Capacitive measuring device for the quantity of fluid in a tank.

Abstract

The invention relates to a method for a capacitive measuring device (200) for measuring the quantity of fluid in a tank, comprising: an external electrode (102) immersed in said tank, an internal longitudinal electrode (104) inserted centered within said external electrode; and measuring electronics (110) for: creating, between said electrodes (102, 104), an alternating electrical potential difference (VG), different from a ground potential at at least one measurement frequency, and measuring an electrical signal relating to a capacitance seen by one of said electrodes (102, 104), and representative of the quantity of fluid in said tank; the external width (Le) of the internal electrode (104) being less than or equal to half the internal width (Lt) of said external electrode. It also relates to a tank equipped with such a measuring device and a vehicle equipped with such a tank or such a device. See Figure 2

Description

Title of the invention: Capacitive measuring device for a quantity of fluid in a reservoir.

[0001] The present invention relates to a capacitive measuring device for a quantity of fluid, and in particular hydrogen, contained in a tank. It also relates to a tank equipped with such a measuring device and a vehicle equipped with such a tank or such a device.

[0002] The field of the invention is generally the field of measuring the quantity of fluid, and in particular hydrogen, contained in a tank. Prior art

[0003] Hydrogen vehicles are equipped with a tank to store the hydrogen used as fuel. Such a tank can generally be a cryogenic tank, and in particular a thermally insulated tank (with a double vacuum jacket) whose purpose is to limit the unavoidable heat input from the outside.

[0004] For obvious reasons, it is important to know the amount of hydrogen in a vehicle's tank. However, hydrogen is more difficult to store compared to currently known fossil fuels. Therefore, the sensors used for fuels are not suitable for use with a hydrogen tank.

[0005] Several methods currently exist for determining the amount of hydrogen in a hydrogen tank. For example, some solutions use a combination of temperature and pressure sensors. These solutions suffer from a lack of precision, preventing them from accurately measuring the amount of hydrogen in a tank.

[0006] Other solutions implement a capacitive measurement device, such as that described in document FR2763124A1. These solutions are more precise than those mentioned above but do not allow the desired precision to be achieved.

[0007] One object of the present invention is to remedy at least one of the aforementioned drawbacks.

[0008] Another object of the invention is to propose a solution for measuring the quantity of fluid, and in particular hydrogen, in a tank more accurately than current solutions.

[0009] Another object of the invention is to offer a solution for measuring the quantity of fluid, and in particular hydrogen, in a tank, which is easier and less expensive to manufacture and implement. Description of the invention

[0010] The invention proposes to achieve at least one of the aforementioned objectives by means of a capacitive measurement device for a quantity of fluid contained in a reservoir, said device comprising: - a capacitive electrode, called external, in the form of a hollow, open, longitudinal tube immersed in said reservoir, - a longitudinal capacitive electrode, called internal, inserted into said external electrode and kept centered, or substantially centered, in said external electrode; - measurement electronics for: • create, between said electrodes, an alternating electrical potential difference (VG), different from a ground potential (M) at at least one measurement frequency, • measure an electrical signal relating to a capacitance seen by one of said electrodes, and representative of the quantity of fluid in said tank; characterized in that the outer width (Le) of the inner electrode is less than or equal to half the inner width (Lt) of said outer electrode.

[0011] Thus, the invention proposes a capacitive measurement device for the quantity of fluid in a tank; this solution is more precise and less expensive compared to a prior art solution based on a combination of pressure and temperature sensors.

[0012] Furthermore, the invention proposes dimensioning the internal electrode so that its external width, denoted Le, is less than half the internal width, denoted Lt, of the external electrode in which said internal electrode is immersed. Such an architecture allows for a more precise measurement of the quantity of fluid in a tank, compared to current capacitive measurement solutions. Indeed, the inventors observed that a distance that is too small between the internal electrode and the external electrode in which said internal electrode is placed leads to measurement errors that degrade measurement accuracy, particularly due to any lateral movement, even very slight, between the two electrodes. The invention makes it possible to limit these interferences by imposing a minimum distance between the internal electrode and the external electrode in which it is placed.

[0013] Furthermore, the inventors have noted that a small distance between the inner and outer electrodes implies very tight tolerances both on the respective architectures of the inner and outer electrodes, and on the positioning of the inner electrode within the outer electrode, in order to avoid degrading measurement accuracy. Adherence to these tight tolerances results in high complexity and cost, both for manufacturing and for the implementation of prior art capacitive solutions. By placing the internal electrode at a greater distance from the walls of the tube forming the external electrode, the invention avoids overly demanding tolerances, thereby reducing the complexity and cost associated with the manufacture and implementation of the proposed solution.

[0014] In this application, the term "quantity" of fluid means the mass of fluid in a tank, or the height of fluid in a tank if the fluid is a liquid, or the level of fluid in a tank if the fluid is a liquid. The quantity of fluid in the tank, and in particular its mass, can be measured or calculated based on the measured electrical signal, for example, by using the Clausius-Mossotti law relating the measured capacity to the mass of the fluid in the tank, or by using a predetermined calibration table.

[0015] In some embodiments, the fluid may be solely a liquid. In this case, the measured quantity may be the mass of the liquid, or the liquid level in the reservoir.

[0016] In other embodiments, the fluid may be a gas. In this case, the measured quantity may be the mass of the gas in the reservoir.

[0017] According to yet other embodiments, the fluid may be a mixture of liquid and gas. In this case, the invention makes it possible to measure the total quantity of the fluid, that is to say, the total quantity of the liquid and gaseous parts of the fluid in the tank. It should be noted that in some cases, the quantity of the gaseous part may be negligible, or neglected, compared to the liquid part. In this case, the quantity measured may be the mass of the liquid part, or the liquid level in the tank.

[0018] The "width" of the internal electrode is defined as the width of the electrode in a plane perpendicular to its longitudinal direction. For example, when the internal electrode has a circular cross-section, then the width corresponds to the diameter of the cylindrical section. When the internal electrode has a polygonal cross-section, then the width of the internal electrode corresponds to the greatest width of said polygonal section.

[0019] The "inner width" of the external electrode is defined as the inner width of the hollow tube forming said external electrode, in a plane perpendicular to its longitudinal direction. For example, when the external electrode has a circular cross-section, then the inner width corresponds to the inner diameter of the tube. When the external electrode has a polygonal cross-section, then the inner width of the external electrode corresponds to the smaller of the inner widths of the tube.

[0020] In this application, "liquid hydrogen" means fully liquid hydrogen, hydrogen in a supercritical state, or a mixture of hydrogen liquid-gas.

[0021] According to embodiments, the external electrode can be immersed in the reservoir in a vertical direction.

[0022] Alternatively, the external electrode can be immersed in the reservoir in a non-vertical direction, and in particular inclined with respect to the vertical direction.

[0023] The external electrode may be straight, or curved, at least in part. The internal electrode may be straight, or curved, at least in part.

[0024] According to embodiments, the internal electrode and the external electrode can be dimensioned so that 2.The <Lt< 50.Le.

[0025] According to embodiments, the internal electrode and the external electrode can be dimensioned so that 5.The <Lt< 50.Le.

[0026] According to embodiments, the internal electrode and the external electrode can be dimensioned so that 10. The <Lt< 50.Le.

[0027] According to embodiments, the internal electrode and the external electrode can be dimensioned so that 2O.The <Lt< 50.Le.

[0028] According to embodiments, the internal electrode can be flexible, or elastically deformable.

[0029] Thus, it is easier to insert the inner electrode into the outer electrode. For example, it is possible to bend the inner electrode during its insertion into the outer electrode. Therefore, inserting the inner electrode into the outer electrode requires less space and can be done in a more confined environment, for example, when the tank is installed in a vehicle.

[0030] Of course, alternatively, the internal electrode can be rigid or non-flexible.

[0031] According to embodiments, the internal electrode can be made of any electrically conductive material.

[0032] In particular, the internal electrode can be made of beryllium copper, steel, stainless steel, etc.

[0033] According to embodiments, the internal electrode may have a circular cross-section such that the width of said internal electrode corresponds to its diameter.

[0034] Such an internal electrode allows for more precise measurement and easier positioning in the external electrode.

[0035] Of course, the internal electrode may have a cross-section of a shape other than circular, and the invention is not limited to an internal electrode with a circular cross-section. For example, the internal electrode may have a square, triangular, elliptical, rectangular, etc., cross-section. In this case, the outer width of the internal electrode corresponds to the largest outer width of said cross-section.

[0036] According to some embodiments, the external electrode may be in the form of a tube with a circular cross-section such that its internal width corresponds to the inner diameter of said tube.

[0037] Such an external electrode allows for more precise measurement and easier positioning of the internal electrode in the external electrode.

[0038] Of course, the external electrode may have a cross-section of a shape other than circular, and the invention is not limited to an external electrode with a circular cross-section. For example, the external electrode may have a square, triangular, elliptical, rectangular, etc., cross-section. In this case, the inner width of the external electrode corresponds to the smallest inner width of said cross-section.

[0039] In all cases, the tube is open to allow the fluid in the reservoir into said tube.

[0040] The tube may be open at one end, or at each of its ends. Alternatively, or in addition, the tube may be open along its longitudinal wall, or at least one of its longitudinal walls.

[0041] According to embodiments, the external electrode can be made of an electrically conductive material, and in particular of a conductive metal.

[0042] In particular, the external electrode can be made of steel, stainless steel, carbon composite, etc.

[0043] According to advantageous embodiments, the device according to the invention may include at least one centering device to keep the internal electrode centered, or substantially centered, in the external electrode.

[0044] Thus, the position of the internal electrode relative to the external electrode is kept fixed and does not change over time, and in particular when the tank is moved or filled with fluid. This makes it possible to obtain and maintain good measurement accuracy of the quantity of fluid in the tank over time, regardless of tank movements or the quantity of fluid in the tank.

[0045] By "substantially centered", we mean an electrode which is centered with a tolerance of 10%, and in particular of 5%, of decentering with respect to the internal width of the external electrode.

[0046] According to embodiments, at least one centering device can be disposed on the internal electrode.

[0047] In this case, at least one centering device can be attached to the inner electrode before its insertion into the outer electrode. Then, the inner electrode, equipped with at least one centering device, is inserted into the outer electrode.

[0048] At least one centering device can be fixed to the internal electrode by any known fixing technique, for example by gluing, welding, clamping, brazing, etc.

[0049] When at least one centering device is disposed on the internal electrode, said centering device may have a suitable dimension chosen so as to have lateral, or radial, clearance. sufficient to allow, and in particular facilitate, the insertion of the inner electrode into the outer electrode, and the removal of the inner electrode from the outer electrode. Following a non-limiting example, the lateral clearance may be at least 100 µm to facilitate the installation or removal of the inner electrode.

[0050] Alternatively, or in addition, at least one centering device may be arranged in the external electrode. In this case, the external electrode, being in the form of a tube, has in said tube one or more centering devices fixed to the inner face of said tube, for example during the manufacture of said tube.

[0051] At least one centering device can be fixed in the external electrode by any known technique, for example by gluing, by welding, by clamping, etc.

[0052] At least one centering device may be an integral part of the external electrode and manufactured during the manufacture of the tube forming the external electrode, for example by molding or any other manufacturing process.

[0053] At least one centering device can be made of any material, compatible with the fluid in the tank, and not electrically conductive.

[0054] According to embodiments, at least one centering device can be made of Teflon, polyimide, and more generally of any material or composite in dielectric form and not electrically conductive.

[0055] At least one centering device can be of any known shape.

[0056] According to embodiments, at least one centering device may be in the general form of a disk, a cross, or a sphere, through which the internal electrode passes.

[0057] The device according to the invention may further include at least one means for positioning the internal electrode in the external electrode, making it possible to ensure the correct positioning of said internal electrode in said external electrode, in the longitudinal direction.

[0058] In particular, this positioning means ensures that the inner electrode is correctly inserted into the outer electrode in the longitudinal direction and that it is not pushed in too far or too far. This positioning means also prevents damage to the inner electrode during its insertion into the outer electrode.

[0059] According to embodiments, such a positioning means may include, or be presented in the form of, a graduation provided on the internal electrode.

[0060] Alternatively, such a positioning means may include a stop provided for the inner electrode, corresponding to the correct positioning of the inner electrode within the outer electrode, in the longitudinal direction. The stop may be disposed at a distal end of said inner electrode, i.e., the end immersed in the reservoir, or at a proximal end of said electrode internal, that is to say the one located on the side of the tank wall.

[0061] Alternatively, such a positioning means may include a stop provided for the external electrode, corresponding to the correct positioning of the internal electrode within the external electrode, in the longitudinal direction. The stop may be disposed at a distal end of said external electrode, i.e. the end immersed in the reservoir, or at a proximal end of said external electrode, i.e. the end located on the side facing the reservoir wall.

[0062] According to one embodiment, the device may include a mechanical stop disposed at the base, i.e. at the proximal end, of the internal electrode, or a stop at the proximal end of the external electrode, this end being able for example to come into contact with an electrically insulating interface.

[0063] According to embodiments, the external electrode may include, on the side of its proximal end, an interface for connecting said external electrode with the fluid reservoir.

[0064] Such an interface can be in any form. According to embodiment examples, this connecting interface can be in the form of a hollow tube, allowing the internal electrode to pass through when it is inserted into the external electrode.

[0065] The connecting interface can be electrically insulating. Thus, this connecting interface can act as an electrical insulator between the external electrode and the reservoir.

[0066] The connecting interface can be thermally insulating. Thus, this connecting interface can act as thermal insulation with the inside of the tank and the outside of the tank.

[0067] Thus, in these cases, the insertion of the internal electrode into the external electrode can be carried out by first passing through the interface between the external electrode and the wall of the fluid reservoir.

[0068] The measurement electronics can be configured to perform the measurement according to any known technique.

[0069] According to embodiments, the measurement electronics can be configured to perform a self-capacitance measurement.

[0070] In this case, according to an example embodiment, the external electrode can be biased at a ground potential (M), and the measurement electronics can be configured to: - bias the internal electrode at an alternating electrical potential (VG), different from said ground potential (M) at at least one measurement frequency, - measure an electrical signal, relative to a capacitance seen by said internal electrode, and representative of the quantity of fluid in said tank.

[0071] According to some embodiments, the measurement electronics can be configured to perform a measurement in transceiver mode. In this case, the internal electrode, respec tivement the external electrode, is used as the transmitter, and the external electrode, respectively the internal electrode, is used as the receiver.

[0072] In this case, the measuring electronics can be configured to: - polarize the internal electrode, respectively the external electrode, at an alternating potential different from a ground potential (M) and different from a potential of the external electrode, respectively of the internal electrode, at at least one measurement frequency, - to measure an electrical signal received by said external electrode, respectively by said internal electrode, at said measurement frequency, relating to a coupling capacitance between said electrodes, and representative of the quantity of fluid in said tank.

[0073] Advantageously, the device according to the invention can be used for the capacitive measurement of the quantity of hydrogen in a cryogenic tank.

[0074] According to another aspect of the invention, a fluid reservoir equipped with a capacitive measuring device according to the invention is proposed.

[0075] According to embodiments of the reservoir according to the invention, the external electrode may be integral with a wall of said reservoir, said wall comprising: - opposite said external electrode, an opening allowing the internal electrode to be inserted into said external electrode; and - a plug to seal said opening after insertion of the internal electrode into said external electrode.

[0076] In this case, the external electrode can be attached to a wall, and in particular to an internal wall of the tank, and immersed in the tank so that if the tank contains fluid, the internal electrode will be immersed in the fluid whose quantity is to be measured. The internal electrode can be inserted into the external electrode through an opening provided in the tank wall, opposite the tube. This opening allows for easy insertion of the internal electrode into the external electrode from outside the tank, so that it is not necessary to position the internal electrode inside the external electrode during the tank's manufacture. Most importantly, this opening allows for easy maintenance of the internal electrode, for example, for repair or replacement, from outside the tank.

[0077] The tank can be of any shape.

[0078] According to embodiments, the reservoir may have a cylindrical shape, arranged vertically or horizontally.

[0079] According to other embodiments, the reservoir may have a cubic, polygonal, spherical, etc. shape.

[0080] The tank can be of any size.

[0081]

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[0090] Depending on the embodiment, the tank can have the classic dimensions of tanks used in current vehicles. According to embodiments, the reservoir according to the invention can be a cryogenic hydrogen reservoir. According to another aspect of the invention, a vehicle is proposed equipped with a tank according to the invention, or with a capacitive measuring device according to the invention. The vehicle according to the invention can be a land vehicle, such as a car, a truck, a bus, a coach, etc. The vehicle according to the invention can be a railway vehicle, such as a locomotive, a train, a tram, etc. The vehicle according to the invention can be a maritime vehicle, such as a boat, a passenger liner, a ship, a submarine, etc. The vehicle according to the invention can be a flying vehicle, such as an airplane, a helicopter, a drone, etc. The vehicle according to the invention can be a space vehicle, such as a rocket, a satellite, etc. Description of the figures and methods of realization Other advantages and features will become apparent upon examination of the detailed description of non-limiting embodiments and the accompanying drawings, in which: - Fig. 1 is a schematic representation of a non-limiting example of an embodiment of a device according to the invention; - [Fig. 2] is a schematic representation of another example of a realization non-limiting description of a device according to the invention; - Fig. 3 is a schematic representation of an example of a non-implementation limiting of a measurement electronics that can be implemented in the present invention; and - [Fig. 4] is a schematic representation of another example of a realization non-limiting list of measurement electronics that can be implemented in the present invention; - [Fig. 5] is a schematic representation of an example of a non-implementation limiting of a reservoir according to the invention; and - [Fig. 6] is a schematic representation of an example of a non-implementation limiting of a vehicle according to the invention. It is understood that the embodiments described below are by no means limiting. In particular, variants of the invention may be conceived comprising only a selection of the features described below, isolated from the other features described, if this selection of features is sufficient to to confer a technical advantage or to differentiate the invention from the prior art. This selection includes at least one preferably functional feature without structural details, or with only some of the structural details if that part alone is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

[0091] In particular, all the variants and embodiments described are combinable with each other if there is no technical obstacle to this combination.

[0092] In the figures and in the rest of the description, elements common to several figures retain the same reference.

[0093] Fig. 1 is a schematic representation of a non-limiting example embodiment of a device according to the present invention.

[0094] Device 100 of [Fig. 1] can be used for the capacitive measurement of the quantity of fluid in a tank. For example, device 100 of [Fig. 1] can be used for the capacitive measurement of the quantity of hydrogen in a cryogenic tank.

[0095] The device 100 includes a capacitive electrode 102, referred to as the external electrode.

[0096] This external electrode 102 is in the form of a hollow, longitudinal tube designed to be immersed in the reservoir in a given direction, and in a non-limiting embodiment, in a vertical direction. The tube forming the external electrode 102 has one or more openings allowing the fluid in the reservoir to enter the tube. In the example shown, the tube forming the external electrode has openings on its sides and also at its lower end, in a vertical direction.

[0097] The external electrode 102 can be made of any electrically conductive material, for example steel, carbon composite, or stainless steel.

[0098] The tube forming the external electrode 102 has a cross-section of a given shape, for example square, elliptical, triangular, etc. In the example shown in [Fig.1], without loss of generality, the tube is considered to have a circular cross-section.

[0099] The tube forming the external electrode 102 has an internal width, and in particular an internal diameter, denoted Lt in the following.

[0100] The device 100 includes a capacitive electrode 104, referred to as the internal electrode.

[0101] The internal electrode 104 is disposed centered, or substantially centered, in the external electrode 102, that is to say in the tube forming the external electrode 104. The internal electrode 104 is electrically isolated from the external electrode 102 for example by an electrically insulating joint 108.

[0102] This internal electrode 104 can be in any form, for example in the form of shape of an electrically conductive wire.

[0103] The external electrode 104 can be made of any electrically conductive material, for example steel, or copper, or even stainless steel.

[0104] The internal electrode 104 has a cross-section of a given shape, for example square, elliptical, triangular, etc. In the example shown in [Fig.1], without loss of generality, the internal electrode 104 is considered to have a circular cross-section.

[0105] The internal electrode 104 has an external width, and in particular an external diameter, denoted Le in the following.

[0106] Preferably, the internal electrode 104 is flexible and elastically deformable, facilitating its insertion into the tube forming the external electrode 102.

[0107] In this configuration, the external electrode 102 is immersed in a fluid reservoir, and the internal electrode 104 is inserted centered within the external electrode 102. When the reservoir contains fluid, the fluid enters the internal space of the external electrode 102 and fills the space between the external electrode 102 and the internal electrode 104 to a height corresponding to the fluid level in the reservoir. The fluid between the external electrode 102 and the internal electrode 104 modifies the capacitive coupling between the electrodes 102 and 104. This modification of the capacitive coupling between the electrodes 102 and 104 is a function of the fluid level in the external electrode 102 between said external electrode and the internal electrode 104, and therefore of the fluid level in the reservoir.

[0108] Thus, by measuring a signal relating to this capacitive coupling, it is possible to determine the quantity of fluid in the tank.

[0109] The device 100 further comprises measuring electronics 110 for: - creating, between said electrodes, an alternating electrical potential difference (VG), different from a ground potential (M) at at least one measurement frequency, - to measure an electrical signal relating to a capacitance seen by one of said electrodes, this signal being representative of the quantity of fluid in said tank, as explained above.

[0110] Non-limiting examples of measurement electronics are described below with reference to FIGURES 3 and 4.

[0111] The device 100 may further include a linkage interface 112 at the proximal end of the external electrode 102, that is, the end opposite the end immersed in the reservoir, or the end intended to be on the side of a reservoir wall. In the example shown, and without loss of generality, the interface 112 is in the form of a hollow tube, allowing the internal electrode 104 to pass through when inserted into the external electrode 102. Furthermore, the linkage interface 112 may be thermally insulating. Optionally, the interface of The connection can be electrically insulating, thus allowing the external electrode 102 to be polarized at a different electrical potential than that of the reservoir, depending on the measurement technique used.

[0112] Under these conditions, the external electrode 102 can be fixed to, or made integral with, a wall of the tank through the linking interface 112.

[0113] Furthermore, the invention proposes dimensioning the internal electrode 104 such that its external width Le is less than half the internal width Lt of the tube, forming the external electrode 102, in which said internal electrode 104 is immersed. Such an architecture makes it possible to perform a more precise measurement of the quantity of fluid in a tank compared to current capacitive measurement solutions. Indeed, the inventors observed that too small a distance between the internal electrode 104 and the external electrode 102 (in which said internal electrode is located) introduces interference that degrades the measurement accuracy. The invention makes it possible to limit this interference by imposing a minimum distance between the internal electrode 104 and the external electrode 102 in which it is placed.

[0114] Furthermore, the inventors noted that a small distance between the internal electrode 104 and the external electrode 102 implies very tight tolerances both on the respective architectures of the internal electrode 104 and the tube forming the external electrode 102, and also on the positioning of the internal electrode 104 within said tube, in order to avoid degrading measurement accuracy. Adherence to these tight tolerances results in high complexity and cost for both the manufacture and implementation of prior art capacitive solutions. By placing the internal electrode 104 at a greater distance from the walls of the tube forming the external electrode 102, the invention avoids overly demanding tolerances, thereby reducing the complexity and cost associated with the manufacture and implementation of the proposed solution.

[0115] Thus, in the example of [Fig. 1], and in no way limitingly, the internal electrode 104 has an external width of 1 mm while the internal diameter Lt of the external electrode 102 can be on the order of 20 mm. Thus, we have Lt / Le=20.

[0116] In general, the invention proposes to dimension the electrodes 102 and 104 such that Lt>2.Le

[0117] Fig. 2 is a schematic representation of another non-limiting embodiment of a device according to the present invention.

[0118] Device 200 of [Fig. 2] can be used for the capacitive measurement of the quantity of fluid in a tank. For example, device 200 of [Fig. 2] can be used for the capacitive measurement of the quantity of hydrogen in a cryogenic tank.

[0119] Device 200 of [Fig.2] includes all the elements of device 100 of [Fig.1]

[0120] Furthermore, the device 200 includes several, in particular four, centering devices 202 arranged between the external electrode 102 and the internal electrode 104 to keep the internal electrode 104 centered, or substantially centered, within the external electrode 102. Thus, the internal electrode 104 is correctly positioned and its position is maintained throughout its use. This ensures greater measurement accuracy and maintains measurement accuracy over time.

[0121] The centering devices 202 can be arranged on the inner electrode 104 before its introduction into the outer electrode 104. In particular, the centering devices can be fixed to the inner electrode 104, for example by welding.

[0122] Each centering device 202 can have a suitable dimension so as to have a lateral, or radial, clearance sufficient to allow its insertion into the external electrode 102. The lateral clearance can, for example, be at least 100 µm to facilitate the installation or removal of the internal electrode 104 in the external electrode 102.

[0123] The centering devices 202 can be made of any non-conductive material compatible with the fluid in the tank. For example, and without loss of generality, each centering device 202 can be made of Teflon.

[0124] Each centering device 202 can have any shape adapted to its function, for example a disc or cross shape.

[0125] Of course, the number of centering devices 202 is not limited to the example given. Moreover, alternatively or in addition, at least one centering device may be arranged attached to the external electrode 102, or may be an integral part of the external electrode 102.

[0126] Furthermore, the device 200 also includes a mechanical stop 204 for ensuring correct positioning of the inner electrode 104 within the outer electrode 102 in the longitudinal direction. In the non-limiting example of [Fig. 2], this mechanical stop 102 is attached to the outer electrode 102, on the distal end of said outer electrode 102. Thus, the inner electrode 104 is inserted into the outer electrode 102 until the centering 202 closest to the distal end of the inner electrode 104 comes to rest against the mechanical stop 204. When this occurs, it indicates that the longitudinal positioning of the inner electrode 104 within the outer electrode 102 is correct, i.e., that the inner electrode 104 is correctly inserted into the outer electrode 102.

[0127] Of course, another means of longitudinally positioning the inner electrode in the outer electrode can be used instead of or in addition to the mechanical stop 204. Furthermore, the mechanical stop can be positioned elsewhere on the outer electrode 102, or elsewhere than on the outer electrode 102.

[0128] Figure 3 is a schematic representation of a non-limiting example of a measurement electronics that can be implemented in the device according to the invention.

[0129] The measuring electronics 300, shown in [Fig.3], can be the measuring electronics 110 of devices 100 and 200 of FIGURES 1 and 2.

[0130] The measuring electronics 300 can be realized in an analog or digital form, or a combination of at least one analog component and at least one digital component.

[0131] The measuring electronics 300 includes an oscillator 302 delivering an alternating voltage, denoted VG, and referenced to a ground potential 304.

[0132] The voltage VG is used as an excitation or detection potential to bias the internal electrode 104. It therefore includes at least one spectral component at the measurement frequency used by the measurement electronics 300. The external electrode 102 is biased to ground potential 304, which can for example be earth: for example, the external electrode 102 can be connected directly to the tank and thus be biased to the ground of this tank.

[0133] It should be noted that the internal electrode 104 and external electrode 102 are schematically represented in [Fig.3].

[0134] The measuring electronics 300 includes a current amplifier, or a charge amplifier, 310 represented by an operational amplifier (AO) 312 and a feedback capacitor 314 looping the output of the AO 312 back to the inverting input "-" of the AO 312.

[0135] Furthermore, in the example shown, the non-inverting input "+" of the AO 312 receives the voltage VG and the inverting input "-" of the AO 312 is intended to be connected to the internal electrode 104.

[0136] Under these conditions, the charge amplifier 310, and in particular the AO 312, provides at output a voltage Vs at the measurement frequency whose amplitude is proportional to the capacitance, denoted Ct, seen by the internal electrode 104 connected to its inverting input “-”.

[0137] The measuring electronics 300 may further include a conditioner 316 for obtaining a signal representative of the desired capacitance Ct. This conditioner 316 may include, for example, a synchronous demodulator for demodulating the signal with respect to a carrier at the measurement frequency. The conditioner 316 may also include an asynchronous demodulator or an amplitude detector. This conditioner 316 may, of course, be implemented in analog and / or digital (microprocessor) form and include all necessary means for filtering, conversion, processing, etc.

[0138] The conditioner 316 measures and provides the value of the voltage Vs.

[0139] The detection electronics 300 may further include a computing module 318 arranged to determine the quantity of fluid in a tank based on of the signal Vs, and therefore as a function of the capacitance Ct seen by the internal electrode, for example using the Clausius-Mossotti law relating the measured capacitance to the mass of the fluid in the tank or by using a predetermined calibration table.

[0140] This computing module 316 may, for example, include, or be implemented in the form of, a microcontroller, or an FPGA.

[0141] Of course, the measuring electronics 300 may include other components than those described.

[0142] The measuring electronics 300, or at least its sensitive part with the charge amplifier 310, can be referenced (or powered by referenced power supplies) to the potential VG, to minimize parasitic capacitances.

[0143] The potential of the non-inverting input (+) of the AO 3le can be used as an electrical guard at the connection and the connecting cable between the internal electrode 104 and the measuring electronics 300, in order to eliminate or greatly reduce the parasitic capacitances seen by the measuring electronics.

[0144] The measuring electronics 300 can also be referenced, in a more conventional way, to the ground potential 304.

[0145] The example given with reference to [Fig. 3] allows for a self-capacitance measurement. Of course, the invention is not limited to this example of measurement, and it is possible to perform a capacitive measurement using one of the internal and external electrodes as a transmitter and the other of said electrodes as a receiver.

[0146] Fig. 4 is a schematic representation of another non-limiting example of a capacitive measurement electronics that can be implemented in the device according to the invention.

[0147] The measuring electronics 400, shown in [Fig.4], can be the measuring electronics 110 of devices 100 and 200 of FIGURES 1 and 2.

[0148] The measuring electronics 400 can be realized in an analog or digital form, or a combination of at least one analog component and at least one digital component.

[0149] The measuring electronics 400 includes all the elements of the measuring electronics 300 of [Fig.3], except with regard to the differences indicated below.

[0150] In the measuring electronics 400, the external electrode 102 is used as a transmitter and the internal electrode 104 is used as a receiver. To achieve this, the external electrode is biased to potential VG with the source 302. The non-inverting input of the op-amp 312 is connected to the ground potential 304, and the inverting input of the op-amp 312 is connected to the internal electrode 104. Under these conditions, the charge amplifier 310, and in particular the op-amp 312, provides an output voltage Vs at the detection frequency and with an amplitude proportional to the coupling capacitance, denoted Cc, between the external electrode 102 and the internal electrode 104. It should be noted that in the configuration described with reference to [Fig.4], the external electrode 102 and the internal electrode 104 must be electrically isolated from the reservoir.

[0151] In this case, the electrical ground 304 can serve as a guard to eliminate or reduce possible leakage capacities of the connectors and cable used to connect the measuring electronics 300 to the electrodes 102 and 104, and in particular to the receiving electrode 104.

[0152] Alternatively, the internal electrode 104 and external electrode 102 can be interchanged for the measurement. In other words, the internal electrode 104 can be biased at potential Vg and used as the transmitter, and the external electrode 102 can be biased at ground potential 304 and used as the receiver by being connected to the inverting input of the op-amp.

[0153] More generally, the invention is not limited to the 300 and 400 measurement electronics examples described with reference to FIGURES 3 and 4.

[0154] Fig. 5 is a schematic representation of a non-limiting example embodiment of a tank according to the invention.

[0155] The reservoir 500 of [Fig.5] can be a fluid reservoir, and in particular a cryogenic hydrogen reservoir.

[0156] The tank 500 is equipped with a device according to the invention for capacitive measurement of the quantity of fluid 502 present in said tank 500.

[0157] In the example of [Fig.5], and without loss of generality, the reservoir 500 is a cryogenic hydrogen reservoir 502.

[0158] In the example of [Fig.5], and without loss of generality, the tank 500 is equipped with the device 200 of [Fig.2].

[0159] In the example shown, the external electrode 102, in the form of a tube, is fixed to a wall 504 of the tank 500. This wall 504 is, in use, an upper wall of the tank 500, so that the external electrode 102 is immersed in the tank in a vertical direction. Of course, alternatively, the external electrode 102 can be immersed in the tank in an inclined direction, and the invention is not limited to the embodiment shown in [Fig. 5] in which the external electrode 102 is immersed in the tank in a vertical direction.

[0160] According to one embodiment, the external electrode 102 can be fixed directly to the wall 504 of the tank 500. According to another embodiment, the external electrode 102 can be fixed to the wall 504 of the tank 500 by means of a connecting tube, this tube also serving to electrically isolate said external electrode 102 from the wall 504 of the tank 500.

[0161] Furthermore, the wall 504 has, at the point where the external electrode 102 is attached to said wall 504, an opening allowing the internal electrode 104 to be inserted into said external electrode 102. A plug 506 allows said opening to be closed after insertion of the internal electrode 104 into the external electrode 102.

[0162] In this configuration, the external electrode 102 is fixed to the wall 504 of the tank 500, and in particular to an internal face of the wall 504 and is immersed in the tank 500 and therefore in the fluid 502 contained in the tank 500. The internal electrode 104 can be inserted into the external electrode, or removed, through the opening provided in the wall of the tank 500, opposite the external electrode 102.

[0163] The 500 tank can be of any shape.

[0164] According to embodiments, the reservoir 500 may have a cylindrical shape, arranged vertically so that its cross-section is constant in the vertical direction.

[0165] The 500 tank can be of any size.

[0166] Fig. 6 is a schematic representation of a non-limiting example embodiment of a vehicle according to the invention.

[0167] The vehicle 600 of [Fig.6] can be equipped with a tank according to the invention, and in particular a cryogenic hydrogen tank according to the invention.

[0168] In particular, the 600 vehicle can be equipped with the 500 tank of the [Fig.5].

[0169] In the non-limiting example of [Fig.6], vehicle 600 is a car.

[0170] Generally speaking, the vehicle according to the invention can be any type of land vehicle, such as a car, a bus, a truck, a heavy goods vehicle, etc.

[0171] The vehicle according to the invention may be a railway vehicle, such as a locomotive, a train, a tram, etc.

[0172] The vehicle according to the invention may be a maritime vehicle, such as a boat, a passenger liner, a ship, a submarine, etc.

[0173] The vehicle according to the invention may be a flying vehicle, such as an airplane, a helicopter, a drone, etc.

[0174] The vehicle according to the invention may be a space vehicle, such as a rocket, a satellite, etc.

[0175] Of course, the invention is not limited to the examples just described.

Claims

Demands

1. Device (100;200) for capacitively measuring a quantity of fluid in a reservoir (500), said device (100;200) comprising: - a capacitive electrode (102), referred to as external, in the form of a hollow, open, longitudinal tube immersed in said reservoir (500), - a capacitive electrode (104), referred to as internal, longitudinal, inserted in said external electrode (102) and maintained centered, or substantially centered, in said external electrode (102); and - a measuring electronics (110;300;400) to: • create, between said electrodes (102,104), an alternating electrical potential difference (VG), different from a ground potential (304) at at least one measurement frequency, and • measure an electrical signal relating to a capacitance seen by one of said electrodes (102,104), and representative of the quantity of fluid in said tank (500);characterized in that the external width (Le) of the internal electrode (104) is less than or equal to half the internal width (Lt) of said external electrode (102).;

2. Device (100;200) according to the preceding claim, characterized in that the inner electrode (104) and the outer electrode (102) are dimensioned such that 2.The <Lt< 50.Le, et de préférence 5.Le < Lt <50.Le.

3. Device (100;200) according to any one of the preceding claims, characterized in that the internal electrode (104) is flexible, or elastically deformable.

4. Device (100;200) according to any one of the preceding claims, characterized in that the internal electrode (104) is made of beryllium copper, steel, stainless steel.

5. Device (100;200) according to any one of the preceding claims, characterized in that the internal electrode (104) has a circular cross-section such that the width of said internal electrode (104) corresponds to its diameter.

6. Device (100;200) according to any one of the preceding claims, characterized in that the external electrode (102) is in the form of a tube with a circular cross-section such that its internal width corresponds to the internal diameter of said tube.

7. Device (100;200) according to any one of the preceding claims, characterized in that the external electrode (102) is made of an electrically conductive material, and in particular of a conductive metal, or of carbon composite.

8. Device (200) according to any one of the preceding claims, characterized in that it further comprises at least one centerer (202) for keeping the internal electrode (104) centered in the external electrode (102).

9. Device (200) according to the preceding claim, characterized in that at least one centering device (202) is disposed on the internal electrode (104), for example by welding or brazing.

10. Device (200) according to any one of claims 8 or 9, characterized in that at least one centering device (202) is made of Teflon, polyimide, and more generally of any material or composite in dielectric form and not electrically conductive.

11. Device (200) according to any one of claims 8 to 10, characterized in that at least one centering device (202) is in the general form of a disc, a cross, or a sphere, through which the internal electrode (104) passes.

12. Device (100;200) according to any one of the preceding claims, characterized in that the external electrode (104) is polarized at a ground potential (304), and the measuring electronics (110;300) is configured to: - polarize the internal electrode (104) at an alternating electrical potential (VG), different from said ground potential (304) at at least one measurement frequency, - measure an electrical signal relating to a capacitance seen by said internal electrode (104) and representative of the quantity of fluid in the tank (500).

13. Device (100;200) according to any one of claims 1 to 11, characterized in that the measuring electronics (110;400) are configured

14.

15.

16.

17.

18. For : - polarize the internal electrode (104), respectively the external electrode (102), at an alternating potential different from a ground potential (304) and different from a potential of the external electrode (102), respectively of the internal electrode (104), at at least one measurement frequency, and - measure an electrical signal received by said external electrode (104), respectively by said internal electrode (102), at said measurement frequency, relating to a coupling capacitance between said electrodes (102,104), and representative of the quantity of fluid in the reservoir (500). Use of the device (100;200) according to any one of the preceding claims for the capacitive measurement of the quantity of hydrogen in a cryogenic tank (500). Fluid reservoir (500) equipped with a capacitive measuring device (100;200) according to any one of claims 1 to 13. Reservoir (500) according to the preceding claim, characterized in that the external electrode (102) is integral with a wall (504) of said reservoir (500), said wall (504) comprising: - opposite said external electrode (102), an opening allowing the internal electrode (104) to be inserted into said external electrode (102); and - a plug (506) allowing said opening to be closed after insertion of said internal electrode (104) into said external electrode (102). Reservoir (500) according to any one of claims 15 or 16, characterized in that it is a cryogenic hydrogen reservoir. Vehicle (600) equipped with a tank (500) according to any one of claims 15-17, or with a capacitive measuring device (100;200) according to any one of claims 1 to 13.

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