MEASURING TRANSDUCER WITH A CONDUCTOR PLATE

Description

[0001] The invention relates to the field of measurement transformers comprising a printed circuit board. BACKGROUND OF THE INVENTION

[0002] A flow valve current sensor utilizes the property of a magnetic material forming a magnetic core to saturate above a certain level of magnetic excitation. In reference to the figure 1 For an increasing magnetic field H, the slope of the transfer function between the magnetic field H and the magnetic induction B decreases significantly from a value called the saturation point of the magnetic core. The saturation value, on the figure 1 , corresponds to the intervals ΔH and ΔB.

[0003] With reference to figures 2 et 3 In a conventional flow valve current sensor 1 designed to measure a current Im flowing through a conductor, a square wave signal generator 2 applies a square wave excitation voltage Vex across the terminals of an excitation winding 3 wound around a magnetic core 4. The excitation current Iex flowing in the excitation winding 3 is measured by a measuring module 5. A peak detector 6, connected to the measuring module 5, provides two pieces of information: the saturation level and the difference in peak currents of the excitation current Iex. The saturation level allows the amplitude of the excitation voltage Vex to be controlled.The difference in peak currents of the excitation current Iex allows us to estimate the current to be measured Im and to control, via a voltage-to-current converter 7, the amplitude of a demagnetizing current which flows in a demagnetizing winding 8 and which allows us to compensate for the magnetic flux produced in the magnetic core 4 by the current to be measured Im.

[0004] Flow valve current sensors are preferred in a number of applications. This is particularly the case for measuring current flowing in an SSPC (Solid State Power Controller) type switching device destined for user equipment, or for measuring current flowing in a PEM (Power Electronic Module) type energy conversion device connected to a phase of a motor.

[0005] Document EP1884783A1 discloses a current measuring device comprising a current sensor with: - a magnetic circuit, - a plurality of windings, including at least one excitation winding responsible for energizing the magnetic circuit, - at least one sensing winding. The sensor is equipped with windings forming a transformer, including at least one primary winding opposite the magnetic circuit through which a current I to be measured is intended to enter, and at least one secondary winding opposite the magnetic circuit capable of producing a feedback magnetic field. The current I to be measured is intended to be divided between the conducting branches of the primary winding. SUBJECT OF THE INVENTION

[0006] The invention aims to improve industrial reproducibility and reduce the cost of a flow valve current sensor. SUMMARY OF THE INVENTION

[0007] To achieve this goal, a measuring transformer according to claim 1 is proposed, comprising a printed circuit board and a magnetic core, the printed circuit board comprising an insulating layer, a primary through-hole assembly comprising primary first plated holes and primary second plated holes extending through the insulating layer, the primary through-hole assembly forming a portion of a primary winding of the measuring transformer, said primary winding comprising a single turn, the printed circuit board further comprising a secondary through-hole assembly comprising secondary first plated holes and secondary second plated holes extending through the insulating layer, the secondary through-hole assembly forming a portion of a secondary winding of the measuring transformer, said secondary winding comprising several turns connected in series,the magnetic core extending through a thickness of the printed circuit board.

[0008] The electrical characteristics of the primary and secondary plated-through holes of the printed circuit board are perfectly reproducible. Furthermore, by integrating the magnetic core of the measurement transformer according to the invention within a thickness of the printed circuit board, the material used for its manufacture, its structure, and therefore its characteristics, are perfectly controlled.

[0009] Furthermore, the measuring transformer according to the invention is inexpensive, since it consists of a printed circuit board, plated holes and a magnetic core directly integrated into the printed circuit board.

[0010] Thus, by integrating the measuring transformer according to the invention into a current sensor with a flow valve, industrial reproducibility is improved and the cost of said current sensor with a flow valve is reduced.

[0011] The invention will be better understood in light of the following description of a particular, non-limiting embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Reference will be made to the attached drawings, including: there figure 1 represents the curve of a transfer function between a magnetic field and a magnetic induction; the figure 2 represents an existing flow valve current sensor; the figure 3 represents the curve of an excitation voltage and the curve of an excitation current that excite a magnetic core of the existing flow valve current sensor; the figure 4 represents a new flow valve current sensor comprising a transformer according to the invention; the figure 5 represents a current divider bridge integrated into a printed circuit board and used to measure a current; the figure 6 is a cross-sectional view of the transformer according to the invention used in the new flow valve current sensor; the figure 7 is a view analogous to that of the figure 6 , but from above. DETAILED DESCRIPTION OF THE INVENTION

[0013] With reference to the figure 4 , a flow valve current sensor 10 is used here to measure a current to be measured Im which flows over a conductor 11.

[0014] The flow valve current sensor 10 includes a measuring transformer according to the invention 12 comprising a magnetic core 13, a primary winding, and a secondary winding. The primary winding is the conductor 11. The magnetic core 13 extends around the conductor 11. The secondary winding is a measuring winding 14 wound around the magnetic core 13.

[0015] The flow valve current sensor 10 comprises a plurality of electronic components forming a digital part 15 and an analog part 16.

[0016] The digital part 15 includes a digital processing component which is in this case an FPGA but which could be a different component: microcontroller, processor, ASIC, etc.

[0017] The flow valve current sensor 10 further includes an acquisition circuit 17. The acquisition circuit 17 belongs to the analog part 16.

[0018] The acquisition circuit 17 is connected to the measuring winding 14.

[0019] The acquisition circuit 17 includes a high-pass filter 19 and an analog-to-digital converter 20 connected to an output of the high-pass filter 19.

[0020] The analog-to-digital converter 20 is a 12-bit converter operating at a specific frequency, Fech. Here, Fech = 100 MHz. The analog-to-digital converter 20 could, of course, have different characteristics.

[0021] The acquisition circuit 17 acquires an analog measurement voltage Ve across the terminals of the measurement winding 14. The measurement voltage Ve is applied to the input of the high-pass filter 19.

[0022] The resulting voltage is applied to the input of the analog-to-digital converter 20, which produces a digital measurement signal Sm.

[0023] The flow valve current sensor 10 includes a high-frequency generator 22. The high-frequency generator 22 is integrated into the FPGA (the term "integrated" could be replaced by one of the following terms: programmed, implemented, deployed, etc.)

[0024] The high-frequency generator 22 produces a digital reference signal of frequency f0, a digital reference signal of frequency 2.f0 and a digital reference signal of frequency 3.f0.

[0025] The digital reference signal with frequency f0 is of the form: S 1 r = sin ω 0 t .

[0026] The digital reference signal with frequency 2.f0 is of the form: S 2 r = cos 2 . ω 0 t .

[0027] The digital reference signal with frequency 3.f0 is of the form: S 3 r = sin 3 . ω 0 t .

[0028] The flow valve current sensor 10 further includes an excitation circuit 23. The excitation circuit 23 is implemented in the FPGA.

[0029] The excitation circuit 23 is connected to the high-frequency generator 22.

[0030] The excitation circuit 23 comprises a raw excitation circuit 24 and an excitation control circuit 25.

[0031] The raw excitation circuit 24 receives the digital reference signal of frequency f0 and the digital reference signal of frequency 3.f0 and produces from these signals a digital partial excitation signal of frequency f0 and a digital partial excitation signal of frequency 3.f0.

[0032] The partial digital excitation signal with frequency f0 is here of the form: S 1 p = k 1 . sin ω 0 t .

[0033] The partial digital excitation signal with frequency 3.f0 is here of the form: S 3 p = k 2 . sin 3 . ω 0 t .

[0034] The raw excitation circuit 24 adds the partial digital excitation signal at frequency f0 and the partial digital excitation signal at frequency 3f0 to generate a raw digital excitation signal. The raw digital excitation signal is of the form: Seb = S 1 p + S 3 p = k 1 . sin ω 0 t + k 2 . sin 3 ω 0 t .

[0035] The excitation control circuit 25 is connected to the high-frequency generator 22.

[0036] The excitation control circuit 25 receives the digital reference signal of frequency 3.f0 and produces from the digital reference signal of frequency 3.f0 a digital demodulation signal of frequency 3.f0.

[0037] The digital demodulation signal with frequency 3.f0 is of the form: S 3 d = k 3 . sin 3 . ω 0 t .

[0038] The excitation control circuit 25 includes a first multiplier 27, a second multiplier 28, an integrator 29 and a first amplifier 30. The first amplifier 30 is connected to an output of the integrator 29.

[0039] The first multiplier 27 multiplies the digital measurement signal Sm by the digital demodulation signal of frequency 3.f0. The resulting signal is applied to the input of the integrator 29.

[0040] It is noted that the first multiplier 27 and the integrator 29 play the role of a first synchronous demodulator.

[0041] The first amplifier 30 then produces a digital error signal. The second multiplier 28 multiplies the raw digital excitation signal Seb by the digital error signal to obtain a digital excitation signal. The digital excitation signal is of the form: Se = k 0 . k 1 . sin ω 0 t + k 2 . sin 3 ω 0 t .

[0042] The flow valve current sensor 10 further includes a demagnetization control circuit 32. The demagnetization control circuit 32 is integrated into the FPGA.

[0043] The demagnetization control circuit 32 is connected to the high-frequency generator 22.

[0044] The demagnetization control circuit 32 receives the digital reference signal of frequency 2.f0 and produces from the digital reference signal of frequency 2.f0 a digital demodulation signal of frequency 2.f0.

[0045] The digital demodulation signal with frequency 2.f0 is of the form: S 2 d = k 4 . cos 2 . ω 0 t .

[0046] The demagnetization control circuit 32 includes a third multiplier 33, a low-pass filter 34 and a second amplifier 35. The second amplifier 35 is connected to an output of the low-pass filter 34.

[0047] The third multiplier 33 multiplies the digital measurement signal Sm by the digital demodulation signal of frequency 2.f0. The resulting signal is applied to the input of the low-pass filter 34. The second amplifier 35 then produces a digital image signal of the current to be measured Im, which is also a digital demagnetization signal Sdm. The digital image signal, or digital demagnetization signal Sdm, is of the form Sdm = k.Im.

[0048] Note that the third multiplier 33 and the low-pass filter 34 act as a second synchronous demodulator.

[0049] The flow valve current sensor 10 further includes a summing 36. The summing 36 is implemented in the FPGA.

[0050] The summing unit 36 ​​sums the digital excitation signal Se and the digital demagnetization signal Sdm to obtain a digital injection signal Si.

[0051] We have: Si = k 0 . k 1 . sin ω 0 t + k 2 . sin 3 ω 0 t + kIm .

[0052] The flow valve current sensor 10 further includes an injection circuit 37. The injection circuit 37 belongs to the analog part 16.

[0053] The injection circuit 37 is connected to the summing 36 and to the measuring winding 14.

[0054] The injection circuit 37 includes a digital-to-analog converter 38.

[0055] The digital-to-analog converter 38 is a 12-bit converter operating at the Fech frequency (Fech = 100 MHz). The digital-to-analog converter 38 could, of course, have different characteristics.

[0056] The digital-to-analog converter 38 acquires the digital injection signal Si, produces an analog excitation current Ie from the digital injection signal Si, and injects the excitation current Ie into the measuring winding 14.

[0057] The operation of the flow valve current sensor 10 is now described.

[0058] The excitation circuit 23 generates a digital excitation signal Se, which is transformed into an excitation current Ie and injected into the measuring winding 14.

[0059] The measurement voltage Ve is acquired and then digitized to produce a digital measurement signal Sm.

[0060] At the output of the second amplifier 35, a digital image signal of the current to be measured, Im, is obtained. This digital image signal is used to estimate the current to be measured, Im.

[0061] The digital image signal is also a digital degaussing signal Sdm which allows compensation for the magnetic flux produced by the current to be measured Im.

[0062] Thanks to the summing junction 36 and by connecting them in parallel, the digital demagnetization signal Sdm and the digital excitation signal Se are easily added together. The excitation current Ie thus allows both the excitation and demagnetization of the magnetic core 13. The demagnetization current is therefore integrated into the excitation current Ie.

[0063] The saturation of the magnetic core 13 causes an asymmetry of the measurement voltage Ve, said measurement voltage Ve being constituted by the sum of a frequency component f0 in sin(ω0t), corresponding to the fundamental, and a frequency component 2.f0 in cos(2ω0t), corresponding to the 2nd order harmonic component.

[0064] Note that the amplitude of the partial digital excitation signal of frequency f0 and that of the partial digital excitation signal of frequency 3.f0 are set to obtain an excitation current Ie whose frequency component 3.f0 (or 3rd order harmonic component) is in phase with the frequency component f0 (or fundamental).

[0065] The third-order harmonic component of the measured voltage Ve, obtained after synchronous demodulation via the first synchronous demodulator, is positive. In the event of saturation of the magnetic core 13, the third-order harmonic component is attenuated more strongly than the fundamental, and the third-order harmonic component after synchronous demodulation becomes negative, because the third-order harmonic is in opposite phase with the fundamental.

[0066] Thus, when the excitation current Ie is such that the magnetic core 13 approaches saturation, the ratio of the amplitude of the first-order harmonic component to the amplitude of the third-order harmonic component of the measurement voltage Ve evolves until the third-order harmonic component is canceled, and then until the phase of the third-order harmonic component is reversed. The operating point corresponding to the cancellation of the third-order harmonic component of the measurement voltage Ve is therefore an optimal operating point of the flow valve current sensor 10. This optimal operating point corresponds to the bend 9 of the transfer function curve of the figure 1 .

[0067] At the output of the first amplifier 30, a digital error signal is obtained.

[0068] The digital error signal allows the excitation current Ie to be controlled. This control consists of adjusting the excitation current Ie to cancel the third-order harmonic component of the measurement voltage Ve. The flow valve current sensor 10 thus operates continuously at its optimal operating point. This results in maximum gain from the asymmetries introduced by the current to be measured, Im, and detectable in the measurement voltage Ve. It should be noted that this control, achieved through synchronous demodulation of the third-order harmonic component, is relatively insensitive to external electromagnetic interference, because all signals with frequencies other than 3f0 generate intermodulation products whose components are filtered by the low-pass filter 34 connected to the output of the third multiplier 33.It is also noted that this control does not need to be very fast, because the variations from external parameters (temperature, aging) are relatively slow.

[0069] Thus, the measuring winding 14 is used both to excite the magnetic core 13, to control this excitation, to measure the current to be measured Im, and to compensate for the magnetic flux produced in the magnetic core 13 by the current to be measured Im (demagnetization).

[0070] Combining these functions on a single measuring winding 14 simplifies, reduces cost and mass, and facilitates the manufacture of the flow valve current sensor 10.

[0071] It is also noted that the measurement processing chain is mainly digital: a single FPGA allows for the implementation of a large part of this processing chain.

[0072] Digitizing the processing chain increases its reliability and robustness (particularly in temperature), reduces its cost, facilitates its manufacture and improves its industrial reproducibility.

[0073] Furthermore, improving the regulation of the operating point through demodulation by the first synchronous demodulator allows for better noise immunity.

[0074] Furthermore, the use of synchronous demodulators allows operation at high frequency, which permits a large bandwidth of the current to be measured Im while maintaining very good immunity to external electromagnetic disturbances.

[0075] Since the measurement is always taken at the optimal operating point corresponding to the saturation bend 9, the sensitivity of the flow valve current sensor 10 is constant across the temperature range. Therefore, the accuracy of the flow valve current sensor 10 is good over a wide temperature range.

[0076] As mentioned earlier, the flow valve current sensor 10 measures a current to be measured Im flowing over a conductor 11.

[0077] This situation does not pose any particular difficulty when the current to be measured Im is low (less than 1A for example).

[0078] However, when the current to be measured is significant, a major difficulty arises.

[0079] The demagnetizing current, which compensates for the magnetic flux produced in the magnetic core 13 by the current to be measured Im, must also be very high. The value of the demagnetizing current must be equal to that of the current to be measured divided by the turns ratio of the measuring transformer 12, combined with the characteristics of the primary and secondary windings.

[0080] However, the number of turns in the measuring winding 14 is limited by its size and the resulting inductance. The higher the inductance, the more limited the rate of change of the demagnetizing current (from the digital demagnetizing signal Sdm) will be, and therefore the more limited the bandwidth of the flow valve current sensor 10 will be. Thus, increasing the number of turns in the secondary winding is not an effective solution.

[0081] Increasing the demagnetization current is also not an effective solution. This is because it requires generating a very high demagnetization voltage under a high demagnetization current, which is difficult to achieve with standard components.

[0082] Note that this problem is not specific to the flow valve current sensor 10 just described, but concerns all flow valve current sensors (and in particular those which have a winding dedicated to demagnetization).

[0083] To solve this difficulty, a current divider bridge is implemented in order to reduce the value of the current to be measured.

[0084] With reference to figures 5 à 7 , the flow valve current sensor 10 includes a printed circuit board 40 on which are mounted, in particular, the plurality of electronic components forming the digital part 15 and the analog part 16.

[0085] The printed circuit 40 here comprises a first conductive layer 41, a second conductive layer 42 and an insulating layer 43. The first conductive layer 41 and the second conductive layer 42 each extend over an opposite face of the printed circuit 40.

[0086] The first conductive layer 41 includes a first track 44 and the second conductive layer 42 includes a second track 45. The insulating layer 43 therefore extends between the first track 44 and the second track 45.

[0087] The printed circuit board 40 further comprises a first through-hole assembly of at least one first primary plated hole 47 and a second through-hole assembly of at least one second primary plated hole 48. Here, in this case, the first through-hole assembly comprises several first primary plated holes 47 and the second through-hole assembly comprises several second primary plated holes 48. The first primary plated holes 47 and the second primary plated holes 48 all have the same first diameter.

[0088] A "plated hole" could also be called a "via." A "plated hole" can be created by any type of process. In particular, a "plated hole" can be made conductive by depositing a metallic material or any type of conductive material. A "plated hole" can also be made conductive by inserting a metallic tube or rivet, or any type of conductor.

[0089] Each first primary plated hole 47 and each second primary plated hole 48 connect the first track 44 and the second track 45 by extending through the insulating layer 43. Each first primary plated hole 47 thus comprises a first end connected to the first track 44 and a second end connected to the second track 45. Similarly, each second primary plated hole 48 comprises a first end connected to the first track and a second end connected to the second track 45.

[0090] The first through set, i.e. the first primary plated holes 47, and the second through set, i.e. the second primary plated holes 48, respectively form a first branch 51 and a second branch 52 of a current divider bridge 53.

[0091] Thus, the current to be measured, Im, is not actually a main current, Ip, whose value we want to know, but rather the current to be measured, Im, is derived from a division of the main current, Ip, and is used to estimate the value of the main current, Ip. The main current, Ip, flows in the first track 44, in the first branch 51 and the second branch 52 of the current divider bridge 53, and in the second track 45.

[0092] We can clearly see here that the conductor 11 mentioned above, on which the current to be measured flows, is the second crossing assembly (or the second branch 52).

[0093] Here, the main current Ip is equal to 10A.

[0094] The number of primary plated-through holes 47 in the first through-hole assembly is nine times greater than the number of primary plated-through holes 48 in the second through-hole assembly. Therefore, the second resistance of the second branch 52 is nine times greater than the first resistance of the first branch 51.

[0095] The current to be measured Im, flowing in the second branch 52 of the current divider bridge 53, is equal to 1A, while the current flowing in the first branch 51 of the current divider bridge 53 is equal to 9A.

[0096] We take advantage here of the reproducibility properties of the electrical characteristics of several plated holes of the same diameter and adjacent on the same printed circuit 40.

[0097] The first resistance of the first branch 51 and the second resistance of the second branch 52 are poorly known, but their ratio is known very precisely thanks to this reproducibility.

[0098] The first through-circuit and the second through-circuit are therefore equivalent to two resistors. shunt of perfectly controlled ratio.

[0099] The ratio between the current to be measured, Im, and the main current, Ip, is therefore known with great precision. Measuring the current to be measured, Im, allows for a very precise estimation of the main current, Ip, while simultaneously reducing it to lower the required demagnetization current.

[0100] The current to be measured Im is measured using the measuring transformer according to invention 12, which is now described in more detail.

[0101] The measuring transformer according to the invention 12 comprises the printed circuit 40 or, more precisely, a portion of the printed circuit 40, since the printed circuit also carries the digital part 15 and the analog part 16.

[0102] The first and second through-hole assemblies just described form a "primary through-hole assembly." The primary through-hole assembly thus comprises the first primary plated holes 47 and the second primary plated holes 48. The printed circuit board 40 further comprises a third through-hole assembly including at least one first secondary plated hole 56 extending through the insulating layer 43, and a fourth through-hole assembly including at least one second secondary plated hole 57 extending through the insulating layer 43. In this particular case, the third through-hole assembly includes several first secondary plated holes 56 and the fourth through-hole assembly includes several second secondary plated holes 57.The first secondary plated holes 56 and the second secondary plated holes 57 here all have the same second diameter which, for reasons of space, is smaller than the first diameter of the first primary plated holes 47 and the second primary plated holes 48. The number of first secondary plated holes 56 is equal to the number of second secondary plated holes 57.

[0103] The third traversing set and the fourth traversing set form a set referred to here as the "secondary traversing set".

[0104] The measuring transformer 12 further comprises the magnetic core 13. The magnetic core 13 extends into a thickness of the printed circuit board 40.

[0105] The magnetic core 13 has the shape of a tube with rectangular outer and inner cross-sections. The magnetic core 13 comprises a primary core portion 60 and a secondary core portion 61.

[0106] The first primary metallized holes 47 extend outside the magnetic core 13, near the primary core portion 60. The second primary metallized holes 48 extend inside the magnetic core 13, near the primary core portion 60.

[0107] The primary through-assembly thus forms a portion of a primary winding of the measuring transformer 12, said primary winding here comprising a single turn.

[0108] The first secondary metallized holes 56 extend inside the magnetic core 13, near the secondary core portion 61. The second secondary metallized holes 57 extend outside the magnetic core 13, near the secondary core portion 61.

[0109] We can see that the first secondary plated holes 56 and the second secondary plated holes 57 are connected to each other by conductive elements 65 (for example, but not necessarily, tracks) which extend over the first conductive layer 41 and the second conductive layer 42. Only two conductive elements 65 are shown on the figure 7 .

[0110] The third through-assembly thus forms a first portion of the secondary winding of the measuring transformer 12. The fourth through-assembly thus forms a second portion of the secondary winding of the measuring transformer 12. The secondary through-assembly therefore forms a portion of the secondary winding of the measuring transformer 12.

[0111] The secondary winding comprises a plurality of turns connected in series, each turn comprising a first secondary metallized hole 56, a second secondary metallized hole 57 and a conductive element 65.

[0112] As will be understood, the secondary winding of the measuring transformer 12 is the measuring winding 14 mentioned earlier.

[0113] The measuring transformer 12 according to the invention is very advantageous.

[0114] The fluxes produced by the currents flowing in the first primary metallized holes 47 and in the second primary metallized holes 48 are opposite.

[0115] The difference in flux produced by the difference in the number of plated holes generates the resulting flux actually received by the magnetic core 13. It is this resulting flux that is used for measuring the current to be measured Im. The current to be measured Im is precisely the ratio between the number of primary first plated holes 47 and primary second plated holes 48, which makes it possible to produce a precise current divider at very low cost.

[0116] Thus, unlike a "classical" transformer of the prior art, which is designed to carry as much energy as possible through the smallest possible volume and mass, the measuring transformer 12 allows saturation to be achieved with a very weak magnetic field. Under these conditions, the size of the magnetic core 13 can be reduced, especially since the flux in the core is minimized by a demagnetizing flux opposite to that generated by the current to be measured, Im.

[0117] We now describe the manufacture of the printed circuit board 40 and the magnetic core 13 which extends into a thickness of the printed circuit board 40.

[0118] Printed circuit board 40 comprises a first layer of "prepreg" (for "prepreg") and a second layer of "prepreg". The first and second layers of prepreg are not polymerized.

[0119] The magnetic core 13 comprises a mixture of a magnetic powder and a resin which acts as a binder for the magnetic powder.

[0120] Magnetic powder is formed of a crystalline structure, in this case of yttrium and iron garnet (Y3Fe15O12).

[0121] The resin is an epoxy resin.

[0122] The magnetic core 13 is deposited on the first layer of prepreg by screen printing.

[0123] Then, the magnetic core 13 is covered by the second layer of prepreg.

[0124] The printed circuit board 40 is then placed in an oven.

[0125] The printed circuit board 40 is then drilled to create the plated holes that have been described.

[0126] Alternatively, it is possible to manufacture the magnetic core 13 using laser sintering additive manufacturing technology.

[0127] The magnetic powder is deposited on a first layer of prepreg. Then, a laser beam is used to agglomerate the layer of magnetic powder in predefined areas in order to form the magnetic core 13.

[0128] The magnetic core 13 is then covered by the second layer of prepreg.

[0129] Manufacturing the magnetic core 13 by laser sintering appears to be more efficient. Indeed, in the case of screen printing, the mixture of magnetic powder and resin contains as many air gaps as there are magnetic powder particles. These air gaps reduce the performance of the magnetic core 13. In the case of laser sintering, the magnetic powder particles are fused together, thus avoiding the creation of these air gaps.

[0130] Of course, the invention is not limited to the embodiment described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0131] It has been stated that the flow valve current sensor has a digital and an analog section, and that the analog-to-digital converter and the digital-to-analog converter belong to the analog section. Of course, one could consider these components to be digital components, and even argue that they are directly integrated into the FPGA (or into a microcontroller or other digital component), thus belonging to the digital section.

[0132] It has been indicated here that the first conductive layer, comprising the first track, and the second conductive layer, comprising the second track, each extend over opposite faces of the printed circuit board. Of course, the first and second conductive layers could be internal layers of the printed circuit board, separated by one or more insulating layers.

[0133] We have also described through-hole assemblies, each comprising one or more plated-through holes. Here, the plated-through holes pass through a single insulating layer. Of course, the plated-through holes could pass through several insulating layers, or even one or more insulating layers and one or more conductive layers. Separate through-hole assemblies could also pass through separate stacks of layers.

[0134] Of course, the transformer according to the invention can be used in any type of application requiring a transformer: the invention is in no way limited to flow valve current sensors.

Claims

1. A measurement transformer comprising a printed circuit (40) and a magnetic core (13) extending in a thickness of the printed circuit, the magnetic core (13) being in the shape of a tube having inside and outside sections that are rectangular, the printed circuit including an insulating layer (43), a primary through assembly comprising first primary plated through holes (47) and second primary plated through holes (48) extending through the insulating layer (43), the first primary plated through holes (47) extending outside the core in the proximity of the primary core portion (60) and the second primary plated through holes (48) extending inside the core in the proximity of the primary core portion (60), each of the first and second primary plated through holes (47, 48) has a first end connected to a common first track (44) of a first conductive layer (41) of the printed circuit and a second end connected to a common second track (45) of a second conductive layer (42) of the printed circuit, the primary through assembly and the two tracks (42, 44) forming a primary winding having a single turn, the printed circuit further including a secondary through assembly comprising first secondary plated through holes (56) and second secondary plated through holes (57) extending through the insulating layer (43), the secondary through assembly forming a portion of a secondary winding of the measurement transformer, said secondary winding comprising a plurality of turns connected in series, the first secondary plated through holes (56) extending inside the core in the proximity of a secondary core portion and the second secondary plated through holes (57) extending outside the core in the proximity of the secondary core portion (61).

2. A measurement transformer according to claim 1, wherein the first primary plated through holes (47) and the second primary plated through holes (48) form respectively a first branch (51) and a second branch (52) of a current divider bridge (53), the measurement transformer being arranged to measure a current (Im) that is to be measured flowing in the second branch (52) and obtained by dividing a main current (Ip) flowing in the first branch (51).

3. A measurement transformer according to any preceding claim, wherein the magnetic core (13) comprises a magnetic powder.

4. A measurement transformer according to claim 3, the magnetic core comprising a mixture of the magnetic powder and of a resin and being deposited on a layer of the printed circuit by silkscreen printing.

5. A measurement transformer according to claim 3, the magnetic core being made by laser sintering magnetic powder deposited on a layer of the printed circuit (40).

6. A measurement transformer according to one of claims 3 to 5, wherein the magnetic powder comprises yttrium iron garnet.