High resolution current sensing apparatus

• US 6,348,788 B1
• Filed: 09/28/1999
• Issued: 02/19/2002
• Est. Priority Date: 09/28/1999
• Status: Expired due to Fees

• Current Assignee: Allen-Bradley Company LLC (Rockwell Automation, Inc.)
• Original Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Inventors: Sullivan, Gerard J., Anderson, Robert J., Yao, Jun Jason
• Primary Examiner(s): Nguyen, Vinh P.
• Application Number:
  US09/406,509
• Time in Patent Office: 875 Days
• Field of Search: 324/661, 324/99.R, 324/99.D, 324/98, 324/244, 324/260, 324/259, 324/252, 324/117.R, 324/117.H, 324/684, 324/658, 177/210.C, 340/664, 340/686.1
• US Class Current: 324/99.00R
• 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
• CPC Class Codes: G01R 17/08 in which a force or torque representing the measured value is balanced by a force or torque representing the reference value
• CPC Class Codes: G01R 19/20 using transductors , i.e. a magnetic core transducer the saturation of which is cyclically reversed by an AC source on the secondary side
• CPC Class Codes: G01R 33/0286 comprising microelectromechanical systems [MEMS] MEMS devices in general B81B

Abstract

A current sensor includes a deflectable member disposed in a magnetic field. Nulling or compensating members may be mechanically coupled to the deflectable member. Feedback or readout devices coupled to the structure provide signals indicative of deflection of the deflectable member under the influence of applied current and the magnetic field. Nulling current applied to the nulling members tends to oppose deflection of the deflectable member. The nulling current may be modulated to drive the feedback signal to a desired level and is used as a basis for calculating the current to be measured. The current may be measured directly upon calibration of feedback devices coupled to the deflectable member or to the nulling members. Arrays of sensors may be coupled to common busses for applying measured and nulling currents to sensors of the arrays and for detecting feedback signals.

Claims

1. A current sensor comprising:

a magnetic field source for generating a magnetic field;

a current sensing system including a sensing element and a nulling element, the sensing element disposed in the magnetic field and configured to receive a current to be sensed, the sensing element being deflectable under the influence of the magnetic field and the current, the nulling element being linked to the sensing element and disposed in the magnetic field, the nulling element being configured to receive a nulling current to resist deflection, under the influence of the magnetic field, of the sensing element; and

a feedback element coupled to the current sensing system and configured to produce a signal representative of deflection of the sensing element.

2. The sensor of claim 1, wherein the sensing element and the nulling element are generally parallel beams formed by a micromachining operation.

3. The sensor of claim 1, wherein the feedback element includes a capacitive sensor.

4. The sensor of claim 3, wherein the feedback element includes a pair of capacitors coupled to respective nulling elements.

5. The sensor of claim 1, wherein the nulling element comprises a pair of nulling members disposed on sides of and generally parallel to the sensing element.

6. The sensor of claim 1, wherein the magnetic field source includes a permanent magnet.

7. A current sensor comprising:

a magnetic base for producing a magnetic field;

an insulating layer disposed adjacent to the base;

a micromachined current sensing system disposed within the magnetic field over said insulating layer and configured to receive a current to be measured and to deflect under the influence of the current and the magnetic field; and

a readout device coupled to the sensing system for determining deflection of the sensing system;

wherein the sensing system further includes at least one micromachined sensing member and at least one micromachined compensation member disposed generally parallel to the sensing member, the compensation member being coupled to the sensing member and configured to receive a compensating current to counter deflection of the sensing member.

8. The current sensor of claim 7, wherein the magnetic base includes a permanent magnet.

9. The current sensor of claim 7, wherein the sensing system includes a sensing member having first and second ends and conductive regions at each of the first and second ends for transmitting current to be measured to and from the sensing member.

10. The current sensor of claim 7, including first and second compensation members disposed on first and second sides of the sensing member.

11. The current sensor of claim 10, wherein the readout device includes first and second capacitors coupled to the first and second compensation members, respectively, the capacitors being configured to provide output signals representative of deflection of the sensing member.

12. The current sensor of claim 7, wherein the readout device includes at least one capacitor coupled to the sensing system for providing output signals representative of deflection of the sensing system.

13. A current sensor comprising:

a magnetic field source for producing a magnetic field;

an elongated sensing element disposed within the magnetic field, the sensing element being configured to receive a current to be measured and to deflect from a normal position under the combined influence of the magnetic field and the current;

first and second compensation elements disposed on first and second sides, respectively, of the sensing element and coupled to the sensing element, each compensation element being configured to receive a compensation current and to restrain the sensing element from deflection under the influence of the magnetic field and the compensation current; and

first and second feedback devices coupled to the compensation elements for sensing deflection of the sensing element.

14. The current sensor of claim 13, wherein at least the sensing element and the compensation elements are formed by micromachining.

15. The current sensor of claim 13, wherein the sensing element and the compensation elements are supported at respective ends thereof, and wherein the sensor includes conductive regions for transmitting current to and from the sensing element and the compensation elements.

16. The current sensor of claim 13, wherein the first and second feedback devices each include a capacitive element adapted to produce an output signal indicative of deflection of the sensing element.

17. A current sensor comprising:

a substrate including a magnetic field source and at least one insulating layer;

a device layer disposed over the substrate and forming a deflectable current sensing structure, a readout device, and a link between a portion of the readout device and the sensing structure, the device layer including at least a conductive layer forming conductive paths on the sensing structure and conductive regions on the readout device, and a non-conductive layer forming the link between the readout device and the sensing structure, and

a support layer disposed between the device layer and the substrate, the support layer bounding a cavity between the device layer and the substrate to support the sensing structure and the readout device while allowing deflection of the sensing structure under the influence of a measured current and a magnetic field from the field source;

wherein the sensing structure includes a sensing beam for receiving a current to be measured, and a nulling bema for receiving a nulling current.

18. The current sensor of claim 17, wherein the substrate includes a permanent magnet and an electrical isolation layer overlying the permanent magnet.

19. The current sensor of claim 17, wherein the device layer includes a structural layer disposed adjacent to the conductive layer.

20. The current sensor of claim 19, wherein the structural layer consists essentially of silicon or polysilicon.

21. The current sensor of claim 17, wherein the non-conductive layer consists essentially of silicon dioxide.

22. The current sensor of claim 17, wherein the cavity is contiguous with gaps formed between portions of the device layer, the gaps being configured to vary in width during deflection of the sensing structure.

23. The current sensor of claim 17, wherein the sensing beam is coupled to the sensing beam by a link formed in the non-conductive layer.