High-resolution inductive sensor

Abstract

The invention relates to an inductive sensor (D1) comprising a fixed part (1) and a moving part (2). The moving part comprises a movable or deformable sensing element (SE) and a magnetic coupling element (Fe) mechanically fixed to the sensing element (SE). The fixed part comprises a voltage generator (G1) and a coil transformer (12) comprising a transmitting inductor (L1) connected in parallel with the generator and a receiving inductor (L2). The magnetic coupling element (Fe) is separated from one end of the transmitting inductor (L1) by a separation distance (d). The fixed part includes a data acquisition chain (11) connected to the receiving inductor (L2) and configured to generate a measurement signal (Vout) of the variation in the distance (d). The measurement signal (Vout) corresponds to a measurement of the variation in frequency or amplitude of the voltage across the receiving inductor (L2). Figure for the abridged version: Fig.1a.

Description

Title of the invention: High-resolution inductive sensor

[0001] Scope of application

[0002] The invention relates to the field of proximity and displacement or deformation detection for producing sensors. More particularly, the invention relates to a displacement sensor for a mobile or deformable test body coupled to an inductive flux. The scope of the invention may cover high dynamic weighing devices applied for laboratories (1g to 200g), people (1g to 200kg) or large works (1kg to 200 tonnes).

[0003] Problem raised

[0004] In the fields of measuring devices, sensitivity is a crucial parameter, especially in weighing devices or pressure sensors. The sensitivity of a measuring device represents its ability to detect small variations in the measurement. The more sensitive the device, the more accurately it is able to measure variations in the measured quantity. More specifically, in the case of weighing devices, increased sensitivity allows smaller quantities to be measured and more accurate results to be obtained. This can be particularly important in fields such as pharmacology, laboratory research or the food industry, where accurate and reliable measurements are essential to ensure the quality and safety of products or scientific research results. Therefore, adequate sensitivity is essential to ensure the accuracy of the results and to meet the quality standards in force.

[0005] Furthermore, dynamic range is another important parameter in measuring devices generally, and in weighing or pressure measuring devices in particular. By "dynamic range" is meant the interval comprising the values ​​measurable by the measuring device, going from the smallest detectable measurement to the largest. A high dynamic range means that the device can measure very small quantities as well as very large quantities. More particularly, in the case of weighing devices, a wider dynamic range can be particularly useful in situations where objects of different masses need to be weighed. For example, a balance with a wider dynamic range can be used to weigh small samples in a research laboratory, as well as to weigh larger quantities of raw materials in industry.By having a wider dynamic range, users can achieve accurate and reliable results for a wide range of measurements, which is essential for many applications.

[0006] In this context, exploiting the deformation of a test body presents a suitable solution for measuring an applied mass or force. This method uses an elastic test body, which is a structural element designed to undergo deformation in response to an applied force. The deformation causes a variation in the physical characteristics of the test body which can be converted into electrical signals. For example, the relative deformation of a test body comprising piezoresistive strain gauges causes a relative variation in the resistance of the strain gauges. Measuring this variation in resistance requires bonding the gauges to the test body and establishing a physical electrical connection between the test body and an electronic circuit.The sensitivity to mechanical shocks and the connectivity significantly reduce the robustness of the sensor because part of the measuring electronics is subjected to the mechanical forces applied during measurement. In engineering, the robustness of a system is defined as the stability of performance despite external conditions with large variations that can reduce the reliability of the system. In addition, the total or partial implementation of the measuring electronics on the test body limits the dynamic range of the sensor to avoid damage to the measuring electronics.

[0007] Thus, the objective is to develop a measuring sensor based on a deformable and / or mobile test body with high sensitivity, a wide dynamic range while ensuring its mechanical and electronic robustness making it possible to improve the reliability and the lifetime of the sensor.

[0008] Prior art / state of the art restrictions

[0009] International patent application WO98 / 19133 describes a dimensional control device by local and selective generation and detection of ultrasound. The solution is based on the coupling of the ultrasonic field between the reading head and the surface of the object being probed. The disadvantage of the described solution is that the measuring device has a strong temperature dependence of the order of 1700 ppm / °C, which requires compensation for the temperature drift of the measurement signal by means of a high-resolution temperature sensor.

[0010] Patent application DE10048435A1 describes an inductive sensor for lateral displacement of a moving object relative to a fixed object. The device detects variations in translation by maintaining a fixed distance between a conductive surface and a circuit in the form of a serpentine. Although it is effective for detecting the passage of objects, this configuration does not offer high dynamics in a direction perpendicular to the plane of the detector, nor high resolution perpendicular to the plane of the serpentine.

[0011] Response to the problem and provision of a solution

[0012] To overcome the limitations of existing solutions with regard to sensitivity, dynamic range and robustness, the invention proposes a sensor which exploits the variation of the relative magnetic permeability of an inductive impedance coupled directly or indirectly with a magnetic coupling element integral with a test body. The invention is based on the variation of a frequency response of said inductive impedance in response to a pulsed stimulation and / or the variation of an amplitude measured in response to a voltage ramp signal. The invention allows a contactless measurement between the electronic signal processing circuit and the test body which is subjected to mechanical stresses. In addition, the device according to the invention has a low temperature dependence, which improves its stability compared to state-of-the-art solutions.

[0013] Summary / Claims

[0014] The subject of the invention is an inductive sensor comprising a fixed part and a mobile part; the mobile part comprising: - a mobile or deformable test body, in a first direction, - and a magnetic coupling element mechanically secured to the test body; the fixed part including: - a voltage generator configured to generate an excitation signal; - a coil transformer comprising a transmitting inductance mounted in parallel with the generator and a receiving inductance; the axis of the transmitting inductance and the axis of the receiving inductance being oriented in the first direction; the magnetic coupling element being placed relative to the coil transformer so as to magnetically couple the transmitting inductance and the receiving inductance; the magnetic coupling element being separated from one end of the transmitting inductance by a separation distance; - an acquisition chain connected to the receiving inductance and configured to generate a signal for measuring the variation in distance following a displacement or deformation of the test body; the measurement signal corresponding to a measurement of the variation in frequency or amplitude of the voltage across the receiving inductance.

[0015] According to a particular aspect of the invention, the acquisition chain comprises an analog-digital converter for converting the voltage across the receiving inductance into a first digital signal.

[0016] According to a particular aspect of the invention, the acquisition chain comprises a calculator configured to: - extract the resonant frequency of the voltage across the receiving inductance from the first digital signal. - calculate the deviation between the extracted resonance frequency and a predetermined reference frequency.

[0017] According to a particular aspect of the invention, the excitation signal is a rectangular pulse.

[0018] According to a particular aspect of the invention, the fixed part further comprises a capacitive element and a resistive element mounted in series with the emission inductance so as to produce an RLC circuit powered by the voltage generator.

[0019] According to a particular aspect of the invention, the acquisition chain comprises a calculator configured to: - carry out a sampling of the first digital signal in order to extract the amplitude of the voltage across the receiving inductance; - calculate the difference between the extracted amplitude and a predetermined reference amplitude.

[0020] According to a particular aspect of the invention, the excitation signal is a voltage ramp.

[0021] According to a particular aspect of the invention, the acquisition chain comprises an amplifier circuit mounted upstream of the analog-digital converter to amplify the voltage across the receiving inductance.

[0022] According to a particular aspect of the invention, the magnetic coupling element is an object made of a ferrite material in the form of ir or in the form of a half-torus or in the form of a rod or in the form of a sheet.

[0023] According to a particular aspect of the invention, the ferrite material is chosen such that the thermal sensitivity of the relative magnetic permeability of said material is less than 1% / °C.

[0024] According to a particular aspect of the invention, the emission inductance and the reception inductance are produced by coplanar metal tracks deposited on a printed circuit.

[0025] According to a particular aspect of the invention, each of the transmitting inductance and the receiving inductance is produced by a coil wound around a solid rod.

[0026] According to a particular aspect of the invention, the transmission inductance is arranged next to the reception inductance or superimposed on the reception inductance.

[0027] According to a particular aspect of the invention, the mobile part comprises N magnetic coupling elements mechanically secured to the test body aligned in a row with N an integer strictly greater than 1; and in which the fixed part comprises Nl intermediate magnetic coupling elements arranged between the emission inductance and the reception inductance.

[0028] The invention also relates to a weight or pressure measuring device comprising an inductive sensor according to the invention. Detailed Description

[0029] Other characteristics and advantages of the present invention will appear better on reading the description which follows in relation to the following appended drawings.

[0030] [Fig. 1a] illustrates the electrical diagram of the inductive sensor according to a first embodiment of the invention.

[0031] [Fig.lb] illustrates a spectral analysis of the voltage across the receiving inductance of the inductive sensor according to the first embodiment of the invention.

[0032] [Fig. 1c] illustrates the electrical diagram of the inductive sensor according to a second embodiment of the invention.

[0033] [Fig.2a] illustrates the electrical diagram of the inductive sensor according to a third embodiment of the invention.

[0034] [Fig.2b] illustrates an example of the temporal evolution of the electrical signals of the inductive sensor according to the third embodiment of the invention.

[0035] [Fig.3] illustrates a sectional view of a first embodiment of the inductive part of the sensor according to the invention.

[0036] [Fig.4] illustrates a sectional view of a second embodiment of the inductive part of the sensor according to the invention.

[0037] [Fig.5a] illustrates a sectional view of a third embodiment of the inductive part of the sensor according to the invention.

[0038] [Fig.5b] illustrates a partial top view of the third embodiment of the inductive part of the sensor according to the invention.

[0039] [Fig.6] illustrates a sectional view of a fourth embodiment of the inductive part of the sensor according to the invention.

[0040] [Fig.7] illustrates a sectional view of a fifth embodiment of the inductive part of the sensor according to the invention.

[0041] [Fig. 1a] illustrates the electrical diagram of the inductive sensor DI according to a first embodiment of the invention. The inductive sensor DI comprises a fixed part 1 and a movable part 2 in a first direction Z in an orthonormal reference frame (X,Y,Z).

[0042] The mobile part 2 comprises a test body CE and a magnetic coupling element Fe mechanically secured to the test body CE.

[0043] The test body CE is a bridge or a plate orthogonal to the first direction Z. The test body CE may be mobile or elastically deformable along the first direction Z following the application of a force F along said first direction. The applied force F corresponds for example to the weight of a physical object resting on the CE test body or to pressure exerted on its upper surface. In the case of a CE test body movable by translation in the first direction Z, elastic means are attached to the CE test body in order to return it to its initial position in the absence of an applied force F.

[0044] The magnetic coupling element Fe mechanically secured to the test body CE so as to follow its displacement or its deformation in the first direction Z. The magnetic coupling element Fe is an object made of a ferromagnetic material in the form of ir or in the form of a half-torus or in the form of a rod or in the form of a sheet. For example, the ferromagnetic material is a ferrite made of an alloy of Ni-Zn or Mn-Zn or Co-Ni-Zn.

[0045] Advantageously, the ferromagnetic material has a thermal sensitivity of said relative magnetic permeability pr of less than 1% / °C. In addition, the ferromagnetic material has a high bandwidth of up to 50 MHz.

[0046] Advantageously, with the exception of the case of the sheet, it is possible to wind metal turns around the magnetic coupling element Fe in order to improve the magnetic coupling capacities of the magnetic coupling element Fe.

[0047] In the illustrated example, the magnetic coupling element Fe in the form of ji, comprises a base and two parallel protrusions which extend from said base in the first direction Z. The protrusions may be straight rods, or conical in shape. The base is fixed on a surface, preferably the lower surface, of the test body CE and the protrusions extend orthogonally to said surface downwards.

[0048] The fixed part 1 comprises a voltage generator Gl, a coil transformer 12 comprising a transmission inductance Li mounted in parallel with the generator Gl and a reception inductance L2, and an acquisition chain 11 connected to the reception inductance L2.

[0049] The generator Gl is configured to generate an excitation signal Vin in the form of an electrical pulse and has an output resistance Rs less than 0.5Ω. The fixed part 1 further comprises a capacitive element Cl connected in series with the output resistance Rs and the emission inductance Lb. The capacitive element Ci, the output resistance Rs and the emission inductance Li together form an RLC circuit excited by the electrical pulse Vin generated by the generator GL. The sizing of the capacitive element Cl and the emission inductance Li is chosen so as to have a damping factor Ç less than 0.7 so as to obtain a damped oscillatory regime following the application of the electrical pulse Vin.

[0050] The receiving inductance L2 is placed close to the transmitting inductance Li to allow magnetic coupling between the two inductances and thus obtain a operation as an energy transformer 12. The axis of the emission inductance Li and the axis of the reception inductance L2 are oriented along the first direction Z. Thus, the variations in the voltage across the emission inductance Li are reproduced across the reception inductance L2. The initial state of the inductive sensor DI corresponds to the absence of a force F along Z applied to the test body CE. In the initial state of the sensor D1, the first protuberance of the magnetic coupling element Fe in ir is placed at a predetermined initial distance d=d0 relative to the upper end of the emission inductance Lb

[0051] Advantageously, in the initial state of the sensor D1, the second protuberance of the magnetic coupling element Fe at ir is placed at said predetermined distance d=d0 relative to the upper end of the receiving inductance L2. This configuration has the advantage of duplicating twice the dependence of the magnetic flux produced at the axial output of the transmitting inductance Li with the variation of the distance d: a first dependence characteristic of the axial decrease of the magnetic flux produced by the transmitting inductance Li when the magnetic coupling element is moved away or brought closer and a second dependence which characterizes the transfer of the magnetic field from the magnetic coupling element to the receiving inductance L2.

[0052] The emission inductance Lb, the reception inductance L2 and the magnetic coupling element Fe form an assembly called the “inductive part” of the sensor DL. The “inductive part” has an equivalent inductance value Leq.

[0053] The response to excitation by a rectangular pulse Vin of the circuit RsLeqCi is a damped pseudo-periodic oscillation. The oscillatory response is also reproduced at the terminals of the receiving inductance L2 by magnetic coupling. The resonant frequency f observed at the terminals of the receiving inductance L2 is determined by the following expression:

[0054] f = ____1___1 J 2^Le9Ci

[0055] with N the number of contiguous turns of the emission inductance Lb R the radius of the turns of the emission inductance Li, 1 the length of the contiguous turns of the emission inductance Lb the magnetic permeability of the vacuum and the equivalent relative magnetic permeability of the inductive part as a function of the relative magnetic permeability qr of the magnetic coupling element and the distance d separating the magnetic coupling element Fe from the emission inductance Lp

[0056] Among the aforementioned parameters, the distance d is the only variable parameter following the application of a force F on the test body CE. The application of the force F in the Z direction induces the translation or deformation of the test body CE in the Z direction. This induces a variation of the distance d separating the element from magnetic coupling Fe of the emission inductance Lb This induces a variation in the equivalent relative magnetic permeability of the inductive part. This induces a variation in the resonant frequency of the voltage VL2 observed at the terminals of the reception inductance L2 in response to the rectangular electric pulse Vin. This chain of dependence thus makes it possible to convert the amplitude of the applied force F into a measurable parameter, namely the variation in the resonant frequency f.

[0057] The acquisition chain 11 comprises an analog-to-digital converter DAC for converting the voltage VL2 (analog signal) across the receiving inductance L2 into a first digital signal Vdig. The first digital signal Vdig thus corresponds to a digitized oscillatory signal with a resonant frequency f equal to that of the voltage VL2. The analog-to-digital converter DAC is characterized by a predetermined sampling frequency fDAc. The values ​​of the capacitance Ci and the emission inductance Li are chosen so as to always have a resonant frequency f less than half the sampling frequency fDAc of the analog-to-digital converter DAC. For example, the sampling frequency fDAc is equal to 12 MHz, so the resonant frequency f is always less than 6 MHz during operation of the sensor DI.

[0058] The acquisition chain 11 further comprises an ECU computer configured to: - perform a Fourier analysis of the first digital signal Vdig in order to extract the resonant frequency fi of the voltage V at the terminals of the reception inductance L2 in response to the rectangular pulse Vin with a non-zero force F and d=di ^d0. - calculate the deviation Af between the extracted resonance frequency fi and a predetermined reference frequency f0.

[0059] The reference frequency fo is measured beforehand in a calibration step corresponding to the following conditions: F=F0 and d=d0. The reference frequency fo is then stored as digital data in the memory of the ECU. In the calibration operation, it is possible to rely on a non-zero reference applied force F=Fo.

[0060] The sensor thus generates a measurement signal Vout of the variation in the distance Ad following a displacement or deformation of the test body CE. The measurement signal Vout corresponds to a measurement of the variation in the frequency Af=frf0.

[0061] Advantageously, the ferromagnetic material of the magnetic coupling element Fe has an initial relative magnetic permeability pr of between 1 and 1500. This makes it possible to increase the effect of the variation in the distance separating the magnetic coupling element Fe on the variation in the equivalent inductance Leq with a range variation between 10% and 400% and more particularly around 50% to 150%.

[0062] Advantageously, the protrusions of the magnetic coupling element Fe have a diameter smaller than that of the inductances Li and L2. Their profile may be conical. Thus, the insertion of the protrusions of the magnetic coupling element Fe into each of the inductances Li and L2 makes it possible to considerably increase the dynamic range of the sensor D1. In addition, this makes it possible to maximize the magnetic coupling between the inductances Li and L2 and thus to increase the sensitivity of the inductive sensor according to the invention.

[0063] In the solution according to the invention, the variable physical quantity following the application of a force is a separation distance. The fixed part 1 corresponds to the electronic measurement circuitry which is not implemented directly on the CE test body. This makes it possible to avoid applying mechanical stresses to the electronic measurement circuitry when using the DL sensor. This makes it possible to avoid degradation of the electrical components and connections and thus makes it possible to improve the robustness of the D1 sensor compared to state-of-the-art solutions.

[0064] [Fig. 1b] illustrates a spectral analysis of the voltage VL2 across the receiving inductance L2 of the inductive sensor D1 according to the first embodiment of the invention. The curve CrO corresponds to the initial state (d=dO); the curve Cri corresponds to the approach of the magnetic coupling element Fe towards the excitation inductance L1 (d=dl <dO) ; la courbe Cr2 correspond à l’éloignement de l’élément de couplage magnétique Fe de l’inductance d’excitation L1 (d=d2> d0).

[0065] When the magnetic coupling element Fe approaches the ends of the inductances Li and L2, the distance d decreases. This induces an increase in the equivalent relative magnetic permeability ^eq of the inductive part, which results in an increase in the equivalent inductance Leq and simultaneously a stronger magnetic coupling between the emission inductance Li and the reception inductance L2. This effect is amplified if the magnetic losses in the magnetic coupling element Fe are low, which is the case for a II-shaped or half-torus ferrite. Advantageously, the number of turns of the reception inductance L2 is greater, preferably 2 to 5 times, than the number of turns of the emission inductance Li so as to improve the sensitivity of the inductive sensor according to the invention.

[0066] Three results are then obtained simultaneously: a decrease in the measured resonance frequency Af=frf0 >0; an increase in the amplitude of the resonance peak because the magnetic coupling is improved; and an increase in the quality factor Q of the inductive part because the width of the resonance peak is reduced (BWl-BW0<0). Conversely, when the magnetic coupling element Fe moves away from the ends of the inductances Li and L2, the distance d increases. This induces a decrease in the equivalent relative magnetic permeability of the inductive part; which reduces the value of the equivalent inductance Leq and simultaneously results in a weaker magnetic coupling between the emission inductance Li and the reception inductance L2. We then obtain three results simultaneously: an increase in the measured resonance frequency Af=f2-f0 >0; a decrease in the amplitude of the resonance peak because the magnetic coupling is reduced; and a decrease in the quality factor Q of the inductive part because the width of the resonance peak is increased (BW2-BW0<0).

[0067] An inductive DI sensor is thus obtained having improved performance in terms of sensitivity, dynamic range and robustness. For example, the resonance frequency can vary by 50%, with a range preferably between 2 and 6 MHz with a maximum travel of 3 mm in the first direction Z, preferably less than 1 mm. The frequency resolution is approximately 2.5 ppm (parts per million) with a measurement rate of 5 Hz, while the resolution in variation of the distance d is approximately 10 nm.

[0068] Figure 1c illustrates the electrical diagram of the inductive sensor DI according to a second embodiment of the invention. The structural and functional characteristics described for the first embodiment remain valid for the second embodiment. In the illustrated embodiment, the fixed part 1 further comprises an amplifier circuit AMP mounted upstream of the analog-to-digital converter DAC to amplify the voltage VL2 across the receiving inductance L2. This makes it possible to improve the sensitivity of the inductive sensor DI. As a non-limiting example, the amplifier circuit is produced by a wideband operational amplifier AO configured in a non-inverting assembly with an amplification gain equal to j between 2 and 11. The amplification circuit AMP has an input impedance RL greater than or equal to 105 times the residual resistance of the turns of the receiving inductance L2.

[0069] Figure 2a illustrates the electrical diagram of the inductive sensor DI according to a third embodiment of the invention. In this embodiment, the quantification of the variation of the distance d is done by a measurement of amplitude and not of frequency. The generator G1 is configured to generate an excitation signal Vin in the form of a voltage ramp. The voltage ramp Vin creates a transient magnetic flux by the emission inductance Li with a constant temporal variation of current tL. [Fig.2b] illustrates an example of the temporal evolution of the electrical signals of the inductive sensor DI according to the third embodiment of the invention. The voltage ramp of the excitation signal Vin is reproduced at the terminals of the emission inductance Li because of the residual resistance of said emission inductance. We illustrate on diagram (202) continuously a voltage ramp VL1 obtained for a distance di less than the initial distance d0. Diagram (202) illustrates in dotted lines a voltage ramp VL1 obtained for the distance d0 corresponding to a zero force F. On diagram (203), a voltage plateau Vital is obtained at the terminals of the receiving inductance L2 having an amplitude Ai presented in solid lines. The amplitude Ai associated with a distance di <d0 est supérieure à l’amplitude ao correpondant la distance initiale d0. le plateau de tension vi^est obtenu grâce haute impédance d’entrée chaîne d’acquisition 11 connectée l’inductance réception l2. dans le troisième mode réalisation, calculateur ecu configuré pour : - carry out a sampling of the first digital signal Vdig in order to extract the amplitude Ai of the voltage VL2 at the terminals of the reception inductance L2; - and to calculate the difference between the extracted amplitude Ai and a predetermined reference amplitude Ao.

[0070] The reference amplitude Ao is measured beforehand in a calibration step corresponding to the following conditions: F=F0 (with F0 possibly zero) and d=d0. The reference amplitude Ao is then stored as digital data in the memory of the ECU.

[0071] The sensor thus generates a measurement signal Vout of the variation in the distance Ad following a displacement or deformation of the test body CE. The measurement signal Vout corresponds to a measurement of the variation in the amplitude AA=Ai-A0.

[0072] The voltage plate VL2 makes it possible to obtain a plurality of amplitude measurement points. The calculator is thus configured to carry out an acquisition of several measurement points and then calculate an average to improve the measurement resolution.

[0073] [Fig. 3] illustrates a sectional view of a first embodiment of the inductive part of the DI sensor according to the invention. It is recalled that the inductive part of the sensor is made up of the emission inductance Lb, the reception inductance L2 and the magnetic coupling element Fe. In this first example, the emission inductance Li and the reception inductance L2 are placed next to each other and are laterally weakly magnetically coupled by using external magnetic shielding such as a ferrite cylinder if necessary. Each inductance Li and L2 is made by winding a conductive wire around a separate hollow support (S1 and S2) filled with air, typically a non-magnetic insulating hollow cylinder, made of polymer for example. The turns are contiguous, having a diameter of between 40 pm and 100 pm.The length 1 of the cumulative contiguous turns of each conductive wire is less than 3mm to obtain a residual resistance of the winding less than 1Q. This improves the quality factor of the inductive part and thus improves the sensitivity of the inductive sensor Dl.

[0074] [Fig.4] illustrates a sectional view of a second embodiment of the inductive part of the sensor D1 according to the invention. In this embodiment, the emission inductance Li is superimposed on the reception inductance L2 along the same axis. This is then a direct magnetic coupling. Thus, the direct magnetic coupling between the two inductances is improved and the reception inductance L2 contributes greatly to defining the resonance of the inductive part of the sensor according to the invention. The magnetic coupling element Fe is a rod made of the ferromagnetic material described above. Each inductance Li and L2 is produced by winding an enamelled conductive wire around a common hollow support SI filled with air, typically a non-magnetic insulating hollow cylinder, made of polymer for example. The rod Fe is inserted into the hollow support SL Advantageously, the rod Fe is inserted on the side of the reception inductance L2.This allows to increase first mainly the reception inductance L2 without increasing the emission inductance Lb and thus to create a voltage step-up transformer while starting to lower the resonance frequency by mutual inductance. Then when the rod reaches the core of Lb the mutual inductance is the strongest and the frequency minimum. The rod Fe is mechanically secured to the CE test body. The translation of the rod Fe in the hollow support SI therefore modifies the magnetic coupling between the emission inductance Li and the reception inductance L2 This induces a modification of the frequency and the amplitude of the output signal Vout as described previously.

[0075] [Fig.5a] illustrates a sectional view of a third embodiment of the inductive part of the sensor D1 according to the invention. [Fig.5b] illustrates a partial top view of the third embodiment of the inductive part of the sensor D1 according to the invention. The emission inductance Li and the reception inductance L2 are coplanar. The two inductances are arranged flat with a snail winding next to each other on the same face of a printed circuit PCB. The windings are made by metal tracks deposited on the printed circuit PCB.

[0076] [Fig. 6] illustrates a sectional view of a third embodiment of the inductive part of the sensor D1 according to the invention. The emission inductance Li is produced by winding a metal track on the upper face of a printed circuit PCB. The reception inductance L2 is produced by winding a metal track on the lower face of the printed circuit PCB. The emission inductance Li and the reception inductance L2 have the same axis A. The printed circuit PCB comprises a through hole from the upper face to the lower face along the axis A of the two inductances. The magnetic coupling element Fe is a rod made of the ferromagnetic material described above. The rod Fe is inserted into the through hole, preferably starting on the side of the receiving inductance L2. The rod Fe is mechanically secured to the proof body CE. In the absence of deformation of the proof body, the end of the rod preferably stops halfway through the thickness of the printed circuit PCB. The translation of the rod Fe in the through hole modifies the magnetic coupling between the transmitting inductance Li and the receiving inductance L2. This induces a modification of the frequency and / or the amplitude of the output signal Vout as described above.

[0077] [Fig.7] illustrates a sectional view of a fifth embodiment of the part inductive of the DI sensor according to the invention. The emission inductance Li and the reception inductance L2 are arranged next to each other. The mobile part 2 comprises N (here N = 2) magnetic coupling elements Fei Fe2 mechanically secured to the CE test body with N an integer strictly greater than 1. The magnetic coupling elements Fei Fe2 are aligned in a row. The first magnetic coupling element Fei is coupled with the emission inductance Lp The second magnetic coupling element Fe2 is coupled with the reception inductance L2.

[0078] On the other hand, the fixed part 1 comprises Nl (in the illustrated case only one) intermediate magnetic coupling elements Fei' arranged between the emission inductance Li and the reception inductance L2. Each intermediate magnetic coupling element Fe / of rank i is intended to magnetically couple the magnetic coupling element Fe; of the same rank i in the row of the mobile part 2 to the following magnetic coupling element Fei+i. A cascade magnetic coupling is thus produced.

[0079] The magnetic coupling elements Fe; of the mobile part 2 are separated by a distance d from the magnetic coupling elements Fe / of the fixed part 1. Said distance is equal to the separation distance between the magnetic coupling elements Fe; of the mobile part 2 and the inductances Li and L2. This makes it possible to increase the dependence of the frequency and / or the amplitude according to the variation of said separation distance d. More particularly, a dependence in dN is obtained which considerably improves the sensitivity of the sensor.

[0080] In practice, the high losses in the magnetic coupling elements associated with this configuration lead to the influence of the receiving inductance L2 on the resonant frequency or amplitude being negligible compared to the cumulative effect of the magnetic permeability of the coupling elements as a function of the distance d on the equivalent magnetic permeability of the circuit. It is thus possible to achieve a configuration where the introduction of lateral magnetic insulation between the inductances Li and L2 is strong by magnetic shielding. This implies that the contribution of the lateral direct magnetic coupling between the inductances Li and L2 is negligible compared to the effect of the magnetic coupling elements Fe; and Fc,'. This results in the contribution of the receiving inductance L2 to the variations of the resonant frequency or the amplitude of the output signal Vout being negligible, especially if the number of turns of the receiving inductance L2 is small, for example 2 to 5 times smaller, than the number of turns of the transmitting inductance Li.

[0081] Conversely, if the number of turns of the receiving inductance L2 is large compared to that of the transmitting inductance Li, for example 2 to 5 times larger, and if the direct lateral magnetic isolation between Li and L2 is large (by shielding), then the contribution of the receiving inductance L2 to the variations of the resonant frequency or to the amplitude of the output signal Vout can become significant for small variations of d. This induces a significant increase in the variation range of the frequency and / or the amplitude of the output signal Vout.

Claims

Claims

1. Inductive sensor (Dl) comprising a fixed part (1) and a movable part (2), the movable part (2) comprising: - a test body (CE) movable or deformable, in a first direction (Z), - and a magnetic coupling element (Fe) mechanically secured to the test body (CE); the fixed part (1) comprising: - a voltage generator (Gl) configured to generate an excitation signal (Vin); - a coil transformer (12) comprising a transmission inductance (Li) mounted in parallel with the generator (Gl) and a reception inductance (L2); the axis of the emission inductance (LJ) and the axis of the reception inductance (L2) being oriented in the first direction (Z); the magnetic coupling element (Fe) being placed relative to the coil transformer (12) so as to magnetically couple the emission inductance (Li) and the reception inductance (L2);the magnetic coupling element (Fe) being separated from one end of the emission inductance (Li) by a separation distance (d); - an acquisition chain (11) connected to the reception inductance (L2) and configured to generate a measurement signal (Vout) of the variation of the distance (d) following a displacement or deformation of the test body (CE); the measurement signal (Vout) corresponding to a measurement of the variation of the frequency or the amplitude of the voltage at the terminals of the reception inductance (L2).;

2. Inductive sensor (Dl) according to claim 1 in which the acquisition chain (11) comprises an analog-digital converter (DAC) for converting the voltage across the receiving inductance (L2) into a first digital signal (Vdig).

3. Inductive sensor (Dl) according to claim 2 in which the acquisition chain (11) comprises a computer (ECU) configured to: - extract the resonant frequency (fi) of the voltage across the receiving inductance (L2) from the first digital signal (Vdig). - calculate the difference between the extracted resonant frequency (fi) and a predetermined reference frequency (f0).

4. Inductive sensor (Dl) according to any one of claims 2 or 3 in which the excitation signal (Vin) is a rectangular pulse.

5. Inductive sensor (Dl) according to any one of claims 2 to 4 in which the fixed part (1) further comprises a capacitive element (Cl) and a resistive element (Rs) mounted in series with the emission inductance (Li) so as to produce an RLC circuit powered by the voltage generator (Gl).

6. Inductive sensor (Dl) according to claim 2 wherein the acquisition chain (11) comprises a computer (ECU) configured to: - carry out a sampling of the first digital signal (V^g) in order to extract the amplitude (Ai) of the voltage at the terminals of the reception inductance (L2); - calculate the difference between the extracted amplitude (Ai) and a predetermined reference amplitude (Ao).

7. Inductive sensor (Dl) according to claim 6 in which the excitation signal (Vin) is a voltage ramp.

8. Inductive sensor (Dl) according to any one of claims 2 to 7 in which the acquisition chain (11) comprises an amplifier circuit (AMP) mounted upstream of the analog-digital converter (DAC) to amplify the voltage across the receiving inductance (L2).

9. An inductive sensor (Dl) according to any preceding claim wherein the magnetic coupling element (Fe) is an object made of a ferrite material in the form of ir or in the form of a half-torus or in the form of a rod or in the form of a sheet.

10. Inductive sensor (Dl) according to claim 9 wherein the ferrite material is chosen such that the thermal sensitivity of the relative magnetic permeability (qr) of said material is less than 1% / °C.

11. Inductive sensor (Dl) according to any one of the preceding claims in which the emission inductance (LJ) and the reception inductance (L2) are produced by coplanar metal tracks deposited on a printed circuit (PCB).

12. An inductive sensor (Dl) according to any one of claims 1 to 10 wherein each of the transmitting inductance (LJ) and the receiving inductance (L2) is made by a coil wound around a solid rod.

13. Inductive sensor (Dl) according to any one of the preceding claims in which the transmitting inductance (LJ is arranged next to the receiving inductance (L2) or superimposed on the receiving inductance (L2).

14. Inductive sensor (Dl) according to any one of the preceding claims in which the mobile part (2) comprises N magnetic coupling elements (Fei Fe2) mechanically secured to the test body (CE) aligned in a row with N an integer strictly greater than 1; and in which the fixed part (1) comprises Nl intermediate magnetic coupling elements arranged between the emission inductance (Li) and the reception inductance (L2).

15. Weight or pressure measuring apparatus comprising an inductive sensor (Dl) according to any one of the preceding claims.

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