Portable device for contactless current measurement using an induced magnetic field

Abstract

Portable device for non-contact current measurement using an induced magnetic field, the portable device (12) for non-contact measurement of an electric current I passing through an electric conductor (10A), the device comprising a measurement module (14) and a processing module (16), the measurement module (14) being configured to be held in contact with the conductor by an operator without clamping the conductor in a plane P substantially orthogonal to the conductor, the measurement module (14) comprising one or two sets of magnetic field sensors made up of a plurality of magnetic field sensors, and the processing module (16) being configured to perform a determined linear combination of a plurality of signals transmitted by said one or two sets of magnetic field sensors, thereby performing an angular space filtering that isolates the current I to be measured from other interfering currents passing through other conductors.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of non-contact current measurement, in particular to a measuring device using an induced magnetic field. BACKGROUND

[0002] Current sensors ensuring non-contact measurement, such as Hall effect sensors, Rogowski loops, magnetoresistors, fluxgates or even magneto-optical devices, are well known. However, these sensors require to be wrapped around the conductor through which the current to be measured passes, and such an arrangement is not always possible or desirable. SUMMARY

[0003] The present invention thus relates to a portable device for non-contact current measurement, which does not require clamping the conductor to perform the measurement. It is also an object of the invention to prevent the current measurement from being disturbed by other conductors present in the environment of the conductor being measured. Another object of the invention is to obtain an accurate measurement with a large dynamic, so as to be able to cover a large current measurement range, typically from 1 to 100 amperes.

[0004] These objects are achieved by a portable device for non-contact measurement of an electric current I passing through an electric conductor, the device comprising a measuring module configured to be held by an operator in contact with the conductor in a plane P substantially orthogonal to the conductor without clamping the conductor, the measuring module comprising a plurality of first magnetic field sensors, and a processing module configured to perform a determined linear combination of a plurality of signals transmitted by said plurality of first magnetic field sensors, so as to perform an angular spatial filtering isolating the current I to be measured from other disturbing currents passing through other conductors.

[0005] With such a spatial filtering, it is possible to ensure an angular selectivity adapted to the device so as to isolate the current sought in the disturbing currents around it with a minimum of error, typically less than 1% maximum error.

[0006] Advantageously, the angular spatial filtering is performed in a predetermined spatial region limited to a circular sector defined by an angle 2a and a radius d and centered on the electric conductor disposed at a determined distance r+d0 from the center of said plurality of first sensors, r being the radius of said plurality of sensors and d0 being the measurement distance, and r+d0

[0007] Preferably, the measuring module comprises one of the following shapes: circular, elliptical, rectangular, square, star-shaped or T-shaped, and the magnetic field sensors are distributed around the periphery of the measuring module.

[0008] Advantageously, the magnetic field sensors have a maximum tangential sensitivity and / or a radial sensitivity.

[0009] Preferably, the magnetic field sensors are chosen from the following sensors: Hall effect sensors, GMR sensors or AMR sensors, fluxgate sensors, and the number of magnetic field sensors is between 2 and 30.

[0010] Advantageously, this determined linear combination constitutes a digital filter of the equation VS =∑Fi x Vi, i being the number of sensors in the measurement module, and the weighting coefficients Fi of the digital filter being obtained from two predetermined templates representative of the angular spatial filtering desired.

[0011] Preferably, the processing module is configured to reconstruct an image in the plane P of the angular distribution of the magnetic sources formed by the other conductors present around the measurement module. When each magnetic sensor is formed by three identical sensors arranged orthogonally, the processing module can be configured to reconstruct an image of the magnetic environment around the measurement module.

[0012] Advantageously, in order to cover a larger current measurement range, the magnetic field sensors alternate between high-sensitivity sensors of the fluxgate type and low-sensitivity sensors of the Hall effect type.

[0013] Preferably, in order to determine the measurement distance do, the measurement device can comprise a telescopic sensing finger, the sensing finger being arranged at the end of the processing module and having a rest position and a deployed position, the switching between these two positions at a predetermined distance being carried out by means of an operator-manipulable button, or the measurement device comprises a plurality of second magnetic field sensors, the centers of said plurality of second magnetic field sensors being spaced apart from the centers of said plurality of first sensors by a predetermined distance Ado. BRIEF DESCRIPTION OF DRAWINGS

[0014] Other features and advantages of the application will emerge from the description given below, with reference to the appended drawings, which show an exemplary embodiment of the application, without being limited to this exemplary embodiment, and in which:

[0015] [ Figure 1 ] Figure 1 shows schematically and in perspective view a first example of a current measurement device according to the application,

[0016] [ Figure 2 ] Figure 2 is a block diagram of the process implemented in the current measurement device of Figure 1 ,

[0017] [ Figure 3 ] Figure 3 is the result of the filtering of a by the first template on a used in the process of the current measurement device according to the application,

[0018] [Figure 4 ] Figure 4 is the result of filtering d used in the process of the current measuring device according to the present application by the second template, and

[0019] [ Figure 5 ] Figure 5 A second example of a current measuring device according to the present application is shown in perspective. DETAILED DESCRIPTION

[0020] In Figure 1 , the portable device 12 for contactless current measurement according to the first example of the present application is positioned facing and at a distance from the conductor 10A and in a plane P orthogonal to the conductor, aiming to measure the current I passing through the conductor 10A without clamping said conductor. For example, the conductor under test 10A is arranged adjacent to two other conductors 10B, 10C in the same plane perpendicular to the plane P. These two conductors are also crossed by the current and constitute interference elements for measuring the current I passing through the conductor under test 10A.

[0021] According to the present application, the measuring device essentially comprises a measuring module 14 and a processing module 16, the measuring module being arranged at the end of the processing module, which advantageously has the shape of a handle in terms of outer shape, thus allowing easy gripping by the operator who performs the measurement.

[0022] The measuring module 14 consists of a plurality of sensors sensitive to the magnetic field, comprising from 2 to 30 sensors, and generally comprising 8 sensors, which form a constellation and are distributed over 360°, preferably uniformly around the periphery of the module. The position of each of the sensors is accurately known, whether they are uniformly distributed or not, and unlike the devices in the prior art, the sensors together do not ensure clamping of the target conductor.

[0023] The magnetic field sensors that can be used for this module are generally Hall effect sensors, sensors known as XMR sensors, i.e. anisotropic magnetoresistive (AMR) or giant magnetoresistive (GMR) sensors or fluxgate sensors.

[0024] In the example shown, the measuring module has a substantially circular shape, but it can also be elliptical or square in shape. Likewise, a cross or T shape can be envisaged, the crossbar and the legs of the T being arranged in a plane perpendicular to the target conductor, the most suitable shape being chosen according to the type of sensors used and the performance required, in particular in terms of filtering the magnetic signals obtained from these sensors.

[0025] Since the sensors, whatever their type, generally have a preferred direction of measurement or an axis of maximum sensitivity, it is preferable to seek sensors sensitive in a direction tangential to the measurement module.

[0026] However, radial orientations are conceivable (in the case of circular, elliptical or square clusters), so that the combined use of radially and tangentially oriented sensors in the same module is also possible.

[0027] Now, with reference to the attached drawings, Figure 2 The processing module 16 is described, Figure 2 A simplified block diagram of this module is shown, which receives from each of the sensors 140 to 154 (that is, in the non-limiting example, 8 sensors) forming the cluster of the measurement module 14, a first voltage U1 to U8 representative of the magnetic field B1 to B8 recorded at each of these sensors. This voltage U1 to U8 is transmitted to a gain compensation circuit 160 to 174 which allows to compensate the various gain dispersions inherent in each of the sensors and which transmits a second normalized voltage V1 to V8.

[0028] Depending on the type of sensor, for example when AMR sensors with very low output voltage (of the order of a few millivolts) are used, this gain compensation circuit can also ensure the amplification of the received signal.

[0029] Each of the second normalized and possibly amplified voltages V1 to V8 is then digitized in an analog-to-digital converter 180 to 194 before being transmitted to a processing unit of the microcontroller type 196 (for example, an STM32 from the STM Microelectronics company integrated with random access and flash memory) or a similar processing unit (for example, an ASIC or an FPGA) in which these voltages will be processed by appropriate digital filtering (which will be explained later) to recover the voltage V S characteristic.

[0030] The final calibration circuit 198 can switch from this voltage value to the voltage value of the current measured according to the equation of the known proportion:

[0031]

[0032] where μ0 is the magnetic permeability in vacuum, d0 is the measurement distance and Kcal is a calibration parameter determined before leaving the factory by tests based on a known calibration current (typically 1 A) and known disturbance currents (for example, ranging from 10 to 400 A). The determination of the measurement distance d0 can be made, for example, by means of a sensing device which will be described later.

[0033] The current I thus determined is then converted into a root mean square value and displayed on the display 200 of the device (other parameters such as the frequency and the continuous average value can also be displayed selectively). Obviously, all these components are powered by a rechargeable or non-rechargeable battery 202, typically 5 V, the charge level of which is visible for example on a display screen, which is preferably a touch display screen. In combination with the microcontroller, this display screen can also display many other statuses, so that the correct operation of the device can be verified.

[0034] According to the application, the digital filtering performed in the processing unit 196 consists of a determined linear combination of the normalized voltage values Vi representative of the magnetic field recorded by the sensors, this determined linear combination being VS =∑Fi x Vi, where i is the number of sensors in the measurement module.

[0035] In the example of the cluster of eight sensors shown, the 8th order filter corresponding to the weighting coefficients F1 to F8 obtains the following relationship: Figure 1

[0036] VS = F1V1 + F2V2 + F3V3 + F4V4 + F5V5 + F6V6 + F7V7 + F8V8

[0037] This determined linear combination tends to perform an angular space filtering, so that it makes it possible to isolate the current I to be measured from the interference currents passing through the other conductors than the target conductor. This angular space filtering has the property of being sensitive only to the fields emitted by the conductors located in a predetermined spatial region defined as a passage region through the space. Advantageously, this passage region is a circular sector of angle 2a (-a, +a) and radius d, this sector being centered on the target conductor, located at a = 0, this circular sector being arranged at a given distance r + d0 from the center of the cluster of sensors (r being the radius of the cluster of sensors, and r + d0 < d). The radius r of the cluster of sensors is preferably between 1 cm and 5 cm, typically 3 cm, and the distance d0 is preferably between 1 mm and 10 mm.

[0038] To perform this angular space filtering, as Figure 3 and Figure 4 shown, a spatial template is established, so that it is possible to prescribe the performance of the filter by defining the passage and attenuation (or cut-out) regions reflecting the desired sensitivity. More particularly, a first template is arranged on a (a1, a2) ( Figure 3 showing the result of the filtering), and a second template is arranged on d (d1, d2) ( Figure 4 ​(see the results of the filtering), a and d can each be composed of a simple rectangular gate centered on the direction of the target source (typically a from -π / 2 to π / 2 and d less than 1 m). But it is clear that a Hamming or Hanning or any other similar window function such as a Blackman or Kaiser function can also be envisaged.

[0039] By thus defining the two filter templates, the synthesis of the desired filter can be obtained simply by an iterative process using a synthesis software called PYTHON. More specifically, it involves finding the best combination of measurements that allow to comply with the two templates representative of the desired filtering (for this, the field measurements given by the cluster of N sensors can be used for each point of the plane). This amounts to minimizing the distance from the filter to the template by bilinear least squares. This calibration process, usually carried out in the factory, allows to determine the weighting coefficients Fi of the digital filter and depends in particular on the position and orientation of the sensors. Thus, for a circular measuring module with a cluster radius of 3 cm and comprising eight Hall effect sensors distributed uniformly over 360° and oriented tangentially at a measurement distance do of 3 mm, the following weighting coefficients are obtained:

[0040] F1 = F8 = 0.105692149; F2 = F7 = 0.217712759; F3 = F6 = 0.378621237; and F4 = F5 = 1

[0041] In addition, in order to increase the measurement dynamic, it is advantageous to use different sensors. For example, the cluster can comprise both very sensitive fluxgate sensors (for example, the DRV425 sensor from the Texas Instrument company) with a linear dynamic of ±2 mT and Hall effect sensors (for example, the EQ733L sensor from the AKM semiconductor Inc.) with a lower sensitivity but which can reach ±100 mT. This embodiment combines low sensitivity sensors and high sensitivity sensors arranged alternately, allowing to cover a large current measurement range (typically 1 A to 100 A). It should be noted that these sensors can also be arranged on either side of the same electronic board to minimize the space required.

[0042] It is also noted that when the cluster is in the shape of a circle, by a permutation of the set of simple numerical filter weighting coefficients, it is possible to move the passing spatial region of the directive lobe in a circular manner at the processing unit, thus mapping the magnetic field into the plane of the sensor, without modifying its orientation. In fact, the cluster remains fixed, passing through the region described in its periphery a disc and thus scanning the space around the cluster. In this particular configuration, after a complete rotation, it is then possible to reconstruct the image of the angular distribution of the magnetic sources around the cluster and display it on the display. With three identical sensors orthogonally arranged instead of each sensor (i.e. 24 sensors similar to the configuration of Figure 1 The mapping becomes 3D. It is possible to reconstruct the image of the magnetic environment of the measuring device.

[0043] Finally, the measuring device of the application comprises a telescopic feeler 18, also arranged at the end of the processing module 16 and having two different and stable positions d 01 , d 02 , i.e. a rest position and a deployed position, which are only separated from each other by a known Δd0, which is a few millimetres (typically 3 mm, d 01 = 2 mm and d 02 = 5 mm).

[0044] The switching between these two positions is simply carried out by the operator through a button 20 and allows to determine the measurement distance d0 to the conductor by obtaining two current measurements on the same conductor with the same cluster of sensors.

[0045] In fact, the magnetic field is inversely proportional to the distance.

[0046] d0 -> B1 gives the output VS1, the distance is modified.

[0047] d0 + Δd0 -> B2 gives the output VS2.

[0048]

[0049] The analytical solution is found by combining:

[0050]

[0051] The solution is therefore:

[0052]

[0053] where B1 > B2, as when B1 / B2 is replaced with VS1 / VS2:

[0054]

[0055] where V s1V s2

[0056] Ad0 is a constant of the sensing device.

[0057] Thus, the distance d0, i.e. the actual measurement distance, can be determined from the different measurement voltages resulting from the clusters of sensors, which will allow, if necessary, to correct the various measurements (the measurement device has been calibrated at the factory with a calibration distance which can actually be different from the actual measurement distance).

[0058] It should be noted that, as Figure 5 indicated, the sensing device can be replaced by a second cluster 140B of sensors, the center of which is at Ad0 from the center of the first cluster 140A. This second example of current measurement device according to the application allows to replace the physical displacement of the device by an electronic switching from one cluster to another, the outermost cluster being in contact with the target conductor 10A.

[0059] The operation of the measurement device is particularly simple, as described below. The operator holds the device and, after ensuring that the battery is sufficiently charged (a simple touch on the display allows to move the device out of its standby state and provides this information), the operator places the device facing the conductor whose current is to be measured in a plane substantially orthogonal to the conductor until the device is in contact with the telescopic sensing finger. Pressing the telescopic sensing finger against the conductor has the effect of automatically triggering the first magnetic field measurement by the cluster of sensors. Retracting the sensing finger into its second stable position by action on the button will trigger the second magnetic field measurement, allowing to automatically determine the distance d0 and to automatically determine the value of the detected current I, the display of which is practically performed instantaneously (at most a few hundred milliseconds depending on the computing tool used). When the current measurement device comprises two clusters of sensors, the first and second measurements can be performed simultaneously upon contact with the target conductor.

Claims

1. A portable device for contactless measurement of an electric current I passing through a conductor (10A), the portable device (12) comprising a measurement module (14) and a processing module (16), the measurement module (14) being configured to be held by an operator in contact with the conductor in a plane P substantially orthogonal to the conductor without clamping the conductor, the measurement module (14) comprising a plurality of first magnetic field sensors, and the processing module (16) being configured to perform a determined linear combination of a plurality of signals transmitted by the plurality of first magnetic field sensors (140-154) in order to perform an angular space filtering isolating the electric current I to be measured from other interfering electric currents passing through other conductors, wherein, Said angular spatial filtering is performed in a predetermined spatial region limited to a circular sector defined by an angle 2a and a radius d and centered on said conductor (10A) set at a determined distance r+d0 from the center of said plurality of first magnetic field sensors, r being the radius of said plurality of first magnetic field sensors, d0 being a measurement distance, and r+d0 < d.

2. The portable device of claim 1, wherein, In order to determine said measurement distance d0, said portable device further comprises a telescopic sensing finger (18) set at the end of said processing module and having a rest position and a deployed position, the switching between these two positions at a predetermined distance Δd0 being performed by means of a button (20) actuable by said operator.

3. The portable device of claim 1, wherein, Said portable device further comprises a plurality of second magnetic field sensors (140A, 140B) whose center is spaced apart from the center of said plurality of first magnetic field sensors by a predetermined distance Δd0.

4. The portable device of claim 1, wherein, Said measurement module comprises one of the following shapes: circular, elliptical, rectangular, square, star-shaped or T-shaped.

5. The portable device of claim 1, wherein, Said magnetic field sensors are distributed around the periphery of said measurement module.

6. The portable device of claim 1, wherein, Said magnetic field sensors have a maximum tangential sensitivity and / or radial sensitivity.

7. The apparatus of claim 1, wherein, Said magnetic field sensors are chosen from the following sensors: Hall effect sensors, GMR sensors or AMR sensors, fluxgate sensors.

8. The apparatus of claim 1, wherein, The number of said magnetic field sensors is between 2 and 30.

9. The apparatus of claim 1, wherein, Said determined linear combination constitutes a digital filter of the equation VS =∑Fi×Vi, i being the number of sensors in said measurement module, and the weighting coefficients Fi of said digital filter being obtained from two predetermined templates representative of a desired angular spatial filtering.

10. The apparatus of claim 9, wherein, Said processing module is configured to reconstruct an image in said plane P of the angular distribution of the magnetic sources formed by other electrical conductors present around said measurement module.

11. The portable device of claim 9, wherein, Each magnetic field sensor is formed by three identical sensors set orthogonally, and said processing module is configured to reconstruct a 3D image of the magnetic environment around said measurement module.

12. The portable device of claim 1, wherein, In order to cover a greater current measurement range, said magnetic field sensors alternate between high-sensitivity sensors of the fluxgate type and low-sensitivity sensors of the Hall effect type. In order to determine said measurement distance d0, said portable device further comprises a telescopic sensing finger (18) set at the end of said processing module and having a rest position and a deployed position, the switching between these two positions at a predetermined distance Δd0 being performed by means of a button (20) actuable by said operator. Said portable device further comprises a plurality of second magnetic field sensors (140A, 140B) whose center is spaced apart from the center of said plurality of first magnetic field sensors by a predetermined distance Δd0. Said measurement module comprises one of the following shapes: circular, elliptical, rectangular, square, star-shaped or T-shaped. Said magnetic field sensors are distributed around the periphery of said measurement module. Said magnetic field sensors have a maximum tangential sensitivity and / or radial sensitivity. Said magnetic field sensors are chosen from the following sensors: Hall effect sensors, GMR sensors or AMR sensors, fluxgate sensors. The number of said magnetic field sensors is between 2 and 30. Said determined linear combination constitutes a digital filter of the equation VS =∑Fi×Vi, i being the number of sensors in said measurement module, and the weighting coefficients Fi of said digital filter being obtained from two predetermined templates representative of a desired angular spatial filtering. Said processing module is configured to reconstruct an image in said plane P of the angular distribution of the magnetic sources formed by other electrical conductors present around said measurement module. Each magnetic field sensor is formed by three identical sensors set orthogonally, and said processing module is configured to reconstruct a 3D image of the magnetic environment around said measurement module. In order to cover a greater current measurement range, said magnetic field sensors alternate between high-sensitivity sensors of the fluxgate type and low-sensitivity sensors of the Hall effect type.

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