WO2018154472A2

WO2018154472A2 - A current sensing device

Info

Publication number: WO2018154472A2
Application number: PCT/IB2018/051091
Authority: WO
Inventors: Cilliers Du Preez
Original assignee: Individual
Current assignee: Individual
Priority date: 2017-02-22
Filing date: 2018-02-22
Publication date: 2018-08-30
Anticipated expiration: 2019-08-22
Also published as: WO2018154472A3; ZA201905672B

Abstract

A current sensing device (100) for sensing a current in a conductor (10) includes at least one PCB (Printed Circuit Board) (102) which provides a coreless coil (11). The coil (110) is split into two opposed arcuate coil arms (110.1, 110.2) and defines a central aperture (112) between the coil arms (110.1, 110.2) to accommodate a conductor (10) in which a current is to be sensed. An on-board electronic amplifier (120) is in electrical connection with the coil (110), the amplifier (120) being configured to amplify an induced current in the coil (110) responsive to the conductor current and to generate a reading output. A clamp mechanism (118) comprising a pair of opposed jaws, wherein the coil arms are provided in respective jaws and the jaws are displaceable between open and closed positions.

Description

A current sensing device

FIELD OF INVENTION

This invention relates broadly to measuring of electricity and specifically to a current sensing device which has a coreless coil.

BACKGROUND OF INVENTION

The Applicant seeks a device to measure current flowing through a conductor in a non-invasive or non-contacting fashion. When current flows through a conductor, it induces a magnetic field around the conductor. This magnetic field is indicative of the current and can be measured to estimate the current, rather than by measuring the current directly. This is the principle employed by current clamps (https://en.wikipedia.org/wiki/Current clamp, accessed on 31 January 2017) which are well-known in the art.

However, conventional current clamps of which the Applicant is aware do have drawbacks. They employ a ferrite core which, in certain applications, is prone to saturation. Also, the presence of the ferrite core in jaws of the current clamp can make the clamp bulky and cumbersome.

The Applicant desires a device which can, among other things, measure current flowing to various lines from a residential, commercial, or industrial distribution box or switchboard. Such switchboards usually have a plurality of lines which are closely spaced or in close proximity to one another. The lines are simple conductors and are connected to various loads, e.g., appliances, lighting, etc. A plurality of current measuring devices could be used - one for each line.

Upon investigating coreless options, the Applicant discovered the Rogowski coil

(https://^'en.vv^/ikipedia.org/wiki/^'Rogowski coil, accessed on 31 January 2017). The Applicant noted that commercially available Rogowski coils are prohibitively expensive.

Accordingly, the Applicant desires a current sensing device which overcomes or alleviates these drawbacks and which may have some of the following advantages: compact, cheap to manufacture, reliable, and accurate at lower currents (in the region of Amps are even lower than 1 A).

SUMMARY OF INVENTION

Accordingly, the invention provides a current sensing device which is operable to sense a current in a conductor, the current sensing device including: at least one PCB (Printed Circuit Board) which provides a coreless coil, wherein: the coil is split into two opposed arcuate coil arms; and the coil defines a central aperture between the coil arms to accommodate a conductor in which a current is to be sensed; an on-board electronic amplifier in electrical connection with the coil, the amplifier being configured to amplify an induced current in the coil responsive to the conductor current and to generate a reading output; a clamp mechanism comprising a pair of opposed jaws, wherein the coil arms are provided in respective jaws and the jaws are displaceable between open and closed positions. The current sensing device may include plural PCBs. There may be two PCBs. The coil arms may be provided on different PCBs. There may be a major PCB, comprising one of the coil arms and the amplifier, and a minor PCB, comprising the other coil arm. The PCBs may be in electrical communication with each other. The current sensing device may include one or more electrical bridges between the PCBs. The bridge may be deformable or flexible, permitting displacement between the jaws while maintaining electrical contact there-between. Instead, the current sensing device may include electrical contacts at one or both jaws, the contacts being open when the jaws are open and closed when the jaws are closed.

In a conventional coil about a core, the coil comprises a plurality of windings or turns. In the coreless coil of the present invention, the coil may be provided by a plurality of tracks on the PCB. The tracks may be on both sides of the PCB. The coil of the present invention may comprise a plurality of radially extending, angularly spaced apart straight tracks on both sides of the PCB. A pair of tracks, comprising one track on each side of the PCB, may approximate a winding or turn of a conventional coil.

The coil may include no conductor returning through the coil, in contrast with a Rogowski coil. Accordingly, although the coil of the present invention may resemble a Rogowski coil in that it is coreless, it may technically not be a Rogowski coil in that it lacks a returning conductor within the coil. Instead, the current sensing apparatus may include a connector returning through the coil, e.g., provided by a multi-layer PCB.

The clamp mechanism may comprise a hinge about which the jaws are hingedly displaceable. The clamp mechanism may comprise a bias to urge the jaws into a position, e.g., the closed position. The clamp mechanism may comprise a clip to clip the jaws in a position, e.g., the closed position. The clamp mechanism may comprise a lever or actuator to permit a user to displace the jaws into a position, e.g., the open position and/or the closed position. The current sensing device may comprise a housing. The housing may be of an insulating material, e.g., plastic. The housing may be provided in two layers which sandwich the PCB there-between. Instead, the housing may completely enclose the PCB. The housing may include a displaceable member to house at least one the displaceable jaws.

The current sensing device may include an electronic output port. The output port may serve to connect the current sensing device to a data logger. The output port may include two pins for connection via a two-wire cable to the data logger. The current sensing device may lack an internal power source. The output port may serve both to receive power and to transmit the reading output. The current sensing device may include an on-board power storage element, e.g., a capacitive power storage element.

Instead, the current sensing device may include an internal power source, e.g., a battery. The current sensing device may include a wireless transmitter to transmit the reading output wirelessly.

The current sensing device may include a microcontroller. The amplifier may be realised by the microcontroller or may be separate from the microcontroller. The PCB may carry other circuitry, e.g., resistors, capacitors, indicator LEDS, supporting tracks, and the like.

The microcontroller may be configured to receive and store power from an external power source and sense the current in the conductor in a first operational cycle. The microcontroller may be operable to transmit the reading output using the stored power in a second operational cycle. The first operational cycle may be immediately followed by the second operational cycle.

The amplifier may be a relatively short distance from the coil, being on the same or part of the same PCB. This may permit reliable and calibrated amplification of the induced current in the coil. In contrast, when a coil is connected to an amplifier by a long or variable-length lead or cable, very low level induced currents (mA or less) may be subject to interference before reaching the amplifier, which would amplify inaccuracies.

The invention extends to a current sensing assembly which includes at least one current sensing device, as defined above, connected or connectable to a data logger. The current sensing assembly may include plural current sensing devices connected to the data logger, operable to measure plural electrical conductors, e.g., plural lines from a switchboard.

A size of the current sensing device may vary according to application. For a residential application, the size may be about 4 cm (length) x 2 cm (height) x 1 cm (width) with the central aperture being about 1 cm (diameter). For more industrial or commercial applications, the current sensing device may be larger, providing a larger central aperture to accommodate a thicker conductor capable of carrying a higher current.

BRIEF DESCRIPTION OF DRAWINGS The invention will now be further described, by way of example, with reference to the accompanying diagrammatic drawings.

In the drawings:

FIG. 1 shows a first schematic view of a PCB, and associated components, which constitute a current sensing device in accordance with the invention;

FIG. 2 shows a second schematic view of the PCB of FIG. 1 ;

FIG. 3 shows a third schematic view of the PCB of FIG. 1 ; FIG. 4 shows a three-dimensional view of a current sensing device, in accordance with the invention, from a front end;

FIG. 5 shows a three-dimensional view of the current sensing apparatus of FIG. 4 from a back end; FIG. 6 shows a three-dimensional view of the current sensing apparatus of FIG. 4 in an open condition; and

FIG. 7 shows a three-dimensional view of the current sensing apparatus of FIG. 4 in a closed condition around a conductor to be measured.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENT

The following description of the invention is provided as an enabling teaching of the invention. Those skilled in the relevant art will recognise that many changes can be made to the embodiment described, while still attaining the beneficial results of the present invention. It will also be apparent that some of the desired benefits of the present invention can be attained by selecting some of the features of the present invention without utilising other features. Accordingly, those skilled in the art will recognise that modifications and adaptations to the present invention are possible and can even be desirable in certain circumstances, and are a part of the present invention. Thus, the following description is provided as illustrative of the principles of the present invention and not a limitation thereof.

FIGS 1 -3 illustrate schematic views of a PCB 102 of a current sensing device 100 in accordance with the invention. In this example, the current sensing device has two PCBs 102, namely a major PCB 102.1 and a minor PCB 102.2. The PCBs 102 are so configured to provide a clamping action (see further below).

The PCBs 102 provide a coreless coil 1 10 which is composed of two semi- annular coil arms 1 10.1 and 1 10.2 which together form a full annulus and define a central aperture 1 12 therein. In FIG. 1 , only vias of the coil 1 10 are illustrated. In FIG. 2, tracks of the coil 1 10 are illustrated. The tracks extend radially between the central aperture 1 12 and a periphery of the coil arms 1 10.1 , 1 10.2. The tracks alternate between a front face of the PCBs 102 (as illustrated in FIGS 1 -3) and a rear face of the PCBs 102 (not illustrated) to create back and forth "windings". An electrical bridge 1 13 (refer to FIG. 3) is provided between the coil arms 1 10.1 , 1 10.2 to link them electrically. The electrical bridge 1 13 is in the form of flexible copper wires.

A hinge 1 14 is provided which permits the minor PCB 102.2 to be hingedly displaced relative to the major PCB 102.1 . The hinge 1 14 may be a simple pin about which the minor PCB 102.2 is displaceable. A level 1 17 is provided by the minor PCB 102.2; the lever 1 17 is merely a spur or protrusion of the PCB material which a user may press towards the major PCB 102.1 to displace the second coil arm 1 10.2 outwardly. The coil arms 1 10.1 , 1 10.2, hinge 1 14, and lever 1 17 form a clamp mechanism 1 18 which is further described in FIG. 4 onwards with reference to the remainder of the current sensing apparatus 100 including a housing. The electrical bridge 1 13 ensures connection of the major and minor PCBs 102.1 , 102.2 even though they are relatively displaceable.

The current sensing device 100 has a microcontroller 120 which functions at least as an on-board electronic amplifier. The current sensing device 100 also includes supporting circuitry 122 such as resistors, capacitors, diodes (e.g., including an indicator LED), and the like, as well as an electronic output port 124 in the form of a simple two-pin spigot connector. The microcontroller 122 is provided on the major PCB 102.1 and the distance and electrical configuration relative to the coil 1 10 is thus fixed and pre-defined. Accordingly, the microcontroller 122 can be specifically calibrated to amplify even small currents induced in the coil 1 10.

FIGS 4-7 illustrate the current sensing apparatus 100 with its housing 150. The housing 150 comprises four housing elements 150.1 -150.4 which together have the same outline as the PCB 102. The PCB 102 is sandwiched inside the housing 150 but its peripheral edge is exposed between the housing elements 150.1 -150.4. The housing 150 comprises two major housing elements 150.1 , 150.2 provided each side of the major PCB 102.1 and two minor housing elements 150.3, 150.4 provided each side of the minor PCB 102.2. The housing 150 also includes a spacer element 151 sandwiched between a component side of the PCB 102 and one side of the housing 150.2, 150.4. The spacer element 151 defines recesses to accommodate raised components (e.g., the microcontroller 120 and other circuitry 122) on the PCB. The housing elements 150.1 , 150.3; 150.2, 150.4 on opposed sides can be identical.

The minor housing elements 150.3, 150.4 define curved projections which, together with the coil arms 1 10.1 , 1 10.2, constitute jaws of the current sensing apparatus 100.

A pair of screws 152, 154 respectively secure the housing components 150.1 - 150.4 together. A first screw 152 fixedly secures the major housing elements 150.1 , 150.2 and the major PCB 102.1 together and a second screw fixedly secures the minor housing elements 150.3, 150.4 and the minor PCB 102.2 together. A third screw 156 forms a component of the hinge 1 14 and hingedly secures major and minor portions together 150.1 -150.4 , so that the minor portions 150.3, 150.4 can hinge about axis 156.1 relative to the major portions 150.1 , 150.2.

The housing 150 defines a clip 160 which can best be seen in FIG. 6. The clip 160 comprises a pair of complemental formations 162, 164 provided at free ends of the respective jaws. A male formation 162 is in the form of an arcuate, elongate projection while a female formation 164 is a matched elongate, arcuate groove. The complemental formations 162, 164 fit together with an interference fit and can be opened or closed with moderate manipulation by hand. A slot 166 cut in one of the jaws imparts sufficient deformabiiity or "give" to the female formation 166 to permit it to accommodate the male formation 162 resiliency.

In use, and with reference to FIGS 6-7, the jaws of the current sensing device

100 can be opened (as indicated by arrows 172) by squeezing the lever 1 17 inwards, e.g., with a thumb and forefinger (as indicated by arrows 170) of a user. A conductor 10 can then be fed into the aperture 1 12 (as indicated by arrow 174) - or, more likely, the jaws can be threaded around a conductor 10 which is fixed to a switchboard. The jaws are closed by squeezing, e.g., again with the thumb and forefinger, the jaws together (as indicated by arrow 176).

A connection cable (not illustrated) is connected, at one end, to the output port 124 and, at the other end, to a data logger (not illustrated). Optionally, plural current sensing devices 100 may be used for measuring current in plural electrical lines. In such case, a separate connection cable is connected to each output port 124 and all of the connection cables are connected to the data logger.

The Applicant believes that the invention as exemplified is advantages in that it provides an accurate, cost effective, and easy to use current sensing apparatus 100, which can function as a current clamp or probe of a current sensing assembly. The current sensing apparatus 100 is relatively accurate, because the amplifier (embodied by the microcontroller 120) is provided on-board and has a fixed, defined relationship relative to at least part of the coil 1 10. Also for this reason, and because the current sensing apparatus 100 has no ferrite core which may saturate, the current sensing apparatus 100 can sense relatively low currents (under 1 A) which make it well-suited for residential switchboards, but can also sense much higher currents (over 100 A) which make it suitable too for commercial/industrial applications. The current sensing apparatus 100 is relatively cheap to manufacture and relatively compact because there is no ferrite core.

Claims

1. A current sensing device which is operable to sense a current in a conductor, the current sensing device including: at least one PCB (Printed Circuit Board) which provides a coreless coil, wherein: the coil is split into two opposed arcuate coil arms; and the coil defines a central aperture between the coil arms to accommodate the conductor in which the current is to be sensed; an on-board electronic amplifier in electrical connection with the coil, the amplifier being configured to amplify an induced current in the coil responsive to the conductor current and to generate a reading output; and a clamp mechanism comprising a pair of opposed jaws, wherein the coil arms are provided in respective jaws and the jaws are displaceable between open and closed positions.

2. The current sensing device as claimed in claim 1 , which includes plural PCBs.

3. The current sensing device as claimed in claim 2, which: includes two PCBs; and the coil arms are provided on different PCBs.

4. The current sensing device as claimed in claim 3, in which there is a major PCB, comprising one of the coil arms and the amplifier, and a minor PCB, comprising the other coil arm.

5. The current sensing device as claimed in any one of claims 2-4, in which the PCBs are in electrical communication with each other and which includes one or more electrical bridges between the PCBs.

6. The current sensing device as claimed in 5, in which the bridge is deformable or flexible, permitting displacement between the jaws while maintaining electrical contact there-between.

5

7. The current sensing device as claimed in any one of claims 1 -6, in which the coil is provided by a plurality of tracks on the at least one PCB.

8. The current sensing device as claimed in 7, in which the tracks are on both sides o of the at least one PCB.

9. The current sensing device as claimed in claim 8, in which the coil comprises a plurality of radially extending, angularly spaced apart straight tracks on both sides of the at least one PCB. 5

10. The current sensing device as claimed in any one of claims 1 -9, in which the coil includes no conductor returning through the coil, in contrast with a Rogowski coil.

11. The current sensing device as claimed in any one of claims 1 -10, in which the0 clamp mechanism comprises a hinge about which the jaws are hingedly displaceable.

12. The current sensing device as claimed in any one of claims 1 -1 1 , in which the clamp mechanism comprises a clip to clip the jaws in a position. 5

13. The current sensing device as claimed in any one of claims 1 -12, in which the clamp mechanism comprises a lever or actuator to permit a user to displace the jaws into a position.

14. The current sensing device as claimed in any one of claims 1 -13, which comprises a housing to house the at least one PCB and in which the housing includes a displaceable member to house at least one of the displaceable jaws.

15. The current sensing device as claimed in any one of claims 1 -14, which includes an electronic output port.

16. The current sensing device as claimed in claim 15, in which: the current sensing device lacks an internal power source; and the output port serves both to receive power and to transmit the reading output.

17. The current sensing device as claimed in any one of claims 1 -16, which includes a microcontroller configured to: receive and store power from an external power source and sense the current in the conductor in a first operational cycle; and transmit the reading output using the stored power in a second operational cycle.

18. The current sensing device as claimed in any one of claims 1 -17, in which the amplifier and the coil are on the same or part of the same PCB.

19. A current sensing assembly which includes at least one current sensing device as claimed in any one of claims 1 -18, connected to a data logger.

20. The current sensing assembly as claimed in claim 19, which includes plural current sensing devices connected to the data logger, operable to measure plural electrical conductors.