Magnetic field probe which measures switching current of magnetic element at moment the element switches as measure of external field

摘要

A probe for sensing the strength of the magnetic field that surrounds a current-carrying conductor has a square-loop magnetic material wrapped about a conductor which is placed in the magnetic field to be sensed. An alternating signal is applied to the conductor, of sufficient intensity to cause successive reversals of the polarity of the magnetic material. A sense winding around the magnetic material issues a switch signal every time the magnetic material reverses polarity. The switch signal is used to sample the alternating drive signal current in order to store the amplitude of the drive signal at the instant at which the magnetic material reverses polarity. The sampled signal amplitude is averaged over a period of time, and the resultant amplitude is a linear function of the strength of the magnetic field. A second conductor, magnetic material and sense winding are arranged in a position remote from the magnetic field in order to sense the effect of the Earth's magnetic field. The averaged output signal resulting from the measurement of the Earth's magnetic field is then subtracted from the averaged output signal derived from the measurement of the magnetic field that surrounds the current-carrying conductor. The difference signal is displayed as an indication of the current-produced magnetic intensity or the magnitude of the electric current which produces it.