FR2932564A1 - Capacitive liquid level transmitter sensor for e.g. electricity conductive liquid in automobile field, has substrate on which bipolar electrodes constituted of segments modulated in length, width, number and space are integrated - Google Patents

Abstract

The sensor has an insulating substrate (2) on which longitudinal bipolar electrodes constituted of segments modulated in length, width, number and space are integrated. A structure of conductive zones is constituted of two electrical capacitors, where the electrical capacitors vary depending on the height of the fluid after transfer characteristics is mathematically determined in accordance with a specific equation. The substrate has surfaces in contact with liquid and coated with a resin e.g. high temperature resin or reflecting insulating resin.

Description

LIQUID LEVEL CAPACITIVE SENSOR-TRANSMITTER

SUMMARY The present invention relates to a fully static liquid level transmitter sensor (no moving part even micro displacement) that can be adapted to conductive and non-conductive liquids electricity.

It is based on the principle of a variable electrical capacitance as a function of the height rendered independent of the dielectric characteristics of the liquid in question (nature and temperature of the latter).

The geometry, nature and surface treatment of this substrate, allows this technology to realize liquid level measurement systems applicable to products such as urea, any water, brake fluid, liquids containing antifreeze, liquid cooling, lubricating oil, fuel oil and different gasolines for internal combustion engines.

This system also makes it possible to deliver an additional measurement of the dielectric characteristic of the liquid, which is significant, of its nature and of its level of pollution by conductive particles (oil in particular).

The multi-layer and multi-face monolithic structure of this sensor substrate reduces the risk of fouling that can occur in the assemblies. The acquisition of capacitive measurement and correction variables is performed by a miniature electronic circuit integrated at one of the ends of this substrate.

The very small width and adaptable length make this system compatible with most of the 30 projected applications.

A particular design of the base of this system allows the latter to ensure a measurement from the zero level. SUMMARY OF THE PRIOR ART The measurement of levels in conductive liquids (water, urea, etc.) and non-conductive liquids (oil, gasoline, fuel oil, etc.) has been the subject of several decades of developments and achievements. the most diverse of which may be mentioned in a non-exhaustive manner: - Float system associated with a potentiometer for conversion into electrical signal - Float system associated with an optical or magnetic coding - Float system remotely operating a device electrical conversion - Ultra-sonic device - Discontinuous variable capacitance-dependent system (low resolution) - High-level-triggered dry multi-contact system (low resolution) - Continuously variable capacitance system as a function of level (high resolution) - Optical sensing system - System measuring impedance proportional to height - Converting an Archimedean thrust by a strain gauge sensor - Pressure sensor located at the bottom of the tank

After having analyzed the international patents relating to liquid level measurements oriented particularly on so-called capacitive systems, we have noted the following elements: Absence of stability or precision characteristics

  No transfer function characterized 25 More or less complex structure resulting in high cost assemblies

  Heterogeneous structure with obstacles to fluid flow that can change the transfer characteristic due to disruptive deposition layers

No quantification of relative capacitance variations (capacitive versus height / base capacitance variation) It is important to emphasize that this factor has a direct influence on the long-term accuracy given the instability of capacitance. base (parallel parasitic capacitance on capacitance variation). 2 Structure showing the very small full-scale amplitude of the capacity variation, it being specified that the latter must have a value sufficient to be processed by acquisition circuits without risk of instability of performance (greater than 10 pF). Complex mechanical structure generating a cost not compatible with large-scale applications (household appliances, automobile, small tanks)

  Technologically different models according to the dielectric constant or the conductivity, forcing the creation of application-specific production tools.

  Mechanical structure whose shape makes it difficult to achieve a non-rectilinear sensor sometimes necessary according to the applications encountered. Discontinuous structures composed of multiple longitudinal electrodes that do not allow infinite resolution and result in a large number of connections between the measuring electrode and the electronic conditioning circuit. It is important to emphasize that this discontinuous measurement, regardless of the poor resolution, does not allow the detection of low amplitude level ripple. This low resolution does not allow to realize alarm systems triggered by a sudden immersion in a liquid at rest.

25 Variation of the permittivity of the liquid acting directly on the measurement. It is important to specify that a thermal correction of the dielectric constant of the liquid solves only partially the problem of the calibration, the permittivity of the various fluids (oil in particular) varying according to its type and its aging in the engines thermal. Parallel parasitic capacitance on the variable measuring capacitance considerably reducing the relative sensitivity resulting in: - Multiplication of the error by subtraction of large numbers - Instabilities due to the variation in temperature or time of these parasitic capacitances 3 indication on the correction of the drift of parallel parasitic capacitances (substrate and assembly) as a function of humidity, temperature and aging time. No calculation of the stability and linearity errors generated by mechanical drifts or dielectric constants due to the non-differential action on the electric field.

  No indication of the order of magnitude of the global accuracies that can be obtained by the proposed solutions.

  Achievement often complex not allowing a mass production in the form of wafers prohibiting any implementation, controls and automated adjustments necessary to reduce costs. Sensor realized by planar or concentric parallel surfaces liable to create instabilities as a result of the modification of the inter-electrode dielectric space. Hereinafter, the essence of the patents consulted for analysis: 1 - Capacitive level sensor provided with a plurality of segments each comprising a capacitor and an inventor circuit: SLEZAK JAN [NL]; Applicant: SIEMENS MILLTRONICS SCHOENMAKERS KEES [NL] PROCESS IN [CA] 25 Publication: EP1902278 (A1) - 2008-03-26 IPC: GO1.F23 / 26; G01F23 / 22

2 Capacitive sensor for detecting the level of electrically conductive substances, in particular liquids Inventor: AGUGLIA JORGE MIGUEL [IT] Applicant: SIE MSRL [IT] Publication: EP1816448 (A1) - 2007-08-08 CIB: GOI.F23 / 26 ; G01F23 / 22

Capacitive level sensor Inventor: MATEA STEIIAN MARIUS [RO] Applicant: MOONHAVEN LLC [US] Publication: EP1677085 (A2) - 2006-07-05 IPC: A47L 1.5 / 42; D06F39 / 08; Gol. F23 / 26 (+3) 30 35 4 Capacitive level sensor for a dielectric liquid Inventor: BOCCACCIO GIOVANNI [IT] Publication: EP1091198 (Al) - 2001-04-11 5 Circuit and capacitive sensor for level measurement Inventor: MARTIN BARRY E [US]; TYMOSZUK STEPHEN [US] (+ 1) Publication: EP1274972 (A2) - 2003-01-15 6 Method and apparatus for evaluating the signals of a capacitive level sensor Applicant: BITRON SPA [IT] IPC: GO1.F23 / 26; G01F23 / 22; (IPCI-7): GOI F23 / 26

Applicant: ROBERTSHAW CONTROLS CO [US]; MARTIN BARRY E [US] IBC: GO1.F23 / 26; G01F23 / 22; (IPCI-7): G01 F23 / 26 Inventor: RAFFALT LIGHTS DIPL-ING [DE]; WOEHRLE SIEGBERT DIPL-ING [DE] Publication: EP0724140 (A1) - 1996-07-31

7 Capacitive liquid level sensor Inventor: LIN YINGJIE [US] Publication: EP1845347 (A2) - 2007-10-17Applicant: GRIESHABER VEGA KG [DE]

IPC: GOI.F23 / 26; G01F23 / 22; (IPC1-7): G01F23 / 26

Applicant: DELPHI TECH INC [US] IBC: GO1.F23 / 26; G01F23 / 22 8 Capacitive level sensor of a liquid Inventor: BARLESI LORENZO [BE]; CHIAFFI MICHEL (EN) (+1) Publication: EP1831653 (A2) - 2007-09-12 9 Capacitive level sensor for a liquid and inventor level estimation method: BARLESI LORENZO [BE]; CHIA FFI Applicant: INERGY AUTOMOTIVE SYSTEMS Applicant: INERGY AUTOMOTIVE SYSTEMS RES [BE] CIB: GO1.F23 / 26; G01F23 / 22 MICHEL [EN] (+ 1) Publication: EP1831652 (A2) - 2007-09-12 RES [BE] IPC: GOLF23 / 26; G01F23 / 22 10 Capacitive level sensor with integrated dirt film detection Inventor: BYATT ANTHONY [CH]; CHRISTEN THOMAS [CH] (+3) Publication: EP0926475 (A2) - 1999-06-30 Applicant: ABB RESEARCH LTD [CH] CIB: GO1.F23 / 26; G01F23 / 22; (IPC1-7): G01F23 / 26 5 1l Capacitive level capacitor Inventor: GOEKLER LEWIS E [US] Applicant: STANDEX INT CORP [US] Publication: EP0377508 (AI) - 1990-07-11 IPC: G01F23 / 26; G01F23 / 22; (IPC1-7): G01F23 / 2

12 Packaging machine for the continuous manufacture of sealed packages for a pourable food product having a capacitive level sensor Inventor: BASSISSI FABIO [IT]; Applicant: TETRA LAVAL HOLDINGS & GALAVOTTI GIORGIO [IT] FINANCE [CH] Publication: EP1053940 (AI) - 2000-11-22 IPC: 86589/10; 86589/20; 865857/10 (+6)

13 Segments Each Comprising a Capacitance and a Circuit Inventor: SCHOENMAKERS KEES [NL]: Applicant: SIEMENS MILLTRONICS SLEZAK JAN [NL] PROCESS IN [CA] Publication: EP1744132 (A1) - 2007-01-17 CIB: G01F23 / 26; G01F23 / 22

Electronic circuit comprising a capacitive sensor with low noise level and accelerometer equipped with this circuit Inventor: WILLEMIN MICHEL [CH]; Applicant: EM MICROELECTRONIC MARINE PFEFFERLI BEAT [CH] SA [CH] Publication: EP1691203 (AI) - 2006-08-16 IPC: G01P15 / 125; GO1P15 / 18; G01P15 / 125 (+1) 15 Capacitive sensor for the level of a liquid. Inventor: DAVIS JAMES EDWARD [US] Publication: EPO438158 (A1) - 1991-07-24 10 Applicant: BRIDGE [US] CIB: G01 F23 / 26; G01N35 / 10; G01F23 / 22 5 + 2) Capacitive liquid level sensor: Capacitive liquid level sensor: Capacitive liquid level sensor: Capacitive liquid level sensor: Capacitive liquid level sensor: Capacitive liquid level: Compensated capacitive liquid level sensor: Capacitive liquid level sensor: capacitive level sensor: US 20070240506 US 6073488 US 622373181 EP1470394 US EP1577085A2 Liquid level sensor: Liquid level sensor: Liquid level sensor: Liquid level sensor: Capacitive liquid level sensor: Capacitive liquid level sensor: Capacitive liquid level sensor: Capacitive level sensor: Capacitive level sensor: Capacitive level sensor: US2007240506 US2007252715 US 4841227 - 5142909 WO 2006128721 US 7145465B2 US 6935173B2 US 6497144B I FR2752053 US PRINCIPLE This invention, referred to as a level sensor-transmitter, consists of a monolithic active multifaceted substrate having a rectangular section and a specific length of the application.

An electrical capacitance (capacitor) is constituted by a dielectric of thickness and variable height depending on the level.

This dielectric is composed laterally of two parts in series, one of which represents a very small constant thickness over the entire height and the other is provided by the liquid to be measured.

The values of these two serial capacities vary according to the height.

The horizontal distribution of these two capacitors in series depends on the value of the dielectric constant of the liquid and the dielectric constant of the surface coating.

This surface coating has been chosen to be insensitive to the action of the different products being sprayed and can operate at a temperature up to 200 ° C.

The variable electrical capacitance according to the height results from the immersion of the sensor in fluids of different permittivities (liquid and surrounding air). 35 7 SPECIFIC CHARACTERISTICS - Identical technological operation for conductive and non-conductive liquids - Measurement of the dielectric characteristics of the fluid to be measured by a second sensor embedded in the level sensor The base of the sensor substrate consists of two capacitive structures juxtaposed not increasing the width and allowing the generation of a linear level measurement from the origin - Possibility of delivering a measurement signal significant of the nature of the liquid or its aging - Possibility of delivering measurement information level independent of the dielectric characteristics of the liquid - Very small dimensions - Height adaptable from a few centimeters to one meter 15 - Integration of the electronic conditioning circuit with standardized transmission on the measuring substrate - Substrate - sensor whose dimensional characteristics can be adapted to the 'applicati it being specified that for heights greater than one meter, a mechanical stiffening structure must be associated therewith. 20 - Possibility of measuring the height of a conductive liquid located at the base of the reservoir regardless of the height of a non-conductive liquid (lower density), located above regardless of the height of the latter. Possibility for certain versions, with a very short response time, to detect very small amplitude ripples of the liquid surface (alarm) as a result of a sudden disturbance causing ripples of the surface. - Mechanical structure of monotonous substrate-sensor without obstacle modifying the flow velocity and likely to increase the permanent retention of deposit.

DESCRIPTION The essential part of the longitudinal part of this sensor having a thickness of less than 3 mm and a width of less than 16 mm consists of parallel conductive lines obtained by etching an insulating substrate and whose upper end comprises the data acquisition and processing circuit. This structure of parallel conductive lines, effective in two perpendicular directions (electric field of juxtaposed surfaces and electric field of parallel planes), results in variable electrical capacitances as a function of the height and the dielectric characteristic of the immersing liquid. The acquisition by the electronic circuit of these variable electrical capacitances, ensures the elimination of the influence of the dielectric characteristics on the measurement of level.

The length, width and design of the connections of these parallel conductive lines are intended to modulate the capacitive transfer function.

The conductive lines parallel to the reference lines (zero) are modulated in length in order to obtain an analog operation in the longitudinal direction and a numerical operation in the lateral direction. The application of this principle for the lower part of the sensor substrate makes it possible to simultaneously have two capacitive measurements without increasing the width.

The electronic processing of these two nested capacitors makes it possible to generate an electrical output signal that is independent of the dielectric variations of the liquid (basic characteristics, temperature, pollution) from the low origin of the sensor (removal of an inefficient height). .

The electrical measurement signals available at the upper end may be analog (variable voltage) or digital (PWM) proportional to the height of the submerged zone and the characteristics of the liquid.

The shape and surface treatment of this substrate ensures proper flow, depending on the viscosities of the liquid, reducing the action of the positive or negative menisci detrimental to accuracy.

The monolithic and monotonous geometry of this sensor substrate eliminates any risk of trap for viscous liquids as opposed to structures composed of electrodes with large parallel surfaces. A high temperature and reflective coating of the substrate protects the substrate against chemical attack and considerably reduces the clinging of disturbing particles that may be contained in the base liquid.

Positive feedback signals can minimize the influence of parallel parasitic capacitances that can create instabilities and reduce sensitivity.

The active capacitive multi-faces of the immersed substrate have complementary functions making it possible to simultaneously take into account the height and the characteristics of the liquid and reduce the drifts due to the variations of the insulations by the use of a differential mode.

The distance of the capacitive parallel planes conjugated with the corresponding surface makes it possible to concentrate the electric fields that do not require metallization of these faces, thereby reducing the manufacturing cost while maintaining a sufficient electrical linear capacitance. The electronic acquisition and processing circuit located at the upper end of the level sensor is etched on the same substrate thus greatly increasing the stability and reliability by the removal of wire lines.

20 OPERATION The sensor substrate is composed of bipolar vertical conductive lines whose combination makes it possible to form one or two capacitors varying with the height of the immersed zone and the differential permittivity.

The absolute permittivity of the capacitor composed by the immersed electrodes of variable length (liquid height) being greater than the absolute permittivity of the capacitor composed by the emerged electrodes (height complementary to the immersed height), the capacitive variable will depend on these differential permittivities.

The geometry of the two-dimensional horizontal section of the substrate makes it possible to have a capacitive variable dependent on the height (Z axis) and the shape of the conductive zones of the horizontal section (X and Y axes). In other words, regardless of the fixed or variable dielectric characteristics, the measurement capacitance is simultaneously proportional to the effective height and width of the immersed surface of the substrate.

It will be recalled that the objective to achieve is to obtain a capacitive variable dependent only on the immersed height and independent of the following parameters: Permitivity of the dielectric of the submerged zone Permittivity of the dielectric of the emerging zone Parasite parallel capacitance of the constituents of the substrate will call C l the total electrical measuring capacity constituted by the immersed zone.

C2 will be referred to as the total reference electrical capacity constituted by the immersed zone.

The capacitance Cl consists of longitudinal conductive lines of lengths, widths and number modulated over the entire measuring height.

The capacitance C2 consists of longitudinal conductive lines of lengths, widths and number modulated over a fraction or the totality of the measurement height. The equations developed below show that the elimination of the dielectric characteristics of the submerging liquid is obtained by performing the quotient C 1 on C2.

In view of the above, it appears that the capacitor C2 should consist of a permanent immersion zone automatically located at the base of the sensor.

On the other hand, the need to have sufficient electrical capacity for a reliable and stable electronic acquisition while maintaining a sensor width of very small dimension does not allow to functionally separate the variables C 1 and C2 without risk of having a height to 30 the base not measurable too important. 11 The solution adopted consists in defining two vertical operating zones obeying laws of variation such that the electronic processing of these two capacities generates a measuring signal linearly proportional to the height and independent of the dielectric constant.

This technique makes it possible to have a measurement without an ineffective base zone, that is to say providing a measurement from the vertical origin of the sensor while taking into account the dielectric characteristics of the liquid to be measured.

The electronic conditioner integrated in the sensor substrate, which is the subject of an independent but complementary patent, performs the following function: S = Cpt + C1ùK1 / Cp2 + C2ùK2 S: Analog or digital measurement output signal 15 Cp: Capacity Parallel parasite K: Constant for canceling the operating constants C: Metrological electrical capacitance ELECTRONIC CONDITIONING CIRCUIT 20 The various assemblies that can be integrated in this sensor substrate are made by analog or digital circuits according to the sought-after accuracies and the datalogy domains. exploitation.

In both cases, the input circuit achieves the acquisition of a capacitive variation of small value made intrinsically stable by the monolithic structure and the treatment of this substrate.

In addition, a differential arrangement can significantly reduce long-term drift of the basic values.

This arrangement performs analog or digital signal processing in accordance with the mathematical development developed hereinafter. These various original assemblies using low-cost passive or active components are the subject of an independent patent intended to be associated with the patent in question but may be used on other substrates comprising one or more electrical capacitors or variable resistances depending physical quantities to measure (time constant). EQUATIONS For the understanding of the development below, the following symbols have been selected:

S: Analogue or digital measurement output signal 10 Cl: Measuring electrical capacitance variable depending on the submerged zone C2: Variable reference electrical capacitance depending on the immersed zone Hm: Height of the liquid to be measured (immersed zone) 15 Hr : Reference liquid height (immersed zone) Ho: Initial height of the sensor close to 0H,: Height of the measurement and reference zone HPe: Maximum measurement height (full scale) 11: Width involved in the electrical capacitance Cl (measurement) 20 12: Width involved in the capacitance C2 (reference) Chl: Measuring capacity variable between 0 and Hl Ch2: Variable reference capacity between 0 and H1 Cp,: Parallel parasitic capacitance on the measuring capacitance Cl Cpt : Parallel parasitic capacitance on the correction capacity C2 25 f (H): Expression of 11 as a function of the immersed height Hl g (H): Expression of 12 as a function of the immersed height Hl CA : Permittivity of non-conductive liquid or surface dielectric go: Absolute Permittivity of Air Absolute Permitability of Insulating Substrate

The parallel capacitors Cpt and Cpt are eliminated, according to the versions, by a capacitive feedback of the form: Effective parasitic capacitance after correction = Cp (1 - X) X: Reinjection factor can vary between 0 and 1.5 by a passive network resistive precision.

CD: 30 13 2932564 It appears that:

If X = 0: The parasitic capacitance Cc is equal to the parasitic capacitance of the substrate

5 If k = 1: The parasitic capacitance Cc is equal to zero regardless of the value of this capacitance.

If? ^,> 1: The parasitic capacitance Cc becomes negative and allows for certain applications to increase the relative capacitive sensitivity of the sensor.

These parasitic capacitances Cp are also eliminated by making K = Cl) and K2 = Cpt in the memories of the processing circuit.

In a general way, the capacitive variation (Ch) as a function of Hm, HPe (full scale measurement) and the permittivity of the fluids is written: Ch = HEoEr + (HPe ûH) Eo Ch = Eo [H (Er ù 1 )] + Eo HPe Eo HPe is a constant eliminated in the memory processing circuit (offset). Consequently S = Eo [Hm (Er ù 1)] / Eo [Hr (Er ù 1)] showing that the parameters Eo and (Er û 1) present in the numerator and denominator are eliminated, the output signal S only depending on the quotient Hm / Hr.

Therefore, this quotient must be linearly proportional to H.

This result is obtained in two ways depending on the height:

Hr = constant 30 - The nonlinear variations by design of the substrate parameters Hm and Hr obey laws making this ratio linearly proportional to Hm. We have previously seen that we have distinguished the following two vertical operating zones (C 1 and C 2):

The so-called measurement zone whose capacitive characteristic as a function of the height obeys a non-linear expression developed below. This expression can be broken down into two parts (from H = 0 to H = H1 and from H = H1 to H = Hpe) mathematically different

The other called reference area whose capacitive characteristic according to the height obeys another nonlinear expression developed below.

The combination of these two morphologies exploiting the entire width of the substrate makes it possible, after treatment, to obtain a linear transfer characteristic as a function of height.

Reference area - measure This area between Ho and H1 is written as: Chl = A.J 11.dH Ch2 = B 512.Dh 11 = f (H) 12 = g (H)

We obtain: Chl = AJ f (H) .d (H) Ch2 = Bj g (H) .d (H) In this zone we put: Chl / Ch2 = CH that is to say that the quotient of the Measurement capacity by the reference capacity varying from 0 to H1 is a linear function of the height from where: AJ f (H) .d (H) / BJ g (H) .d (H) = Ch independent of the characteristics It should be noted that the integrals of the functions f (H) and g (H) are defined in the interval Ho and H1. On the other hand, the maximum use of the substrate surface (minimum width) results in the writing of the following expression:

J (H) .d (H) + B 1 g (H) .d (H) = DH exploiting the entire immersed surface of reference

Solving the above equations results in: f (H) = a5H (2 + aH / (1 + aH) 2) g (H) 5 / (1 + ax) 2 f (H) and g ( H) reflect the active variation of substrate width as a function of the height

The parameters A, B, C, D, a and 5 are constants constants by construction (substrate etching pattern).

The cutting of the lateral electric capacitance by parallel lines makes it possible, by etching the substrate, to respect the above functions (Il = f (H) and 12 = g (H)).

It is important to emphasize that the height H1 between H0 and Hpe can be confused with Hpe. 20 Measuring zone This zone is between HO and Hpe. The transfer characteristic of this area (C1) as a function of height can combine the nonlinear expression defined above with a complementary linear expression of the form C 1 = AH.

In conclusion: The non-discontinuous association of the measurement and reference zones constituted by the variable electrical capacitances as a function of the height makes it possible to obtain a linear variation from Ho while eliminating the action of the dielectric characteristics of the liquid which can vary. depending on its composition and temperature. General Equation S = C1 / C2 with: C 1 = A.sD.H + B.sA HI + C.sD.HPe ù C.sD.H, + D.sA_H ù D.CA. H1 + D. so. Hpe to D. Co. H After simplification: C 1 = D.H (sA - so + sD.KI + sA K 2 + so.K 3)

K ~ = H1 (A-C) + C.He2 K2 = H1 (B-D) K3 = D.He2 C2 = E.CD.H1 + Fc, H1 = H1 (E.sD + F.sA)

The factors A, B, C, D, E, F are constant geometrical parameters. The main variable is H (height) The parameters corresponding to the nature of the liquid and the composition of the substrate are sA and sD. For reasons of sensitivity of the electronic acquisition circuit: - HI is between 2 and 4 cm (see equation above) - Hpe is between 10 and 100 cm The graphical modeling of S = ftl / C2 results in the following highlighting: 20 S is a linear function of H The linearity error is better than 1% A variation of sA in a ratio 3 results in an error of less than 0.5%

ILLUSTRATIONS The referenced drawings in FIG. 1, FIG. 2 and FIG. 3 on page 23 relate to the main embodiment. The aim of the electronic synoptic is to show the possibility of having analog and digital outputs simultaneously. The curve illustrates the longitudinal modulations of the capacitances C1 and C2 obtained by the etching of the electrical conductors. The drawing of FIG. 1 is an exemplary embodiment, but any other morphology of the conductive lines respecting the curve 3 is within the scope of this patent. 17 EMBODIMENTS Two production families are planned according to the specific constraints of use and the production tools.

Mode n ° 1 We can distinguish in this monolithic sensor the following integrated constituents: - An insulating substrate with a width of 10 mm and a length of between 10 cm and 100 cm - A metallization on one side composed of vertical lines of which the lengths are modulated according to the equation defined in the corresponding chapter, whose pitch may be 1 mm with a form factor of 0.5 mm and whose number is between 5 and 10 - These conductive lines are electrically united to constitute two groups called Cl and C2 - The electrical circuit of the electronic conditioner is located at one end in the same width as the sensor substrate Mode No. 2 Structure identical to Mode No. 1 with a pitch of 2 mm and a metallization on both sides.

Mode No. 3 Structure identical to mode No. 2 associated with lines of liquid interface passage between the metallized lines being specified that for reasons of mechanical strength, the individual length of the passage lines will be of the order of 10 cm. In addition, the closed end of these passage lines have a shape inclined in the thickness of the substrate to improve the flow of the fluid.

In conclusion, these different embodiments will be used according to the viscosity of the fluids to be measured, the desired response time and the production tools. UTILIZATION This transducer height suitable for the application can be placed inside a plenum tube also acting as electrical shielding.

This tube must be equipped with lower and upper holes compatible with the speed of variation of the level (flow). 18 Its internal surface must be such that the liquid does not form with the substrate, meniscus likely to cause measurement errors.

The lateral ends of the sensor substrate consist of conductive lines connected to the electrical mass, eliminating any risk of short circuit and moving the protection tube away from the sensitive conductive lines.

Analog or digital output signals have a low electrical impedance allowing a remote connection without risk of metrological damage. For applications in which rapid level ripples are not to be considered as primary information but should instead be omitted, an electronic filter integrated into the electronic conditioner (possibly associated with a protection tube) for A time constant of up to 10 seconds reduces the influence of these ripples to a value less than accuracy.

The electronic circuit of this sensor with a short response time for low viscosity liquids, allows simultaneous delivery of main level information (fast change filtration) and information representative of surface ripples. In this case the channel delivering the ripple electronic signal is rendered insensitive to the base height and the small amplitude of the ripples is amplified.

In the same way, it is possible to set a setpoint circuit at one or more levels on the oscillation path.

This monolithic sensor-transmitter and small dimensions whose operation is identical for conductive and non-conductive liquids, found its use in all areas requiring a level measurement between 10 cm and 100 cm with a precision 30 may be better than 1 % PE.

By way of non-exhaustive examples, priority may be given to the automotive and appliance domains. 20 35 19 In the automotive field, the short-term uses are as follows: - Various species Fuel Urethane additive Coolant - Brake system fluid Lubricating oil

This product is particularly suited to this field, the characteristics of the products of the same nature may have different present or future characteristics depending on the composition, aging and temperature.

As explained above, the variation of the characteristics of the products to be measured is taken into account by the sensor substrate and managed by the electronic acquisition and processing circuit 15 in order to deliver a measurement signal linearly proportional to height and independent. aforementioned characteristics. 20

Claims (10)

REVENDICATIONS1. Capacitive level sensor-transmitter composed of any insulating substrate on which are integrated longitudinal bipolar electrodes consisting of modulated segments in length, width, number and space. 2. Sensor-transmitter according to claim 1 characterized in that the morphology of the conductive zones constitutes at least two electrical capacitors called C1 and C2. 10 3. Sensor-transmitter according to claim 2 characterized in that these electrical capacitances vary as a function of the height of the fluid according to transfer characteristics mathematically determined in accordance with the equations chapter page 16 line 10. 4. Sensor-transmitter according to claim 1 characterized in that the modulation of the bipolar electrodes obeys a monotonous and non-periodic mathematical expression. 5. Sensor-transmitter according to claim 1 characterized in that the longitudinal bipolar electrodes may have any width. 20 6. Sensor-transmitter according to claim 1 characterized in that the bipolar electrodes are located on one or both sides of the substrate. 7. Sensor-transmitter according to claim 1 characterized by a substrate whose main faces are smooth. 8. Sensor-transmitter according to claim 1 characterized by the possibility of producing longitudinal slots connecting the two faces of the substrate. 9. Sensor-transmitter according to claim 8 characterized in that the longitudinal slots 30 may have widths between 0.5 mm and 5 mm. 10. Sensor-transmitter according to claim 1 characterized by a thickness of the substrate may be between 0.2 mm and 3 mm. 21. A sensor-transmitter according to claim 2 characterized by an electrical connection of the bipolar electrodes for electrically differentiating capacitors C1 and C2. Sensor-transmitter according to claim 1 characterized by a monolithic manufacturing structure. 13. Sensor-transmitter according to claims 1 and 6 characterized by a surface state of the substrate having no longitudinal discontinuity on the faces in contact with the liquid. 14. Sensor-transmitter according to claims 5 and 6 characterized in that the surfaces in contact with the liquid are covered with a resin. The sensor-transmitter according to claim 14 characterized by using a high temperature resin. 16. Sensor-transmitter according to claim 14 characterized in that the deposited resin has a thickness between two and a hundred micrometers. 17. Sensor-transmitter according to claim 14, characterized in that the thickness of the resin has a tolerance better than 5%. 18. Transducer-transmitter according to claim 1 characterized in that the insulating material constituting the substrate can be any. 19. Sensor-transmitter according to claim 1 characterized in that the conductive material forming the bipolar electrodes can be any. 20. Sensor-transmitter according to claim 1 characterized in that the conductive material comprising the electrodes can be achieved by etching or by deposition. 21. Sensor-transmitter according to claim 1 characterized by the implantation on the same substrate of an electronic conditioning circuit located at one end. 22. A sensor-transmitter characterized by a continuous link etched between capacitors C1 and C2 and the electronic circuit of claim 21. 23. Sensor-transmitter according to claim 1, characterized in that capacitors C1 and C2 vary in size. height function for conductive and non-conductive liquids. 24. Sensor-transmitter according to claim 1 characterized by a substrate consisting of a stack of conductive layers etched or deposited covered with an insulating resin. 25. Sensor-transmitter according to claim 21, characterized in that the electronic conditioning treatment performs the quotient CI / C2. 26. Sensor-transmitter according to claim 21, characterized in that the analog or digital electronic processing of the Cl / C2 ratio varying according to the height, eliminates the influence of the dielectric constant variation of the measured liquid. The sensor-transmitter of claim 14 wherein the integral surface of the substrate is covered with a reflective insulating resin. 28. Transducer-transmitter according to claim 1 characterized by the establishment around the substrate of a metallized tube providing electrostatic shielding and an interface level of tranquilization device. Sensor-transmitter according to claim 28 characterized by any geometry of the section of the plenum-shielding tube. 23