C _i ^L , C _i ^R ) is electrically connected to ground.

18. Reservoir (2) according to claim 16 or 17, in which the device (1) is arranged at a distance from the fluid of between 0.05 mm and 25 mm, preferably between 4 mm and 6 mm.