Active compensation for ambient, external magnetic fields penetrating closed loop magnetic cores particularly for a fluxgate current sensor

摘要

An apparatus, that is particularly advantageous for compensating for the earth's magnetic field at a fluxgate current sensor. The apparatus and method actively compensate for local anomalies and loop mismatch at local segments distributed around closed loops of ferromagnetic material in order to null out sources of error that arise in the presence of an external magnetic field. External flux nulling circuits null the external magnetic flux at each of a plurality of associated pairs of diagonally opposite segments of coaxial closed loop cores. Each flux nulling circuit has a pair of diagonally opposite segment sensing coils and a pair of diagonally opposite segment cancellation coils. A flux detecting circuit detects the net magnetic flux in associated, diagonally opposite segments. A negative feedback control circuit drives the segment cancellation coils with a current to drive the flux detected by the segment detecting circuit to a minimum.

主权项

1. An apparatus for canceling circumferentially oriented components of an external magnetic field within segments of a pair of coaxial, closed loop cores of magnetic material, the cores having surrounding drive coils connected to an electrical drive circuit that, when operating, drives the cores into simultaneous circumferentially opposite saturation in a periodically alternating sequence, the apparatus comprising:
(a) a plurality of external flux nulling circuits, each flux nulling circuit for nulling the external magnetic flux at an associated pair of diagonally opposite segments of the closed loop cores, each flux nulling circuit comprising
(i) a pair of segment sensing coils, each sensing coil wound around a different one of its associated diagonally opposite segments, the segment sensing coils being serially connected to each other at one end and having their opposite ends as feedback output terminals;(ii) a pair of segment cancellation coils, each cancellation coil wound around a different one of its associated diagonally opposite segments and serially connected to each other at one end and having their opposite ends as input terminals;(iii) a flux detecting circuit connected to the feedback output terminals of the segment sensing coils of its associated segments and having an output representing the magnetic flux in its associated segments; and(iv) a negative feedback control circuit having input terminals connected to the output of the flux detecting circuits and having output terminals connected to the input terminals of associated, diagonally opposite segment cancellation coils, the negative feedback control circuit driving the segment cancellation coils with a current that drives the flux detected by the flux detecting circuit to a minimum value.