Method and apparatus for measuring a DC current in a wire without making a direct connection to the wire
First Claim
1. An apparatus for measuring a DC current flowing through a wire comprising:
- a pair of semi-circular sensors made of a hard magnetic material;
clamp means for removeably positioning the sensors into a split ring about the wire;
means for generating a magnetic field about the sensors which interacts with the magnetic field emanating from the wire so that a magnetic flux is induced in the sensors having a magnitude proportional to the amplitude of the DC current flowing through the wire, the generating means including a pair of first coils longitudinally wound about corresponding ones of the sensors and means for applying a transient signal to the first coils; and
means for simultaneously measuring the magnetic flux induced in both of the sensors after the sensors are removed from around the wire to thereby provide an indication of the amplitude of the DC current flowing through the wire, the measuring means including a pair of second coils circumferentially wound about corresponding ones of the sensors.
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Abstract
A pair of semi-circular, hard magnetic sensors are rigidly fixed within separate blocks which are in turn removably received in corresponding housings mounted to the jaws of a spring biased clamp. The clamp is adapted for positioning the sensors into a split ring around a wire carrying the DC current to be measured. According to a first embodiment of the method, longitudinally wound coils about each of the sensors are momentarily energized by an AC current source connected thereto through a variable transformer, while the sensors are around the wire. Thereafter the sensors are removed from the clamp and placed side by side beneath a compass so that the magnetic flux previously induced in the sensors deflects the compass needle from North. Circumferentially wound coils about each of the sensors are connected to a DC current source which is varied to move the compass needle back to North by cancelling the magnetic flux previously induced in the sensors. The amount of current required to move the compass needle back to North provides an indication of the amplitude of the DC current flowing through the wire about which the sensors were clamped. In a second embodiment of the method, after the sensors have been removed from around the wire, a ballistic galvanometer is connected to the circumferential coils about the sensors. The longitudinal coils about the sensors are energized to cause the magnetic flux previously induced in the sensors to be cancelled. The change in magnetic flux measured by the ballistic galvanometer provides an indication of the amount of DC current flowing through the wire.
114 Citations
13 Claims
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1. An apparatus for measuring a DC current flowing through a wire comprising:
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a pair of semi-circular sensors made of a hard magnetic material; clamp means for removeably positioning the sensors into a split ring about the wire; means for generating a magnetic field about the sensors which interacts with the magnetic field emanating from the wire so that a magnetic flux is induced in the sensors having a magnitude proportional to the amplitude of the DC current flowing through the wire, the generating means including a pair of first coils longitudinally wound about corresponding ones of the sensors and means for applying a transient signal to the first coils; and means for simultaneously measuring the magnetic flux induced in both of the sensors after the sensors are removed from around the wire to thereby provide an indication of the amplitude of the DC current flowing through the wire, the measuring means including a pair of second coils circumferentially wound about corresponding ones of the sensors. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method of measuring a DC current flowing through a wire comprising the steps of:
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positioning a pair of semi-circular sensors made of a hard magnetic material into a split ring about the wire, the sensors each having a coil wound longitudinally therearound; applying a transient signal to the longitudinal coils for generating a magnetic field about the sensors which interacts with the magnetic field emanating from the wire so that the magnetic flux is induced in the sensors having a magnitude proportional to the amplitude of the DC current flowing through the wire; and removing the sensors from around the wire and simultaneously measuring the magnetic flux previously induced in both of the sensors to provide an indication of the amplitude of the DC current flowing through the wire. - View Dependent Claims (11, 12, 13)
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Specification