FR2647899A1 - Device for measuring the level and/or volume of fuel by a capacitive probe with detection of water - Google Patents

Abstract

The present invention relates to a device for measuring the level and/or volume of a liquid contained in a tank, of the type comprising a capacitive probe including at least two parallel and separate main plates 110 which are generally vertical and intended to be immersed in the liquid, and a capacitance measurement means having a detection input and an earth, the detection input being connected to a first main plate and the earth being connected to the second main plate 110. This device is characterised in that the capacitive probe has at its bottom auxiliary plate elements 120 which define a reference capacitance making it possible to determine the permittivity of the fluid; means are provided which are designed to compare the measured permittivity of the fluid with a threshold, generate an alarm if the measured permittivity exceeds the threshold, and perform the level and/or volume measurement on the basis of a predetermined permittivity value if the measured permittivity exceeds the threshold.

Description

 The present invention relates to a device for measuring the level and / or volume of fuel contained in a tank of a motor vehicle.

 The present invention more specifically relates to a measuring device of the type known per se comprising a capacitive probe comprising at least two separate, parallel, generally vertical, main armatures intended to be immersed in the liquid, and a capacitance measuring means having an input detection and a mass, the detection input being connected to a first main armature while the mass is connected to the second main armature.

 Various capacitive probe measuring devices have already been proposed, for example in the documents FR-A-2234555, FR-A-2402195, FR-A-2452G24, FR-A-2500169 and FR-A-2550337.

 In particular, the capacitive probe measuring devices have the advantage, compared to conventional float and resistive strip systems, of not having moving parts.

 However, despite this undeniable advantage, the capacitive probe measuring devices are little used today because they do not give complete satisfaction, especially in terms of accuracy.

 Moreover, capacitive probe measuring devices generally give erroneous information when a significant volume of water accumulates in the bottom of the tank.

 The main object of the present invention is to provide a new capacitive probe measuring device which eliminates the disadvantages of the prior art.

 An auxiliary object of the present invention is to provide a measuring device with capacitive probe compatible with all types of fuels, in particular with oxygenated fuels, high content of methanol or methanol.

 Another ancillary object of the present invention is to provide a measuring device with capacitive probe-having a high sensitivity, that is to say a significant variation in the capacity over the entire extent of the measurement.

 The above-mentioned main object is achieved according to the invention by virtue of the following features: the capacitive probe has, at its lower part, auxiliary reinforcing elements which define a reference capacitance making it possible to determine the permittivity of the fluid; designed to compare the measured permittivity of the fluid with a threshold, generate an alarm if the measured permittivity exceeds the threshold, and perform the level and / or volume measurement on the basis of a predefined permittivity value if the measured permittivity exceeds the threshold .

 These arrangements make it possible to detect the presence of water in the bottom of the tank, while delivering information of optimum precision.

 According to a first variant, the predefined permittivity value is stored in appropriate means during the design of the system.

 According to a second variant, the predefined permittivity value corresponds to the last measured value of the permittivity before detection of threshold crossing.

 Other characteristics, objects and advantages of the present invention will appear on reading the detailed description which follows, and with reference to the accompanying drawings given by way of non-limiting example and in which - Figure I shows a schematic side view . of a capacitive probe according to the present invention, - Figures 2 and 3 show two schematic side views, in views respectively referenced 2 and 3 in Figure 1, two electrodes component of this probe, - Figures 4 and 5 represent views similar to FIGS. 2 and 3, respectively, of another alternative embodiment of electrodes in accordance with the present invention; FIG. 6 diagrammatically illustrates the phenomenon of capillarity of the liquid on one of the electrodes; FIG. the same phenomenon at spacers provided between the electrodes, - Figure 8 shows the diagram of the capacitance measuring means according to the present invention, - Figures 9 and 10 show two timing diagrams schematically illustrating the operation of the measuring means according to In the present invention, FIG. 11 represents, in flow chart form, the measuring method according to the present invention. invention.

 FIGS. 1 to 3 show a capacitive probe S according to a preferred embodiment of the present invention.

 This probe S consists of a central electrode 100 flanked by two external electrodes 200. The external electrodes 200 are spaced from the central electrodes 100 by spacers 300.

The central electrode 100, the outer electrodes 200 and the spacers 300 are held by tubular rivets 350, passing through the spacers 300. The rivets 350 are advantageously formed of brass or aluminum.

 The central electrode 100 is formed of a support body of electrically insulating material, laminated, metallized two faces. This laminate is advantageously made either based on polyimide or based on epoxy resin loaded with fiberglass fabrics. The support body 150 bears on each of its two main faces 102, 104, the armatures illustrated in FIG.

 These reinforcements are advantageously made of copper and, by subtractive method.

 The polyimide or epoxy resin laminates loaded with glass fibers have a perfect dimensional and geometric hold (twisting and deflection), as well as an excellent adhesion of the copper, after immersion in any type of fuel).

 On each of the faces 102, 104 of the electrode 100, a main armature 110, an auxiliary armature 120 associated with a connection track 122, a secondary armature 130 and a guard ring 140 are produced by subtractive method.

 The electrical connections between the plates 110, 120, 130 and 140 and the measuring means shown in FIG. 8 are provided in the upper part of the electrode 100.

 The outer electrodes 200 may be made in the form of a support body of a laminated electrically insulating material, based on polyimide or epoxy resin filled with glass fibers, metallized on one side, to define a second main reinforcement 210, as shown in FIG. 3. This armature 210 must extend facing the first main armature 110, the auxiliary armature 120, the connecting track 122, the auxiliary track 130 and the guard ring 140. however, the electrodes 200 may be formed simply of a single sheet of tin-plated iron or stainless steel.

 The two outer electrodes 200 are advantageously of identical structure. The probe thus presents a plane of symmetry corresponding to the mean plane of the central electrode 100. This symmetry makes it possible, with a substantially identical size, to double the capacitive value of the probe, respectively electrically connecting the reinforcements 110, 122, 130, 140 formed on each of the two main faces of the central electrode 100 on the one hand, and connecting the two outer electrodes 200 on the other hand.

The first main frame 110 constitutes with the second frame 210 the measurement capacity itself. For this, the first armature 110 is formed essentially of a metallized beach elongated vertically. The auxiliary armature 120 is formed of a metallized zone provided in the lower part of the central electrode 100. The auxiliary armature 120 is electrically separated from the main armature 110.

The auxiliary reinforcement 120 constitutes, with the reinforcement 210 placed opposite, a reference capacity placed at the bottom of the reservoir and consequently permanently immersed in the liquid, and the surface of the auxiliary reinforcement 120 being known, serving as a capacity reference for determining the exact permittivity of the liquid concerned.

 According to the representation given in FIG. 2, the auxiliary armature is of rectangular shape, elongated horizontally. This provision is however not limiting.

 The auxiliary armature 120 is extended by a connecting track 122. This connection track 122 has a small width.

It extends over the entire height of the first electrode 100, parallel to the main armature 110, to allow a connection with the measuring means, in the upper part of the electrode.

 Note however that the value of this reference capacity changes depending on the level of the liquid in the tank, due to the presence of the connecting track 122.

 To overcome this difficulty, there is provided the secondary armature 130. It has the same geometry, the same surface and the same layout as the connection track 122. Thus, the secondary armature 130 defines with the main frame 210, a capacity identical to that defined by the connection track 122 and the main frame 210, regardless of the level of the liquid in the tank.

 By subtracting the capacitance value determined by the armature elements 130, 210 from the capacitance value determined by the armature elements 120, 122 and 210, a reference capacitor value is obtained that is independent of the capacitance level. liquid in the tank.

This reference capacity makes it possible to know the permittivity of the liquid.

In fact, the reference capacity is equal to ES / d, in which relation E denotes the permittivity of the liquid, S represents the surface of the auxiliary reinforcement 120 and d represents the distance separating the auxiliary reinforcement 120 from the reinforcement. main 210.

 Finally, FIG. 2 shows the guard ring 140. It will be noted that it completely surrounds the main armature 110, that it completely surrounds the auxiliary armature 120 and its associated connection track 122 and that it also completely surrounds the secondary armature 130.

 The guard ring 140 makes it possible to eliminate any edge effect, both at the level of the measuring capacitor formed by the main armature 110 and the armature 210, and at the reference capacitor formed by the auxiliary armature 120. , the associated connection track 122 and the main armature 210, or at the compensation capacitor formed by the secondary armature 130 and the main armature 210.

The aforementioned struts 300 are designed to allow the penetration of the liquid to be measured in the space of thickness d between the central electrode 100 and the two external electrodes 200.
Applicant has determined that the distance d separating the external electrodes 200 from the central electrode 100 must be between 0.1 mm and 1.2 mm. Indeed, if the difference d is greater than 1.2 mm, the capacitive probe loses its sensitivity (the capacitance being inversely proportional to the distance of the reinforcements).

 On the contrary, if the difference d is less than 0.8 mm, the probe has significant errors due to the capillary effect and the retention of liquid droplets between the electrodes.

The capillary effect remains for a difference of between 0.8 and 1.2 mm. However for this value range, the capillarity effect is easily controllable. It answers the relation h = A / F, relation in which
A represents the surface tension of the liquid, d represents the gap between the reinforcements, p represents the density of the liquid and, g represents the acceleration of the weight.

 This capillary effect is illustrated schematically in the appended FIG.

 This figure shows a face of the central electrode 100. The free level of the liquid, at a distance from the central electrode 100 is referenced 10. The level of the liquid with respect to the electrode 100 is referenced 12. Note that levels 10 and 12 are separated by a distance h.

 The effect of capillarity h is independent of the volume of the liquids and not very variable in temperature. It suffices therefore to get rid of having means for subtracting the level value obtained according to the measurement, the differential height h.

By way of example, it will be pointed out that for the various fuels currently available on the market, the surface tension
A is between 26.8 and 28.10-3N / m.

 For species the density p is 0.7 to 0.75, and for gasolines ro is G 85.

 This gives for gasolines a differential height h of 4.6 mm and 5 mm, and for gas oils a differential height h of between 3.9 mm and 4.2 mm.

r
It will be noted that for water the differential height obtained is 9.3 mm.

 As previously indicated to overcome the effect of capillarity, it is sufficient to take into account the differential height h once and for all for level measurement.

 However, it is also imperative to provide the spacers 300 and fastening rivets 350 out of the area of the capacitive reinforcements.

 According to the representation given in Figures 2 and 3, the spacers 300 and fastening rivets 350 are thus provided at ears 150, 250, projecting on the respective vertical edges of the central electrode 100 and the outer electrodes 200 .

 Indeed, if, as shown in FIG. 6, between the planar electrodes, the level 12 of the liquid is parallel to the actual level 10 of the liquid, and at a constant distance h of it, in contrast at the level of the spacers 300, I capillary action effect, as shown schematically in Figure 7, uncontrollable and non-repetitive errors.

 The spacers 300 defining the distance between the armatures are preferably made of either alumina or steatite, or liquid crystal polymer, such as for example the materials marketed under the trademark VECTRA.

 The three aforementioned materials likely to compose the spacers 300 have a very good dimensional stability in the various fuels, as well as in temperature.

 According to another advantageous characteristic of the present invention, the two faces of the central electrode 100, and the metallized facing side of the outer electrodes 200, in the case where they are laminated, are covered with a neutral coating. fuels.

This coating must be of constant thickness, since it intervenes in the permittivity of the capacitors thus formed, without any porosity. and stand up perfectly to the different fuels, whether they are overexposed or not.

 The present invention provides various materials capable of composing this coating.

 According to a first variant, the protective coating is formed by screen-printing a cationic varnish. It may be for example a varnish marketed by Holden Europe under the name IEC 9346. This varnish is preferably deposited in the form of a thickness of the order of 25 u.

 According to a second variant, the protective coating is formed by silk screen deposition of a polyimide or epoxy varnish.

 According to a third variant according to the present invention, the coating is formed by vacuum deposition of a polymer / poly-p-xylene type parylene C. The coating may have a few u of thickness.

 According to yet another alternative embodiment, the protective coating may be formed by depositing a layer of an epoxy impregnated glass cloth and hot pressed.

 Of course, the necessary electrical connection between the armatures and the electronic measuring means, in the upper part of the electrodes, must be ensured through the aforementioned protective coating.

The guard ring 140 is placed at the potential of the first main armature 110, thanks to a potential copying stage 410 (see FIG. 8). To effectively eliminate errors, in the determination of the permittivity and in the measurement, caused by edge effects,
The guard ring preferably has a width I (see Figure 2) greater than or equal to twice the difference d between the armatures. The guard ring 140 must also be at most ready guarded frames. According to the invention, the distance separating the guard ring 140 from the guarded frames is of the order of 0.4 mm.

 According to the representation given in Figure 2, the main armature 110 is formed of a rectangular range extending over almost the entire height of the tank, and having parallel vertical free edges 111, 112.

 Where appropriate, the main reinforcement 110 may have non-rectilinear and non-parallel edges 111, 112, adapted according to the tank gauging curve.

 According to the embodiment previously described with reference to FIGS. 2 and 3, the potential error in the determination of the permittivity of the liquid, due to the evolution of the reference capacity as a function of the level of the liquid, is eliminated thanks to a differential capacity, of the same value, delimited by the secondary reinforcement 130 and the main reinforcement 210.

 It is also possible to eliminate the error due to the connection track 122, by removing the second armature 210 with respect to this connecting track, as represented in FIG. 5 in the form of a window or cutout 212 in the armature 210.

 In this case, of course, as shown in Figure 4, there is no need to provide a secondary armature 130 on the central electrode 100. The geometry of the guard ring 140 is also simplified.

 The geometry of the reinforcements given in the appended figures is of course only schematic, to clearly show the guard ring 140, the connecting track 122 and the secondary compensating armature 130. In practice, the armatures 122, 130 and 140 will have much smaller widths relative to the width of the detection armature 110.

 The embodiments described above can be the subject of numerous variants.

 For example, it is conceivable to place the electrodes 110, 120, 130 and 140 on each of the outer electrodes 200 and to place a main electrode 210 on each of the faces of the central electrode 100.

 It is also conceivable to use a single-face electrode 100 and a single outer electrode 200 facing each other.

 We will now describe the structure of the measuring means 400 shown in Figure 8 attached and intended to be connected to the various aforementioned reinforcements.

 Essentially, the measuring means 400 comprise a multiplexing element 420 and a potential copy-over stage 41G, an oscillator 430, and a microprocessor central unit 440.

 The means 400 exploits the fact that the various capacitors mentioned above making up the capacitive probe have a common armature formed by the second main armature 210.

 Thanks to the multiplexer 420, the armatures 110, 120, 130 are successively connected to the oscillator 430, so that it generates a frequency as a function of the capacitance of the capacitor in question.

 The timing of the multiplexer 420 is controlled by the central unit 440, via the links 441, 442 and 443.

 The potential copy stage 410 is formed of an operational amplifier. This has its non-inverting input connected to the output 422 of the multiplexer unit. The inverting input of the operational amplifier 410 is looped back to its output. Similarly, the output of the operational amplifier 410 is connected to the guard ring 140.

 The oscillator 430 is formed by the combination of an operational amplifier 431 and resistors R432 to R436.

 The output of the oscillator 400 is connected to the input 444 of the central unit 440.

 Thus, the central unit 440 receives on its input 444 a frequency directly linked to the capacity delimited either by the armatures 110, 210, or by the armatures 120 and 122, 210, or by the armatures 130 and 210.

 Preferably, the system has a cyclic calibration phase of the oscillator 430, comprising two steps during which the multiplexer 420 connects the oscillator 430 not to one of the armatures provided on the electrodes 100, 200, but to capacitors with a known capacity gap.

 It may be for example in a first step, of a zero capacitance (shown schematically by the input 424 in FIG. 8) and in a second step of a precise and known capacitance C426.

 Since the frequency available at the output of the oscillator 430 is of the form F = aC + b, the two aforementioned calibration steps easily make it possible, knowing the value of the capacitance C426, to calibrate the oscillator 430 by determining the constants a and b.

 This calibration subsequently makes it possible to precisely define the capacitances formed by the capacitors 110-210 or 120 and 122-210 or 130-210.

 This process is illustrated schematically in Figure 9.

 In this figure there are measurement cycles divided into five steps referenced TI to T5.

 In steps T1, no capacitor is connected to the oscillator 430. In the steps T2 the capacitor C426 is connected to the oscillator 430 by the multiplexer 420. The steps T1 and T2 make it possible to calibrate the oscillator 430.

 In steps T3, the multiplexer 420 connects the armature 130 to the input of the oscillator 430. The step T3 therefore makes it possible to measure the value of the capacity defined by the secondary armature 130 and the main armature 210. It is recalled that this capacity is equal, regardless of the level of the liquid to that defined by the connecting track 122 and the main frame 210.

 In steps T4, the multiplexer 420 connects to the connection track 122 to the oscillator 430. During the steps T4, an output of the oscillator 430 is thus obtained, a frequency that is a function of the capacity defined by the auxiliary armature 120 combined with this connection track 122 and the main frame 21i.

 By subtracting the capacity obtained in steps T3 from those obtained in steps T4, a reference capacitor is obtained directly, which knowing the surface of the secondary armature 120 and the distance d between the armatures, makes it possible to know the permittivity of the liquid.

 In steps T5, the multiplexing member 420 connects the main frame 110 and the oscillator 430. The measurement thus obtained allows, knowing the permittivity of the liquid, to determine the level in the tank.

 Where appropriate, the measuring system according to the present invention can exploit a plurality of capacitive probes oriented differently in the reservoir, to take account, for example, of the attitude thereof.

 In this case, it is not necessary that the auxiliary capacitive probes used have reference frames. It then suffices to connect the main armatures similar to the armature 110, on appropriate inputs of the multiplexer member 420. This arrangement is schematically represented in FIG. 8, in the form of an input referenced 110bis and 110ter for the multiplexing organ.

 The guard rings of the various probes can be connected together.

 Note that the second main frames 211 are all connected to the mass of the assembly.

 In the case of auxiliary capacitive probes (eg 10A, 10Oter), the measuring cycle must be increased by the same number of multiplexing strips, as shown in T6 and T7 for the frames 110b and 110b in the figure. 10.

 The measuring means 400 are moreover advantageously adapted to detect any possible presence of water accumulated in the bottom of the tank. For this, the central unit 440 continuously compares the permittivity g of the liquid obtained with the reference armature 12. i a predetermined threshold permittivity.

 It is known that the permittivity of fuels is very different from the permittivity of water.

 As an example, the permittivity for the various fuels currently available on the market is between 2 and 4.5, while the permittivity of the water is greater than 80.

Preferably, the central unit 440 is associated with storage means 450 able to hold a mean permittivity value,
medium, which will be operated in case of water detection in the tank bottom, that is to say when the permittivity measured by auxiliary armature 120 is no longer representative.

 The complete measurement method according to the present invention is shown schematically in the attached FIG.

 As shown in this figure, in an initial step 500, the average permittivity value E, mean, is stored in the means 450.

 At step 502, which corresponds to steps T1 and T2 of FIGS. 9 and 10, the multiplexer 420 successively connects its input 424 and the capacitor C426 to the oscillator 430, to calibrate it.

 In step 504, the multiplexer member 420 connects the secondary armature 130 to the oscillator 430. The central unit 440 can thus determine a capacitance equal to that of the connection track 122.

 In step 506, the multiplexing member 420 connects the connection track 122 to the oscillator 430. The central unit 440 thus determines a capacity equal to the sum of that defined by the auxiliary reference frame 120 and the connection track J22.

 In step 508, the central unit 440 subtracts the capacity obtained in step 504 from that obtained in step 506. The result makes it possible to determine the permittivity of the liquid, knowing the surface-of the armature 120 and the distance between this frame and the main frame 210.

 In step 510 the central unit 440 tests whether the permittivity t obtained at step 508 is greater than a given threshold.

 If so, central unit 440 considers that water is present in the bottom of the tank and generates an alarm at step 512.

Moreover, in the consecutive step 514, the central unit 440 imposes a value of permittivity equal to g average contained in the means 450.

 Step 514 is followed by step 516. Similarly, the test 510 when it receives a negative response is followed by step 516.

 During this step -516, the multiplexer 420 connects the main armature 110 to the oscillator 430.

 The central unit 440 thus makes it possible to determine the measurement capacity defined between the main armatures 110 and 210.

 This value is exploited in step 518, knowing the permittivity of the liquid, to determine the level in the tank.

 In step 520, the central unit 440 displays a visualization of the level and / or the volume of the liquid contained in the reservoir.

 According to the representation given in FIG. 8, the alarm information (step 512) is delivered on the output 452 of the central unit, whereas the level and / or liquid volume information is delivered on the output 454 of the central unit. this unit.

 According to a variant, in the case of detection of water in the test step 510, the central unit may not exploit a pre-stored average value, but use as the permittivity value the last acceptable stored value, which is constantly refreshed in the means 450.

 If necessary, the central unit 440 may be designed to further apply smoothing on the information obtained.

 In a manner known in itself, the capacitive probe S is advantageously formed in a vertical tube of tranquilization, anti-waves, connected to the reservoir by a calibrated bore.

 If necessary, the wall of this wave-preventing tube may be formed by the external electrodes 200 themselves.

 If necessary, the detection of water in the bottom of the tank can be operated not by measuring the permittivity of the liquid, but by measuring the resistance between the plates 120 and 210.

 Naturally, the present invention is not limited to the particular embodiments which have just been described, but extends to any variant within its spirit.

Claims (31)

R E V E N D I C A T IO N S  1. A device for measuring the level and / or volume of a liquid contained in a reservoir, of the type comprising a. capacitive probe comprising at least two main armatures (110, 210) separated, parallel, generally vertical, intended to be immersed in. the liquid, and capacitance measuring means (400) having a detection input and a mass, the detection input being connected to a first main armature (210) and the mass connected to the second main armature (110) characterized in that - the capacitive probe has at its lower part, auxiliary reinforcing elements (120, 210) which define a reference capacitor for determining the permittivity of the fluid, - means are provided for comparing the measured permittivity of the fluid with a threshold, generating an alarm if the measured permittivity exceeds the threshold, and performing the level and / or volume measurement on the basis of a predefined permittivity value if the measured permittivity exceeds the threshold.  2. Measuring device according to claim 1, characterized in that it comprises means capable of storing an average permittivity value, corresponding to the predefined permittivity value.  3. Measuring device according to claim 1, characterized in that it comprises means adapted for storing as the predefined permittivity value the last obtained value of measured permittivity, as long as the latter does not exceed the threshold.  4. Measuring device according to one of claims 1 to 3, characterized in that the first frame (110) is surrounded by a guard ring (140).  5. Measuring device according to claim 4, characterized in that it comprises a potential copying stage (410) which has its input connected to the first armature (110) and its output to the guard ring (140). ).  6. Measuring device according to one of claims I to 5, characterized in that one of the auxiliary reinforcing elements is coincident with the main frames of the main (210).  7. Measuring device according to one of claims I to 6, characterized in that one of the auxiliary reinforcing elements is integral with the second frame, main (210).  8. Measuring device according to claim 6 or 7, characterized in that the other auxiliary reinforcing element (120) is connected to a connection track (122) 22) which extends to the upper part of the probe.  9. Measuring device according to claim 8, characterized in that it comprises secondary reinforcing elements (130, 210) defining a capacity of the same geometry and same location as that delimited by the connecting track and the second reinforcement. principal (210).  10. Measuring device according to claim 9, characterized in that one of the secondary reinforcing elements is merged with the second main frame (210).  11. Device according to one of claims 9 or 10 characterized in that it comprises means designed to subtract the capacity value determined by the secondary reinforcing elements (130, 210), the capacitance value determined by the auxiliary reinforcing elements and the associated connecting track (120, 122; 210).  12. Device according to one of claims I to 11 characterized in that it comprises at least one support of electrically insulating material which carries the first main frame (110), an auxiliary frame (120) placed in the lower part of the support below the main frame (110), a connecting track (122) connected to the auxiliary frame (120) and extending to the part. upper support member, a secondary reinforcing member (130) having the same geometry as the connecting track (122) and extending parallel thereto, and the guard ring (140) surrounding the frame main (110), which surrounds the auxiliary armature (120) and its associated connecting track (122). and that surrounds the secondary armature element (130), the second armature ('15)  being supported parallel to the support by spacers (300) in  electrically insulating material, and extending opposite the armature  main (110), of the auxiliary frame (120), of its connection track  (122), and the secondary armature (130).  13. Device according to one of claims I to 8 characterized in that the capacitive probe comprises at least one support in  electrically insulating material that carries the first main frame  (110), an auxiliary frame (120) 20) placed in the lower part of the support  below the main frame (110), a connection track (122)  connected to the auxiliary armature and extending to the upper part of the  support, and the guard ring (140) surrounding the main frame (110) 10)  and which surrounds the auxiliary armature (i20) and its associated connection track,  the second armature (210) being supported parallel to the support by  spacers (300) of electrically insulating material, and being shaped  to extend opposite the main frame (110) and the frame  auxiliary (120) but not extend opposite its connection track (122).  14. Device according to one of claims 1 to 13 characterized  in that the capacitive probe comprises a central support (100). in  electrically insulating material coated, on each of its two faces,  of reinforcements, and two external electrode elements (250) placed  respectively facing the faces of the support and separated therefrom by  spacers (300) of electrically insulating material.  Device according to claim 14, characterized by the fact  that the central support (100) 00) bears on each of its two faces, at least  a main frame (110) and an auxiliary frame (120) defining  a reference capacitor, connected to a connection track (122) which extends  to the top of the probe.  Device according to one of claims 14 or 15,  characterized in that the different reinforcing elements (110, 120,  130, 140) provided on both sides of the central support (100) are connected  electrically respectively two by two and the two elements  external electrodes (250) are electrically connected to each other.  17. Device according to one of claims 1 to 16+ characterized in that at least some reinforcements are carried by a support of electrically insulating material selected from the group comprising: polyimides and epoxy resins loaded with glass fabric.  18. Device according to one of claims I to 17, characterized in that the armatures are made of copper by subtractive method.  19. Device according to one of claims I to 18, characterized in that the distance separating the two main armatures (110, 210) is between 0.8 and 1.2 mm.  20. Device according to one of claims I to 19, characterized in that it comprises means designed to correct the information obtained by a value related to the effect of capillarity and defined by the relationship.  A h = where df> g A represents the surface tension of the liquid, d represents the distance separating the reinforcements.  P represents the density of the liquid and, g represents the acceleration of gravity.  21. Device according to one of claims 1 to 20, characterized in that the distance separating the armatures (110, 210) is defined by spacers (300) of electrically insulating material placed outside the active zones of reinforcements.  22. Device according to one of claims 1 to 21, characterized in that the second frame (210) is made of tin-plated iron or stainless steel.  23. Device according to one of claims I to 22, characterized in that the spacers (300) are made of the material selected from the group consisting of: alumina, steatite, and liquid crystal polymers.  24. Device according to one of claims I to 23, characterized in that at least some of the armatures are protected by a layer of electrically insulating material.  25. Device according to claim 24, characterized in that the electrically insulating material. is chosen from the group comprising a cationic varnish, a polyimide varnish, an epoxy varnish, a polymer / poly-p-xylene, an epoxy resin filled with glass fibers.  26. Device according to one of claims 1 to 25, characterized in that the geometry of the main armatures reproduces the gauging curve of the reservoir.  27. Device according to one of claims 1 to 26, characterized in that the width of the guard ring (140) is equal to 2d, where d represents the distance between the armatures.  28. Device according to one of claims 1 to 27, characterized in that the distance separating the guard ring, armatures, is less than 1 mm and preferably of the order of 0.4 mm.  29. Device according to one of claims 1 to 2S, characterized in that the capacity measuring means comprises an oscillator (430) loaded by the capacitive probe and a sensitive means (440) at the frequency of the oscillator ( 43G).  30. Device according to one of claims 1 to 29, characterized in that it comprises a multiplexer member (42C) adapted to successively connect the various frames to the oscillator (430).  31. Device according to one of claims 29 or 3û, characterized in that it comprises means designed to successively charge the oscillator (430) by capacitors having a known capacity difference, in an initial calibration phase. .