Device for the capacitive measurement of a quantity of fluid present in a tank

Abstract

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

Description

DESCRIPTION CAPACITIVE MEASURING DEVICE FOR A QUANTITY OF FLUID IN A TANK

[0001] The present invention relates to a device for capacitively measuring a quantity of fluid, and in particular hydrogen, located 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, found in a tank. State of the 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 inevitable heat input from outside.

[0004] For obvious reasons, it's important to know how much hydrogen is 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] There are currently various solutions available to determine 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 to allow the amount of hydrogen in a tank to be measured with sufficient accuracy.

[0006] Other solutions implement a capacitive measuring device, such as that described in document FR.2763124A1. These solutions are more precise than those mentioned above but do not allow the desired precision to be achieved.

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

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

[0009] Another aim of the invention is to propose 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. Statement of the invention

[0010] The invention proposes to achieve at least one of the aforementioned aims by a device for capacitively measuring a quantity of fluid located 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 capacitive electrode, called internal, longitudinal, inserted into said external electrode and kept centered, or substantially centered, in said external electrode; - measuring electronics for: ■ create, between said electrodes, an alternating electric potential difference (G), different from a ground potential (M) at at least one measurement frequency, ■ measuring an electrical signal relating to a capacity seen by one of said electrodes, and representative of the quantity of fluid found in said reservoir; characterized in that the external width (Le) of the internal electrode is less than or equal to half the internal width (Lt) of said external electrode.

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

[0012] Furthermore, the invention proposes to dimension the internal electrode so that its external width, denoted Le, is smaller than half of the internal width, denoted Lt, of the external electrode, in which said internal electrode is immersed. Such an architecture makes it possible to carry out a more precise measurement of the quantity of fluid in a tank, compared to current capacitive measurement solutions. Indeed, the inventors have noticed that too small a distance between the internal electrode and the external electrode in which said internal electrode is arranged is a source of measurement errors which degrade the measurement accuracy, in particular due to any lateral movement, even very small, 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 internal electrode and the external electrode implies very small tolerances both on the respective architectures of the internal electrode and the external electrode, but also on the positioning of the internal electrode introduced into the external electrode, in order not to degrade the measurement accuracy. Compliance with these small tolerances results in high complexity and cost both for the manufacturing and for the implementation of the capacitive solutions of the prior art. By placing the internal electrode at a greater distance from the walls of the tube forming the external electrode, the invention makes it possible to avoid having excessively demanding tolerances, which makes it possible to reduce the complexity and cost related to the manufacturing and implementation of the proposed solution.

[0014] In this application, "quantity" of fluid means the mass of fluid in a reservoir, or the height of fluid in a reservoir in the case where the fluid is a liquid, or the level of fluid in a reservoir in the case where the fluid is a liquid. The quantity of fluid in the reservoir, and in particular its mass can be measured, calculated, as a function of the measured electrical signal, for example by using the Clausius-Mossotti law linking 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 level of liquid 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 still 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 part and the gaseous part of the fluid in the tank. It should be noted that in certain cases, the quantity of the gaseous part may be negligible, or neglected, compared to the liquid part. In this case, the measured quantity may be the mass of the liquid part, or the level of liquid in the tank.

[0018] The "width" of the internal electrode means 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 cross-section. When the internal electrode has a polygonal cross-section, then the width of the internal electrode corresponds to the largest width of said polygonal cross-section.

[0019] The internal "width" of the external electrode means the internal 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 section, then the internal width corresponds to the internal diameter of the tube. When the external electrode has a polygonal section, then the internal width of the external electrode corresponds to the smallest internal width of the tube.

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

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

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

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

[0024] According to embodiments, the inner electrode and the outer electrode may be sized so that 2.The <Lt< 50. Le.

[0025] According to embodiments, the inner electrode and the outer electrode may be sized so that 5.The <Lt< 50. Le.

[0026] According to embodiments, the inner electrode and the outer electrode may be sized so that 10.The <Lt< 50. Le.

[0027] According to embodiments, the inner electrode and the outer electrode may be sized so that 2O.The <Lt< 50. Le.

[0028] Depending on the embodiments, the internal electrode may be flexible or elastically deformable.

[0029] This makes it easier to insert the inner electrode into the outer electrode. For example, it is possible to bend the inner electrode when inserting it into the outer electrode. Thus, inserting the inner electrode into the outer electrode requires less space and can be carried out 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 inflexible.

[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 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 of circular cross-section. For example, the internal electrode may have a cross-section of square, triangular, elliptical, rectangular, etc. shape. In this case, the external width of the internal electrode corresponds to the largest external width of said cross-section.

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

[0037] Such an external electrode allows for more accurate 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 of circular cross-section. For example, the external electrode may have a cross-section of square, triangular, elliptical, rectangular, etc. shape. In this case, the internal width of the external electrode corresponds to the smallest internal width of said cross-section.

[0039] In all cases, the tube is opened to allow the fluid in the reservoir to flow into the 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 at 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 comprise 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 have and maintain good measurement accuracy of the quantity of fluid in the tank, over time, and this independently of the movements of the tank, or the quantity of fluid in the tank.

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

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

[0047] In this case, the 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 the at least one centering device, is inserted into the outer electrode.

[0048] At least one centering device may 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 arranged on the internal electrode, said centering device may have a dimension adapted and chosen so as to have sufficient lateral or radial clearance to allow, and in particular to facilitate, the insertion of the internal electrode into the external electrode, and the disinsertion of the internal electrode from the external electrode. According to a non-limiting example, the lateral clearance can be at least 100 pm to facilitate installation or removal of the internal electrode.

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

[0051] At least one centering device may 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 and non-electrical conductive form.

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

[0056] According to embodiments, at least one centering device may be in the general form of a disc, a crosspiece, or a sphere, crossed by the internal electrode.

[0057] The device according to the invention may further comprise 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 makes it possible to ensure that the internal electrode is correctly inserted into the external electrode, in the longitudinal direction, and that it is not pushed too far, or not far enough, into the external electrode. This positioning means also makes it possible to avoid damaging the internal electrode when it is inserted into the external electrode.

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

[0060] Alternatively, such positioning means may comprise a stop provided on the internal electrode, corresponding to the correct positioning of the internal electrode in the external electrode, in the longitudinal direction. The stop may be arranged at a distal end of said internal electrode, i.e. the end immersed in the reservoir, or at a proximal end of said internal electrode, i.e. the one located on the side of the wall of the reservoir.

[0061] Alternatively, such positioning means may comprise a stop provided on the external electrode, corresponding to the correct positioning of the internal electrode in the external electrode, in the longitudinal direction. The stop may be arranged 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 one located on the side of the wall of the reservoir.

[0062] According to an exemplary embodiment, the device may comprise a mechanical stop arranged 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 comprise, on 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 exemplary embodiments, this connection 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 bonding interface can be electrically insulating. Thus, this bonding interface can act as an electrical insulator between the external electrode and the reservoir.

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

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

[0068] The measuring electronics can be configured to perform the measurement using 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 exemplary embodiment, the external electrode can be polarized to a ground potential (M), and the measuring electronics can be configured to: - polarizing the internal electrode at an alternating electric potential (G), different from said ground potential (M) at at least one measurement frequency, - measure an electrical signal, relating to a capacity seen by said internal electrode, and representative of the quantity of fluid found in said reservoir.

[0071] According to embodiments, the measuring electronics can be configured to perform a transmitter-receiver measurement. In this case, the internal electrode, respectively the external electrode, is used as a transmitter, and the external electrode, respectively the internal electrode, is used as a receiver.

[0072] In this case, the measuring electronics can be configured to: - polarizing 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 measuring frequency, - measuring an electrical signal received by said external electrode, respectively by said internal electrode, at said frequency of measurement, relating to a coupling capacity between said electrodes, and representative of the quantity of fluid found in said reservoir.

[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, there is provided a fluid reservoir equipped with a capacitive measuring device according to the invention.

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

[0076] In this case, the external electrode may be secured 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, said internal electrode will be immersed in said fluid whose quantity is to be measured. The internal electrode may be inserted into the external electrode through an opening provided in the wall of the tank, 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 place said internal electrode in the external electrode when manufacturing the tank. Above all, this opening allows for easy maintenance of the internal electrode, for example for its repair or replacement, from outside the tank.

[0077] The tank can be of any shape.

[0078] Depending on the 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] According to embodiments, the tank may have the classic dimensions of tanks used in current vehicles.

[0082] According to embodiments, the tank according to the invention may be a cryogenic hydrogen tank.

[0083] According to another aspect of the invention, a vehicle is provided equipped with a tank according to the invention, or with a capacitive measuring device according to the invention.

[0084] The vehicle according to the invention may be a land vehicle, such as a car, a truck, a bus, a coach, etc.

[0085] The vehicle according to the invention may be a railway vehicle, such as a locomotive, a train, a tram, etc.

[0086] The vehicle according to the invention may be a maritime vehicle, such as a boat, a liner, a ship, a submarine, etc.

[0087] The vehicle according to the invention may be a flying vehicle, such as an airplane, a helicopter, a drone, etc.

[0088] The vehicle according to the invention may be a space vehicle, such as a rocket, a satellite, etc. Description of figures and embodiments

[0089] Other advantages and characteristics will appear on examining the detailed description of non-limiting embodiments, and the attached drawings in which: - FIGURE 1 is a schematic representation of a non-limiting exemplary embodiment of a device according to the invention; - FIGURE 2 is a schematic representation of another non-limiting exemplary embodiment of a device according to the invention; - FIGURE 3 is a schematic representation of a non-limiting exemplary embodiment of measuring electronics that can be implemented in the present invention; and - FIGURE 4 is a schematic representation of another non-limiting exemplary embodiment of measuring electronics that can be implemented in the present invention; - FIGURE 5 is a schematic representation of a non-limiting exemplary embodiment of a tank according to the invention; and - FIGURE 6 is a schematic representation of a non-limiting exemplary embodiment of a vehicle according to the invention.

[0090] It is understood that the embodiments which will be described below are in no way limiting. In particular, it is possible to imagine variants of the invention comprising only a selection of characteristics described below isolated from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art. This selection includes at least one preferably functional characteristic without structural details, or with only a part of the structural details if it is this part which is only sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art.

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

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

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

[0094] The device 100 of FIGURE 1 may be used for capacitive measurement of the quantity of fluid in a reservoir. For example, the device 100 of FIGURE 1 can be used for capacitive measurement of the amount of hydrogen in a cryogenic tank.

[0095] The device 100 comprises a capacitive electrode 102, called the external electrode.

[0096] This external electrode 102 is in the form of a hollow, longitudinal tube, intended to be immersed in the reservoir in a given direction, and according to a non-limiting example of embodiment in a vertical direction. The tube forming the external electrode 102 comprises one or more openings allowing the fluid in the reservoir to penetrate into said tube. In the example shown, the tube forming the external electrode comprises openings on the sides but also in the lower part, 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 section of a given shape, for example square, elliptical, triangular, etc. In the example shown in FIGURE 1, without loss of generality, it is considered that the tube has a circular section.

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

[0100] The device 100 comprises a capacitive electrode 104, called the internal electrode.

[0101] The internal electrode 104 is arranged 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 insulated 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 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 section of a given shape, for example square, elliptical, triangular, etc. In the example shown in FIGURE 1, without loss of generality, it is considered that the internal electrode 104 has a circular section.

[0105] The internal electrode 104 has an external width, and in particular an external diameter, noted 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 outer electrode 102 is immersed in a reservoir of fluid, and the inner electrode 104 is inserted centered in the outer electrode 102. When the reservoir comprises fluid, the latter penetrates into the interior space of the outer electrode 102, and fills the space between the outer electrode 102 and the inner electrode 104, to a height corresponding to the fluid level in the reservoir. The fluid between the outer electrode 102 and the inner electrode 104 modifies the capacitive coupling between the electrodes 102 and 104. The modification of the capacitive coupling between the electrodes 102 and 104 is a function of the fluid level in the outer electrode 102 between said outer electrode and the inner 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 electric potential difference (G), different from a ground potential (M) at at least one measurement frequency, - measure an electrical signal relating to a capacity seen by one of said electrodes, this signal being representative of the quantity of fluid found in said reservoir, as explained above.

[0110] Non-limiting examples of measurement electronics are described below with reference to FIGURES 3 and 4. [YES] The device 100 may further comprise a connecting interface 112 at the proximal end of the external electrode 102, i.e. the end opposite the one immersed in the reservoir, or the end intended to be on the side of a wall of the reservoir. 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 when it is inserted into the external electrode 102. In addition, the connecting interface 112 may be thermally insulating. Optionally, the connecting interface may be electrically insulating, thus making it possible to polarize the external electrode 102 at an electrical potential different from 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 connection interface 112.

[0113] Furthermore, the invention proposes to dimension the internal electrode 104 so that its external width Le is smaller than half of 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 carry out a more precise measurement of the quantity of fluid in a tank compared to current capacitive measurement solutions. Indeed, the inventors have noticed that too small a distance between the internal electrode 104 and the external electrode 102 (in which said internal electrode is arranged) introduces interference which 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 have noted that a small distance between the internal electrode 104 and the external electrode 102 implies very small tolerances both on the respective architectures of the internal electrode 104 and the tube forming the external electrode 102, but also on the positioning of the internal electrode 104 in said tube, in order not to degrade the measurement accuracy. Compliance with these small tolerances results in high complexity and cost both for manufacturing but also for implementation of the capacitive solutions of the prior art. By placing the internal electrode 104 at a greater distance from the walls of the tube forming the external electrode 102, the invention makes it possible to avoid having excessively demanding tolerances, which makes it possible to reduce the complexity and cost linked to the manufacture and implementation of the proposed solution.

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

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

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

[0118] The device 200 of FIGURE 2 may be used for capacitive measurement of the amount of fluid in a tank. For example, the device 200 of FIGURE 2 may be used for capacitive measurement of the amount of hydrogen in a cryogenic tank.

[0119] The device 200 of FIGURE 2 includes all of the elements of the device 100 of FIGURE 1.

[0120] In addition, the device 200 comprises 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, in the external electrode 102. Thus, the internal electrode 104 is well positioned and its position is maintained throughout its use. This makes it possible to ensure better measurement accuracy, and to maintain the measurement accuracy over time.

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

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

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

[0124] Each centering device 202 may have any shape suitable for its function, for example a disc or crosshead shape.

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

[0126] In addition, the device 200 further comprises a mechanical stop 204 allowing correct positioning of the internal electrode 104 in the external electrode 102 in the longitudinal direction. In the non-limiting example of FIGURE 2, this mechanical stop 102 is arranged integral with the external electrode 102, on the side of the distal end of said external electrode 102. Thus, the internal electrode 104 is inserted into the external electrode 102 until the centering device 202 closest to the distal end of the internal electrode 104 abuts against the mechanical stop 204. When this is the case, this indicates that the longitudinal positioning of the internal electrode 104 in the external electrode 102 is correct, that is to say that the internal electrode 104 is correctly pushed into the external electrode 102.

[0127] Of course, another means of longitudinally positioning the inner electrode in the outer electrode may be used instead of or in addition to the mechanical stop 204. In addition, the mechanical stop may 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 exemplary embodiment of measuring electronics that can be implemented in the device according to the invention.

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

[0130] The measuring electronics 300 may be implemented 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 comprise an oscillator 302 delivering an alternating voltage, denoted VG, and referenced to a ground potential 304.

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

[0133] It should be noted that the internal 104 and external 102 electrodes are shown schematically in FIGURE 3.

[0134] The measurement electronics 300 include a current amplifier, or 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 G 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, noted Ct, seen by the internal electrode 104 connected to its inverting input “-”.

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

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

[0139] The detection electronics 300 may further comprise a calculation module 318 arranged to determine a quantity of fluid located in a reservoir as a function of the signal V s, and therefore depending on the capacitance Ct seen by the internal electrode, for example using the Clausius-Mossotti law linking the measured capacitance to the mass of the fluid in the tank or using a predetermined calibration table.

[0140] This calculation module 316 may for example comprise, or be produced 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 G, to minimize parasitic capacitances.

[0143] The potential of the non-inverting input (+) of the AO 31é can be used as an electrical guard at the level of the connectors 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 manner, to the ground potential 304.

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

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

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

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

[0149] The measurement electronics 400 include all of the elements of the measurement electronics 300 of FIGURE 3, except for the differences noted 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 do this, the external electrode is polarized at the potential G with the source 302. The non-inverting input of the AO 312 is connected to the ground potential 304 and the inverting input of the AO 312 is connected to the internal electrode 104. Under these conditions, the charge amplifier 310, and in particular the AO 312, provides at output a voltage Vs at the detection frequency and with an amplitude proportional to the coupling capacitance, denoted Ce, between the external electrode 102 and the internal electrode 104. It should be noted that in the configuration described with reference to FIGURE 4, the external electrode 102 and the internal electrode 104 must be electrically isolated from the tank.

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

[0152] Of course, alternatively, the internal 104 and external 102 electrodes can be interchanged for the measurement. In other words, the internal electrode 104 can be polarized at the potential g and be used as a transmitter, and the external electrode 102 can be biased to the ground potential 304 and be used as a receiver by being connected to the inverting input of the AO.

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

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

[0155] The tank 500 of FIGURE 5 may be a fluid tank, and in particular a cryogenic hydrogen tank.

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

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

[0158] In the example of FIGURE 5, and without loss of generality, the tank 500 is equipped with the device 200 of FIGURE 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 plunges into the tank in a vertical direction. Of course, alternatively, the external electrode 102 can be plunged into the tank in an inclined direction, and the invention is not limited to the embodiment shown in FIGURE 5 in which the external electrode 102 plunges into the tank in a vertical direction.

[0160] According to an exemplary embodiment, the external electrode 102 can be fixed directly to the wall 504 of the tank 500. According to an exemplary embodiment, the external electrode 102 can be fixed to the wall 504 of the tank 500 via a connecting tube, this tube also being able to serve to electrically insulate said external electrode 102 from the wall 504 of the tank 500.

[0161] In addition, the wall 504 comprises, at the level of the attachment of the external electrode 102 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 secured to the wall 504 of the reservoir 500, and in particular to an internal face of the wall 504 and plunges into the reservoir 500 and therefore into the fluid 502 located in the reservoir 500. The internal electrode 104 can be inserted into the external electrode, or removed, through the opening provided in the wall of the reservoir 500, opposite the external electrode 102.

[0163] The 500 tank can be any shape.

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

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

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

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

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

[0169] In the non-limiting example of FIGURE 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 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 which have just been described.

Claims

CLAIMS 1. Device (100;200) for capacitively measuring a quantity of fluid located in a reservoir (500), said device (100;200) comprising: - a capacitive electrode (102), called external, in the form of a hollow, open longitudinal tube, immersed in said reservoir (500), - a capacitive electrode (104), called internal, longitudinal, inserted into said external electrode (102) and kept centered, or substantially centered, in said external electrode (102); and - measuring electronics (110;300;400) for: ■ create, between said electrodes (102, 104), an alternating electric potential difference (G), different from a ground potential (304) 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 located in said reservoir (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 internal electrode (104) and the external electrode (102) are dimensioned so 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 section circular so 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 of circular section so 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 centering device (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 arranged 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 and non-electrical conductive form.

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 crosspiece, or a sphere, crossed by the internal electrode (104).

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

13. Device (100;200) according to any one of claims 1 to 11, characterized in that the measuring electronics (110;400) is configured to: - polarizing 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 - measuring an electrical signal received by said external electrode (104), respectively by said internal electrode (102), at said measurement frequency, relating to a coupling capacity between said electrodes (102, 104), and representative of the quantity of fluid in the reservoir (500).

14. 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).

15. Fluid reservoir (500) equipped with a capacitive measuring device (100; 200) according to any one of claims 1 to 13.

16. Tank (500) according to the preceding claim, characterized in that the external electrode (102) is integral with a wall (504) of said tank (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) for closing said opening after insertion of said internal electrode (104) into said external electrode (102).

17. Tank (500) according to any one of claims 15 or 16, characterized in that it is a cryogenic hydrogen tank.

18. 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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