Current-shunt system for known conductors
First Claim
1. Apparatus for measuring the magnitude of at least one of a DC current and an AC current flowing through a single conductor having a known one of a plurality of known, but different, characteristics, said single conductor being located within an insulative sheath, comprising:
- means, comprising a pair of conductive contacts, for directly contacting the single conductor through said insulative sheath, at two points along the axial length thereof;
means for maintaining the contacting means at a fixed separation therebetween, to define a single conductor resistance providing, at said contacting means, a single voltage of magnitude directly proportional to the magnitude of current flowing through said single conductor;
amplifier means directly connected to said contacting means for actively buffering the voltage provided at said contacting means; and
means receiving only the buffered output voltage of said buffering means for providing a user-viewable display of the magnitude of the voltage;
said buffering means being the only portion of said apparatus connected to said contacting means, and multiplying the voltage at said contacting means by a scale factor selected to cause said display means to display a value numerically equal to the magnitude of current then flowing through said conductor, and including;
an operational amplifier having a non-inverting input connected to a first one of said contacts, an inverting input and an output; and
a first resistance element of known magnitude having a first terminal connected to the inverting input and a second terminal connected to the remaining contact; and
means for setting the scale factor to one of a like plurality of values, each selected to properly scale the voltage developed responsive to the known characteristics of the associated conductor, and including;
a plurality of feedback resistance elements equal in number to the number of the plurality of different conductor characteristics to be accommodated, each feedback resistance element having a first terminal connected in parallel to one of said operational amplifier output and inverting input, and a second terminal; and
switching means for connecting to the remaining one of said operational amplifier output and inverting input, the second terminal of that feedback resistance associated with the characteristics of the conductor being utilized.
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Accused Products
Abstract
A system for measuring currents flowing through a conductor uses the current-carrying conductor itself as the measurement shunt. The voltage developed across the inherent resistance of a fixed length of current-carrying conductor is measured and scaled to provide a displayable voltage of magnitude equal to the magnitude of current flowing in the conductor. Compensation for conductor temperature rise can be utilized, as can a multimeter accommodating various conductor materials and/or sizes.
32 Citations
14 Claims
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1. Apparatus for measuring the magnitude of at least one of a DC current and an AC current flowing through a single conductor having a known one of a plurality of known, but different, characteristics, said single conductor being located within an insulative sheath, comprising:
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means, comprising a pair of conductive contacts, for directly contacting the single conductor through said insulative sheath, at two points along the axial length thereof; means for maintaining the contacting means at a fixed separation therebetween, to define a single conductor resistance providing, at said contacting means, a single voltage of magnitude directly proportional to the magnitude of current flowing through said single conductor; amplifier means directly connected to said contacting means for actively buffering the voltage provided at said contacting means; and means receiving only the buffered output voltage of said buffering means for providing a user-viewable display of the magnitude of the voltage; said buffering means being the only portion of said apparatus connected to said contacting means, and multiplying the voltage at said contacting means by a scale factor selected to cause said display means to display a value numerically equal to the magnitude of current then flowing through said conductor, and including;
an operational amplifier having a non-inverting input connected to a first one of said contacts, an inverting input and an output; and
a first resistance element of known magnitude having a first terminal connected to the inverting input and a second terminal connected to the remaining contact; and
means for setting the scale factor to one of a like plurality of values, each selected to properly scale the voltage developed responsive to the known characteristics of the associated conductor, and including;
a plurality of feedback resistance elements equal in number to the number of the plurality of different conductor characteristics to be accommodated, each feedback resistance element having a first terminal connected in parallel to one of said operational amplifier output and inverting input, and a second terminal; and
switching means for connecting to the remaining one of said operational amplifier output and inverting input, the second terminal of that feedback resistance associated with the characteristics of the conductor being utilized. - View Dependent Claims (2, 3, 4, 5)
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6. Apparatus for measuring the magnitude of a current, having at least one of a DC component and an AC component, flowing through a single conductor of known characteristics and enclosed within an insulative sheath, comprising:
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means for directly contacting only the single conductor through said insulative sheath at two points along the axial length thereof; means for maintaining the contacting means at a fixed separation therebetween, to define a single conductor resistance providing, at said contacting means, a single voltage of magnitude directly proportional to the magnitude of current flowing only through the single conductor; means directly connected, as the only directly connected circuitry, to said contacting means for actively buffering the single voltage provided at said contacting means; means receiving the buffered output voltage of said buffering means for providing a user-viewable display of the magnitude of the voltage; and means for compensating the voltage provided to said display means for changes induced therein responsive to the temperature of said conductor, and comprising;
an inverting amplifier having an input receiving the output of said buffering means, and an output; and
a feedback network positioned to sense the temperature of said conductor and connected to said inverting amplifier to temperature-compensate the voltage output therefrom responsive to conductor temperature changes. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14)
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Specification