DEVICE FOR MEASURING THE ELECTRICAL CONDUCTIVITY OF A LIQUID IN A PIPE

Abstract

The invention relates to a device for measuring the presence and electrical conductivity of a liquid inside a pipe (7), comprising: - at least one resonant electrical circuit (3) arranged on a contour of the pipe (7), the resonant frequency of said at least one resonant electrical circuit being representative of the presence of the liquid and its electrical properties, - a microcontroller (5) coupled to said at least one resonant electrical circuit (3), said microcontroller being configured to acquire at least one current value of the resonant frequency of said at least one resonant electrical circuit and to determine the presence and electrical conductivity of the liquid inside the pipe (7) on the basis of said at least one current value of the resonant frequency. Figure for abstract: Fig. 1

Description

Description Title of the invention: DEVICE FOR MEASURING THE ELECTRICAL CONDUCTIVITY OF A LIQUID IN A CONDUCT Technical field

[0001] — The present invention relates to the field of measuring electrical conductivity. and the filling level of a liquid inside a material pipe electrically insulating. STATE OF THE PRIOR ART

[0002] — The electrical properties of a liquid are mainly the permittivity and the conductivity. Capacitive measurement is often used to measure the filling of various containers. When the geometry and spacing of the capacitive armatures are constants, the capacity is directly proportional to the permittivity of the medium which separates the two frames. If the liquid has a relative permittivity different from that of air (of the order of 80 for water compared to 1 for air) then the value of the capacity is proportional to the filling of the container.

[0003] — The complex permittivity is composed of two terms: £(w)=eo(er"(w)-ier""(w)). The first er'(w) named real relative permittivity can be considered as constant for a given liquid at constant temperature and frequency. The second er”'(w) named imaginary relative permittivity or dielectric loss factor depends on the conductivity of the liquid and also of the temperature and the frequency of measurement.

[0004] The capacitive measurement therefore depends both on the filling level but also in a lesser extent of the conductivity of the liquid. A variation in conductivity can thus disrupting the filling measurement.

[0005] In many industrial, environmental, and medical fields we are looking for to measure the conductivity of a liquid to assess the concentration of ions in it liquid (usually water) in order to control its quality. Conductivity allows us to de- terminate the presence of ions in the liquid. For example, soft water, low in minerals, has low conductivity, while hard water, rich in minerals, has high conductivity. Thus, measuring conductivity makes it possible to control the quality of drinking water or irrigation water.

[0006] There are several types of devices for measuring the electrical conductivity of a liquid. Most solutions use impedance measurement requiring contact electrical which is not always easy to use to measure the conductivity of a liquid inside a pipe, particularly with risks of corrosion.

[0007] There are also devices which measure conductivity using probes inductive. However, inductive probes are expensive and do not adapt to all pipe diameters. They also cannot detect partial filling, which can impact the accuracy of the measurement. Thus, the object of the present invention is to overcome the aforementioned drawbacks by proposing a device for measuring in real time the electrical conductivity of a liquid inside a pipe automatically and without contact with the liquid, while making it possible to provide additional measurements on the filling of the pipe. Presentation of the invention The subject of the invention is a device for measuring the presence and electrical conductivity of a liquid inside a pipe made of electrically insulating material, comprising: -at least one resonant electrical circuit arranged on a contour of the pipe, the resonant frequency of said at least one resonant electrical circuit being representative of the presence of the liquid and its electrical properties, -an electronic system coupled to said at least one resonant electrical circuit, said electronic system being configured to acquire at least one current value of the resonant frequency of said at least one resonant electrical circuit and to determine the presence of a liquid inside a pipe and to measure without contact the conductivity of the liquid representative of the concentration of ions in the liquid. Depending on the arrangement of the resonant circuits, it is possible to determine the conductivity of the liquid and / or to check the filling level of the pipe automatically. Advantageously, the resonant electrical circuit is an inductive-capacitive circuit comprising an active reactance associated with a corresponding passive coupling element. According to one embodiment of the present invention, the active reactance is a capacitor formed from a pair of metal armatures placed on two distinct areas of the contour of the pipe, the corresponding passive coupling element being an inductive element. This driving instrumentation is very easy to implement and allows precise measurements to be taken. According to a first embodiment, the device comprises a single resonant electrical circuit comprising a pair of metal armatures, and said electronic system is configured to acquire during a calibration phase the resonance frequency values ​​when the pipe is empty and when the pipe is filled with deionized water. According to a second embodiment, the device comprises first and second resonant electrical circuits comprising first and second pairs of metal armatures respectively, the first pair of metal armatures being arranged on a first half-contour of the pipe and the second pair of metal armatures being arranged on a second half-contour of the pipe. Advantageously, the electronic system is configured to acquire, during a calibration phase, first and second empty resonant frequency values ​​from the first and second resonant electrical circuits when the pipe is empty and first and second reference resonant frequency values ​​from the first and second resonant electrical circuits when the pipe is filled with deionized water. Advantageously, the electronic system is configured to acquire first and second current values ​​of resonant frequencies from the first and second resonant electrical circuits, and to detect the filling of the pipe by comparing said first and second current values ​​of resonant frequencies with the first and second values ​​of no-load frequencies and with the first and second values ​​of reference resonant frequencies. According to another embodiment, the device comprises a resonant electrical circuit comprising an active coil associated with a capacitor, said coil being wound around the pipe. Thus, measurements can be made with a single circuit in the case where the axis of the pipe is substantially oriented in the direction of gravity. In this case, for a given level, the section of the pipe is either empty or filled with liquid and a single circuit is sufficient. Advantageously, the device comprises a communication module configured to transmit the results of filling the pipe and the electrical conductivity of the liquid. Advantageously, the device comprises at least one temperature probe, and / or at least one pressure sensor, and / or at least one flow sensor. Advantageously, the device comprises an electrical power supply module supplying said at least one resonant electrical circuit, said electronic system, and possibly the other sensors, said electrical power supply module possibly being an energy recovery module. Advantageously, the operating frequency is adapted to the conductivity range that one wishes to measure. Advantageously, the operating frequency is lower than 1MHz for conductivity values ​​lower than 200uS / Cm. Other advantages and characteristics of the invention will appear in the description detailed but not exhaustive below. Brief description of the drawings Embodiments of the invention will now be described, by way of non-limiting examples, with reference to the accompanying drawings, in which: [Fig. 1] illustrates very schematically a device for automatic and contactless measurement of the presence and electrical conductivity of a liquid inside a pipe, according to one embodiment of the invention: [Fig.2] very schematically illustrates a device for measuring the presence and electrical conductivity of a liquid inside a pipe, according to a first preferred embodiment of the invention; [Fig.3] is a flowchart illustrating the calibration, detection of the filling level of the pipe, and measurement of the conductivity of the liquid using the device according to the embodiment of [Fig.2]; [Fig.4] very schematically illustrates a device for measuring the presence and electrical conductivity of a liquid inside a pipe, according to a second preferred embodiment of the invention; [Fig.5] is a flowchart illustrating the calibration, detection of the fill level of the pipe, and measurement of the conductivity of the liquid using the device according to the embodiment of [Fig.4]; [Fig.6] very schematically illustrates a device for measuring the presence and electrical conductivity of a liquid inside a pipe, according to a third preferred embodiment of the invention; [Fig.7] very schematically illustrates a device for measuring the presence and electrical conductivity of a liquid inside a pipe, according to yet another preferred embodiment of the invention; [Fig.8] illustrates graphs indicating the evolution of the capacity, over the 10KHz to 10MHz range, of two armatures placed on a tube containing liquids of different conductivities: [Fig.9] illustrates a method for characterizing the measurement of the conductivity of a liquid according to an embodiment of the present invention; and [Fig.10] illustrates graphs indicating the sensitivity of the different resonant circuits of [Fig.9]. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT The principle of the invention is to determine automatically and without contact the electrical conductivity of a liquid inside a pipe from the measurements of resonance frequencies of an LC circuit placed on the external wall of the pipe. [Fig.1] very schematically illustrates a device for automatic and contactless measurement of the presence and electrical conductivity of a liquid inside a pipe, according to one embodiment of the invention. The device 1 comprises at least one resonant electrical circuit 3 and an electronic system 5. The resonant electrical circuit(s) 3 is (are) arranged on a contour of a pipe 7 intended to conduct a liquid from one place to another. The pipe 7 is made of an electrically insulating material of the PVC, PET, polycarbonate, glass, etc. type. The resonant frequency of the resonant electrical circuit(s) 3 depends both on the filling level of the pipe and on the electrical properties (permittivity and conductivity) of the liquid circulating inside the pipe 7. Each resonant electrical circuit 3 is an inductive-capacitive circuit of inductance L and capacitance C and having a natural resonance frequency f inversely proportional to the square root of the product LC. The inductive-capacitive circuit comprises an active reactance associated with a corresponding passive coupling element. For a given filling rate of the pipe 7, the resonance frequency f varies according to the electrical conductivity of the liquid. The measurement of this resonance frequency thus provides information on the electrical conductivity and the nature of the liquid. The electronic system 5 is coupled to the resonant electrical circuit(s) 3 and comprises a frequency measurement module 51 which measures the frequency of the oscillations of the resonant circuits, a data processing module 53 (for example a microcontroller) and a corresponding memory 55. The frequency measurement module 51 is configured to acquire at least one current value of the resonant frequency of the resonant electrical circuit(s) 3. For example, the frequency measurement module 51 is a Colpitts circuit coupled to the resonant electrical circuit 3. The Colpitts circuit is robust and simple to implement. It generally comprises a Tank circuit composed of an inductor and two capacitors. The active part may comprise a transistor (bipolar, JFET, or MOSFET), or an inverter, or an amplifier.Alternatively, the frequency measurement module 51 may be a Hartley circuit or a Clapp circuit associated with an electronic component (for example a microcontroller) which makes it possible to measure a frequency greater than 100KHz. The processing module 53 is configured to determine the electrical conductivity of the liquid inside the pipe 7 on the basis of the current value(s) of the resonance frequency in comparison with reference values ​​taken in air and deionized water. The results can be recorded in the memory 55. In the case of a single resonant electrical circuit, if the value of the no-load resonant frequency is greater than the value of the current resonant frequency which its turn is greater than the value of the resonance frequency in deionized water, then we deduce that the pipe is partially full. On the other hand, if the value of the current resonant frequency is lower than the value of the resonant frequency in deionized water, then we deduce that the pipe is full. The conductivity can then be estimated from the value of the current resonant frequency. The device 1 also comprises an electrical power supply module 9 supplying the resonant electrical circuit(s) 3 possibly via the electronic system 5. Advantageously, the device 1 also comprises a communication module 11 (with or without wires) configured to transmit the results of measurements of the electrical conductivity of the liquid. Conductivity is used to determine the concentration of ions in the liquid, since the ions in the liquid produce an ionic electric current whose intensity depends on this concentration. Ions can be cations (e.g., calcium, magnesium, potassium, sodium, aluminum, lead, mercury, etc.) or anions (e.g., bicarbonates, chlorides, nitrates, sulfates, fluorides, cyanides, etc.). As an example, the table below gives values ​​of the electrical conductivity of water according to its nature, as well as of blood. Liquid conductivity Liquid conductivity Pure water 0.055 μS / cm | Max. drinking water | 1055 μS / cm (deionized) Distilled water 0.5 μS / cm Brine water 2 to 20 mS / cm Rainwater 50 μS / cm Seawater 50 μS / cm Mountain water 130 to 300 μS / cm | Blood at 37°C 5.4 μS / cm Running water 200 to 800 μS / cm The value of the electrical conductivity thus makes it possible to control and analyze the nature of the liquid. Advantageously, the device 1 is suitable for analyzing the nature of a liquid over a wide range of conductivity, preferably over an interval between 100 uS / cm and 1000 uS / cm. [Fig.2] very schematically illustrates a device for measuring the presence and electrical conductivity of a liquid inside a pipe, according to a first preferred embodiment of the invention. According to this embodiment, the active reactance of the inductive-capacitive LC circuit is a capacitor 31 formed of a pair of metal plates 32, 33. The element of corresponding passive coupling is an inductive element 35. The pair of metal armatures 32, 33 of the capacitor 31 is placed on two distinct zones of the contour of the pipe 7. In particular, the two conductive armatures 32 and 33 are arranged opposite each other on the external surface of the pipe 7, matching the shape of this external surface which is, for example, cylindrical. Thus, according to this example, a tubular capacitor is formed by the two armatures 32, 33 separated from each other by a dielectric constituted by the insulating walls of the pipe 7 as well as by the nature of the liquid 13 or fluid inside the pipe 7 at the levels of the armatures 32, 33. It will be noted that, as a variant, the conductive armatures 32 and 33 can be produced according to other geometries (for example, annular or interdigitated electrodes). Given that the geometry of the capacitor 31 is invariant, its capacitance C depends essentially on the nature of the dielectric and more particularly on the nature and composition of the liquid 13 contained inside the conduit 7 between the armatures 32, 33. Furthermore, the armatures 32, 33 of the capacitor 31 of capacitance C are connected to a coil 35 of predetermined inductance L, thus forming a resonance circuit whose frequency depends on the capacitance C which can be variable and on the inductance L which is constant. The electronic system 5 is configured to acquire the current value of the resonant frequency of the resonant circuit 3 and to deduce the value of the capacitance C and consequently, the value of the conductivity of the liquid 13 in the case where the liquid (for example, ionized water) inside the pipe 7 fills the space between the armatures 32, 33, according to the method described by [Fig.3]. Indeed, [Fig.3] is a flowchart illustrating the calibration, the detection of the filling level of the pipe, and the measurement of the conductivity of the liquid using the device according to the embodiment of [Fig.2]. More particularly, steps E1-E4 are preliminary steps relating to the calibration of the measuring device 1. In step E1, an empty measurement is carried out, that is to say, when the pipe 7 is empty, an empty resonance frequency fv relative to the resonant electrical circuit 3 is measured. In step E2, a reference resonance frequency [edi] is measured relative to the resonant electrical circuit 3 when the pipe 7 contains deionized water (during a factory calibration) according to different filling levels. In step E3, two adjustment parameters are defined: tolerance interval I and threshold values ​​S according to the filling level of pipe 7. Step E4 is a test to check if the calibration is performed. If so, the interval of tolerance I and threshold values ​​S are stored. Otherwise, we loop back to step El. For example, we consider that the calibration has been carried out when the pipe is completely filled with deionized water. Step ES concerns the acquisition of the current resonant frequency in operating conditions of the measuring device 1. The electronic system 5 and more particularly, the frequency measuring module 51 measures the current value f of the resonant frequency relating to the resonant electrical circuit 3. Steps E6-E1 | concern the detection of pipe filling. Step E6 is a first test in which the electronic system 5 and more particularly, the data processing module 53 compares the current value f of the resonant frequency of the electrical circuit 3 with the value of the no-load resonant frequency fv. If the absolute value of the difference between the values ​​f and fv is within the predetermined interval I, then we proceed to step E7 and otherwise, we proceed to step E8. At step E7, the processing module 53 deduces that the pipe is empty and we then move on to step E13 to display the result. Step E8 is a second test in which the processing module 53 compares the current value f of the resonant frequency with the value of the reference resonant frequency fedi. If the absolute value of the difference between the values ​​f and fedi is within the predetermined interval I, then we proceed to step E9. Otherwise, we proceed to step E10. In step E9, the processing module 53 deduces that the pipe is partially full and more than half full. The processing module 53 then estimates the filling of the pipe as a function of the difference f-fv and then moves on to step E13 to display the result. Step E10 is a third test in which the processing module 53 compares the current resonance frequency value f with the corresponding reference resonance frequency fedi. If the difference between the values ​​fedi and f is less than the predetermined threshold S, then we proceed to step E11. Otherwise, we proceed to step E12. At step E11, the processing module 53 deduces that the pipe is full and we then move on to step E12 to calculate the conductivity of the liquid. In step E12, given that the pipe is full, the processing module 53 calculates the conductivity from the fedi-f gap relating to the resonant electrical circuit 3. We then move on to step E13 to display the result. Finally, in step E13, the processing module 53 displays and / or transmits the results obtained in steps E7, E9, E11 and E12. [Fig.4] very schematically illustrates a device for measuring the presence and electrical conductivity of a liquid inside a pipe, according to a second preferred embodiment of the invention. According to this second embodiment, the device 1 comprises first 3a and second 3b resonant electrical circuits comprising first 32a, 33a and second 32b, 33b pairs of metal armatures respectively. The first pair of metal armatures 32a, 33a is arranged on a first half-contour of the pipe 7 and the second pair of metal armatures 32b, 33b is arranged on a second half-contour of the pipe 7. The electronic system 5 is configured to acquire first and second current values ​​of resonant frequencies from the first 3a and second 3b resonant electrical circuits. The electronic system 5 makes it possible to compare these values ​​with frequencies of the two circuits recorded on the one hand when the pipe was empty and on the other hand when the pipe was filled with ionized water, according to the method described by [Fig.3]. It will be noted that a difference in resonant frequency between the first and second current values ​​is indicative of a difference in the permittivity of the insulator between the armatures due to the presence of a liquid-air interface. Indeed, the relative permittivity of a liquid compared to air is quite significant. For example, the relative permittivity of water compared to air is of the order of 80. Thus, the proportion of liquid 13 in the insulator between the armatures significantly affects the capacitance of the capacitor. An increase in the level of liquid 13 inside the pipe 7 increases the capacitance, generating a drop in the resonant frequency. Thus, different values ​​of resonant frequencies of the first 3a and second 3b resonant circuits are indicative of non-filling of the pipe 7. On the other hand, when the pipe 7 is filled, there is no air-liquid interface at the level of the armatures of the first 3a and second 3b resonant electrical circuits and consequently, the measured resonance frequency is indicative only of the nature and in particular, of the conductivity of the liquid 13. In the case where the axis of the pipe 7 at the level of the resonant electrical circuit(s) 3a, 3b is substantially vertical (i.e. in the direction of gravity), the pipe 7 can only be empty or filled, which facilitates the measurement of the conductivity of the liquid. However, in the case where the axis of the pipe at the level of the resonant electrical circuit(s) 3a, 3b is not substantially vertical, then one of the pairs of metal armatures will be located in a lower section of the pipe 7 while the other pair of metal armatures will be located in an upper section of the pipe 7. Thus, if the pipe 7 is not filled, the value of the resonant frequency from the pair of armatures placed in the lower section is smaller than that from the pair of armatures placed in the upper section of the pipe 7. In this case, if the value of the conductivity associated with the pair of armatures placed in the upper section is not almost zero, then the electronic system 5 deduces that the air-liquid interface exists at the level of the upper section of the pipe and consequently, the value of the conductivity from the pair of reinforcements placed in the lower section of the pipe 7 represents the conductivity of the liquid. Alternatively, the electronic system 5 can be configured to evaluate the filling of the pipe 7 by comparing the first and second current values ​​of resonant frequencies in order to ensure the filling of the pipe 7 before determining the electrical conductivity of the liquid 13 inside this pipe 7. Furthermore, for a liquid 13 whose conductivity is already known, the rate of variation between the first and second current values ​​of the resonant frequency allows the electronic system 5 to evaluate the level of the liquid 13 in the pipe 7. For example, the conductivity of the liquid 13 can first be determined at the level of a pipe 7 oriented vertically. Then, the filling rate of a pipe 7 oriented horizontally can be deduced as a function of the rate of the first and second current values ​​of resonant frequencies from the first 3a and second 3b resonant circuits respectively. A calibration of the pipe 7 according to different levels as a function of the resonant frequency or the conductivity can be carried out beforehand with different liquids. Generally speaking, it is possible to detect, according to the invention, the filling level of the pipe 7 as well as the measurement of the conductivity of the liquid when the pipe is at least half full. Indeed, the first and second frequency values ​​from the first 3a and second 3b resonant electrical circuits can be compared to the frequency values ​​of these same circuits when the pipe is empty and when it is filled with deionized water (edi). If for the first 3a resonant electrical circuit, the value of the first resonant frequency in no-load condition is greater than the value of the first resonant frequency in current condition which in turn is greater than the value of the first resonant frequency in deionized water, then we deduce that the pipe is partially full. If for the second 3a resonant electrical circuit, the value of the second no-load resonant frequency is greater than the value of the second current resonant frequency which in turn is greater than the value of the second resonant frequency in deionized water, then it is deduced that the pipe is at least half full. The conductivity can then be estimated from the value of the first current resonant frequency. [Fig.5] is a flowchart illustrating the calibration, pipe fill level detection, and liquid conductivity measurement using the device according to the embodiment of [Fig.4]. More particularly, steps E11-E14 are preliminary steps relating to the calibration of the measuring device 1. In step El 1, an off-load measurement is carried out, that is to say, when the pipe 7 is empty, first and second off-load resonance frequencies fv1 and fv2 relating to the first 3a and second 3b resonant electrical circuits respectively are measured. In step E12, first and second reference resonance frequencies fledi and f2edi relating to the first 3a and second 3b resonant electrical circuits are measured when the pipe 7 comprises deionized water (during a factory calibration) according to different filling levels, In step E13, two adjustment parameters are defined: tolerance interval I and threshold values ​​S according to the filling level of pipe 7. Step E14 is a test to check whether the calibration has been carried out. If so, the tolerance interval I and the threshold values ​​S are stored. Otherwise, we return to step E11. For example, we consider that the calibration has been carried out when the pipe is completely filled with deionized water. Step E15 concerns the acquisition of the current resonance frequencies in operating conditions of the measuring device 1. The electronic system 5 and more particularly, the frequency measurement module 51 measures first and second current values ​​f] and f2 of the resonance frequencies relating to the first 3a and second 3b resonant electrical circuits respectively. Steps E16-E23 concern the detection of pipe filling. Step E16 is a first test in which the electronic system 5 and more particularly, the data processing module 53 compares the first current value f1 of the resonant frequency of the first 3a electrical circuit to the corresponding first no-load resonant frequency flv. If the absolute value of the difference between the first values ​​f1 and flv is within the predetermined interval I, then step E17 is moved on and otherwise step E18 is moved on. At step E17, the processing module 53 deduces that the pipe is empty and we then move on to step E26 to display the result. Step E18 is a second test in which the processing module 53 compares the second current value f2 of the resonant frequency of the second 3b electrical circuit with the corresponding second no-load resonant frequency (2v). If the absolute value of the difference between the second values ​​f2 and f2v is within the predetermined interval I, then we proceed to step E19. Otherwise, we proceed to step E20. In step E19, the processing module 53 deduces that the pipe is partially full and less than half full. The processing module 53 then estimates the filling of the pipe as a function of the difference f1-f1v and we then move on to step E26 to display the result. Step E20 is a third test in which the processing module 53 compares the first current resonance frequency value f1 with the corresponding first reference resonance frequency fedil. If the difference between the first values ​​fedil and f1 is less than the predetermined threshold S, then step E21 is moved on. Otherwise, step E22 is moved on. In step E21, the processing module 53 deduces that the pipe is partially full and more than half full. The processing module 53 then estimates the filling of the pipe as a function of the difference f2-f2v and we then move on to step E25 to calculate the conductivity of the liquid. Step E22 is a fourth test in which the processing module 53 compares the second current resonance frequency value f2 with the corresponding second reference resonance frequency fedi2. If the difference between the second values ​​fedi2 and f2 is greater than the predetermined threshold S, then step E23 is passed. Otherwise, step E21 is passed to estimate the filling of the pipe as a function of the difference f2-f2v. At step E23, the processing module 53 deduces that the pipe is full and we then move on to step E24 to calculate the conductivity of the liquid. Steps E24 and E25 concern the calculation of the conductivity of the liquid in pipe 7. In step E24, given that the pipe is full, the processing module 53 calculates the conductivity from the gap fedi2-f2 relating to the second 3b resonant electrical circuit. We then move on to step E26 to display the result. In step E25, since the pipe is not completely full but more than half full, the processing module 53 calculates the conductivity from the gap fedi1-f1 relating to the first 3a resonant electrical circuit. We then move on to step E26 to display the result. Finally, in step E26, the processing module 53 displays and / or transmits the results obtained in steps E17, E19, E21, E24 and E25. [Fig.6] very schematically illustrates a device for measuring the presence and electrical conductivity of a liquid inside a pipe, according to a third preferred embodiment of the invention. According to this third embodiment, the device comprises at least one resonant circuit 3c whose active reactance is a coil 37 wound around the pipe 7. The corresponding passive coupling element is a capacitive element 39. In the case where the Z axis of the pipe 7 at the level of the coil 37 is substantially vertical, that is to say substantially oriented in the direction of gravity P, the pipe 7 can only be full or empty. So either we have a conductivity of almost Zero, or a conductivity above a predetermined value which, for example, may correspond to the conductivity of pure water. More particularly, a calibration can be carried out by measuring the resonant frequency when distilled or deionized water is placed in the pipe 7. The value of this resonant frequency corresponds to a threshold value. Thus, if the electronic system 5 finds that the measurement of the resonant frequency is lower than the threshold value, then it considers that the pipe 7 is full and this measurement makes it possible to determine the conductivity of the liquid inside the pipe 7 with precision. Thus, this configuration makes it possible to carry out precise measurements with a single resonant circuit 3c. [Fig.7] very schematically illustrates a device for measuring the presence and electrical conductivity of a liquid inside a pipe, according to yet another preferred embodiment of the invention. According to this embodiment, the device 1 comprises a set of resonant circuits 3 according to the mode of [Fig.2] or [Fig.4] and / or according to the mode of [Fig.6]. For example, at least two resonant circuits 31a, 31b having at least two pairs of armatures 32a, 33a, 32b, 33b according to the mode of [Fig.4] can be placed in a substantially horizontal section of the pipe 7 and at least one resonant circuit 31c having a coil 37 according to the mode of [Fig.6] can be placed in a substantially vertical section of the pipe 7. The number, choice and integration of the resonant circuits 31a, 31b, 31c can be determined according to the needs and constraints of the application. In the case where the sensitive part is capacitive, the geometry of the capacitive armatures (cylindrical, interdigitated, etc.) and the operating frequency make it possible to adjust the sensitivity of each resonant circuit according to the needs of the application. For a given electrode geometry, the operating frequency is determined by the value of the associated inductance; it makes it possible to adapt the sensitivity of the device 1 to the desired conductivity range. In this way, the accuracy of the measurement of the electrical conductivity inside the pipe 7 can be increased. The use of several configurations of resonant circuits 3 at different frequencies has the advantage of expanding the measurement range. Indeed, [Fig.8] illustrates graphs indicating the evolution of the capacity, over the 10KHz to 10MHz range, of two armatures placed on a tube containing liquids of different conductivities. The abscise represents a frequency interval between 10KHz and 10MHz while the ordinate represents a capacitance range between approximately 10pF and 20pF. More specifically, curves G1-G10 show the evolution of the capacitance as a function of frequency for conductivity values ​​of OuS / Cm; 3uS / Cm; 631 S / Cm; 129uS / Cm; 408uS / Cm; 625uS / Cm; 10601 S / Cm; 1360uS / Cm; 1786pS / Cm; and 2370uS / Cm respectively. The operating frequency can thus be adapted to the conductivity range that one wishes to measure. For example, for a conductivity range from 0 to 63uS / Cm, an operating frequency of 200kHz will be preferred because the sensitivity (capacitance variation as a function of conductivity variation) will be maximum. On the other hand, for a range from 63 to 1060uS / Cm, an operating frequency of 4MHz will offer better sensitivity. Overall, the higher the salinity, the more it will be beneficial to increase the operating frequency. For example, the operating frequency is lower than 1MHz for conductivity values ​​lower than 200uS / Cm. Their placement in multiple positions can also provide an indicator of homogeneity. Conductivity calibration can be performed by measuring the conductivity of different reference liquids. The electronic system 5 is configured to acquire the current values ​​of resonant frequencies from the different resonant electrical circuits 31a, 31b, 31c. These different current values ​​allow the electronic system 5 to determine the conductivity of the liquid and / or estimate the filling of the pipe 7. According to a first feature, the memory 55 of the microcontroller 5 can locally store the measured values ​​and the results while waiting for a control operation. Advantageously, the wireless communication module 11 is configured to transmit the results by LORA communication or other low-power protocol to a control center (not shown). Alternatively, the electronic system 5 is configured to locally analyze the measurement results. For example, the electronic system 5 can be configured to detect the exceeding of a safety threshold and trigger actions such as, for example, triggering an alert and / or a modification of flow rate instructions and / or a modification of input dosage, etc. According to one embodiment, the device 1 comprises at least one temperature probe 13, at least one pressure sensor 15, and at least one flow sensor 17. These probes and sensors embedded in the device 1 can be used to control or correct the measurements of the electrical conductivity of the liquid. The electrical power supply module 9 supplies the resonant electrical circuit(s) 3, the system 5 and possibly the other probes 13 and sensors 15, 17. Advantageously, the electrical power supply module is an energy recovery module such as for example a photovoltaic panel or a micro turbine. allowing autonomous use of the device 1. According to yet another particular embodiment, the device 1 comprises a specific antenna 19 such as for example a zero mutual inductance antenna configured to receive a signal from an external device 21 for example a portable reader. This signal received by the antenna 19 is configured to excite the resonant circuit(s) 3 remotely and to measure their resonant frequencies. This embodiment has the advantage of not embedding any electronic components on the pipe 9. [Fig.9] illustrates a method for characterizing the measurement of the conductivity of a liquid according to an embodiment of the present invention. According to this embodiment, a glass beaker 25 is used to simulate the pipe 7. The tests are carried out here with first 31a, second 31c and third 31b resonant circuits, according to different configurations. The following values ​​are given as examples to illustrate how the system works for these three configurations. The first resonant circuit 31a comprises two metal armatures 32a, 33a placed around a lower section of the beaker 25. The two armatures 32a, 33a are for example 35 mm long, 24 mm wide and spaced 40 mm apart. The first resonant circuit 3la is completed by an inductance of 10mH and a parallel capacitance of 33pF (internal impedance of the measurement system) to obtain a resonant frequency of approximately 0.7MHz. The third resonant circuit 31b comprises two metal armatures 32b, 33b placed around an upper section of the beaker 25. The two armatures are 60 mm long, 24 mm wide and spaced 40 mm apart. The third resonant circuit 31b is completed by an inductance of 0.003mH and a parallel capacitance of 33pF (internal impedance of the measurement system) to obtain a resonant frequency of approximately 12MHz. The second resonant circuit 31c comprises a coil 37 placed around an intermediate section of the beaker 25. The coil 37 comprises for example 30 turns over a length of 20 mm and a diameter of 40 mm or approximately 0.047 mH which gives a resonant frequency of approximately 4 MHz when coupled with the 33 pF capacitance of the measuring circuit. The process is started by putting distilled water at 50 uS / cm in beaker 25. Then, the resonant frequencies of the three circuits are varied by increasing the conductivity by 50 uS / cm at each measurement. The electronic system 5 is used to measure the resonant frequencies of the three circuits at each increase in salinity. This makes it possible to measure the variations in the resonant frequencies of the three circuits according to different concentrations of salt water. The measurements are carried out on a liquid conductivity range between 50 uS / Cm and 1000 uS / Cm. Indeed, [Fig.10] illustrates graphs indicating the sensitivity of the different resonant circuits of [Fig.9]. The y-axis represents the frequency in MHz and the x-axis represents the conductivity of the liquid in uS / Cm. We observe in the graphs that the sensitivities are different depending on the configuration of the resonant circuit. Curve C1 shows the evolution of the resonance frequency as a function of the conductivity corresponding to the first resonant circuit 31a over the range 50-1000 us / Cm. The frequency variation of the C1 curve is greater (about 2% frequency variation for a conductivity variation of 50uS / Cm) for low conductivities between 50 and 200 uS / Cm. The sensitivity then decreases (about 0.6% frequency variation for a conductivity variation of 50uS / Cm) for higher conductivities up to 1000uS / Cm. The C1 curve can be approximated by a polynomial curve of degrees 4 whose equation is: y = 3.10-°x* — 7.10-10x3 + 6.107x2 - 0.0002x + 0.6797 (1) This configuration is therefore better suited to conductivities below 200 uS / Cm. Curve C2 shows the evolution of the resonant frequency as a function of the conductivity corresponding to the second resonant circuit 31c over the range 50-1000 pS / Cm. The frequency variation is approximately 0.3% for a conductivity variation of S / Cm over the entire range. Curve C2 can be approximated by a polynomial curve of degrees 2 whose equation is: y = |. 107x? - 0.0003x + 3.5415 (2) Curve C3 shows the evolution of the resonance frequency as a function of the conductivity corresponding to the third resonant circuit 31b over the range 50-1000 pS / Cm. This varies by approximately 0.5% for a conductivity variation of 50uS / Cm over the entire range. The response of curve C3 is almost linear according to the following equation: y = -0.0009x + 11.109 (3) The inverse functions of equations (1)-(3) allow us to calculate the values ​​of the liquid conductivity as a function of the values ​​of the resonance frequencies of the three circuits. These examples show the possibility of adapting the present invention to different configurations and for different resonant frequencies. Tests can also be performed over a wider conductivity measurement range, for example between 1000 uS / Cm and 9000 uS / Cm. Tests have shown lower sensitivities but still acceptable for some applications. In cases of conductivities above 200uS / Cm, the example of the third 31b resonant circuits showed better performances in terms of sensitivity and linearity than those of circuits 31a and 31c. The same circuits as those in [Fig.7] were placed around a pipe on a hydraulic bench. Measurements were made on a moving liquid at different liquid flow rates. Similar results to those in [Fig.7] were found and that the measurements are not influenced by the liquid flow rate when the pipe is full. Advantageously, the device according to the different embodiments of the present invention can provide an on-board predictive maintenance means for different systems. According to a first example, the device can be used for process regulation (anomaly detection, ionic concentration above a threshold, etc.). In a second example, the device can be used for connected agriculture (irrigation, dosing of inputs, control of operating effluents, etc.). According to a third example, the device can be used for health (water quality, blood, urine, drug dosage, etc.). Advantageously, the control can be carried out periodically at a frequency adapted to the dynamics of the phenomenon to be observed. Generally the variations are slow, an acquisition frequency of 0.01Hz to 1Hz should be suitable for most cases. Of course, various modifications may be made by those skilled in the art to the invention which has just been described, solely by way of non-limiting examples.

Claims

Claims

1. Device for measuring the presence and electrical conductivity of a liquid inside a pipe (7) made of electrically insulating material trically, characterized in that it comprises: -at least one resonant electrical circuit (3) arranged on a contour of the conduit (7), the resonant frequency of said at least one circuit resonant electric being representative of the presence of the liquid and its electrical properties, - an electronic system (5) coupled to said at least one electrical circuit resonant (3), said electronic system being configured to acquire at minus a current value of the resonant frequency of said at least one a resonant electrical circuit and to determine the presence and electrical conductivity of the liquid inside the pipe (7) on the base of said at least one current value of the frequency of resonance.

2. Device according to claim 1, characterized in that said system electronics (5) is configured to detect the filling level of driving.

3. Device according to claim 1 or 2, characterized in that the circuit resonant electric (3) is an inductive-capacitive circuit comprising a active reactance associated with a passive coupling element cor- respondent.

4. Device according to claim 3, characterized in that the reactance active is a capacitor (31) formed of a pair of metal plates- metals (32, 33) placed on two distinct areas of the contour of the conduit (7), the corresponding passive coupling element being a inductive element (35).

5. Device according to claim 3 or 4, characterized in that said electronic system (5) is configured to acquire during a phase of calibration of resonance frequency values ​​when driving is empty and when the pipe is filled with deionized water.

6. Device according to claim 3 or 4, characterized in that it comprises first and second resonant electrical circuits (31a, 31b) comprising first and second pairs of metal frames respectively, the first pair of metal frames being arranged on a first half-contour of the pipe (7) and the second pair of metal reinforcements being arranged on a second half-contour of the conduct (7).

7. Device according to claim 3 or 4, characterized in that said electronic system (5) is configured to acquire during a phase of calibration of the first and second resonance frequency values empty from the first and second resonant electrical circuits when the pipe is empty and the first and second values ​​of reference resonance frequencies from the first and second resonant electrical circuits when the pipe is filled with water deionized.

8. Device according to claim 7, characterized in that said system electronics (5) is configured to acquire first and second current values ​​of resonant frequencies from the first and second resonant electrical circuits, and to detect filling of the pipe (7) by comparing said first and second values resonant frequency currents at the first and second no-load frequency values ​​and at the first and second values ​​of reference resonance frequencies.

9. Device according to any one of the preceding claims, ca- characterized in that it comprises a resonant electrical circuit (3) comprising an active coil (37) associated with a capacitor (39), said coil being wound around the pipe.

10. Device according to any one of the preceding claims, ca- characterized in that it includes a communication module (11) configured to transmit the pipe filling results and of the electrical conductivity of the liquid inside the driving (7).

11. — Device according to any one of the preceding claims, ca- characterized in that it comprises at least one temperature probe (13), and / or at least one pressure sensor (15), and / or at least one sensor flow rate (17).

12. Device according to any one of the preceding claims, ca- characterized in that it comprises a power supply module (9) powering said at least one resonant electrical circuit (3), said electronic system (5), and possibly other sensors, said power supply module being a recovery module of energy.

13. Device according to any one of the preceding claims, ca- characterized in that the operating frequency is adapted to the conductivity range that we wish to measure.

14. Device according to claim 13, characterized in that the frequency operating frequency is less than 1MHz for values ​​of conductivities less than 200uS / Cm.