Fluxgate current transducer

Abstract

Fluxgate current transducer (1) comprising a fluxgate head (2) and a primary conductor arrangement (5), the fluxgate head comprising a soft magnetic core (14) surrounding a central passage (20, 20a) and an excitation coil (16) wound around the soft magnetic core. The fluxgate transducer further comprises a flat substrate extending through the central passage between a first connection edge (10) and second connection edge (11), and the primary conductor arrangement comprises a plurality of primary conductor layers formed on or in said flat substrate, each primary conductor layer separated from an adjacent primary conductor layer by an insulating layer.

Description

[0001] FLUXGATE CURRENT TRANSDUCER

[0002] The present invention relates to a fluxgate current transducer, in particular for mounting on a circuit board.

[0003] It is known to provide fluxgate transducers that are configured for mounting on a circuit board of an electronic circuit, the fluxgate transducer adapted for measuring a leakage current in a single phase or multiphase primary conductor arrangement extending through a central passage of the fluxgate transducer. The magnetic fields generated by the primary conductors should cancel each other unless there is a residual current resulting from leakage or short circuit of a least one of the phase currents. Fluxgate transducers are well-known and comprise a soft magnetic core surrounded by an excitation coil, the core configured to saturate alternatingly when an alternative excitation current is fed through the excitation coil. An external magnetic field affects the alternating saturation and thus the behaviour of the excitation which may be measured to determine the magnitude of the external magnetic field. In the case of a residual current transducer, in case of leakage of at least one of the phases, the magnetic field of the primary conductor arrangement is non-zero and corresponds to the amplitude of the leakage current.

[0004] In certain conventional fluxgate transducers T, as illustrated in figure 4, the primary conductors 5’ are in the form of wires that pass through a circular passage 20’ of an annular transducer. The annular magnetic core has a certain height and the pin solder connections of the primary conductors to the circuit board 10T in conjunction with the height of the annular magnetic core results in a component exceeding the height of other electronic components, whereby it is desirable to reduce the height of the electronic components of circuit board in view of space requirements in various electronic applications. Moreover, the diameter and position of wires of the primary conductor arrangement, means that the primary conductors are positioned relative to the fluxgate transducer at different distances that leads to a resultant magnetic field which is not entirely cancelled. One of the consequences of the electric field distribution of the wire conductors is the need to have an electrical shielding layer between the fluxgate transducer and the primary conductors to reduce the effects of dipolar fields generated by each wire. Such shielding also generates additional costs. Such conventional residual current transducers are also costly to produce and to assemble to a circuit board that requires manual intervention in view of the difficulty of assembling pin connections from the primary conductor arrangement that have slight imprecisions in their positioning relative to the corresponding connections holes in the circuit board. In view of the foregoing, it is an object of this invention to provide a fluxgate current transducer that is compact, accurate and cost effective to produce and install.

[0005] It is advantageous to provide a fluxgate transducer for mounting on a circuit board of external electronics system that has a low height.

[0006] It is advantageous to provide a fluxgate transducer for residual current measurement mounting on a circuit board of electronics system that may be assembled in an automated manner with conventional assembly machines for electronic component assembly.

[0007] It is advantageous to provide a fluxgate transducer for residual current measurement that is robust and reliable and accurate.

[0008] It is advantageous to provide a fluxgate current transducer that is lightweight.

[0009] In certain applications it is advantageous to provide a fluxgate current transducer that may be easily installed and connected on a circuit board of an external electronic system.

[0010] In certain applications it is advantageous to provide a fluxgate current transducer that is well adapted for measurement of residual currents.

[0011] In certain applications it is advantageous to provide a fluxgate current transducer that is well adapted for measurement of residual currents of a multi-phase conductor arrangement.

[0012] Objects of this invention have been achieved by providing a system according to claim 1. Dependent claims set forth various advantageous features of embodiments of the invention.

[0013] Disclosed herein is a fluxgate current transducer comprising a fluxgate head and a primary conductor arrangement, the fluxgate head comprising a soft magnetic core surrounding a central passage in the form of an elongate slot and an excitation coil wound around the soft magnetic core.

[0014] The fluxgate transducer further comprises a flat substrate extending through the central passage between a first connection edge and second connection edge, and the primary conductor arrangement comprises a plurality of overlapping primary conductor layers formed on or in said flat substrate, each primary conductor layer separated from an adjacent primary conductor layer by an insulating layer. In an advantageous embodiment, the primary conductor arrangement comprises first connection terminals along the first connection edge of the substrate and second connection terminals along the second connection edge of the substrate, the first connection edge arranged outside of the central passage on one side of the fluxgate head and the second connection edge formed outside the centre passage on a second axial side of the fluxgate head.

[0015] In an advantageous embodiment, the substrate is in the form of a circuit board, the primary conductor layers being formed on different layers within the circuit board.

[0016] In an advantageous embodiment, the first connection end terminals comprise conductive pads arranged along and in a spaced apart manner from adjacent connection terminals, the conductive pads configured for surface mount solder connection to conductive tracks of an external circuit board.

[0017] In an advantageous embodiment, the soft magnetic core of the fluxgate head is mounted within a core receiving cavity of a coil support housing, the excitation coil being wound around the coil support housing.

[0018] In an advantageous embodiment, the fluxgate head is mounted within a housing, the housing provided with a central passage through which the substrate in which the primary conductor arrangement is formed is inserted.

[0019] In an advantageous embodiment, the primary conductor layers of the primary conductor arrangement each comprise a centre portion interconnecting the first and second connection terminals wherein the centre portions of the plurality of the stacked primary conductor layers fully overlap each other.

[0020] In an advantageous embodiment, the primary conductor layers each comprise slots extending from lateral edges, the lateral edges extending in the axial direction of the central passage.

[0021] In an advantageous embodiment, the first and second connection end terminals of each primary conductor layer are arranged in a diametrically opposed manner, symmetrically about a centre line extending in the axial direction of the central passage. Also disclosed herein is an electronic system comprising a fluxgate current transducer according to any preceding embodiment and a system circuit board having conductive tracks, the system circuit board further comprising a fluxgate head receiving cut-out in which a portion of the fluxgate head is inserted.

[0022] Further objects and advantageous features of the invention will be apparent from the claims, from the detailed description, and annexed drawings, in which:

[0023] Figure 1a is a perspective schematic view of a fluxgate current transducer according to an embodiment of the invention;

[0024] Figure 1 b is a perspective exploded view of the embodiment of figure 1a;

[0025] Figure 2a is a perspective view of an embodiment of a current transducer according to the invention about to be assembled to a circuit board of an external electronic system;

[0026] Figure 2b is a view of the current transducer assembled and connected on the circuit board of external electronic system;

[0027] Figure 3 is a schematic perspective exploded view of layers of a primary conductor arrangement, in particular of a 3 phase plus neutral primary conductor arrangement, of a fluxgate transducer according to an embodiment of the invention;

[0028] Figure 4a is a top view of a fluxgate transducer for residual current measurement according to the prior art;

[0029] Figure 4b is side view of the transducer of figure 4a.

[0030] Referring to the figures 1a to 3, a fluxgate transducer 1 according to an embodiment of the invention comprises a fluxgate head 2 and a circuit board 4 including a primary conductor arrangement 5.

[0031] The fluxgate head 2 comprises a saturable soft magnetic core 14 surrounded by an excitation coil 16. The soft magnetic core 14 may be optionally be supported and mounted in a coil support housing 18 having a core receiving cavity 19 for lodging the soft magnetic core therein. The excitation coil 16 may be wound around the coil support housing 18 lodging the soft magnetic core. The excitation coil and optional coil support housing 18 may be lodged within a housing 3. In the illustrated embodiment, the housing comprises a base 3a having a cavity receiving the fluxgate head 2 therein, and a cover 3b closing the fluxgate head 2 within the housing. The skilled person will understand that the housing 3 may have different configurations whereby instead of a base and cover being separately assembled parts, the fluxgate head could also be overmolded with an insulating material, for instance a plastic overmolding.

[0032] Although in an embodiment the fluxgate head 2 is provided with a coil support housing 18 with a cavity 19 in which the soft magnetic core 14 is mounted, it is also possible in a variant to have the excitation coil wound directly around the soft magnetic core without providing the coil support housing. In such case, the conductor forming the excitation coil 16 may be provided with an insulating layer that provides sufficient electrical separation and protection for direct wire winding around the soft magnetic core. Other variants are possible in which a foil of insulating material is wrapped around the soft magnetic core prior to winding of the excitation coil.

[0033] In an embodiment of the invention, the fluxgate transducer 1 is configured for an open loop operation, however in variants it is possible to further provide a compensation coil wound around the soft magnetic core 14 for closed loop operation of the fluxgate transducer.

[0034] In a variant it is also possible to have a separate test coil wound around the soft magnetic core in an addition to the excitation coil for injecting a test current signal as perse known in the field of fluxgate transducers.

[0035] The fluxgate head 2 has a central passage 20 which allows a primary conductor to extend through the central passage. The cross-sectional surface area of the central passage for extension of a primary conductor arrangement therethrough may be defined by the housing 3 which is provided with the central passage 20a within the central passage 20 of the fluxgate head.

[0036] The primary conductor arrangement 5 comprises a plurality of primary conductor layers 6 including a primary conductor layer for at least one electrical phase. In the case of a single phase electrical system, there is a second primary conductor layer that constitutes the return or neutral conductor. In the case of a multiphase electrical system with a multiphase primary conductor arrangement, the primary conductor layers include one primary conductor layer for each phase and optionally a further primary conductor layer for the neutral phase. It may be noted that in a multiphase system it is not mandatory to have the neutral phase in the primary conductor arrangement that extends through the central passage of the fluxgate transducer in order to measure a residual current since the sum of the currents in a multiphase system should be zero in absence of any leakage or other forms of residual current. It is nevertheless preferable to include the neutral conductor as one of the primary conductor layers extending through the central passage of the fluxgate head 2.

[0037] According to an aspect of the invention, the primary conductor arrangement 5 is formed on a circuit board 4 that extends through the central passage 20 of the fluxgate head 2, from a first surface mount connection edge 10 to a second surface mount connection edge 11. The first surface mount connection edge 10 is positioned outside of the central passage on one side of the fluxgate head and the second surface mount connection edge 11 is positioned outside of the central passage of the fluxgate head on an opposite side of the fluxgate head, a central portion of the primary conductor arrangement being positioned within the central passage 20 of the fluxgate head and thereby surrounded by the soft magnetic core 18 and excitation coil 16.

[0038] Each primary conductor layer comprises a conductive track, typically a metallized conductive track, separated from adjacent primary conductor layer or layers by an insulating layer. The primary conductor layers 6a, 6b, 6c, 6d may be formed on different layers in the circuit board as conductive tracks in a perse known method of producing circuit boards with different layers in which conductive tracks are separated by insulating layers. In variants however, the conductive layers may be separated by insulating layers that are assembled in a stacked relationship as separately formed conductive and insulating foils, or by assembling and stacking insulating foils with metal tracks deposited, or by various other perse known methods for forming stacked insulating and conductive layers, without departing from the scope of this invention. In these manufacturing variants, the reference to the term “circuit board” is not intended to be limited specifically to printed circuit board technology but to any other of the aforementioned variants for producing substantially flat substrates with a stacked layered primary conductor arrangement that may then be connected to an external circuit board of an electronic system.

[0039] Each primary conductor layer comprises a first connection end pad 7, a centre portion 9 and a second connection end pad 8. The centre portion 9 interconnects the first connection end pad to the second end connection end pad, the first connection end pad 7 positioned at the first surface mount connection edge 10 of the circuit board 4 and the second connection end pad 8 being positioned at the second surface mount connection edge 11 . The first and second connection end pads 7, 8 are configured for surface mount direct connection to corresponding conductive pads or tracks on an external circuit board 101 , these conductive tracks being shown in figures 2a and 2b as conductive tracks 102. The fluxgate current transducer is thus configured for surface mount connection to an external circuit board 101 in a conventional surface mount connection manner perse known to the skilled person.

[0040] It may however be noted that in variants the first and second connection end pads may have various configurations that allow for instance pluggable connection to a pluggable connector with receptacle contacts that spring bias against the respective connection end pads, whether at the first end, or the second end, or at both ends. For instance, one end of the fluxgate transducer may be soldered to a circuit board or flexible circuit with conductive tracks, and the other end of the transducer may be configured for plugging connection to a pluggable receptacle connector. In other variants, both of the first and second connection edges 10, 11 may be configured for pluggable connection to complementary connectors.

[0041] The primary conductor layers 6a, 6b, 6c, 6d overlap each other fully in their centre portions 9, or at least partially in the centre portions 9, such that the magnetic fields generated by each of the primary conductor layers 6a, 6b, 6c, 6d are closely aligned and cancel each other out without the adverse effect of spatial distribution due to the physical size of the primary conductors (such as found in a conventional system with primary conductors formed by wires). The overlapping relationship of the primary conductor layers also avoids the need for shielding because the electrical fields generated by the primary conductors are also effectively cancelled with very little uneven spatial distribution effect.

[0042] The primary conductor layers may advantageously comprise slots 22 extending into the primary conductor transverse to the outer edges of the conductor layer that extend in the axial direction of the central passage 20. The slots 22 allow the primary conductor layer to have a large surface area that is useful for spreading the heat generated by the primary phase current flowing through the primary conductor layer, while at the same time directing the flow of the primary current. The slots ensure that the primary current of the respective phases goes through the centre portion 9 configured to optimize the overlap and cancellation of the magnetic generated by each of the primary conductor phases.

[0043] The first connection end pads 7 and second connection end pads 8 of each of the primary conductor layers are preferably arranged in a diametrically opposed manner, The connection end pads of different layers 6a, 6b, 6c, 6d are offset such that the positions of the first connection end pads 7 and second connection end pads 8 are distributed along the respective first surface mount connection edge 10 and second surface mount connection edge 11 of the circuit board.

[0044] In order to have connection pads configured for surface mount coupling on one side or on both sides of the circuit board 4, conductive vias through layers of the circuit board are provided between the primary conductor layer connection end pads and the connection end pads configured for external connection. Such conductive vias may be provided in a per se known manner for interconnecting conductive layers in a stacked arrangement in circuit boards.

[0045] The primary conductor arrangement may advantageously be provided in the circuit board 4 which may be inserted through the centre passage 20, 20a in the axial direction of the central passage, thus allowing for easy assembly of the fluxgate transducer. The fluxgate head 2 and housing 3 may also being assembled in said axial direction. Moreover, with the primary conductor arrangement 5 being formed on a circuit board 4, a very flat primary conductor arrangement which can be inserted in a low height centre passage 20, 20a leads to a fluxgate transducer that has a low thickness which is particularly advantageous for integration in and on a circuit board of an external electronic system 100.

[0046] The external electronic system may have a circuit board 101 with conductive tracks 102 for connection to the first and second connection end pads 7, 8 of the primary conductor arrangement 5. The external circuit board 101 may advantageously have a fluxgate head receiving cut-out 103 through which a portion of the fluxgate head 2 is inserted such that the overall height of the fluxgate transducer is reduced to a minimum.

[0047] The excitation coil 16 and any other coils such as a test or compensation coils may further be connected by various means to coil connection pads formed on the circuit board 4 which may also have connection pads configured for surface mount connection to the complementary conductive pads or tracks 112 on the system circuit board 101 . List of references used

[0048] Fluxgate current transducer 1

[0049] Fluxgate head 2

[0050] Soft magnetic core 14

[0051] Excitation coil 16

[0052] Test or compensation coil

[0053] Coil support housing 18

[0054] Core receiving cavity 19

[0055] Central passage 20

[0056] Housing 3

[0057] Base 3a

[0058] Cover 3b

[0059] Circuit board 4

[0060] Primary conductor arrangement 5

[0061] Primary conductor layers 6, 6a, 6b, 6c, 6d

[0062] First Connection end pads 7

[0063] Second connection end pad 8

[0064] Centre portion 9

[0065] Slots 22

[0066] First surface mount connection edge 10

[0067] Second surface mount connection edge 11

[0068] Electronic system 100

[0069] System circuit board 101

[0070] Conductive tracks 102

[0071] Fluxgate head receiving cut-out 103

[0072] Secondary conductor connection pads 112

Claims

Claims1 . Fluxgate current transducer (1) comprising a fluxgate head (2) and a primary conductor arrangement (5), the fluxgate head comprising a soft magnetic core (14) surrounding a central passage (20, 20a) in the form of an elongate slot, and an excitation coil (16) wound around the soft magnetic core, characterized in that the fluxgate transducer further comprises a flat substrate extending through the central passage between a first connection edge (10) and second connection edge (11), and the primary conductor arrangement comprises a plurality of overlapping primary conductor layers formed on or in said flat substrate, each primary conductor layer separated from an adjacent primary conductor layer by an insulating layer.

2. Fluxgate current transducer according to claim 1 wherein the primary conductor arrangement comprises first connection terminals (7) along the first connection edge (10) of the substrate and second connection terminals (8) along the second connection edge (11) of the substrate, the first connection edge arranged outside of the central passage (20) on one side of the fluxgate head (2) and the second connection edge formed outside the centre passage on a second axial side of the fluxgate head.

3. Fluxgate current transducer of any preceding claim wherein the substrate is in the form of a circuit board (4), the primary conductor layers being formed on different layers within the circuit board.

4. Fluxgate current transducer according to any preceding claim wherein the first connection end terminals (7) comprise conductive pads arranged along and in a spaced apart manner from adjacent connection terminals, the conductive pads configured for surface mount solder connection to conductive tracks of an external circuit board (101).

5. Fluxgate current transducer according to any preceding claim wherein the soft magnetic core (14) of the fluxgate head is mounted within a core receiving cavity (19) of a coil support housing (18), the excitation coil (16) being wound around the coil support housing (18).

6. Fluxgate current transducer according to any preceding claim wherein the fluxgate head is mounted within a housing (3), the housing (3) provided with a central passage (20a) through which the substrate in which the primary conductor arrangement is formed is inserted.

7. Fluxgate current transducer according to any preceding claim wherein the primary conductor layers of the primary conductor arrangement (5) each comprise a centre portion (9)interconnecting the first and second connection terminals wherein the centre portions of the plurality of the stacked primary conductor layers fully overlap each other.

8. Fluxgate current transducer according to any preceding claim wherein the primary conductor layers each comprise slots (22) extending from lateral edges, the lateral edges extending in the axial direction of the central passage.

9. Fluxgate current transducer according to any preceding claim wherein the first and second connection end terminals of each primary conductor layer are arranged in a diametrically opposed manner, symmetrically about a centre line extending in the axial direction of the central passage.

10. An electronic system (100) comprising a fluxgate current transducer according to any preceding claim and a system circuit board (101) having conductive tracks (102), the system circuit board further comprising a fluxgate head receiving cut-out (103) in which a portion of the fluxgate head (2) is inserted.

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