WO2011064506A1 - Magnetic field circulation sensor provided with a verification means and method for verifying such a sensor - Google Patents

Abstract

The invention relates to a magnetic field circulation sensor which includes: an excitation unit (3, 20) suitable for generating an excitation current in an elongate main excitation coil (10) extending around a flexible superparamagnetic core (11) that is elongate and includes a flexible matrix having magnetic particles dispersed therein; a verification means (23, 24, 30) including a verification excitation coil suitable for generating a verification excitation magnetic field in the core using a predetermined verification current; and a measurement means (3, 21) for providing a measurement of magnetic field circulation in the core in operating mode and in verification mode.

Description

 "Magnetic field circulation sensor equipped with a verification means, and method of checking such a sensor."

The present invention relates to the technical field of sensors used to measure magnetic quantities such as the magnetic field in order to know an intrinsic value of the latter or to extrapolate values quantifying the physical phenomena that are at the origin. In a preferred but not exclusive application, the invention relates to current sensors that determine the intensity of an electric current flowing in a conductor from the magnetic field radiated by the latter. Document US5469058 describes a magnetic field sensor with a flexible core of high relative permeability and a feedback device for zero field operation.

 Document US2004 / 0201373 is also known which describes a current sensor with a fluxgate type transducer whose core has a high relative permeability.

 However, these systems of the prior art do not have a high sensitivity and the accuracy of the measurements is degraded over time due to a drift of the measurement chain.

 The object of the present invention is a sensor for the circulation of magnetic fields of high precision; this great precision being guaranteed in time. Another object of the invention is a sensor whose calibration, implementation, maintenance and re-verification are simplified. The present invention also aims a sensor whose calibration can be done very accurately.

 Another object of the present invention is the measurement of alternating currents and continuous currents.

 At least one of the aforementioned objectives is achieved with a permanent or variable magnetic field circulation sensor comprising: magnetic excitation means comprising:

at least one elongated main excitation coil for exciting an elongated flexible magnetic core and comprising a flexible or flexible matrix in which magnetic particles are dispersed, an excitation unit capable of generating an excitation current in the main excitation coil, so as to generate a main excitation magnetic field in the core over substantially the entire length of the coil,

verification means comprising a verification excitation coil able to generate a verification excitation magnetic field in the core from a predetermined verification current, and

measuring means comprising:

 at least one magnetic measurement transducer for sensing a magnetic field induced in the core,

 a measuring unit connected to the magnetic measurement transducer and adapted to provide a measurement of the magnetic field circulation induced in the core.

 The sensor according to the invention is a circulation sensor, that is to say that the measuring means are adapted to integrate the value of the magnetic field along the core or at least the length of the core covered by the coil. 'excitation. In particular, the excitation unit excites the main excitation coil so as to reveal an electromotive force of even harmonics, (preferably the two harmonic is measured). This electromotive force is due to a physical phenomenon discovered by the physicist Néel and that we can qualify here of Néel effect which is characterized by the presence of nonlinearity and the absence of hysteresis in the nucleus. The magnetic field to be measured and the field due to the counter-reaction modulate the main excitation magnetic field. The circulation of the magnetic field induced in the core is restored by differential measurement and synchronous demodulation analog or digital performed in the measurement unit.

The present invention explicitly refers to FR2891917 which provides more detailed information relating to the constitution of a superparamagnetic core and the field flow measurement in such a core. The elements disclosed in FR2891917 are incorporated in the present invention to the extent that these elements are not inconsistent with the teaching of the present invention. The implementation of the magnetic excitation means makes it possible to generate in the core an excitation magnetic field which will be modulated by the magnetic field to be measured thanks to the magnetic non-linearities introduced by the magnetic particles of the magnetic core. The flow of the modulated magnetic field will be determined by the measuring means which integrates the values of the magnetic field along the elongated magnetic core. Thanks to this excitation, the sensor according to the invention is sensitive to both permanent and variable magnetic field circulations.

 According to an advantageous characteristic of the invention, the magnetic particles of the flexible magnetic core are superparamagnetic grains, forming in particular aggregates, and having sub-micrometric and preferably nano-sized dimensions obtained from a ferromagnetic material. The implementation of such a superparamagnetic behavior nucleus has the advantage of taking advantage of the substantially complete absence of hysteresis, which makes it possible to increase the accuracy of the sensor for the low values of field circulations. By superparamagnetic behavior is meant a superparamagnetic behavior as defined by the work of Etienne du Trémolet de Lacheisserie et al. "Magnetism" TOME 1, published in 1999 by the editions "EDP Sciences" in the collection "Grenoble sciences", ISBN 2- 86883-463-9.

 These nanoparticles allow a reduction in the relative permeability of the core which can be set lower than a few hundred. It is said to be a low relative permeability. It is even possible to consider values less than 100, or even less than 10, or even less than 5, advantageously equal to 1.5.

According to the invention, the excitation coil can be realized in various ways. Thus, the excitation coil may comprise a conductor wound around the core in contiguous turns or not, the connecting ends of the conductor then being each located at a different end of the elongated body. These ends are then brought together to allow their connection to the excitation unit and / or to the measurement unit when the core is closed on itself so as to surround the electrical conductor or conductors in which a current to be measured circulates. . Of course, such an embodiment of the excitation coil is not strictly necessary or even the only conceivable. The main excitation coil can notably be embedded in the core. According to the invention, the measuring means can be made in any appropriate manner. Thus, the measurement means may comprise a plurality of Hall effect transducers distributed in the core and connected to the measurement unit so as to integrate the local values of the magnetic field into the latter. The Hall effect transducers will preferably be uniformly distributed in the core to ensure homogeneous integration of the magnetic field. Of course, it could be envisaged to implement other types of discrete magnetic transducers such as magnetoresistances for example.

 Preferably, the magnetic measurement transducer comprises at least one conductor wound around the elongate flexible magnetic core.

 Advantageously, the sensor comprises counter-reaction means associated with a counter-reaction coil. These counter-reaction means are adapted to maintain when the sensor is in a closed loop the induced magnetic field circulation in a predefined range, and preferably substantially close to or equal to zero. More precisely and preferably, the counter-reaction coil is energized so as to cancel the electromotive force due to the Néel Effect, thus canceling the magnetic excitation field circulation. The current sensor according to the invention in a closed loop allows a direct measurement of a current flowing in a conductor of any shape. The transformation ratio between the counter-reactive current and the current to be measured is imposed in particular by the number of feedback turns, and therefore particularly linear and insensitive to temperature.

According to another advantageous characteristic of the invention, the sensor comprises a memory in which are stored characteristic data of the magnetic field circulation sensor; this memory being preferably placed within the measurement unit, but it can be placed at a distance. This data may include:

 the transformation ratio related to the number of turns of at least one coil of the sensor,

 - sensor identification data,

 - traceability data of measurements already carried out, and / or

- correction data to be applied during measurements. The invention is notably remarkable in that such a memory makes it possible to save the number of turns of each coil, preferably a feedback coil and a verification coil, these numbers being determined precisely using the verification means. It is also possible to save the transformation ratios between the verification current and the counter-reaction current.

 The sensor according to the invention may comprise a processing unit for comparing the predetermined verification current with a current from the induced magnetic field flow measurement in the core. This processing unit can be confused with the measurement unit which comprises software and hardware means capable of performing different functionalities.

 Advantageously, the sensor according to the invention comprises a current generator capable of generating the predetermined verification current. This generator can be removable or integrated in an electronic box containing the excitation unit and the measurement unit.

 Preferably, the predetermined verification current is a periodic signal distinct from the main excitation current in order to avoid any disturbance during a measurement of current or voltage. According to one characteristic of the invention, the amplitude of the predetermined verification current is substantially between ΙμΑ and 100A.

 According to another aspect of the invention, there is provided a method for checking a magnetic field circulation sensor as defined according to the invention, this method comprising the following steps:

a predetermined checking current is injected into the verification excitation coil,

 at least one inductive magnetic field circulation measurement is carried out in the core, and

 said at least one measurement thus made is compared with the predetermined verification current, taking into account the characteristic data of the sensor contained in a memory.

The memory can be contained in the sensor or in a remote storage unit accessible in particular via an Internet type communication network. This storage unit may be the sensor manufacturer's server according to the invention which retains all the characteristics, obtained in particular after calibration, of each sensor marketed. The characteristic data may comprise at least one predetermined ratio between a verification current and a measurement of the magnetic field circulation induced in the nucleus. When the sensor comprises a counter-reaction, the predetermined ratio is advantageously a transformation ratio between at least one verification current and a counter-reactive current.

Advantageously, the aforementioned steps are performed in situ, the sensor being in operation or not.

 In particular, the result obtained after the comparison can be injected into the measurement unit so as to perform a self-calibration of the sensor.

The verification excitation coil according to the invention allows to check at any time the proper operation of the sensor and to monitor any drift gain over time.

 With such a sensor according to the invention, it is thus possible to achieve high accuracy measurements with a guarantee of performance over time since the sensor can be continuously monitored and corrected.

 It is thus possible to implement processes of re-verification, calibration, self-calibration or re-calibration of the sensor.

 Verification or re-verification consists of injecting into the verification means a perfectly known re-verification cycle of the current, then of checking whether this current cycle known in the measurement means is well found. If the measurement is made at the same time that the main excitation coil is energized (in normal operation), a frequency (this may be quasi-static) is provided which is different between the main excitation coil and the excitation coil of verification.

To set up the reverification, it is possible to provide a pre-calibration step during which it is desired to calibrate the verification current with respect to a given primary current (current to be measured). In other words, it is verified that this is the same as injecting a primary current or a re-verification current. This is a step that allows you to "calibrate" the reverification. We define the relation Nreverif * Ireverif = Ip. Ncr * Icr = Ip is also defined. Then we deduce Nreverif * Ireverif = Ncr * Icr; Ip being the current to be measured, Nreverif and Ireverif respectively the ratio of transformation related to the number of turns of the verification excitation coil and the verification current, Ncr and I being respectively the transformation ratio related to the number of turns of the counter-reaction coil and the counter-reaction current.

 The calibration consists of determining the transformation ratio related to the number of turns of the measuring coil and the verification excitation coil. To do this, two measurements can be made by respectively injecting two different currents so as to obtain two Nlil = N2i2-type two-unknown equations (NI and N2 being the transformation ratio related to the number of turns of the verification and measurement coils, respectively). it and i2 the currents injected and measured respectively) and deduce the transformation ratios related to the number of turns. The calibration also makes it possible to measure a residual current or offset or offset of the sensor.

 The self-calibration consists in injecting a known current into the verification means when the main excitation coil is active, and then checking whether there is a gain drift (amplitude of the measured signal) with respect to measurements. previously carried out.

 Re-calibration consists of performing calibration operations on a regular basis in situ.

Of course, the various features, forms and variants of the invention may be associated with each other and with embodiments described in document FR2891917 according to various combinations insofar as they are not incompatible or exclusive. each other.

 Other advantages and characteristics of the invention will appear on examining the detailed description of a non-limiting embodiment, and the appended drawings, in which:

 FIG. 1 is a schematic perspective view of a sensor according to the invention implementing a flexible superparamagnetic core equipped with a verification coil and a counter-reaction coil.

Figure 2 is a schematic sectional view of the sensor shown in Figure 1, the transducer or the core-coil assembly is closed in a loop around an electrical conductor so as to form a current sensor. FIG. 3 is a diagrammatic view in longitudinal section of the transducer or core-coil assembly constituting the sensor illustrated in FIG. 1. Although the invention is not limited thereto, a circulation sensor of FIG. magnetic fields for measuring current in a conductor C.

 It should be noted that the invention can also be applied to magnetic field circulation sensors for the measurement of voltage.

In Figures 1 to 3, the various elements common to the various variants or embodiments have the same references.

 A magnetic field circulation sensor according to the invention, as schematically illustrated in FIG. 1 and designated as a whole by reference numeral 1, comprises, on the one hand, a transduction unit 2 and, on the other hand, an electronic unit 3 connected by electric wires or cables 4, 5, 6, 7 to the transduction unit 2.

 The transducer assembly 2 comprises an elongated coil 10 wound around a magnetic core 11. The verification excitation coil 30 surrounds the elongated coil 10. The elongated anti-reaction coil 32 surrounds the verification excitation coil 30, but the winding order of these coils can be different.

For the purposes of the invention, the term "elongate coil" means a coil having a length greater than twice its diameter. Preferably the coil will extend over most of the magnetic core. Thus, the magnetic core 11 has a length equal to or greater than that of the coil 10. In order to facilitate the realization of the transducer assembly 2 but also make it easier to implement the sensor, the magnetic core 11 has a character flexible at least before its first implementation. By flexible character, it is meant that the core 11 is flexible or flexible at room temperature (20 ° C) and can be deformed by hand without special tools: a linear shape to a circular shape (looped). According to the invention, the magnetic core 11 is then constituted by a flexible material comprising a flexible or flexible matrix of polymer material in which magnetic particles are dispersed which confer their magnetic character on the core. The flexible matrix can then be made, depending on the applications envisaged for the sensor according to the invention, either of a plastic material also called plastomer or natural rubber or synthetic rubber also called elastomer. The matrix may thus be made of a plastic material chosen from thermoplastics or thermosets. By way of example, the matrix may be chosen from the following thermosetting agents: phenoplast, aminoplast, epoxy resin, unsaturated polyester, alkyl crosslinked polyurethane. The matrix may also be chosen from the following thermoplastics: polyvinyl chloride, polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol, polyester and copolymer, acrylic polymer, polyolefin, cellulose derivative, polyamide. The matrix may also be chosen from the following polymers: fluoropolymer, silicone, synthetic rubber, saturated polyester, linear polyurethane, polycarbonate, polyacetal, polyphenylene oxide, polysulfone, polyester sulfone, phenylene polysulfide, polyimide and elastomer.

In order to impart a magnetic character to the core, the constituent material of the latter also comprises magnetic particles dispersed inside the matrix. The magnetic particles will, for example, be chosen from iron oxide particles, iron oxide and other metal oxide particles, nickel oxide particles, cobalt particles or mixed oxides of these metals. The mixed oxides of iron will be, for example, mixed oxides of iron and another metal chosen from Mn, Ni, Zn, Bi, Cu, Co. The magnetic particles may also be chosen from iron oxide particles of the following type: Fe ₃ O ₄ and / or F ₂ O ₃ . The magnetic particles may also be chosen from metal alloy particles of Fe _x Ni (i- _{x )} , Co _x Ni (i- _{x )} or Fe ₂₀ Ni ₈ o-type.

According to the example illustrated in FIGS. 2 and 3, the spool 10 comprises a forward conductor 12 which extends from a first end 13 of the core to the opposite end or second end 14. is wound in contiguous turns around and along the core 11. In order to facilitate the connection of the coil 10, to the electronic unit 3, the coil 10 comprises a return conductor 15 which extends the forward conductor 12 from the end 14 to the first end 13. According to the illustrated example, the return conductor 15 extends in the core substantially along the central axis or average fiber Δ of the latter. Of course it could be considered to return the driver back outside the core or coil extending substantially parallel to the central axis Δ.

 We also see the verification excitation 30 and counter-reactors 32 respectively comprising a forward conductor 31, 33 which extends from the end 13 of the core to the opposite end or second end 14. The drivers 31 and 33 are wound in contiguous turns around and along the coil 10. In the same manner, the verification excitation and counter-reactive coils 32 are connected to the return conductor 15.

 As can be seen in FIGS. 1 and 2, the coils 10, 30 and 32 are connected to the electronic unit 3 which comprises excitation means 20, measurement means 21 and verification means 23, 24 and Controlling means 22. The excitation means 20 comprise electronics which generate, in normal operating mode, an excitation current so as to generate an excitation magnetic field in the core 11 and over the entire length of the coil. 10. Insofar as, according to the illustrated example, the excitation means 20 are directly connected to the coil 10, the magnetic excitation fields, generated by the excitation current generated by the means 20, extend necessarily at least over the entire length of the coil 10. Furthermore, the measuring means 21 are connected to the coil 10 parallel to the excitation means 20. The measuring means 21 are then adapted to exploit the electrical quantities i ssues of the latter.

 In a preferred but non-exclusive embodiment, the measuring means 21 are adapted to determine the intensity of a current flowing in a conductor C from the magnetic field radiated by the latter and flowing in the coil 10. For this purpose , the transducer 2 is, preferably and as shown in Figure 2, closed loop around the conductor C within which circulates the current to be measured. This loop closure is achieved by engaging the end 13 of the core-coil assembly 2 in the sleeve 17 equipping the end 14. Of course, other closure means could be implemented to ensure the implementation of the core-coil assembly 2 around the conductor C.

It should be noted that in the context of the embodiment of the sensor 1 described above, the coil 10 provides a dual function of main excitation coil and measurement. The connection between the coil 10 and the excitation means 20 and measurement 21 is provided by an electric cable 4. The connection between the return conductor 15 and the excitation means 20 and measuring 21 is provided by an electric cable 5.

 In FIGS. 1 and 2, the verification means comprise a current generator 23 which is configured so as to generate in the verification excitation coil 30 a precise current, such as for example 0.03% of the Inominal current and of great intensity. , in situ, without moving the sensor; Inominal being the nominal value of the current to be measured and typically between 5A and 100,000A. In fact, a magnetic field is generated which represents the same magnetic field as the nominal current. For example, for a 5000A Inominal, 10A and 500 turns are used for the reverification. This generator is connected to the verification excitation coil 30 by means of an electric cable 6, the return being provided by the conductor 15 and the electric cable 5.

 With the sensor according to the invention, when a measurement of a current Ip is made using the counter-reaction and the principle of cancellation of the magnetic field circulation, the measurement is immediate since it is shown that Icr = Ip / Ncr ; 1 being the counter-reaction current obtained by servocontrol with respect to the main excitation and Ncr being the transformation ratio related to the number of turns of the counter-reaction coil.

A processing unit 24 is configured to process information from the generator 23 and the measurement unit 21. Advantageously, the latter comprises an EPROM memory, or nonvolatile RAM 25 in which sensor characteristics data such as the number of turns of the coil 10 and the number of turns of the verification excitation coil 30 and the number of turns of the counter-reaction coil 32. These numbers can be obtained during a calibration step in situ or not . When a sensor leaves a manufacturing plant, these numbers of turns are known with a margin of error. Two so-called identical sensors may in fact comprise a different ratio between turns of main excitation and verification. This is detrimental when you want to do very specific measurements. The present invention makes it possible to know precisely these numbers of turns and to keep them in the memory and use them throughout the life of the sensor during verification measurements. The processing unit 24 comprises software and hardware means for performing various processes such as calibration, auto-calibration, recalibration or verification.

 The generator 23 and the processing unit 24 can be integrated in the electronic unit 3 as shown in FIG. 1 and 2, but they can also be external components that are connected to the sensor for carrying out the processes mentioned herein. -above. The processing unit can even be arranged remotely and communicate with the generator and the measuring means by a wireless link.

Of course, the invention is not limited to the examples that have just been described and many adjustments can be made to these examples without departing from the scope of the invention.

Claims

1. Circulation sensor of permanent or variable magnetic fields comprising: magnetic excitation means comprising:  at least one elongated main excitation coil (10) for exciting an elongated flexible magnetic core (11) and comprising a flexible or flexible matrix in which magnetic particles are dispersed,  an excitation unit (3, 20) capable of generating an excitation current in the main excitation coil, so as to generate a main excitation magnetic field in the core over substantially the entire length of the coil,  verification means (23, 24, 30) comprising a verification excitation coil (30) capable of generating a verification excitation magnetic field in the core from a predetermined verification current, and  measuring means comprising:  at least one magnetic measurement transducer (10) for sensing a magnetic field induced in the core,  a measuring unit (3, 21) connected to the magnetic measurement transducer (10) and adapted to provide a measurement of the magnetic field circulation induced in the core. 2. Sensor according to claim 1, characterized in that the magnetic particles of the flexible magnetic core (11) are superparamagnetic grains; and in that the flexible magnetic core (11) has a relative permeability of less than a few hundred. 3. Sensor according to one of the preceding claims, characterized in that it comprises means (22) for counter-reaction associated with a counter-reaction coil. 4. Sensor according to claim 3, characterized in that the means (22) for counter-reaction are adapted to maintain when the sensor is looped. closed magnetic field circulation induced in a predefined range, and preferably substantially close to or equal to zero. 5. Sensor according to any one of the preceding claims, characterized in that it comprises a memory (25) in which are stored characteristic data of the magnetic field circulation sensor. 6. Sensor according to claim 5, characterized in that these data comprise at least one of the following elements:  the transformation ratio related to the number of turns of at least one coil of the magnetic field circulation sensor,  - identification data of the magnetic field circulation sensor, - traceability data of measurements already carried out, and / or  - correction data to be applied during measurements. 7. Sensor according to any one of the preceding claims, characterized in that the amplitude of the predetermined verification current is substantially between ΙμΑ and 100A. 8. A method for checking a sensor (1) for magnetic field circulation as defined in any one of the preceding claims, characterized in that it comprises the following steps: a predetermined checking current is injected into the verification excitation coil,  at least one inductive magnetic field circulation measurement is carried out in the core, and  said at least one measurement thus made is compared with the predetermined verification current, taking into account the characteristic data of the sensor contained in a memory. 9. The method of claim 8, characterized in that the memory is contained in the sensor or in a remote storage unit. 10. Method according to one of claims 8 or 9, characterized in that the characteristic data comprises at least a predetermined ratio between a verification current and a circulation measurement of the magnetic field induced in the core. 11. The method of claim 10, characterized in that, the sensor comprising a counter-reaction, the predetermined ratio is a transformation ratio between at least one verification current and a counter-reactive current. 12. Method according to any one of claims 8-11, characterized in that the above steps are carried out in situ, the sensor being in operation or not. 13. Method according to any one of claims 8-12, characterized in that injects the result obtained after the comparison in the measurement unit so as to perform an autocalibration of the sensor. 14. Application of the method according to any one of claims 8-13 for performing verification, calibration, self-calibration or recalibration of the sensor (1) defined in one of claims 1 at 7.