Current sensor

• US 20130009655A1
• Filed: 12/07/2011
• Published: 01/10/2013
• Est. Priority Date: 03/01/2011
• Status: Abandoned Application

• Current Assignee: Sendyne Corp. (Sensata Technologies Holding Plc)
• Original Assignee: Sendyne Corp. (Sensata Technologies Holding Plc)
• Inventors: Marten, Victor
• Application Number:
  US13/580,377
• Publication Number:
  US 20130009655A1
• Time in Patent Office: Days
• US Class Current: 324/713
• CPC Class Codes: G01R 1/203 Resistors used for electric measuring, e.g. decade resistors standards, resistors for comparators, series resistors, shunts resistors in general H01C; microwave or radiowave terminations H01P1/26; coupling devices H01R
• CPC Class Codes: G01R 1/30 Structural combination of electric measuring instruments with basic electronic circuits, e.g. with amplifier
• CPC Class Codes: G01R 15/146 Measuring arrangements for current not covered by other subgroups of G01R15/14, e.g. using current dividers, shunts, or measuring a voltage drop if no voltage isolation is involved G01R1/203 or G01R19/0092
• CPC Class Codes: G01R 19/0023 Measuring currents or voltages from sources with high internal resistance by means of measuring circuits with high input impedance, e.g. OP-amplifiers electrostatic instruments G01R5/28; measuring electrostatic potential G01R15/165; measuring electrostatic fields G01R29/12; amplifiers per se H03F
• CPC Class Codes: G01R 19/0092 measuring current only all subgroups of G01R19/00 take precedence
• CPC Class Codes: G01R 29/24 Arrangements for measuring quantities of charge
• CPC Class Codes: G01R 35/005 Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references G01R33/0035, G01R35/002 take precedence

Abstract

An apparatus and method make use of a single shunt and two or more instrumentation amplifiers, switchably measuring voltages at the shunt. This permits current measurement. At times each instrumentation amplifier has its input shorted, which permits zeroing out many sources of offset in the signal path of that amplifier. Dynamic range is several orders of magnitude better than known current measurement approaches, permitting coulometry.

Claims

1. Apparatus for use in measuring current with respect to first and second measurement points, the apparatus comprising:

a first instrumentation amplifier, said instrumentation amplifier having first and second input terminals, a first switch controllably connecting the first input terminal of the first instrumentation amplifier with the second input terminal of the first instrumentation amplifier;

a first impedance means connecting the first and second measurement points to the first and second input terminals of the first instrumentation amplifier;

a second instrumentation amplifier, said instrumentation amplifier having first and second input terminals,

a second switch controllably connecting the first input terminal of the second instrumentation amplifier with the second input terminal of the second instrumentation amplifier; and

a second impedance means connecting the first and second measurement points to the first and second input terminals of the first instrumentation amplifier.

2. The apparatus of claim 1 further comprising a shunt with first and second terminals, the current disposed to pass between said first and second terminals, the shunt having the first and second measurement points disposed therebetween.

3. The apparatus of claim 1 wherein the first impedance means comprises a first resistor connecting the first measurement point with the first input terminal of the first instrumentation amplifier and a second resistor connecting the second measurement point with the second input terminal of the first instrumentation amplifier, and wherein the second impedance means comprises a third resistor connecting the first measurement point with the first input terminal of the second instrumentation amplifier and a fourth resistor connecting the second measurement point with the second input terminal of the second instrumentation amplifier.

4. The apparatus of claim 1 wherein the first impedance means comprises a third switch connecting the first measurement point with the first input terminal of the first instrumentation amplifier and an electrical connection connecting the second measurement point with the second input terminal of the first instrumentation amplifier, and wherein the second impedance means comprises a fourth switch connecting the first measurement point with the first input terminal of the second instrumentation amplifier and an electrical connection connecting the second measurement point with the second input terminal of the second instrumentation amplifier.

5. The apparatus of claim 3 further comprising a control means,

the control means disposed at times to open the first switch and close the second switch, and to zero any offset in the second instrumentation amplifier, while providing current-measurement information from the first instrumentation amplifier to external to the apparatus;

the control means disposed at other times to close the first switch and open the second switch, and to zero any offset in the first instrumentation amplifier, while providing current-measurement information from the second instrumentation amplifier to external to the apparatus.

6. The apparatus of claim 4 further comprising a control means,

the control means disposed at times to close the third switch and open the first switch and open the fourth switch and close the second switch, and to zero any offset in the second instrumentation amplifier, while providing current-measurement information from the first instrumentation amplifier to external to the apparatus;

the control means disposed at other times to open the third switch and close the first switch and close the fourth switch and open the second switch, and to zero any offset in the first instrumentation amplifier, while providing current-measurement information from the second instrumentation amplifier to external to the apparatus.

7. The apparatus of claim 1 further comprising:

a third instrumentation amplifier, said instrumentation amplifier having first and second input terminals,

the first input terminal of the third instrumentation amplifier connected with the first input terminal of the first instrumentation amplifier;

the second input terminal of the third instrumentation amplifier connected with the second input terminal of the first instrumentation amplifier;

a fourth instrumentation amplifier, said instrumentation amplifier having first and second input terminals,

the first input terminal of the fourth instrumentation amplifier connected with the first input terminal of the second instrumentation amplifier;

the second input terminal of the fourth instrumentation amplifier connected with the second input terminal of the second instrumentation amplifier;

each of the first, second, third, and fourth instrumentation amplifiers having a respective radio-frequency interference filter at its respective input, each respective radio-frequency interference filter having a respective time constant;

the respective time constant of the radio-frequency interference filter of the first instrumentation amplifier being at least twice that of the respective time constant of the radio-frequency interference filter of the third instrumentation amplifier;

the respective time constant of the radio-frequency interference filter of the second instrumentation amplifier being at least twice that of the respective time constant of the radio-frequency interference filter of the fourth instrumentation amplifier.

8. The apparatus of claim 7, further characterized in that the respective time constant of the radio-frequency interference filter of the first instrumentation amplifier is at least one hundred thousand times that of the respective time constant of the radio-frequency interference filter of the third instrumentation amplifier, and the respective time constant of the radio-frequency interference filter of the second instrumentation amplifier is at least one hundred thousand times that of the respective time constant of the radio-frequency interference filter of the fourth instrumentation amplifier.

9. The apparatus of claim 4 wherein the shunt, the first and second terminals thereof, and the first and second measurement points thereof, are formed on a printed circuit board, and

wherein first, second, and third respective soldering pads for each of the first, second, third and fourth switches are formed on the printed circuit board, and

wherein the shunt, the first and second terminals thereof, and the first and second measurement points thereof, and the first respective soldering pad for each of the first, second, third, and fourth switches are all fabricated of a single continuous extent of copper cladding.

10. The apparatus of claim 9 wherein the first, second, third and fourth switches are closely grouped together in a small area of the printed circuitry board, adjacent to the shunt.

11. The apparatus of claim 10 wherein an air gap is cut into the printed circuitry board around the first, second, third and fourth switches, whereby the first, second, third and fourth switches tend toward the same temperature.

12. The apparatus of claim 5 wherein zeroing of an offset in a instrumentation amplifier is achieved by applying an analog offset to an output terminal thereof.

13. The apparatus of claim 5 wherein zeroing of an offset in a instrumentation amplifier is achieved by digital computation applied to a digitized output therefrom.

14. The apparatus of claim 6 wherein zeroing of an offset in a instrumentation amplifier is achieved by applying an analog offset to an output terminal thereof.

15. The apparatus of claim 6 wherein zeroing of an offset in a instrumentation amplifier is achieved by digital computation applied to a digitized output therefrom.

16. A current measurement method for use with apparatus comprising a shunt having first and second measurement points, the apparatus having first and second instrumentation amplifiers, each having a respective first input terminal and a respective second input terminal, each of the first and second instrumentation amplifiers having an output indicative of measured voltage, the method comprising the steps of:

for a first interval, connecting the first input terminal of the first instrumentation amplifier to the first measurement point and connecting the second input terminal of the first instrumentation amplifier to the second measurement point;

during the first interval, providing current-measurement information from the first instrumentation amplifier to external to the apparatus;

within the first interval, connecting the first input terminal of the second instrumentation amplifier to the second input terminal of the second instrumentation amplifier, and zeroing any offset in the second instrumentation amplifier;

for a second interval, connecting the first input terminal of the second instrumentation amplifier to the first measurement point and connecting the second input terminal of the second instrumentation amplifier to the second measurement point;

during the second interval, providing current-measurement information from the second instrumentation amplifier to external to the apparatus;

within the second interval, connecting the first input terminal of the first instrumentation amplifier to the second input terminal of the first instrumentation amplifier, and zeroing any offset in the first instrumentation amplifier.

17. The method of claim 16 wherein the first interval and second interval alternate continuously, whereby current-measurement information from one or another of the instrumentation amplifiers is continuously provided to external to the apparatus.

18. The method of claim 16 further comprising a step, carried out within the second interval, of connecting the first input terminal of the first instrumentation amplifier to the first measurement point and connecting the second input terminal of the first instrumentation amplifier to the second measurement point, and comparing current-measurement information from the first instrumentation amplifier with current-measurement information from the second instrumentation amplifier.

19. The method of claim 17, further comprising integrating the current-measurement information over a period of time to measure total charge passing through the shunt during that period of time.

20. The method of claim 17, further comprising acting upon the current-measurement information to open an electronic fuse, ceasing current through the shunt.

21. The method of claim 16 wherein zeroing of an offset in a instrumentation amplifier is achieved by applying an analog offset to an output terminal thereof.

22. The method of claim 16 wherein zeroing of an offset in a instrumentation amplifier is achieved by digital computation applied to a digitized output therefrom.

23. The method of claim 16 further comprising:

within the first interval, disconnecting at least one of the first input terminals of the second instrumentation amplifier from at least one of the first and second measurement points; and

within the second interval, disconnecting at least one of the first input terminals of the first instrumentation amplifier from at least one of the first and second measurement points.