Current sensor

• US 6,414,475 B1
• Filed: 11/06/2000
• Issued: 07/02/2002
• Est. Priority Date: 08/06/1999
• Status: Expired due to Term

• Current Assignee: Sentec Ltd. (Xylem, Inc.)
• Original Assignee: Sentec Ltd. (Xylem, Inc.)
• Inventors: Colby, Edward Crellier, Dames, Andrew Nicholas
• Primary Examiner(s): Le, N.
• Assistant Examiner(s): Deb, Anjan K.
• Application Number:
  US09/706,959
• Time in Patent Office: 603 Days
• Field of Search: 324/127, 324/200, 324/142, 324/141, 336/181, 333/12, 307/89, 307/90, 307/91
• US Class Current: 324/127
• CPC Class Codes: G01R 15/18 using inductive devices, e.g. transformers
• CPC Class Codes: G01R 15/185 with compensation or feedback windings or interacting coils, e.g. 0-flux sensors using galvano-magnetic field sensors G01R15/20; conversion of DC into AC using transductors G01R19/20

Abstract

A fiscal electricity meter is described for measuring the energy supplied to a load. The load current flows through the primary winding of a transformer and induces an EMF indicative of the current flowing in the secondary winding. The secondary winding comprises a sense coil, arranged to couple more strongly to the primary, and a cancellation coil which have equal and opposite turns area products so as to provide a null response to extraneous magnetic fields. The coils are arranged so that their magnetic axis are co-located and aligned together so that they also provide a null response to extraneous magnetic fields having a field gradient.

Claims

1. A transducer for use in a current sensor, the transducer comprising:

a first sense coil having an axis about which one or more turns of conductor are formed and having an effective magnetic centre which lies on the axis and which is defined by the configuration of the turns; and

a second sense coil having an axis about which one or more turns of conductor are formed and having an effective magnetic centre which lies on the axis and which is defined by the configuration of the turns;

wherein the first and second sense coils are arranged so that they are substantially co-located.

2. A transducer according to claim 1, wherein the first and second sense coils lie in planes that are substantially parallel.

3. A transducer according to claim 1, wherein the first and second sense coils are located in a substantially common plane.

4. A transducer according to claim 1, wherein the first sense coil has a different area to that of the second sense coil.

5. A transducer according to claim 4, wherein each turn of the second sense coil encloses each turn of the first sense coil.

6. A transducer according to claim 1, wherein the first sense coil has a turns area product which is substantially equal to that of the second sense coil.

7. A transducer according to claim 1, wherein the first sense coil comprises a plurality of turns.

8. A transducer according to claim 7, wherein the turns of said first sense coil are located substantially in a common plane.

9. A transducer according to claim 1, wherein the second sense coil comprises a plurality of turns.

10. A transducer according to claim 9, wherein the turns of said second sense coil are located substantially in a common plane.

11. A transducer according to claim 1, wherein said first and second coils have substantially equal turns area products.

12. A transducer according to claim 1 wherein the first and second sense coils are formed on a common PCB.

13. A transducer according to claim 1, wherein the first and second sense coils are connected in series and arranged so that a signal induced in the first sense coil and the second sense coil by a common electromagnetic field oppose each other.

14. A transducer according to claim 1, further comprising processing means for processing signals induced in the first and second sense coils.

15. A transducer according to claim 14, wherein the processing means comprises means for subtracting a signal output from the second sense coil from a signal output from the first sense coil.

16. A transducer according to claim 14, wherein said processing means comprises an integrator for integrating the signals from the first and second sense coils.

17. A transducer according to claim 14, wherein said processing means and the first and second coils are mounted on a common circuit board.

18. A current sensor comprising a transducer according to claim 1.

19. A method of sensing current characterised by the step of using the transducer or the current sensor of claim 1.

21. A current sensor comprising:

an inlet for receiving current from an electricity supply;

an outlet for outputting the current to a load;

a conductor connected between the inlet and the outlet for providing a current path through the current sensor for the current; and

a transducer according to claim 1, mounted adjacent said conductor so that the conductor magnetically couples to the first sense coil more strongly than to the second sense coil, to provide a measure of the current.

22. A current sensor according to claim 21, wherein the conductor has a loop portion located in proximity to the first sense coil.

23. A current sensor according to claim 22, wherein:

the loop portion of the conductor lies substantially in a plane;

the primary conductor comprises a slot which extends over a plane substantially parallel to the plane of the loop portion; and

the transducer is located in said slot so that the axes of the sense coils are substantially orthogonal to the plane of the loop portion.

24. A current sensor according to claim 21, wherein the conductor comprises a coil with one or more turns.

25. A current sensor according to claim 21, wherein the conductor is detachably mountable to the current sensor.

26. A current sensor according to claim 21, further comprising a ferrite component for providing a closed magnetic path around the conductor, the first sense coil and the second sense coil.

27. A current sensor according to claim 21, further comprising:

at least one further inlet for receiving a further current from a further electricity supply;

at least one further outlet for outputting the at least one further current to at least one further load;

at least one further conductor provided between the at least one further inlet and the at least one further outlet for providing at least one further current path through the current sensor for the at least one further current, wherein the at least one further conductor is arranged to magnetically couple to the first sense coil more strongly than to the second sense coil to provide a measure of the at least one further current.

28. A current sensor according to claim 27, wherein said at least one further conductor comprises a loop portion located in proximity to the first sense coil.

29. A current sensor according to claim 28 comprising one further conductor for providing a return path for current flowing between the inlet and outlet.

30. An electricity meter comprising a current sensor according to claim 21, further comprising:

means for providing a measure of the voltage of the electricity supply; and

means for determining and outputting an indication of an electrical characteristic of the load in dependence upon the current measure and the voltage measure.

32. An electricity meter according to claim 30, wherein the determining means is operable to determine the power being used by the load by multiplying the current measure with the voltage measure.

33. An electricity meter according to claim 30, wherein the determining means is operable to determine the energy consumed by the load by integrating, with respect to time, the power used by the load.

34. An electricity meter according to claim 30, wherein the determining means comprises a phase shift network for altering, by a predetermined amount, the relative phase between the current measure and the voltage measure.

35. An electricity meter according to claim 30, wherein the determining means is operable to output an indication of the cumulative energy consumed by the load.

36. An electricity meter according to claim 35, wherein the determining means is operable to output said cumulative energy consumed by the load on a display.

37. A method of sensing current characterised by the step of using the current sensor of claim 21.

20. A transducer for use in a current sensor, the transducer comprising:

a first sense coil having an axis about which one or more turns of conductor are formed and having an effective magnetic centre which lies on the axis and which is defined by the configuration of the turns; and

a second sense coil having an axis about which one or more turns of conductor are formed and having an effective magnetic centre which lies on the axis and which is defined by the configuration of the turns;

wherein the first and second sense coils are arranged so that their effective magnetic centres are substantially co-axial.

31. An electricity meter according to claim 31, wherein the providing means is operable to measure the instantaneous voltage of the electricity supply.

38. A transducer for sensing the magnetic field associated with a current flowing in a conductor in an electricity meter, the transducer comprising:

a first sense coil having one or more turns of conductor which define an effective magnetic centre of the coil; and

a second sense coil having one or more turns of conductor which define an effective magnetic centre of the second sensing coil;

wherein the first and second sense coils are arranged so that their effective magnetic centres are substantially co-located.

39. A method of sensing current characterised by the step of using the transducer of claim 38.

40. A current sensor component for sensing and for outputting a measure of a current flowing in a conductor, the current sensor component comprising:

a first sense coil having an axis about which one or more turns are formed; and

a second sense coil having an axis about which one or more turns is formed;

wherein the first and second sense coils are arranged so that their axes are substantially co-linear.

41. A method of sensing current characterised by the step of using the current sensor component of claim 40.

42. A current sensor for sensing and for outputting a measure of a current flowing in a conductor, the current sensor comprising:

a first sensing coil having a plurality of turns of conductor located in a substantially common plane and having a magnetic centre defined by the configuration of the turns of conductor;

a second sensing coil having at least one conductive turn located substantially in the same plane as the conductive turns of the first sensing coil and having a magnetic centre defined by the configuration of the at least one conductive turn;

wherein the first and second sensing coil portions (i) have substantially equal turns area products, (ii) are arranged so that their effective magnetic centres are substantially co-located; and

(iii) are arranged to be magnetically coupled to said conductor with different magnetic coupling coefficients; and

means for subtracting an EMF induced in the outer sensing coil from an EMF induced in the inner sensing coil to provide said measure.

43. A current sensor according to claim 42, wherein the turns of said first sensing coil are smaller than those of the second sensing coil and lie within the turns of the second sensing coil so that their turns do not overlap.

44. A method of sensing current characterised by the step of using the current sensor of claim 42.

45. An electricity meter comprising:

an inlet for receiving supply current from an electricity supply;

an outlet for outputting the supply current to a load;

a primary conductor connected between the inlet and the outlet for providing a current path for the supply current through the meter;

a current sensor for sensing and for outputting a measure of the supply current flowing through the primary conductor;

means for providing a measure of the voltage of the electricity supply; and

means for determining and outputting an indication of energy consumed by the load in dependence upon the current measure and the voltage measure;

characterised in that said current sensor comprises a sensing coil having;

(a) an inner sensing coil portion having a plurality of conductive turns located in substantially the same plane and having a magnetic centre defined by the configuration of the conductive turns; and

(b) an outer sensing coil portion having at least one conductive turn located substantially in the same plane as the conductive turns of the inner sensing coil portion and having a magnetic centre defined by the configuration of the at least one conductive turn;

wherein the inner and outer sensing coil portions have substantially equal turns area products, are connected in series and are arranged so that (i) EMFs induced in the inner and outer sensing coil portions by a common background alternating magnetic field oppose each other; and

so that (ii) their effective magnetic centres are substantially co-located;

wherein said primary conductor has a loop portion which is located adjacent one of said inner and outer sensing coil portions and which lies in a plane substantially parallel to the plane in which the sensing coil portions lie; and

wherein the arrangement of the primary conductor and said sensing coil is such that in response to a current flowing in the primary conductor, a signal is induced in said sensing coil which varies in dependence upon the current flowing in the primary conductor.

46. An electricity meter according to claim 45, wherein said loop portion of said primary conductor defines a magnetic centre of the primary conductor, and wherein the arrangement of the primary conductor and said sensing coil is such that the line connecting the magnetic centre of said primary conductor to the magnetic centre of said sensing coil is substantially normal to the plane of said primary conductor.

47. An electricity meter comprising:

an inlet for receiving supply current from an electricity supply;

an outlet for outputting the supply current to a load;

a primary conductor connected between the inlet and the outlet for providing a current path for the supply current through the meter;

a current sensor for sensing and for outputting a measure of the supply current flowing through the primary conductor;

means for providing a measure of the voltage of the electricity supply; and

means for determining and outputting an indication of energy consumed by the load in dependence upon the current measure and the voltage measure;

characterised in that said current sensor comprises;

a first sensing coil having a plurality of conductive turns which define an effective magnetic centre of the first coil;

a second sensing coil having at least one conductive turn which defines an effective magnetic centre of the second sensing coil; and

wherein the first and second sensing coils are arranged to have substantially the same turns area product and arranged so that their effective magnetic centres are substantially co-located.

48. A current sensor comprising:

a magnetic field generator for receiving a current to be sensed and for generating in response thereto a corresponding local magnetic field; and

a sensor configured for sensing the local magnetic field generated by said magnetic field generator and for outputting an output signal that is indicative of the current to be sensed, the sensor comprising

(a) a sensor winding having one or more turns of conductor which define an effective magnetic centre of the sensor winding, for sensing magnetic fields and for generating a sensed signal which varies with the sensed magnetic field, and

(b) a compensation winding having one or more turns of conductor which define an effective magnetic centre of the compensation winding, for sensing magnetic fields and for generating a compensation signal which varies with the sensed magnetic field; and

a circuit configured for determining a difference between the compensation signal and the sensed signal to provide a difference signal, and for generating said output signal in dependence upon the determined difference signal;

wherein the sensor winding and the compensation winding are arranged relatively to said magnetic field generator so that when said magnetic field generator generates a magnetic field in response to a current to be sensed, said sensor winding and said compensation winding are non-ferromagnetically coupled to said magnetic field generator.

49. A current sensor comprising:

a magnetic field generator for receiving a current to be sensed and for generating in response thereto a corresponding local magnetic field; and

a sensor configured for sensing the local magnetic field generated by said magnetic field generator and for outputting an output signal that is indicative of the current to be sensed, the sensor comprising

(a) a sensor winding having one or more turns of conductor which define an effective magnetic centre of the sensor winding, for sensing magnetic fields and for generating a sensed signal which varies with the sensed magnetic field, and

(b) a compensation winding having one or more turns of conductor which define an effective magnetic centre of the compensation winding, for sensing magnetic fields and for generating a compensation signal which varies with the sensed magnetic field; and

circuitry for determining a difference between the compensation signal and the sensed signal to provide a difference signal, and for generating said output signal in dependence upon the determined difference signal;

wherein the sensor winding and the compensation winding are arranged so that they are formed as conductive tracks on a common printed circuit board.

50. A current sensor according to claim 49 in which the tracks enclose an air core through the printed circuit board.

51. An electricity meter comprising a current sensor according to claim 50, further comprising:

a first circuit configured for providing a measure of a voltage of an electricity supply providing the current to be sensed by said current sensor; and

a second circuit configured for determining and outputting an indication of an electrical characteristic of a load to which the sensed current is delivered in dependence upon the current measure and the voltage measure.

52. An electricity meter according to claim 51, wherein said current sensor, said first circuit and said second circuit are implemented on a common printed circuit board.