Current sensor
First Claim
Patent Images
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 second instrumentation amplifier,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.
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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.
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Citations
22 Claims
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1. Apparatus for use in measuring current with respect to first and second measurement points, the apparatus comprising:
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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 second instrumentation amplifier, 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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. 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:
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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 equipment 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 equipment 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, wherein the apparatus further comprises third and fourth instrumentation amplifiers, each having a respective first input terminal and a respective second input terminal, each of the third and fourth instrumentation amplifiers having an output indicative of measured voltage, the method further characterized in that; for the first interval, connecting the first input terminal of the third instrumentation amplifier to the first measurement point and connecting the second input terminal of the third instrumentation amplifier to the second measurement point; during the first interval, providing current-measurement information from the third instrumentation amplifier to equipment external to the apparatus; within the first interval, connecting the first input terminal of the fourth instrumentation amplifier to the second input terminal of the fourth instrumentation amplifier, and zeroing any offset in the fourth instrumentation amplifier; for a second interval, connecting the first input terminal of the fourth instrumentation amplifier to the first measurement point and connecting the second input terminal of the fourth instrumentation amplifier to the second measurement point; during the second interval, providing current-measurement information from the fourth instrumentation amplifier to equipment external to the apparatus; within the second interval, connecting the first input terminal of the third instrumentation amplifier to the second input terminal of the third instrumentation amplifier, and zeroing any offset in the third instrumentation amplifier. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22)
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Specification