Method and system for determining the level of a liquid in a container

Abstract

Method and system for determining the level of a liquid in a container. One aspect of the invention relates to a method for determining the level of a liquid (5) in a container (1), based on the use of four ultrasonic sensors (11) placed on the wall (2) of the container (1), enabling the generation of guided waves in the wall (2) of the container (11). Figure to be published with the abbreviation: Figure 1

Description

Title of the invention: Method and system for determining the level of a liquid in a container. TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of non-destructive testing to assess the presence of a liquid in a container, in particular for fuel in an aircraft tank.

[0002] The present invention relates to a method and a system for determining the level of liquid in a container by means of ultrasonic sensors. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] In aeronautics, knowing the fuel level in a tank is essential for estimating the fuel mass on board. This on-board mass is essential safety information for the pilot, particularly for determining the aircraft's flight range and for balancing the aircraft's mass by compensating for the center of gravity relative to the center of thrust.

[0004] Existing fuel level measurement systems rely on complex measurement technologies using sensors installed inside the tank. Since such measurement systems require a power supply to the tank, for example in electrical or optical form, they are subject to stringent requirements and standards, designated by the acronym ATEX, for ATmosphère EXplosive (Explosive Atmosphere), for installation and maintenance, in order to be compatible with use in such an atmosphere while being resistant to chemical attack.

[0005] It is known to measure a fuel level using approaches based on capacitive sensors immersed in the fuel. There are also approaches using guided waves along a waveguide immersed in the fuel, for example for electromagnetic or ultrasonic waves.

[0006] Other approaches propose a non-intrusive measurement of the fuel level, notably using body-wave ultrasonics. The drawback of this approach is that it is necessary to be able to capture the wave after reflection at the fuel / gas interface. Since the liquid is rarely at rest in the tank, the wave is diffracted rather than reflected specularly, which makes the backscattered wave difficult for the sensor to detect due to its low energy. The use of guided ultrasonic waves rather than body waves, which typically propagate through the tank wall, overcomes this drawback, but does not allow for consideration of the influence of temperature on the error in estimating the fuel level.

[0007] A guided ultrasonic wave approach exploits the conversion of an antisymmetric Lamb mode Ao into a Quasi-Scholte (QS) mode during its propagation in the tank wall (Lingyu Yu and Zhenhua Tian, ​​Case study of guided wave propagation in a one-side water-immersed steel plate, Case Studies in Nondestructive Testing and Evaluation, vol. 3, p. 1-8, 2015). It is shown that the amplitude and time of flight of the wave vary with the fuel level, due to this conversion, providing access to a much more precise and robust measurement of the fuel level.

[0008] A variant of this approach consists of evaluating the phase of the propagating wave rather than its propagation time (Lingyu Yu et al., Ultrasonic gas accumulation detection and evaluation in nuclear cooling pipes, Proc. SPIE 8345, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems, 2012). It is shown that the relationship between the phase and the liquid level is linear, due to the difference in phase velocity between the immersed and non-immersed parts of the wall.

[0009] However, in these last two approaches, no solution is proposed to improve the robustness of the liquid level measurement with respect to environmental conditions, particularly temperature. Consequently, over a temperature range, the proposed level measurement is inaccurate.

[0010] In practice, knowing the temperature, for example through a thermocouple, is not sufficient. This necessitates very precise temperature measurements at various points within the tank, as thermal equilibrium is generally not reached during aircraft operation. Therefore, a large number of temperature measurement points are required.

[0011] At a minimum, a temperature measurement is required at the fuel level and another at the gas level, both within the tank, on either side of the container. Therefore, determining the temperature necessitates additional instrumentation and the integration of two technologies within the same system, which increases installation and maintenance constraints as well as the probability of system failure.

[0012] Therefore, there is a need for a simplified system for determining a liquid level in a container, robust to experimental conditions and compatible with the instrumentation constraints on an aircraft. Summary of the invention

[0013] The invention offers a solution to the problems mentioned above, by proposing a method and a system allowing a robust evaluation under experimental conditions of the liquid level in a container from a single set of sensors.

[0014] A first aspect of the invention relates to a method for determining the level of a liquid in a container comprising a wall delimiting an internal volume of the container containing the liquid, a plurality of ultrasonic sensors being arranged at a distance from the wall and / or on the wall and comprising: • A first and a second sensor positioned at approximately the same height and above the liquid level, • A third and fourth sensor positioned at approximately the same height and below the liquid level; the liquid level in the container being determined from: • A phase of a guided wave, called the first phase, determined by propagation of the guided wave according to a first mode of propagation in the wall between the first and second sensors, the first mode of propagation being the antisymmetric mode Ao of a guided Lamb wave; • A phase of a guided wave, called the second phase, determined by propagation of the guided wave according to a second mode of propagation in the wall between the third and fourth sensors, the second mode of propagation being the Quasi-Scholte mode of a guided elastic wave; and • A phase of a guided wave, called the third phase, determined by propagation of the guided wave in the wall between the first and third sensors, according to the first mode of propagation above the liquid level and according to the second mode of propagation below the liquid level.

[0015] Thanks to the invention, it is possible to determine a liquid level while taking into account the environmental conditions of the container holding it. Indeed, the method allows for self-calibration of the sensors for measuring the liquid level by considering the first and second phases. Thus, the determination of the liquid level is independent of the influence of experimental conditions, including temperature. The level is therefore estimated robustly under these experimental conditions.

[0016] Furthermore, the determination of the liquid level relies on the propagation of guided modes, which are simple to generate and do not require specific instrumentation other than ultrasonic sensors generating guided waves. Moreover, the Ao mode, converting into the Quasi-Scholte mode, is sensitive to the presence of liquid, thus enabling high accuracy in the liquid level calculation.

[0017] The method is also simple to implement since it only requires the emission of ultrasonic waves, particularly in the wall. Moreover, it is advantageously possible to implement the method by generating only two guided ultrasonic waves, since the guided wave generated to determine the first phase or that generated to determine the second phase can also be used to determine the third phase without having to emit an additional guided wave.

[0018] Furthermore, the method does not require multiple measuring instruments to perform the measurements. Indeed, a system comprising only ultrasonic sensors is sufficient to determine the various quantities involved. Therefore, for example, it is not necessary to add temperature sensors to the container to compensate for the effect of temperature on the propagation of guided waves. The method thus allows for rapid instrumentation in terms of preparation and installation time, with low maintenance costs.

[0019] The method also does not require intrusive measurements for implementation, since these sensors can be placed outside the container, for example on an external part of its wall or at a distance. The method is therefore compatible with applications under ATEX regulations and poses no risk of chemical attack to the sensors due to the nature of the liquid, particularly in the case of a fuel. Consequently, the method is compatible with any type of container and any application subject to ATEX-type instrumentation constraints and / or chemical attack.

[0020] Any ultrasonic sensor technology that can be used without compromising the advantages of the method. It is possible to use compact and easy-to-instrument sensor technologies, facilitating access to the acquisition systems and sensors for maintenance.

[0021] The method is therefore compatible for any aeronautical application, in particular during flight, including for semi-rigid or flexible tanks such as those carried in a helicopter.

[0022] Other applications of the method are possible, such as in the automotive, naval or storage sectors, for example for drinking water, chemicals, food products, etc. Although described here for liquids (of different physico-chemical natures: viscosity, density, etc.), the proposed approach is also compatible with powdered or granular compounds.

[0023] In addition to the characteristics just mentioned, the method according to the first aspect of the invention may have one or more complementary characteristics from among the following, considered individually or according to all technically possible combinations.

[0024] In one embodiment, the liquid level is proportional to the third phase according to a linear relationship, the liquid level being determined by said linear relationship, the coefficients of the linear relationship being predetermined during a calibration and then corrected according to the first and second phases.

[0025] In one embodiment, calibration includes: • Determine, for each reference level of a plurality of reference levels of a liquid contained in the container, the phase of a guided wave propagating in the wall between the first and third sensors, according to the first mode of propagation above said reference level and according to the second mode of propagation below said reference level; • Determine the coefficients of the linear relationship as a function of the plurality of reference levels and the phase of the guided wave propagating in the wall between the first and third sensors, corresponding to each of said reference levels.

[0026] In one embodiment, the linear relation is . zxr > [n ], where <Kh) = (pQ + a [2æ]’ ¢(½) is the third phase, A the liquid level, and a'# and ^'() are the corrected linear relation coefficients, such that — a$+ PqS - p^, and + P^D^, where: • a4> and are the predetermined coefficients during calibration, • is the distance between the first and third sensors, and "_ and r_ ^<'with: • the first phase, * the second phase, • D^ the distance between the first and second sensors, • Back the distance between the third and fourth sensors, • A}ref a phase of the guided wave propagating in the wall according -F the first mode of propagation between the first and second sensors during calibration, • f a phase of the guided wave propagating in the wall according the second mode of propagation between the third and fourth sensors during calibration.

[0027] In one embodiment, the method according to the first aspect further comprises, during calibration: • Determine a first set of phases comprising, for each reference level of the plurality of reference levels, a phase of the guided wave propagating in the wall between the first and second sensors; • Determine a second set of phases comprising, for each reference level of the plurality of reference levels, a guided Fonde phase propagating in the wall between the third and fourth sensors; and, during calibration, the guided Fonde phase propagating in the wall between the first and third sensors and determined for each reference level of the plurality of reference levels is corrected from the first set of phases and the second set of phases, and the coefficients of the linear relationship are calculated as a function of the plurality of reference levels and the corrected phase corresponding to each of said reference levels.

[0028] In one embodiment, during calibration, the phase <p'{hj ) de l’onde guidée se propageant dans la paroi entre les premier et troisième capteurs, et déterminée pour chaque niveau ht de référence de la pluralité de niveaux de référence, est modifiée en une phase corrigée ¢(¼) telle que = ÿW _ fi oû : • is the distance between the first and third sensors, * 6 ct ■> with 'a distance between the first ^A> = ^QS = Dqs and second sensors, and Dq$ the distance between the third and fourth

[0029] sensors; • $ is the guided Foundation phase of the first set of phases which 7 A) corresponds to the reference level h, ; and * eSt la P^ase the guided wave of the second set of phases which corresponds to the reference level h; ; * eSt Un P^ase selected from the first set of phases ; and * ^qs eSt A Phase selected from the second set of phases. In one embodiment, the plurality of sensors further comprises a first intermediate sensor positioned between the first and third sensors and a second intermediate sensor positioned between the second and fourth sensors, and: • When the determined liquid level is above the position of the first intermediate sensor, a refined level is determined from: • The first phase, • A phase of a guided wave determined by Fonde propagation guided according to the second propagation mode in the wall between the first and second intermediate sensors, • A phase of a guided wave determined by guided Fonde propagation in the wall between the first sensor and the first intermediate sensor; • When the determined liquid level is below the position of the first intermediate sensor, the refined level is determined from: • The second phase, • A phase of a guided wave, called the first intermediate phase, determined by the propagation of the guided wave according to the first mode of propagation in the wall between the first and second intermediate sensors, • A phase of a guided wave, called the third intermediate phase, determined by propagation of the guided wave in the wall between the third sensor and the first intermediate sensor.

[0030] In one embodiment, the plurality of sensors comprises a first pair of intermediate sensors positioned above the liquid level or above the refined level, and a second pair of intermediate sensors positioned below the liquid level or below the refined level, the intermediate sensors of the same pair being positioned at substantially the same height, one of the intermediate sensors of each of the first and second pairs of intermediate sensors being substantially vertically aligned with the first and third sensors, the first and second pairs of intermediate sensors being positioned between the first and third sensors, the method comprising: • Determine an improved fluid level from: • A phase of a guided wave determined by propagation of the guided wave according to the first mode of propagation in the wall between the intermediate sensors of the first pair of intermediate sensors; • A phase of a guided wave determined by propagation of the guided wave according to the second mode of propagation in the wall between the intermediate sensors of the second pair of intermediate sensors; and • A phase of a guided wave determined by propagation of the guided wave in the wall between the intermediate sensors of the first and second pairs which are substantially vertically aligned with the first and third sensors.

[0031] In one embodiment, the plurality of sensors comprises a plurality of sensor pairs, the sensors of the same sensor pair being positioned substantially at the same height, each sensor of each sensor pair being substantially vertically aligned with one of the sensors of each other sensor pair, the method comprising, before the determination of the first phase: • Determination of a phase velocity for each guided wave of a plurality of guided waves, each guided wave of the plurality of guided waves being emitted by one of the sensors of one of the sensor pairs of the plurality of sensor pairs, said guided wave being captured by the other sensor of said sensor pair; in which the first and second sensors are the sensors of one of the sensor pairs of the plurality of sensors for which the phase velocity of the guided wave emitted by said sensor pair is equal to the phase velocity of the first propagation mode; and the third and fourth sensors are the sensors of one of the sensor pairs of the plurality of sensors for which the phase velocity of the guided wave emitted by said sensor pair is equal to the phase velocity of the second propagation mode.

[0032] It is thus possible to select the first, second, third and fourth sensors so as to ensure that the first and second sensors are positioned above the liquid level and that the third and fourth sensors are below the liquid level.

[0033] A second aspect of the invention relates to a system for determining the level of a liquid in a container, the container comprising a wall delimiting an internal volume of the container containing the liquid, the system comprising: • A plurality of ultrasonic sensors arranged at a distance from the wall and / or on the wall, comprising: • A first and a second sensor positioned at approximately the same height and above the liquid level, • A third and fourth sensor positioned at approximately the same height and below the liquid level; • An acquisition module connected to the plurality of ultrasonic sensors and configured to drive the plurality of ultrasonic sensors so as to generate a guided wave and / or acquire samples of a guided wave captured by one of the sensors in the plurality of ultrasonic sensors; and • A processing module connected to the acquisition module and configured to implement the method according to the first aspect from the acquired samples.

[0034] A third aspect of the invention relates to a computer program product comprising instructions which, when the program is executed on a computer, lead the latter to implement the steps of the method according to the first aspect.

[0035] A fourth aspect of the invention relates to a computer-readable recording medium comprising instructions which, when executed by a computer, lead the computer to implement the steps of the method according to the first aspect.

[0036] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0037] The figures are presented for illustrative purposes only and are in no way limiting of the invention. • Fig. 1 is a schematic representation of a system for determining a liquid level in a container according to an embodiment of the invention. • Fig. 2 is a schematic representation of the propagation of guided waves in the wall of the container of Fig. 1, according to an embodiment of the invention. • Fig. 3 is a schematic representation of the container according to Fig. 1, detailing the physical quantities used to determine the liquid level, according to a first embodiment. • Fig. 4 is a synoptic diagram illustrating the sequence of steps of a method for determining a liquid level, according to an embodiment of the invention. • Fig. 5 is a schematic representation of another instrumentation variant of the measurement system of Fig. 1, according to one embodiment of the invention. • Fig. 6 is a schematic representation of a variant of determining the measurement of the liquid level, according to an embodiment of the invention. DETAILED DESCRIPTION

[0038] Unless otherwise specified, the same element appearing on different figures has a unique reference.

[0039] The invention relates to a method and system for determining the liquid level in a container. The application proposed below concerns an aircraft fuel tank. However, the invention can be used for any other container holding a liquid, particularly in an environment subject to instrumentation constraints and safety requirements, notably those related to explosive atmospheres (ATEX) and risks of chemical attack.

[0040] The invention is based on the generation of guided ultrasonic waves in the wall of the container, here the tank, to determine the level of the liquid, here the fuel, in the tank. In particular, two modes of guided waves are excited: the antisymmetric Ao mode of a Lamb wave and the Quasi-Scholte (QS) mode.

[0041] Figure 1 illustrates the liquid level determination system 10, which is implemented on a container 1, here a reservoir 1.

[0042] The reservoir 1 comprises a wall 2, which includes an inner face 2i and an outer face 2e. The wall 2, in particular its inner face 2i, delimits an internal volume of container 1. The internal volume contains the liquid. The inner face 2i is therefore in contact with the liquid. The outer face 2e is exposed to the surrounding environment in which container 1 is located.

[0043] In the embodiment presented, the tank 1 is carried on board an aircraft, such as an airplane or a helicopter, and the tank 1 is located in a storage space dedicated to said tank 1.

[0044] The reservoir 1 also includes an upper surface 3 and a lower surface 4. The internal volume is therefore also delimited by the upper surface 3 and lower surface 4.

[0045] The tank 1 may also include other elements, such as equipment for circulating fuel to the engine to supply it, such as a pump device and a connecting circuit, and equipment for conveying fuel into the tank for storage, such as a supply circuit.

[0046] The term "liquid level" refers to the height of the interface formed by the upper surface of the liquid with a gas in the container 1 relative to a fixed reference point such as the lower surface 4. The dimension of the liquid level 5 is preferably a distance, for example in millimeters, centimeters, meters, etc. The liquid level 5 thus delimits an upper part 1a and a lower part 1b in said container 1, such that the lower part 1b corresponds to the part of the container where the liquid is located and the upper part 1a corresponds to the part of the container where the gas is located. The gas is a chemical compound comprising, for example, fuel vapors and air or nitrogen-enriched air.

[0047] The wall 2 then comprises an upper section 2a and a lower section 2b, corresponding to the upper part 1a and the lower part 1b, respectively, of the container 1.

[0048] The geometry and dimensions of the container 1 are predefined. That is to say, the geometry and dimensions of the internal volume, the upper surface 3, and the lower surface 4 are predefined. The method proposed here does not require the wall thickness to be predefined. Moreover, the wall thickness may not be constant throughout the entire container 1.

[0049] A characteristic is "predefined" if it is perfectly known at the time the method is implemented and is not a characteristic for which a determination must be made. In particular, the properties of the container and its components are predefined since they are the subject of a controlled design and manufacturing process. The characteristics and positions of the system's components are also predefined because they are controlled and known to the operator.

[0050] The system 10 comprises a plurality of ultrasonic sensors 11, an acquisition module 12 and a processing module 13.

[0051] The plurality of ultrasonic sensors 11 can be arranged, in whole or in part, on the wall 2, in particular on the external face 2e of the wall 2. In other words, each sensor 11 of the plurality of sensors 11 is positioned on the container 1, in contact with the wall 2. The liquid level is therefore determined in a non-intrusive way.

[0052] In some alternatives, depending on the sensor technology used and the intended application, the sensors 11 may be, in whole or in part, non-contact sensors, i.e. at a distance from the wall 2, in particular at a distance from the external face 2e.

[0053] The term "contactless" refers to sensor technologies that generate an ultrasonic wave in a room without requiring the source to be in contact with the room. For example, this could involve a sensor technology located very close to the wall (such as electromagnetic acoustic transducers, or "EMATs") or even at a distance (such as one or more laser sources). In such a case, the sensors 11 can be positioned outside the container, close to and / or at a distance from the wall 2. In this context, "close" means that the distance between the wall and the sensor is between 1 µm and 50 mm, or even between 100 µm and 10 mm, or even between 1 mm and 5 mm. In this context also, "at a distance" means that the distance between the wall and the sensor is greater than 50 mm, or even greater than 100 mm, or even greater than 500 mm.

[0054] In other alternatives, the sensors 11 can be placed inside the container 1, for example on the wall 2 or at a distance from it. The sensors are thus mounted intrusively on the container, but this makes it possible to evaluate the gauged levels (i.e., the puddle and bubble levels described below) more precisely.

[0055] Ultrasonic sensors 11 are sensors 11 enabling the generation and capture of ultrasonic waves propagating in the wall 2 of the container 1. In particular, these sensors 11 serve to generate and capture one or more guided waves in the wall 2, that is to say in the thickness of said wall 2.

[0056] For example, an illustration of such propagation is shown in Figure 2, where, in particular in Figure 2(a), a guided wave 0 propagates in the wall 2 of the container 1, seen from the front, between two sensors 11 positioned one above the other, and where, in particular in Figure 2(b), a guided wave 0 propagates in the wall 2 of the container 1, seen from above, between two sensors 11 positioned at a substantially similar height on said wall 2.

[0057] Similarly, typically when the container 1 is substantially cylindrical in shape along a horizontal direction, particularly in Figure 2(c), a wave guided propagates in the wall 2 of the container 1 between two sensors 11 positioned one above the other, and where a guided wave propagates in the wall 2 of the container 1 between two sensors 11 positioned at a substantially similar height on said wall 2. For the sake of simplification, the thickness of the wall 2 is not shown in the figures other than [Fig.2].

[0058] Preferably, these sensors 11 are configured to excite the zero-order antisymmetric propagation mode, denoted Ao mode, of a Lamb wave and / or the Quasi-Scholte mode, denoted QS mode.

[0059] Any technology can be used for these sensors 11, such as ultrasonic transducers exploiting the piezoelectric effect, which converts mechanical displacement into a voltage, and vice versa. The sensors 11 can then be single-element transducers, also called pellets, or linear or matrix multi-element transducers. In the embodiment presented, these sensors 11 are placed in contact with the wall 2, but they are also suitable for non-contact applications. In the latter case, a coupling device can be used to minimize the impedance mismatch between the wall and the medium surrounding the container.

[0060] Alternatively, some applications may use measurement technologies not based on the piezoelectric effect, such as optoacoustic technologies, for example using one or more laser vibrometers or magnetostrictive transducers.

[0061] The sensors 11 of the plurality of sensors 11 may be based, in whole or in part, on different technologies and / or combine different sensor technologies. The sensors 11 are therefore configured to suit the application (geometry, dimensions, emission frequency, emitted wavelength, emission energy, etc.).

[0062] The position of each sensor 11 of the plurality of sensors 11 at a distance or on the container 2 is predefined.

[0063] As illustrated in [Fig.3], the plurality of sensors 11 comprises a first sensor 11-1, a second sensor 11-2, a third sensor 11-3 and a fourth sensor 11-4.

[0064] The first and second sensors 11 are arranged so as to be positioned on the wall 2 above the liquid level 5.

[0065] The third and fourth sensors 11 are, for their part, arranged so as to be positioned on the wall 2 below the liquid level 5.

[0066] These first, second, third and fourth sensors 11 can alternatively rely, for one or more of them, on contactless sensor technology. In this In this case, the first, second, third, and / or fourth sensors 11 are positioned so as to generate a guided wave in the wall 2 from a first, second, third, and / or fourth source point, these source points being located above and / or below the liquid level 5, respectively. These source points correspond, for example, to the respective positions of the first, second, third, and / or fourth sensors 11, respectively, if they were in contact with the wall 2.

[0067] The position of these four sensors 11 on the wall depends on the instrumentation conditions and constraints related to the environment as well as the geometry, accessibility and size of the container 1. In particular, other elements of the container 1, such as the supply and power supply circuits, as well as the chassis of the device and the presence of other systems around the container 1 such as other containers, can constrain the positioning of the sensors 11.

[0068] Furthermore, the internal volume of the container 1, particularly for a fuel tank, may include an upper zone, called bubble B, and a lower zone, called puddle F. Bubble B acts as a buffer to allow sufficient time for the operator filling the container to stop filling so as not to exceed the internal volume of the container. Puddle F serves as a fuel reserve, guaranteeing the pilot a minimum flight range to complete the flight and land the aircraft.

[0069] According to one embodiment, the first and second sensors 11 can be arranged on the external face 2e so as to be above the lower interface Bb of the bubble B. The advantage is to ensure that the first and second sensors 11 are always above the level of fuel that we wish to measure outside the inert volume.

[0070] In this embodiment, the third and fourth sensors 11 can be arranged on the external face 2e so as to be below the upper interface Fh of the puddle F. The advantage is to ensure that the third and fourth sensors 11 are always below the fuel level that we wish to measure outside the inert volume.

[0071] The first sensor 11-1 is substantially aligned horizontally with the second sensor 11-2, for example in a horizontal plane. Similarly, the third sensor 11-3 is substantially aligned horizontally with the fourth sensor 11-4, for example in a horizontal plane. The horizontal plane is the plane parallel to the liquid level when the device is on the ground and not moving.

[0072] The horizontal alignment of these sensors 11 allows waves to be transmitted along direct propagation paths between these different sensors 11 and thus simplifies the calculations of the level determination method described later.

[0073] In the example of [Fig. 3], the tank is cylindrical and the first sensor 11-1 is positioned at the same height as the second sensor 11-2. Similarly, the third sensor 11-3 is positioned at the same height as the fourth sensor 11-4.

[0074] The relative positioning of these four sensors 11 with respect to each other does not depend on any specific conditions other than those previously mentioned. However, it is preferable that the first and third sensors 11 be arranged on the same side of the container to facilitate the transmission of guided waves from one to the other. Similarly, it is preferable that the second and fourth sensors 11 be arranged on the same side of the container to facilitate the transmission of guided waves from one to the other.

[0075] It is also preferable that the propagation paths between the first and second sensors 11, between the third and fourth sensors 11, between the first and third sensors 11 and between the second and fourth do not have any mechanical interruption, such as an impedance break, for example in the form of a attenuating polymer seal or a geometric discontinuity.

[0076] When the geometry of the container 1 allows, it is preferable that the first sensor 11-1 and the third sensor 11-3 be substantially aligned vertically with each other along a vertical axis of the container. Similarly, it is preferable that the second sensor 11-2 and the fourth sensor 11-4 be substantially aligned vertically with each other along the vertical axis of the container.

[0077] The vertical axis of the container is orthogonal to the plane defined by the surface of the liquid at its interface with the gas when the device is on the ground and not in motion. In other words, when the container is a cylinder, the first and third sensors 11, as well as the second and fourth sensors 11, are positioned so as to be respectively located substantially in the same plane tangent to the wall 2.

[0078] The vertical alignment of these sensors 11 also allows waves to be transmitted along direct propagation paths between these different sensors 11 and thus simplifies the calculations of the level determination method described later.

[0079] In the example shown in [Fig.3], the first sensor 11-1 is, moreover, vertically aligned with the third sensor 11-3, and the second sensor 11-2 is, moreover, vertically aligned with the fourth sensor 11-4.

[0080] The acquisition module 12 is connected to the plurality of sensors 11, typically to each sensor 11 of the plurality of sensors 11. The acquisition module 12 is configured to drive the plurality of ultrasonic sensors 11 so as to generate one or more guided waves in the wall 2. Preferably, the acquisition module 12 is connected to each sensor 11 of the plurality of sensors 11.

[0081] By "connected" is understood that a connection intermediary, for example a wired or wireless connection, links the elements in question and allows the transfer of data from the elements to each other.

[0082] The generation of a guided wave is implemented by exciting one of the sensors 11 with an excitation signal. The excitation signal is optionally digitized by the acquisition module 12. In this case, the excitation signal comprises a plurality of successive samples digitized at a predefined sampling frequency. The sampling frequency is generally greater than or equal to twice the highest frequency of the excitation signal, so as to comply with the Shannon-Nyquist criterion.

[0083] The excitation signal can be any type of signal that allows the generation of the guided wave. The excitation signal therefore depends on the application in question. For example, the excitation signal could be a pulse, a single-frequency sinusoidal wave train, a multi-frequency sinusoidal wave train, a signal modulated around a center frequency (in English, "chirp"), a broadband signal, etc. The excitation signal has a finite time support.

[0084] In the embodiment presented, the excitation signal is a single-frequency sinusoidal wave train with a given excitation frequency, digitized at the given sampling frequency. The excitation frequency is the frequency of the sinusoid of the sinusoidal wave train. The values ​​of these different frequencies depend on the material of the container wall as well as its thickness.

[0085] Typically, the excitation frequency is between 10 kHz and 100 kHz. For example, for a 3 mm thick aluminum wall, the excitation frequency is 50 kHz for the antisymmetric mode Ao of a guided Lamb wave. The sampling frequency is then at least 100 kHz, or even greater than or equal to 500 kHz, or greater than or equal to 1 MHz.

[0086] The acquisition module 12 is also configured to acquire a signal of a guided wave, in particular propagating in the wall 2, and captured by one of the sensors 11 of the plurality of sensors 11. The acquired signal comprises a plurality of samples acquired at an acquisition frequency. The acquisition frequency is generally greater than or equal to the maximum frequency of the propagation mode of the wave captured by the sensor 11 that one wishes to acquire, so as to comply with the Shannon-Nyquist criterion. The acquisition frequency may be equal to the sampling frequency.

[0087] The acquisition module 12 comprises a processor and memory. The memory includes instructions which, when executed by the processor, enable the digitization of the excitation signal, the generation of the guided wave, in particular in the wall, by means of a sensor 11 of the plurality of ultrasonic sensors 11 and / or the acquisition of the signal of a guided wave, in particular a guided wave propagating in the wall.

[0088] The processing module 13 is connected to the acquisition module 12. The processing module 13 includes memory and a processor and is configured to implement the liquid level determination method. The processing module 13 therefore includes, in its memory, instructions which, when executed by the processor of the processing module 13, enable the implementation of the liquid level determination method. The processing module 13 is, for example, a computer.

[0089] Thus, the processing module 13 is configured here to obtain the different signals acquired by the acquisition module 12, and to process these signals in order to determine the different phases necessary for the implementation of the different steps of the method proposed below.

[0090] In an alternative, the acquisition module 12 and the processing module 13 are a single module. In this alternative, this combined module comprising the acquisition module 12 and the processing module 13 is configured both to generate guided waves in the wall 2 via the sensors 11, to produce signals from the capture of guided waves and to analyze the captured signals in order to determine the different phases necessary for the implementation of the different steps of the method proposed below.

[0091] The proposed approach is based on measuring the phase of different propagation modes of guided ultrasonic waves propagating between the sensors 11, in order to deduce the liquid level. It is therefore necessary to use a propagation mode sensitive to the presence of the liquid.

[0092] In particular, these guided waves propagate between the sensors 11 according to the antisymmetric mode Ao of a Lamb guided wave, called the first mode, in the upper section 2a of the wall 2, above the liquid level 5. These waves propagate according to the Quasi-Scholte (QS) mode, called the second propagation mode, in the lower section 2b of the wall 2, below the liquid level 5. The QS mode exists only when the part of the wall that vibrates under its effect is in contact with the liquid.

[0093] The QS mode can be generated in the lower part 2b directly by the third sensor 11-3 or by conversion of the Ao mode at the liquid / gas interface after emission by the first sensor 11-1 (FB Cegla, P. Cawley, and MJS Lowe, Material property measurement using the quasi-Scholte mode - A waveguide sensor, JASA, vol. 117, 1098, 2005; FB Cegla, P. Cawley, and MJS Lowe, Fluid bulk velocity and attenuation measurements in non-Newtonian liquids using a dipstick sensor, Meas. Sci. Technol., vol. 17(2), 264, 2006). The advantage of the QS mode is that it allows for better measurement accuracy than other commonly used methods.

[0094] Due to the conversion of the Ao mode to the QS mode, the excitation signal used to activate the first mode can also be used to activate the second mode, and vice versa. The excitation signal is therefore adapted to activate the first and / or second propagation mode. Thus, the sensors are sized (diameter, emission wavelength, energy, etc.) to activate either the first or second propagation mode.

[0095] Method 100 for determining the liquid level, as illustrated in [Fig.4], comprises several steps and is based on evaluating a phase for each of the two propagation modes and converting them from one to the other.

[0096] These phases can be determined by techniques known per se. For example, a phase 0 of a guided wave can be determined such that $ = V^o) ' The instantaneous phase ) is evaluated at the instant / q which corresponds to the arrival time of the wave packet associated with the propagation mode considered. This instantaneous phase is that of the signal corresponding to the captured wave. The center frequency of this signal is denoted / 0. The instantaneous phase y^t^ can be defined as being equal to the argument of the Hilbert transform of the signal corresponding to the captured wave. Subtracting the term t0 makes the phase 0 independent of the choice of the instant ^o, as long as this instant is within the wave packet corresponding to the guided wave in question.

[0097] The physical quantities used by method 100 are represented in [Fig.3].

[0098] Method 100 includes a step 120 of determining the phase of a wave guided wave propagating between the first sensor 11-1 and the second sensor 11-2. The guided wave is emitted indifferently by the first or second sensor 11 and is captured by the second or first sensor 11, respectively. This phase is called the "first phase".

[0099] The guided wave in question propagates in the wall 2, above the level of the liquid h. Thus, the guided wave propagates according to the first mode of propagation, here the antisymmetric mode Ao. The first phase therefore corresponds to the phase of the wave packet of the mode Ao in the signal corresponding to the captured wave.

[0100] As mentioned above, the first phase can be determined by techniques known per se. Typically, the first phase can be such that °ù y, jest 'a instantaneous phase of the wave in question at the moment of capture of the wave packet in the signal corresponding to this wave.

[0101]

[0102]

[0103]

[0104]

[0105]

[0106]

[0107]

[0108]

[0109] Method 100 also includes a step 130 of determining a phase of a guided wave propagating between the third sensor 11-3 and the fourth sensor 11-4. The guided wave is emitted indifferently by the third or fourth sensor 11 and is received by the fourth or third sensor 11, respectively. This phase is called the "second phase". The guided wave in question propagates through wall 2, below the liquid level. Thus, the guided wave propagates according to the second propagation mode, here the QS mode. The second phase therefore corresponds to the phase of the QS wave packet in the signal corresponding to the captured Fonde. As mentioned above, the second phase 0^ can be determined by techniques known per se. Typically, the second phase can be such that ) " 2æA / qS, °where j is the instantaneous phase of the wave in question at the moment ^os of capturing the wave packet in the signal corresponding to this wave. Method 100 also includes a step 140 of determining a phase of a guided wave propagating between the first sensor 11-1 and the third sensor 11-3. The guided wave is emitted indifferently by the first or the third sensor 11 and is received by the third or the first sensor 11, respectively. This phase is called the "third phase". The guided wave in question propagates in wall 2 according to the first propagation mode above the liquid level h, and according to the second propagation mode below the liquid level h. The third phase therefore corresponds to the phase of the wave packet of the Ao mode after its conversion to QS mode, or vice versa, in the signal corresponding to Fonde captured. As mentioned above, the third phase can be determined by techniques known per se. Typically, the third phase can be such that JA \ , where ... L ] is the instantaneous phase of Fonde in A" J = p The question at time Ia^qs of capturing the wave packet in the signal corresponding to this wave. The third phase depends on the liquid level h in container 1. The center frequency / 0 of each of the signals used in steps 120 to 140 to determine these first, second and third phase signals is the same. It appears that steps 120, 130 and 140 are independent and can be implemented in any order or concurrently with each other. Furthermore, the first phase and the third phase can be determined from the same wave generated by a single sensor 11, for example the first sensor 11-1. Similarly, the second and third phases can be determined from the same wave generated by a single sensor 11, for example the third sensor 11-3. Thus, it is possible to emit only two waves to determine the first, second and third phases.

[0110] The process 100 also includes a step 150 of determining the liquid level h.

[0111] The liquid level h is determined from the first, second, and third phases determined in steps 120, 130, and 140, respectively. The determination of the liquid level h is therefore self-calibrated with respect to the temperature (i.e., without having to directly measure this temperature) in the tank since it takes this temperature into account via the first and second phases.

[0112] In particular, it is possible to determine the liquid level h by a linear relationship. This linear relationship defines that the phase of a guided wave propagating between the first and third sensors is linearly dependent on the liquid level. The liquid level & is therefore proportional to the third phase, according to the linear relationship.

[0113] The coefficients of the linear relationship are preferably predetermined via calibration, in particular via measurements at different known liquid levels of the phase of a guided wave propagating between the first and third sensors 11.

[0114] These coefficients of the linear relationship are corrected, during the implementation of step 150 for determining the liquid level h, based on the first and second phases, to take into account the temperature in the tank. Indeed, the temperature in the tank during calibration is not necessarily the same as for determining the first, second, and third phases. This correction of the coefficients therefore allows the linear relationship coefficients, which are dependent on the temperature in tank 1 at the time of calibration, to self-adjust.

[0115] The linear relation can be defined, without limitation, by at least two coefficients such that > ​​ / 1 \ / ' ■ » ikl, where and are the coefficients of the relation 4 ¢(½) = (p^a [2æ]' 0 linear, predetermined during calibration. [2r] is the modulo 2tt with which the phase ^(h) is determined.

[0116] Thus, the linear relation taking into account the corrected coefficients can be written as , » [o ]. Here and are the coefficients of the linear relation <p(h) = ¢0 + a [2 / 1] ? 0 corrections.

[0117] The corrected coefficients, obtained taking into account the first and second phases, can be determined such that a'^ — + , and + °ù : • is the distance between the first and third sensors 11, and * h and ' aVeC : n — -Al}. -4°.. Q — P DA} Pqs- Dqs • (f>In the first phase, • ^QS the second phase, • D is the distance between the first and second sensors, • &OS is the distance between the third and fourth sensors, • a phase of a guided wave propagating in wall 2 according to the first propagation mode between the first and second sensors 11, called the first reference phase, and determined during calibration, • a phase of a guided wave propagating in the wall 2 according to the second mode of propagation between the third and fourth sensors 11, called the second reference phase, and determined during calibration.

[0118] The first and second reference phases allow the temperature in container 1 to be taken into account without having to measure this temperature during calibration.

[0119] Thus, knowing the third phase, ^(h) and the corrected coefficients and a'^ it is possible to determine the liquid level h from the linear relationship.

[0120] In one embodiment, method 100 may also include a calibration step 110. This calibration may, moreover, be implemented independently of method 100, for example by implementing it prior to the implementation of method 100.

[0121] Calibration is implemented using the same sensors as those used to implement steps 120 to 140 to determine the first, second and third phases.

[0122] The calibration 110 includes a step 111 of determining, for a plurality of reference levels, the phase of a guided wave, called the third reference phase, propagating in the wall 2 between the first and third sensors 11. This guided wave therefore propagates, for each reference level of the plurality of reference levels, according to the first mode of propagation above said reference level and according to the second mode of propagation below said reference level.

[0123] A third reference phase is therefore determined for each of the reference levels, thus forming a plurality of third reference phases.

[0124] The plurality of reference levels corresponds to different known levels for the same liquid contained in the container 1.

[0125] Each third reference phase can be determined by an approach known per se, typically in the same way as for the third phase, determined in step 140. In particular, the third reference phase (Khi}, determined for the i-th reference level hu î being a positive integer less than or equal to the cardinality of the plurality of reference levels, can be such that ht) = V^t^Qs) -

[0126] j is the instantaneous phase of the wave in question at the time caPtati°n of the wave packet in the signal corresponding to that wave. The center frequency / 0 of each of the signals used to determine the plurality of reference third phases is the same as that of the signals used in steps 120 to 140 to determine the first, second and third phases.

[0127] In one embodiment, the plurality of reference levels is predefined such that the difference between two consecutive levels produces a variation in the third reference phase less than or equal to y. In this case, the plurality of reference levels can be predefined by means of a simulation tool, which allows the variation of the third reference phase to be modeled as a function of the variation in the liquid level. This simulation tool can rely on an approximate knowledge of the phase velocities of the Ao and QS modes. This approximate knowledge is, for example, obtained by lowering the difference in phase slowness, i.e., the inverse of the phase velocity, of the Ao and QS propagation modes.

[0128] Such a definition of the plurality of reference levels makes it possible to avoid phase jumps between two measurements of the third reference phase, for two consecutive reference levels. The robustness of the method, particularly with regard to regression and the determination of the coefficients of the linear relationship, is improved.

[0129] By way of example, the spacing between two consecutive reference levels is such that there are between 5 and 50, or even between 10 and 25, reference levels between the first and third sensors. Alternatively, the spacing between two reference levels is between 0.1 and 10 cm, for example between 0.5 and 2 cm, or even between 0.5 and 1.5 cm.

[0130] The calibration 110 may include a step 112 for determining the first reference phase if this is not predefined before the calibration 110 (for example, if it is not estimated via a simulation tool or theoretical calculation). Typically, this first reference phase is determined by the propagation of a guided wave in the wall 2 between the first and second sensors 11. Thus, Just as in step 120, the guided wave propagates according to the first mode of propagation between these two sensors 11. The first reference phase thus corresponds to the phase of the wave packet of the first mode of propagation in the signal corresponding to the guided wave in question.

[0131] The calibration 110 may also include a step 113 for determining the second reference phase if this is not predefined before the calibration 110 (for example, if it is not estimated via a simulation tool or theoretical calculation). Typically, this second reference phase is determined by the propagation of a guided wave in the wall 2 between the third and fourth sensors 11. Thus, just as in step 130, the guided wave propagates according to the second propagation mode between these two sensors 11. The second reference phase therefore corresponds to the phase of the wave packet of the second propagation mode in the signal corresponding to the guided wave in question.

[0132] It appears that steps 111, 112 and 113 are independent and can be implemented in any order or concurrently with each other.

[0133] Furthermore, one or more guided waves generated to determine one of the third reference phases can also be used to determine the first reference phase and / or the second reference phase.

[0134] The calibration 110 also includes a step 115 of determining the coefficients of the linear relationship. These coefficients are determined as a function of the plurality of reference levels and the plurality of third reference phases (i.e., of the phase of the guided wave corresponding to each of said reference levels).

[0135] The coefficients can be determined by an approach known per se, typically by regression. For example, the linear relationship can be the linear function for which the regression error is the smallest for the plurality of third phases determined as a function of the reference levels.

[0136] It can, moreover, be shown that the coefficient can be defined by a^f^ - vÿ propagation, y™f is the phase velocity of the second propagation mode, and / „ is the emission frequency of the guided wave propagating between the first and third sensors. Method 100 therefore allows us to determine this coefficient a <l>without having to determine these phase velocities.

[0137] In one embodiment, the temperature during calibration 110 is not constant, which implies that the phase velocities of the first and second modes are also variable, since they are sensitive to temperature. , where yr^f is the phase velocity of the first mode of

[0138] The variant proposed below is based on the same principle of temperature compensation as that proposed in step 150 of determining the liquid level h. It is thus possible to recalibrate each of the third phases determined before determining the coefficients of the linear relationship.

[0139] In particular, in step 112 of determining the first reference phase, a phase of a guided wave propagating in the wall 2 between the first and second sensors 11 is determined for each reference level of the plurality of reference levels. These phases thus determined form a first set of phases

[0140] The first reference phase is selected indifferently from the first set of phases.

[0141] Furthermore, in step 113 of determining the second reference phase, a phase of a guided wave propagating in the wall 2 between the third and fourth sensors 11 is determined for each reference level of the plurality of reference levels. These phases thus determined form a second set of phases.

[0142] The second reference phase is selected arbitrarily from the second set of phases.

[0143] Preferably, the first reference phase and the second reference phase are selected so as to correspond to the same reference level among the plurality of reference levels. In other words, the first and second reference phases are the phases of the first and second propagation modes, respectively, associated with a reference level selected from among the plurality of reference levels. Any reference level can be selected for this purpose.

[0144] The calibration 110 then includes a step 114 for correcting the plurality of third reference phases. The plurality of third phases is corrected from the first set of phases and the second set of phases. That is to say, the phase of the guided wave propagating in the wall 2 between the first and third sensors 11, and determined for each reference level 5 of the plurality of reference levels, is corrected from the first set of phases and the second set of phases, in particular by the phases of the first and second sets corresponding to said reference level.

[0145] By way of example, for each third reference phase, here denoted ), corresponding to the reference level, it is possible to determine a corrected phase, here denoted 0(hj), such that = ]h- where: • is the distance between the first and third sensors 11, ct ' with 'a distance between the first and second sensor 11, and Dq$ the distance between the third and fourth sensors 11; $ is the guided Foundation phase of the first set of phases which corresponds to the reference level h{ ; and is the phase of the guided wave of the second set of phases which corresponds to audit reference level h, ; is the first reference phase; and is the second reference phase.

[0146] Each phase thus corrected is therefore recalibrated to the third phase corresponding to the same reference level as the first and second reference phases, as if each third reference phase were determined under the same temperature conditions.

[0147] Step 115 of determining the coefficients of the linear relationship is then implemented, and said coefficients are determined as a function of the plurality of reference levels and the plurality of corrected third reference phases.

[0148] In one embodiment, as illustrated in [Fig. 5], compatible with the preceding embodiments, the plurality of sensors 11 comprises at least one pair of intermediate sensors 1 li, or even a plurality of pairs of intermediate sensors lli. For each pair of intermediate sensors, one of the intermediate sensors 1 li is positioned between the first and third sensors 11 so as to be substantially vertically aligned, or even vertically aligned, with the first and third sensors 11, and the other is positioned between the second and fourth sensors 11 so as to be substantially vertically aligned, or even vertically aligned, with the second and fourth sensors 11. Each intermediate sensor 1 li is arranged on the wall 2 at a predefined position.

[0149] By "positioned between", it is understood that the position in which the sensor concerned is located has a height, along the vertical axis of the container, between the height in which the first sensor 11-1 is positioned and the height in which the third sensor 11-3 is positioned, along said vertical axis of the container.

[0150] The intermediate sensors 1 li of each pair are substantially placed at the same height and / or on the same horizontal plane, for example parallel to the liquid level when the device is on the ground and not moving. Typically, in the example of [Fig. 5], the intermediate sensors 1 li within a pair are positioned at the same height.

[0151] The pairs of intermediate sensors 1 li can be regularly spaced according to a step, given in units of length. The step can be constant or can vary depending on the position along the wall 2.

[0152] Depending on the sensor technology used, these intermediate sensors can be arranged at a distance from or in contact with the wall 2 and can be placed inside or outside the container 1.

[0153] The advantage of these intermediate sensors 1 li is to capture the guided wave generated on its path between the first and third sensors and / or between the second and fourth sensors by the intermediate sensors 1 li, which is, for example, advantageous if the container 1 is large and / or if the material of the wall 2 significantly attenuates the propagation of waves according to the first and / or second modes of propagation.

[0154] In addition, these intermediate sensors allow redundancy of measurements in the event of failure of some of the sensors of the plurality of sensors 11, in particular the first and third sensors 11 and / or the second and fourth sensors 11.

[0155] Moreover, the use of these intermediate sensors 1 li is particularly advantageous when the properties of the fuel are subjected to a temperature or density gradient, which is typically the case for a fuel tank.

[0156] Indeed, on the one hand, during its various stops, an aircraft refuels at different refueling points where the properties of the refueled fuel differ, thus producing a stratification of the different fuels added to the tank. On the other hand, the environmental conditions in which an aircraft's tanks are used mean that the temperature within a tank is subject to a temperature gradient, particularly between the first and third sensors. Consequently, having intermediate sensors 1 li allows for a more precise determination of the liquid level h, and thus improves the robustness of Method 100 with respect to a temperature gradient, including for steep gradients, typically ranging from -50 °C to +80 °C.

[0157] To this end, method 100 includes a step 170 for determining an improved liquid level. This improved level is determined by determining the liquid level using two pairs of judiciously selected intermediate sensors lli. It is then possible to determine the improved level in the same way as for the liquid level (i.e., following steps 120 to 150), but this time based on the four intermediate sensors of the two pairs.

[0158] In particular, step 170 includes a step 171 of selecting a first pair of intermediate sensors 1 li, which corresponds to any pair of intermediate sensors 1 li positioned above the liquid level h. For example, it may this refers to the pair of intermediate sensors 1 li whose position is closest to said liquid level.

[0159] Step 170 also includes a step 172 of selecting a second pair of intermediate sensors 1 li, which corresponds to any pair of intermediate sensors 1 li positioned below the liquid level h. For example, it may be the pair of intermediate sensors 1 li whose position is closest to said liquid level.

[0160] Step 170 then includes a step 173 for determining the phase of a guided wave propagating between the sensors of the first pair of intermediate sensors 1 li. This phase is the counterpart of the first phase, determined in step 120, but considering the first pair of intermediate sensors 1 li instead of the first and second sensors. This phase is therefore determined in a similar way to the first phase (i.e., determining the phase of a wave packet in a signal corresponding to a guided wave propagating according to the first propagation mode between the sensors of the first pair of intermediate sensors).

[0161] Step 170 also includes a step 174 for determining the phase of a guided wave propagating between the sensors of the second pair of intermediate sensors 1 li. This phase is the counterpart of the second phase, determined in step 130, but considering the second pair of intermediate sensors 1 li instead of the third and fourth sensors. This phase is therefore determined in a similar way to the second phase (i.e., determining the phase of a wave packet in a signal corresponding to a guided wave propagating according to the second propagation mode between the sensors of the second pair of intermediate sensors).

[0162] Step 170 also includes a step 175 for determining the phase of a guided wave propagating between the sensors of the first and second pairs of intermediate sensors 11, which are positioned between the first and third sensors (and vertically aligned with these sensors). This phase is the counterpart of the third phase, determined in step 140, but considering the intermediate sensors of the first and second pairs that are positioned between the first and third sensors 11, instead of the first and third sensors themselves.

[0163] This phase is therefore determined in a similar way to the third phase (i.e., determination of the phase of a wave packet in a signal corresponding to a guided wave propagating according to the first mode of propagation above the liquid level and according to the second mode of propagation below the liquid level, between the intermediate sensors concerned).

[0164] Just as with steps 120 to 140 for determining the first, second and third phases, respectively, it appears that steps 173, 174 and 175 are independent and can be implemented in any order or concurrently with each other, just as it is possible to generate only two waves to determine the phases at these stages 173 to 175.

[0165] Step 170 also includes a step 176 for determining the improved liquid level. This improved level is determined similarly to the liquid level determination in step 150, using the phases determined in steps 173, 174, and 175, instead of the first, second, and third phases. In particular, the coefficients of the linear relationship are corrected similarly to the correction in step 150, using the phases determined in steps 173, 174, and 175.

[0166] The corrected coefficients can be determined such that a'^C\£2 = «#7tC2 + %X-2 ■ ^yÇV and $ 0.CLC2 = ^O,C1,C2 + WHERE: • «■ / >,£ ic 2 and ÿ0CLC2 are the predetermined coefficients of the linear relationship during a calibration, implemented in a similar manner to the calibration described in step 110, but considering the intermediate sensors of the first and second pairs of intermediate sensors 1 li, denoted C1 and C2, respectively, instead of the first, second, third and fourth sensors 11; • ^ci,c2 is the distance between the intermediate sensors 1 li of the first and second positioned pairs which are positioned between the first and third sensors 11, and • , with : ~ 1 AqL3 „ v OS.C2 y Q&C2 9 = ' / qS.C2~ DqS£2 • Cl the phase determined in step 173, * the Phase determined in step 174, • the distance between the sensors of the first pair of sensors intermediaries lli, • Dqs,C2 the distance between the sensors of the second pair of intermediate sensors lli, * Cl A Pha86 h'unc guided wave determined in a similar way in the first reference phase, at step 112, but considering the intermediate sensors 1 li of the first pair of intermediate sensors 1 li instead of the first and second sensors 11, * $( / C2 A P^ase h'unc guided wave determined in a similar way in the second reference phase, at step 113, but considering the intermediate sensors 1 li of the second pair of intermediate sensors 1 li instead of the third and fourth sensors 11.

[0167] The improved level can thus be determined from the linear relationship taking into account the corrected coefficients for the two pairs of selected sensors.

[0168] For example, the enhanced level ^ciC2 Can be determined from the relation ^C}.C2^C^C1^ ~ $ Q£lC2 + a'^cl£2^ [M

[0169] The determination of the liquid level is thus improved in the event of a thermal gradient within the container 1, between the first and third sensors IL

[0170] This step 170 of determining the improved level can be implemented after another implementation of this same step 170, typically to recalculate an improved level with a new section of the first and second pairs of sensors, for example to improve the accuracy of the liquid level estimation.

[0171] Alternatively, step 170 is implemented for a plurality of combinations of pairs of intermediate sensors 1 li. The plurality of combinations of pairs includes at least two pairs of intermediate sensors, and can include up to all combinations of pairs of intermediate sensors 1 li, including in combination with the pairs formed by the first and second sensors and by the third and fourth sensors.

[0172] The combinations are preferably defined so that each combination of pairs includes a pair of intermediate sensors positioned above the liquid level and a pair of intermediate sensors positioned below the liquid level.

[0173] It is then possible to determine an average liquid level, calculated as being equal to an average, weighted or unweighted, or a median, of the improved levels determined for each of the combinations of pairs of intermediate sensors 1 li.

[0174] Such an embodiment makes it possible to improve the robustness of the estimation of the liquid level with respect to a temperature gradient and to a stratification of the liquid in the container 1.

[0175] In one embodiment, only one of the pairs of intermediate sensors 1 li is considered, for the purpose of determining a refined liquid level. The intermediate sensor 1 li positioned between the first and third sensors 11 is called the first intermediate sensor 1 li, and the intermediate sensor 1 li positioned between the second and fourth sensors 11 is called the second intermediate sensor 1 li.

[0176] To this end, method 100 includes a step 160 for refining the liquid level. This refined level is estimated from a phase, called the third intermediate phase, determined by capturing a guided wave propagating between the first and third sensors 11 by the first intermediate sensor 11. This phase can be determined from the same guided wave used to determine the third phase at step 140 or be determined during a step 161 of determination of the third intermediate phase.

[0177] In particular, when the liquid level determined in step 150 is above the position of the first intermediate sensor 1 li, the refined level is determined from: • The first phase; • A second intermediate phase, corresponding to the phase of a guided wave determined by propagation of said guided wave according to the second mode of propagation in the wall 2 between the first and second intermediate sensors 1 li; • The third intermediate phase.

[0178] Step 160 may include a step 163 for determining the second intermediate phase. The guided wave used to determine this phase is emitted by either the first or second intermediate sensor 1li and is received by the second or first intermediate sensor 1li, respectively. The guided wave in question therefore propagates according to the second propagation mode, since these intermediate sensors are below the liquid level h. The second intermediate phase thus corresponds to the phase of the wave packet of the QS mode in the signal corresponding to the received wave.

[0179] As mentioned above, the second intermediate phase can be determined by techniques known per se. Typically, by the same approach as for determining the second phase.

[0180] Conversely, when the liquid level determined in step 150 is below the position of the first intermediate sensor 1 li, the refined level is determined from: • The second phase; • A first intermediate phase, corresponding to the phase of a guided wave determined by propagation of said guided wave according to the first mode of propagation in the wall 2 between the first and second intermediate sensors 1 li; • The third intermediate phase.

[0181] Step 160 may include a step 162 for determining the first intermediate phase. The guided wave used to determine this phase is emitted by either the first or the second intermediate sensor 1li and is received by the second or the first intermediate sensor 1li, respectively. The guided wave in question therefore propagates according to the first mode of propagation, since these intermediate sensors are above the level of liquid A. The first intermediate phase therefore corresponds to the phase of the wave packet of the Ao mode in the signal corresponding to the captured wave.

[0182] As mentioned above, the first intermediate phase can be determined by techniques known per se. Typically, by the same approach as for determining the first phase.

[0183] Step 160 then includes a step 164 for determining said refined level. This step is implemented similarly to step 150 for determining the liquid level h. In particular, the coefficients of the linear relationship are corrected by the first phase and the second intermediate phase, or by the first intermediate phase and the second phase, depending on whether the pair of intermediate sensors considered is below or above the liquid level determined in step 150, respectively, and where the refined level is estimated from the third intermediate phase.

[0184] Put another way, step 160 again implements steps 120 to 150 presented above, using the first and second intermediate sensors 1 li instead of the first and second sensors 11 or instead of the third and second sensors 11, depending on the liquid level h determined in step 150.

[0185] When the intermediate sensor pair C is below the liquid level h determined in step 150, the corrected coefficients can be determined such that = a^c + Pqsjc - and ^'oc = Kc + where: • and are the coefficients of the linear relationship, predetermined at during a calibration, implemented in a similar manner to the calibration described in step 110, but considering the intermediate sensors 1 li of the pair of intermediate sensors 1 li in question, instead of the third and fourth sensors 11; • is the distance between the first sensor 11 and the first sensor intermediate 1 li, and • ' with : PqSjC~ 'd'c • $QSC 'a second intermediate phase, • Dc the distance between the first and second intermediate sensors 1 li, • a phase of a guided wave determined in a similar way in the second reference phase, at step 113, but considering the first and second intermediate sensors 1 li instead of the third and fourth sensors 11.

[0186] When the intermediate sensor pair C is above the liquid level h determined in step 150, the corrected coefficients can be determined such that — Pqs ” $ A^Ç' oC — A),C Pa^cD^C' °ù • • has<!----> £ and are the coefficients of the linear relationship, predetermined at during a calibration, implemented in a similar manner to the calibration described in step 110, but considering the intermediate sensors 1 li of the pair of intermediate sensors 1 li in question, instead of the first and second sensors 11; • D3c is the distance between the third sensor 11 and the first intermediate sensor 1 li, and • 0. ri^r , with: ~ Dc • $AC 'a First intermediate phase, • Dc the distance between the first and second sensors intermediate 1 li, • a phase of a guided wave determined in a similar way to the first reference phase, at step 112, but considering the first and second intermediate sensors 1 li instead of the first and second sensors 11.

[0187] The refined level can thus be determined, depending on whether the pair of intermediate sensors is below or above the liquid level determined in step 150, from the linear relationship taking into account the corrected coefficients. For example, the refined level hc can be determined from the relationship

[0188] It appears that the first and / or second intermediate phases can be determined concurrently with the first and / or second phases. Thus, alternatively, these intermediate phases can be determined during steps 120 and 130 of determining the first and second phases.

[0189] Similarly, it appears that the third intermediate phase can be determined concurrently with the third phase, in particular by using the same guided wave as that used to determine the third phase. Thus, alternatively, this third intermediate phase can be determined during step 140 of the third phase.

[0190] Step 170 of determining the improved level, detailed above, is presented as using the liquid level h determined in step 150, but this step 170 can also or alternatively be implemented after the implementation of Step 160 of the refined level determination. In this case, the first and second pairs of intermediate sensors 1 li can be selected taking into account the refined level instead of the liquid level determined in step 150.

[0191] In an embodiment compatible with the preceding embodiments, one or more point levels are determined. These point levels indicate whether or not there is a presence of liquid at the sensor. The determination of the point levels is implemented by generating a transmitted wave between two sensors positioned at substantially the same height, or even at the same height, for example between the first and second sensors and / or between the third and fourth sensors, and / or between the first and second intermediate sensors 1 li and / or between the sensors of a pair of intermediate sensors lli.

[0192] The term "point level" refers to an estimate of the liquid level relative to a threshold above or below which the liquid level in the tank is located. It is therefore a binary estimate and less precise than the level determination proposed in steps 150, 160 and / or 170.

[0193] The liquid level is then determined via a step of estimating the point level of liquid in the container. This point level is determined via the emission, by one of the sensors considered, of a guided wave, which is captured by the other sensor considered, these sensors being positioned substantially at the same height.

[0194] Thus, as illustrated in Figure 6, when the wave propagates while the liquid level H is above the position of the sensors, i.e., in Figure 6 a), this wave propagates according to the second mode of propagation. Conversely, when the liquid level H is below the position of the sensors, i.e., in Figure 6 b), this wave propagates according to the first mode of propagation.

[0195] Consequently, the phase of the guided wave propagating between these two sensors provides information on the nature of the mode in which this wave propagates. By comparing the phase of this guided wave with a reference value, typically with the first reference phase and / or the second reference phase corresponding to this pair of sensors, it is possible to determine the propagation mode in which this wave propagates and therefore whether the liquid level H is above or below the position of the two sensors considered.

[0196] In one embodiment, it is possible to determine the first, second, third and fourth sensors 11 by knowledge of the point level.

[0197] In particular, in this embodiment, the plurality of sensors 11 comprises a plurality of pairs of sensors 11. The sensors 11 of each pair of sensors 11 are substantially positioned at the same height. One of the sensors 11 of each pair of sensors 11 is substantially vertically aligned, in particular is vertically aligned, with at least one of the sensors 11 of each other pair of sensors 11. Similarly, the other sensor 11 of each pair of sensors 11 is substantially vertically aligned, in particular is vertically aligned, with one of the sensors 11 of each other pair of sensors 11, for example is vertically aligned with the other sensor 11 of each other pair of sensors 11. In other words, each sensor of each pair of sensors is substantially vertically aligned, or even vertically aligned, with one of the sensors of each other pair of sensors.

[0198] In this embodiment, method 100 further includes a step 115, preliminary to step 120 of determining the first phase, and aimed at determining the first, second, third and fourth sensors.

[0199] Step 115 thus includes a step 115-a of emitting a plurality of guided waves from the sensor pairs 11. One of the sensors 11 of each pair emits one of the guided waves from the plurality of guided waves. This means that each guided wave from the plurality of guided waves is emitted by one of the sensors 11 of one of the sensor pairs 11.

[0200] Step 115 also includes a step 115-b of determining a phase velocity for each guided wave of the plurality of guided waves.

[0201] At this step 115, the first and second sensors are then determined to be the sensors of one of the sensor pairs 11 of the plurality of sensors 11 for which the phase velocity of the guided wave emitted by said sensor pair 11 is equal to the phase velocity of the first propagation mode.

[0202] At this step 115, also, the third and fourth sensors are then determined to be the sensors of one of the pairs of sensors 11 of the plurality of sensors 11 for which the phase velocity of the guided wave emitted by said pair of sensors 11 is equal to the phase velocity of the second propagation mode.

[0203] In particular, in one embodiment, the first and second sensors can be determined as being the sensors of the pair of sensors 11 of the plurality of sensors 11 for which: • The phase velocity of the guided wave emitted by said pair of sensors 11 is equal to the phase velocity of the first propagation mode; and for which. • The phase velocity of the guided wave emitted by the pair of sensors 11 positioned just below said pair of sensors 11 (for which the phase velocity of the emitted guided wave is equal to the phase velocity of the first mode) is equal to the phase velocity of the second propagation mode.

[0204] In this variant, the third and fourth sensors 11 are then the sensors of the pair of sensors 11 of the plurality of sensors 11 which is positioned just below the pair of sensors comprising the first and second sensors 11.

[0205] The phase velocities of the first and second propagation modes are known in particular, for example via a theoretical study or via calibration.

[0206] Furthermore, another aspect of the invention relates to a method for determining the level 5 of the liquid in the container 1 comprising the wall 2 delimiting the internal volume of the container 1 containing the liquid, the plurality of ultrasonic sensors 11 being arranged at a distance from the wall 2 and / or on the wall 2 and comprising a first and a second sensor 11 positioned at substantially the same height, the level 5 of liquid in the container 1 being determined from a phase of a guided wave determined by propagation of a guided wave between the first and second sensors 11. The liquid level is then determined as: • Above the height of the first and second sensors 11 when the phase velocity of the wave which propagates between these sensors 11, after emission by the first sensor 11 or the second sensor 11 and capture by the second sensor 11 or the first sensor 11, reciprocally, is equal to the phase velocity of the second mode of propagation; • Below the height of the first and second sensors 11 when the phase velocity of the wave which propagates between these sensors 11, after emission by the first sensor 11 or the second sensor 11 and capture by the second sensor 11 or the first sensor 11, reciprocally, is equal to the phase velocity of the first mode of propagation.

[0207] In this aspect of the invention, this liquid level is a point level.

[0208] In one embodiment, step 140 of determining the third phase is also implemented to determine a phase of a guided wave propagating between the second and fourth sensors 11 and step 150 of determining the liquid level h is implemented so as to also determine the liquid level h from this phase.

[0209] Such an embodiment makes it possible to compensate for the effects of the attitude of the aircraft and therefore to correct the estimation made of the liquid level by taking into account a possible inclination of the tank, typically by estimating that the liquid level in the tank is equal to an average of the two liquid levels determined.

[0210] For this same reason, it is also possible to determine, in step 161, a phase of a guided wave propagating between the second intermediate sensor 1 li and the second sensor 11-2 or the fourth sensor 11-4. It is thus possible to determine a refined level from this phase.

[0211] Similarly, it is possible to determine, in step 175, a phase of a guided wave propagating between the sensors of the first and second pairs of intermediate sensors 1 li which are positioned between the second and fourth sensors 11, in order to determine an improved level from this phase.

[0212] Implementation tests of Method 100 were carried out on an aluminum tank 3 mm thick and approximately 50 cm high, instrumented with four piezoelectric transducers and placed in a climatic chamber. The tank was filled with water. The tank has a width of 100 mm, a length of 141 mm, and a height of 500 mm.

[0213] Method 100 made it possible to obtain an accuracy of the order of 1 mm, in standard deviation, on the liquid level at constant temperature, and of 3.6 mm, in standard deviation, over a temperature range from 5°C to 55°C.

[0214] For comparison, for this same temperature range, an accuracy of 6.3 mm in standard deviation was obtained without using the correction terms and In this example, the proposed method 100 has an accuracy twice greater than an approach not based on the use of correction terms.< / l>

Claims

Demands

1. Method (100) for determining the level of a liquid (5) in a container (1) comprising a wall (2) delimiting an internal volume of the container (1) containing the liquid, a plurality of ultrasonic sensors (11) being disposed at a distance from the wall (2) and / or on the wall (2) and comprising: - A first and a second sensor (11) positioned approximately at the same height and above the liquid level (5), - A third and fourth sensor (11) positioned at approximately the same height and below the liquid level (5), the level (5) of liquid in the container (1) being determined (150) from: - A phase of a guided wave, called the first phase, determined (120) by propagation of the guided wave according to a first mode of propagation in the wall (2) between the first and second sensors (11), the first mode of propagation being the antisymmetric mode Ao of a guided Lamb wave - A phase of a guided wave, called the second phase, determined (130) by guided Fonde propagation according to a second propagation mode in the wall (2) between the third and fourth sensors (11), the second propagation mode being the Quasi-Scholte mode of a guided elastic wave; and - A phase of a guided wave, called third phase, determined (140) by propagation of guided Fonde in the wall (2) between the first and third sensors (11), according to the first mode of propagation above the level (5) of liquid and according to the second mode of propagation below the level (5) of liquid.

2. Method (100) according to claim 1, wherein the liquid level (5) is proportional to the third phase according to a linear relationship, the liquid level (5) being determined by said linear relationship, the coefficients of the linear relationship being predetermined during a calibration (110) then corrected (150) according to the first and second phases.

3. Method (100) according to claim 2, wherein the calibration (110) comprises: - Determine (111), for each reference level (5) of a plurality of reference levels of a liquid contained in the container (1), the phase of a guided wave propagating in the wall (2) between the first and third sensors (11), according to the first mode of propagation above said reference level (5) and according to the second mode of propagation below said reference level (5); - Determine (115) the coefficients of the linear relationship as a function of the plurality of reference levels and the guided Fonde phase propagating in the wall (2) between the first and third sensors (11), corresponding to each of said reference levels (5).

4. Method (100) according to claim 3, wherein the linear relationship is ¢ + Oa $ is 'a tr²^s² phase, h the level (5) of liquid, and a'# and 0'o are the coefficients of the corrected linear relation, such that a' = a+ , and oû: a# and are the predetermined coefficients during calibration (110), D{ is the distance between the first and third sensors (11), and and with: Pqs~ Dqs • the first phase, • (pQS the second phase, • the distance between the first and second caps eurs, • the distance between the third and fourth ca counters, • a phase of the guided wave propagating in the wall (2) according to the first mode of propagation between the first and second sensors (11) during calibration (110), * A guided phase propagating in the wall (2) according to the second mode of propagation between the third and fourth sensors (11) during calibration (110).

5. Method (100) according to any one of claims 3 and 4, further comprising, during calibration (110): - Determining (112) a first set of phases comprising, for each reference level of the plurality of reference levels, a guided ground phase propagating in the wall (2) between the first and second sensors (11); - Determining (113) a second set of phases comprising, for each reference level of the plurality of reference levels, a guided wave phase propagating in the wall (2) between the third and fourth sensors (11);and in which, during calibration (110), the phase of the guided wave propagating in the wall (2) between the first and third sensors (11) and determined for each reference level (5) of the plurality of reference levels is corrected (114) from the first set of phases and the second set of phases, and the coefficients of the linear relationship are calculated (115) as a function of the plurality of reference levels and the corrected phase corresponding to each of said reference levels.

6. Method (100) according to claim 5 wherein, during calibration (110), the phase of the guided wave propagating in the wall (2) between the first and third sensors (11), and determined for each reference level of the plurality of reference levels, is modified into a corrected phase such that:

7. - D{ is the distance between the first and third sensors (1 1), - and -, with D* the distance between Pa0= ~ï\~ the first and second sensors, and Dqs the distance between the third and fourth sensors; - $ is the phase of the guided wave of the first set of p steps that correspond to the reference level; and - is the phase of the guided wave of the second set of phases which correspond to the reference level h; ; - jfef is a phase selected from the first set dv A? e phases; and - is a phase selected from the second set of phases. Method (100) according to any one of the preceding claims, wherein the plurality of sensors (11) further comprises a first intermediate sensor (1 li) positioned between the first and third sensors (11) and a second intermediate sensor (1 li) positioned between the second and fourth sensors (11), and wherein: When the determined liquid level is above the position of the first intermediate sensor (1 li), a refined level (5) is determined (160) from: • The first phase, • A phase of a guided wave determined by guided Fonde propagation according to the second propagation mode in the wall (2) between the first and second intermediate sensors (lli), • A phase of a guided wave determined by guided Fonde propagation in the wall (2) between the first sensor (11) and the first intermediate sensor (lli); When the determined liquid level is below the position of the first intermediate sensor (lli), the refined level (5) is determined (160) from: • The second phase, • A phase of a guided wave, called the first intermediate phase, determined by propagation of the guided background according to the first mode of propagation in the wall (2) between the first and second intermediate sensors (lli), • A phase of a guided wave, called the third intermediate phase, determined by propagation of guided background in the wall (2) between the third sensor (11) and the first intermediate sensor (lli).

8. A method (100) according to any one of the preceding claims, wherein the plurality of sensors (11) comprises a first pair of intermediate sensors (lli) positioned above the liquid level (5) or above the refined level (5), and a second pair of intermediate sensors (lli) positioned below the liquid level (5) or below the refined level (5), the intermediate sensors (lli) of each pair being positioned substantially at the same height, one of the intermediate sensors (l1) of each of the first and second pairs of intermediate sensors (lli) being substantially vertically aligned with the first and third sensors (11), the first and second pairs of intermediate sensors (lli) being positioned between the first and third sensors (11), the method comprising: Determine (170) an improved liquid level from: • A phase of a guided wave determined (173) by propagation of guided Fonde according to the first mode of propagation in the wall (2) between the intermediate sensors (1 li) of the first pair of intermediate sensors (lli); • A phase of a guided wave determined (174) by guided wave propagation according to the second propagation mode in the wall (2) between the intermediate sensors (1 1i) of the second pair of intermediate sensors (lli); and • A phase of a guided wave determined (175) by guided wave propagation in the wall (2) between the intermediate sensors of the first and second pairs which are substantially vertically a aligned with the first and third sensors (11)•

9. A method according to any one of the preceding claims, wherein the plurality of sensors (11) comprises a plurality of pairs of sensors (11), the sensors (11) of each pair of sensors (11) being positioned substantially at the same height, each sensor (11) of each pair of sensors (11) being substantially vertically aligned with one of the sensors (11) of each other pair of sensors (11), the method comprising, prior to the determination (120) of the first phase: - Determination of a phase velocity for each guided wave of a plurality of guided waves, each guided wave of the plurality of guided waves being emitted by one of the sensors (11) of one of the pairs of sensors (11) of the plurality of pairs of sensors (11), said guided wave being captured by the other sensor (11) of said pair of sensors (11); in which the first and second sensors (11) are the sensors of one of the pairs of sensors (11) of the plurality of sensors (11) for which the phase velocity of the guided wave emitted by said pair of sensors (11) is equal to the phase velocity of the first propagation mode; and the third and fourth sensors (11) are the sensors of one of the pairs of sensors (11) of the plurality of sensors (11) for which the phase velocity of the guided wave emitted by said pair of sensors (11) is equal to the phase velocity of the second propagation mode.

10. A system for determining the level of a liquid in a container (1), the container (1) comprising a wall (2) delimiting an internal volume of the container (1) containing the liquid, the system comprising: - A plurality of ultrasonic sensors (11) arranged at a distance from the wall (2) and / or on the wall (2) comprising: • A first and a second sensor (11) positioned at approximately the same height and above the liquid level (5),

11.

12. • A third and a fourth sensor (11) positioned at approximately the same height and below the level (5) of liquid; - An acquisition module connected to the plurality of ultrasonic sensors (11) and configured to drive the plurality of ultrasonic sensors (11) so as to generate a guided wave and / or to acquire samples of a guided wave captured by one of the sensors (11) of the plurality of ultrasonic sensors (11); and - A processing module connected to the acquisition module and configured to implement method (100) according to one of claims 1 to 9 from the acquired samples. Computer program product comprising instructions which, when the program is executed on a computer, cause the computer to implement the steps of the method according to any one of claims 1 to 9. Computer-readable recording medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method according to any one of claims 1 to 9.

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