Method and apparatus for measuring a DC current in a wire without making a direct connection to the wire

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.

Dependencies are inferred from the claim text.