Patent Description:
A capacitive level gauge is based on measuring the capacitance between two electrodes immersed in a dielectric medium in a container, like a gas or a liquid. The level of the medium in the container determines the length of the electrodes whose capacitance is modified. It can therefore be determined by the measurement of the capacitance.

Prior art patent document published <CIT> discloses a capacitive level gauge according to the preamble of claim <NUM> and a spacer for electrodes of a capacitive level gauge, according to the preamble of claim <NUM>.

Prior art patent document published <CIT> discloses a valve assembly with a capacitive level gauge. The assembly comprises a body to be mounted on a wall of a container, said body comprising a gas passage so as to allow a flow of gas form the container to an outlet, when in service, and also in the reverse direction, when refilling the container. An electrical lead extends also through the body in a gas tight fashion. The assembly comprises also two parallel lamellar electrodes attached to an inner side of the body. More specifically, one of the electrodes is attached to the body, e.g. by press-fitting, whereas the other one is distant from the body and is electrically connected to the electrical lead via a wire. The electrodes are held at a constant distance relative to each other by means of spacers interposed between the electrodes and held in position by a fastener such as a river or a screw extending through holes in said electrodes and spacers. Assembling these spacers is time consuming and also can weaken the electrodes in view of the holes made there through.

Prior art patent document published <CIT> discloses a capacitive level gauge with a tubular electrode and a rod-shaped electrode concentric inside the tubular electrode. The rod-shaped electrode comprises on its front end an axial hole that is inserted and fitted around an electrical lead extending through the body in a gas tight fashion. The mounting of the electrodes is thereby rendered easier and the electrical connection is more reliable. However concentric electrodes have for drawback that they cannot be elastically bent, e.g. during insertion thereof in the container during assembly.

Prior art patent document published <CIT> discloses a capacitive level gauge with two rod-shaped and parallel electrodes. They are held in position relative to each other by means of spacers with a general shape of a C and with two recesses in which the rod-shaped electrodes can snapped. The mounting of the spacers is particularly convenient and rapid. Such spacers are however suitable specifically for rod-shaped electrodes. Such electrodes are not as such flexible. Also the sensitivity of the sensor is potentially lowered in view of the distance between the electrodes and their reduced outer surfaces.

The invention has for technical problem to overcome at least one of the drawbacks of the above cited prior art. More specifically, the invention has for technical problem to provide an improved capacitive level gauge with regard to the electrodes, in particular their sensitivity and the ease of mounting thereof, while remaining versatile for various shapes of containers.

The invention is directed to a capacitive level gauge for a container of a medium like compressed gas or liquid, comprising: a body configured for being mounted on the container two parallel lamellar electrodes extending from the body, for being inside the container and in contact with the medium; wherein the capacitive level gauge further comprises at least one spacer with two slots engaging with the two electrodes, respectively, maintaining a constant distance between said electrodes, wherein the at least one spacer elastically deforms the electrodes so as to generate frictional forces holding said spacer in place without further fixation means.

According to a preferred embodiment, the at least one spacer is made of plastic.

According to a preferred embodiment, several of the at least one spacer are distributed along the electrodes.

According to a preferred embodiment, the at least one spacer is configured to be slid around and along the electrodes.

According to a preferred embodiment, for each of the at least one spacer, the two slots are generally parallel to each other.

According to a preferred embodiment, the electrodes show a curved cross-sectional profile, said profile preferably being curved with a radius greater than <NUM> and/or lower than <NUM>.

Advantageously, the electrodes have a length that is greater than <NUM> and/or less than <NUM>.

Advantageously, the slots have a length that is greater than <NUM> and/or less than <NUM>.

According to a preferred embodiment, for each of the at least one spacer, the two slots are generally straight.

Advantageously, the body is configured for being mounted on the container and has an inner side in contact with the medium when mounted on said container; an electrical lead extending in a gas tight manner through the body; a first one of the electrodes being electrically connected to the electrical lead and the second one of said electrodes being electrically connected to the body; wherein the electrical lead is protruding on the inner side and the first electrode has an end lateral face in pressure contact with the electrical lead, said contact providing the electrical connection between said electrode and lead.

Advantageously, the second electrode has an end lateral face in pressure contact with a body portion, said contact providing the electrical connection between said electrode and body.

Advantageously, the end lateral faces of the first and second electrodes are at the same level along said electrodes.

Advantageously, the body portion is protruding on the inner side of the body.

Advantageously, the electrical lead is at a central position of the body, the body portion being off-set from said central position.

Advantageously, the body portion is arcuate with two ends forming distant contact areas with the second electrode.

Advantageously, the gauge further comprises a member mounted on the body and holding the first electrode in pressure contact with the electrical lead, said member being of electrically insulating material.

Advantageously, the holding member holds the second electrode in pressure contact with the body portion.

Advantageously, the holding member comprises a first slot tightly receiving the first electrode.

Advantageously, the holding member comprises a second slot tightly receiving the second electrode.

Advantageously, the holding member is snap fitted in the body.

Advantageously, the holding member comprises a proximal front end engaging with the body and a distal end holding the first electrode and, where appropriate, the second electrode.

Advantageously, the holding member comprises a fastener extending through the distal end, the first electrode and, where appropriate, the second electrode.

Advantageously, the body comprises on the inner side a cavity receiving the proximal front end of the holding body.

Advantageously, the end lateral face of the first electrode and, if appropriate of the second electrode, is on the convex side of said electrode.

Advantageously, the gauge further comprises an electronic display device electrically connected to the electric lead and the body and configured for displaying an indication of the level of gas in the container.

Advantageously, the body comprises a gas inlet on the inner side, a gas outlet on an outer side, a passage interconnecting said inlet and outlet, and a valve for selectively shutting-off said passage.

The invention is also directed to a spacer for electrodes of a capacitive level gauge, comprising an element with areas configured for receiving and holding the electrodes; wherein the areas are slots configured for receiving lamellar electrodes, wherein each of the slots comprises a main portion and end portions, said end portions having an average width that is less than an average width of the main portion.

Advantageously, the element is plate with a rectangular shape. The outer edge thereof is advantageously rounded.

According to a preferred embodiment, each of the slots is elongate and forms a closed contour.

According to a preferred embodiment, the main portion comprises a central sub-portion with a reduced width.

According to a preferred embodiment, each of the slots shows a straight neutral axis.

The invention is particularly interesting in that it provides an interesting solution for providing a versatile capacitive level gauge that is also easy to manufacture and to customise during installation on a container. Lamellar electrodes are particularly interesting in that they can be elastically bent during insertion into various shapes of containers. The spacer according to the invention provides a cheap and performing solution for keeping a constant distance between the electrodes. Also, during mounting of a capacitive level gauge, it is common to adapt the length of the electrodes to the container. In that case, the spacers can be moved along the pair of electrodes whose length has been adapted, e.g. by cutting, and positioned at proper positions which can depend on the shape of the container. The arcuate or curved cross-sectional profile of the electrodes is interesting in that that it provides a certain rigidity which is useful for keeping a proper configuration and position in a container while being elastically flexible, in particular once the profile of the electrode is flattened upon bending, similarly to a tape measure whose ribbon is made of metal with a curved cross-section. This means also that the electrodes can be elastically rolled for transport and packaging, which is particularly useful, for their length can be of several meters, depending on the application.

<FIG> illustrate a capacitive level gauge according to a first embodiment of the invention.

<FIG> shows a perspective view and a corresponding sectional view of the gauge.

The level gauge <NUM> comprises a body <NUM> designed to be mounted on a wall of a container (not represented). The container can for instance be filled with compressed and liquefied gas like for example butane or propane. In this embodiment, a gasket <NUM> is provided on a ring-shaped surface of the body for contacting a corresponding surface on the wall of the container, so as to provide a gas tight contact between an inner side <NUM> and an outer side <NUM> of the body. For instance, the body <NUM> is provided with four holes receiving fastening screws configured for engaging corresponding female threads on the wall of the container. It is however understood that other configurations for fastening the body to the container and/or for providing a gas tight contact with the container can be considered, in particular according to the technical common knowledge in the field of pressurized containers.

As this is apparent in <FIG>, the gauge <NUM> comprises a pair of electrodes <NUM> and <NUM>. The electrodes <NUM> and <NUM> are lamellar and extend along a main direction parallel to each other. They are kept at a constant distance from each other by means of the spacers <NUM>. The proximal ends of the electrodes <NUM> and <NUM> are attached to the body <NUM> by means of the holding element <NUM>. The latter is made of electrically insulating material, e.g. plastic, and comprises two slots, each receiving one of the electrodes <NUM> and <NUM>. The holding element <NUM> is attached to the body <NUM> on the inner side <NUM> thereof. A fastener <NUM>, e.g. a screw, is inserted transversally through a hole in the holding element and corresponding holes in the electrodes <NUM> and <NUM>, for securely fastening the electrodes to said element. The hole in the holding element <NUM>, receiving the fastener <NUM>, extends through the slots.

Both proximal ends of the electrodes <NUM> and <NUM> protrude from the slots of the holding element <NUM> towards the body <NUM>. The first electrode <NUM> has an end lateral face in pressure contact with an electrical lead <NUM> protruding from the body <NUM> so as to achieve an electrical contact there between. Similarly, the second electrode has an end lateral face in pressure contact with a body portion <NUM> so as to achieve an electrical contact there between. The second electrode <NUM> is thereby grounded and the first electrode <NUM> electrically connected to the electrical lead <NUM>.

As this is apparent in <FIG>, in the present embodiment, the body <NUM> comprises a sleeve on the inner side <NUM> thereof, that forms a cavity <NUM> housing the electrical lead <NUM> and the body portion <NUM> contacting the second electrode <NUM>. Also, the holding element <NUM> is snap-fitted into the cavity <NUM> by engaging with a recess formed in the inner wall of the sleeve <NUM>.

Still with reference to <FIG>, the body <NUM> forms on its outer side <NUM> a cavity <NUM> in which the electrical lead <NUM> also protrudes and is in contact with an electronic display <NUM> via the electrical contacts <NUM>.

<FIG> is an enlarged view of the upper part of the sectional view of <FIG>. Each of the first and second electrodes <NUM> and <NUM> shows a cross-section with an arcuate profile, i.e. with a concave side and a convex side opposed to the concave side. Both cross-sectional profiles are preferably parallel, i.e. the convex side of the first electrode <NUM> is in front of the concave side of the second electrode <NUM>. In the cavity <NUM>, we can observe that this is the convex lateral end side <NUM> of the first electrode <NUM> that contacts the electrical lead <NUM>. Similarly, this is also the convex end lateral side <NUM> of the second electrode <NUM> that contacts the body portion <NUM>. The latter forms an arcuate wall with two end faces that contact the electrode <NUM>. Since the cut-plane of <FIG> does not pass through any of these two end faces, the contact between the second electrode <NUM> and the body portion <NUM> is not visible in <FIG> but well in <FIG>.

Still with reference to <FIG>, we can observe that, in the cavity <NUM>, the electrical lead <NUM> is connected, for instance by brazing, to a plate <NUM>, for instance a printed circuit board or PCB, that is attached to the body by screwing and that shows a pin that engages with the connector <NUM>. The electronic display <NUM> is mounted on a support <NUM> that is inserted into the cavity <NUM> by a movement along the longitudinal axis of the body <NUM>.

The PCB <NUM> can comprise electronics that is configured for storing the calibration parameters independently from any electrical power source. An electric power source such as a battery can be stored in the support <NUM> for supplying power to the electronic display <NUM> and the PCB <NUM> via the connector <NUM>. This is particularly convenient because when the battery is empty, the support <NUM> can be removed for replacing said battery without losing the calibration parameters on the PCB <NUM>.

The electrical lead <NUM> extends through a sleeve <NUM> and is attached thereto in a gas tight fashion, e.g. with molten glass. The sleeve <NUM> engages with a bore in the body <NUM> in a gas tight fashion by means of a gasket, for instance an O-ring, and is secured to the body <NUM> by a nut <NUM> with an outer thread engaging with a corresponding inner thread in the bore. The nut <NUM> holds and presses the sleeve <NUM> against a shoulder portion of the bore, thereby providing a stable fixation of the electrical lead <NUM>. The mounting of the electrical lead can be according to the teaching of patent application <CIT>.

Still with reference to <FIG>, we can observe that an annular airgap is provided between the nut <NUM> and the electrical lead <NUM>. A sleeve <NUM> of electrically insulating material is slid around the electrical lead <NUM> and inside the airgap so as to support the electrical lead <NUM> against the bending force resulting of the radial force of the contact with the first electrode <NUM>, for instance the end lateral side thereof. As this is apparent in <FIG>, the sleeve shows a cut-out on the portion thereof that protrudes out of the body <NUM> and on the side of the first electrode, in order to provide some free space allowing said electrode to contact said lead.

<FIG> is a perspective view of the contact between the electrodes <NUM> and <NUM> and the electrical lead <NUM> and the body portion <NUM>. The holding element is not represented for a better view of the contacts. The holes <NUM> and <NUM> in the electrode that receive the fastener <NUM> through the holding element <NUM> (<FIG> and <FIG>) are however visible. The arcuate cross-sectional profiles of the electrodes <NUM> and <NUM> is also well visible. We can observe that the electrical lead <NUM> contacts the end lateral face <NUM>, for instance the convex end lateral face, of the first electrode <NUM> at a central position thereof. We can also observe that the body portion <NUM> forms an arcuate wall with two end faces contacting the end lateral face <NUM>, for instance the convex end lateral face of the second electrode <NUM>, whereas only one of the two end faces is visible.

<FIG> is a perspective view of the holding element <NUM>. It comprises a proximal front end <NUM> configured for engaging with the body and a distal end <NUM> holding the electrodes.

The proximal front end <NUM> comprises a circular wall <NUM>. <NUM> provided with a toothed outer profile <NUM>. <NUM> for engaging with the recess <NUM> in the sleeve <NUM> of the body (<FIG>). A series of axial cut-outs <NUM>. <NUM> are provided along the wall <NUM>. <NUM> so as to form different sections thereof that can more easily bend during insertion of the proximal front end <NUM> into the cavity <NUM> of the body <NUM> (<FIG>).

The distal end <NUM> features the slots <NUM>. <NUM> configured to receiving the electrodes. As this is apparent, the slots <NUM>. <NUM> show an arcuate profile that corresponds to the profile of the electrodes. The slots extends longitudinally along the whole length of the distal end <NUM> so that the electrodes, once inserted therein, extends through the distal end <NUM> and protrude therefrom in the proximal front end <NUM>. The holding element <NUM> features also a transversal hole <NUM>. <NUM> that extends through the slots <NUM>. <NUM>, designed for receiving the fastener <NUM> (<FIG> and <FIG>).

When assembling the gauge, the electrodes are inserted through the respective slots <NUM>. <NUM> and the fastener <NUM> (<FIG> and <FIG>) is inserted into the hole <NUM>. <NUM> and the corresponding holes <NUM> and <NUM> (<FIG>) of the electrode so as to form a stable assembly. That assembly is then mounted on the body by an insertion movement along the longitudinal direction, until the distal end portion <NUM>, more particularly the toothed profiles <NUM>. <NUM>, snaps into the recess or groove <NUM> (<FIG>). During that operation, the holding element <NUM> can be slightly tilted relative to the longitudinal direction of the body such as to facilitate insertion of the end portion of the electrodes relative to the electrical lead and the body portion. Once the end lateral faces of each electrode has started to pass by the electrical lead and the body portion, the holding element can be aligned with said longitudinal direction until each toothed profile <NUM>. <NUM> snaps into the corresponding groove or recess in the body.

<FIG> is a perspective view of the spacer <NUM>. It is essentially made of a plate <NUM> with two slots <NUM>. Each slot <NUM> is configured to achieve a resilient contact with the corresponding electrode once inserted there into. For instance, when the electrode show a curved cross-sectional profile, as in the present embodiment, the slots <NUM> can show a generally straight profile or at least a less curved profile than the electrodes. More specifically, the slots <NUM> show at a main portion a width that is substantially larger than the wall thickness of the electrodes. The slots <NUM> show end portions <NUM>. <NUM> with a reduced thickness, i.e. of about the wall thickness of the electrodes. It can also show a central portion <NUM>. <NUM> also with a reduced thickness, however preferably greater than the wall thickness of the electrodes.

The spacer <NUM> is advantageously made of plastic, e.g. thermoplastic, by injection moulding. The plate <NUM> can show a thickness greater than <NUM> and/or less than <NUM>. The slots <NUM> can have a length greater than <NUM> and/or less than <NUM>. Each slots <NUM> advantageously shows two opposes profiles that are symmetric with regard to a median plane. The distance between the neutral fibres or axes of two adjacent slots <NUM> of a spacer <NUM> can be greater than <NUM> and/or less than <NUM>. The plate <NUM> of the spacer <NUM> advantageously shows a rounded peripheral border.

<FIG> is a perspective view of a second embodiment of the invention. It shows a capacitive gauge, similarly constructed to the gauge of the first embodiment in <FIG>. The reference numbers of the first embodiment are used for designating the same or corresponding elements; these numbers being however incremented by <NUM>. It is referred to the description of these elements in relation with the first embodiment. Specific numbers comprised between <NUM> and <NUM> are used for designating specific elements.

The gauge <NUM> of <FIG> differs from that the gauge of <FIG>, essentially in the body <NUM> which comprises a gas passage between the inner side <NUM> and the outer side <NUM>, in connection with the gas outlet <NUM>. A shut-off valve (not visible) is provided in the body <NUM> and operated by the hand-wheel <NUM>. Such a gas passage, gas outlet and shut-off valve are as such well known to the skilled person and do not need to be further detailed.

Claim 1:
Capacitive level gauge (<NUM>; <NUM>) for a container of a medium like compressed gas or liquid, comprising:
- a body (<NUM>; <NUM>) configured for being mounted on the container
- two parallel lamellar electrodes (<NUM>, <NUM>; <NUM>, <NUM>) extending from the body (<NUM>; <NUM>), for being inside the container and in contact with the medium;
- at least one spacer (<NUM>; <NUM>) with two slots (<NUM>) engaging with the two electrodes (<NUM>, <NUM>; <NUM>, <NUM>), respectively, maintaining a constant distance between said electrodes;
characterized in that the at least one spacer (<NUM>; <NUM>) elastically deforms the electrodes (<NUM>, <NUM>; <NUM>, <NUM>) so as to generate frictional forces holding said spacer in place without further fixation means.