US 4,050,013 A · Magnetic field probe which measures switching current of magnetic element at moment the element switches as measure of external field

Abstract

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.

Claims12

Dependent claims

A method of indicating the intensity of a sensed magnetic field, wherein square hysteresis loop magnetic material is normally subjected to a magnetic field generated by applying an alternating voltage wave across a pair of coils, characterized by:

sensing when each of first and second portions of the magnetic material switches its magnetic state in response to the magnetic field generated by a respectively associated one of the coils;
measuring, with the first portion of the magnetic material and one of said coils, both exterior of a sensed magnetic field, the intensity of which is to be indicated, the value of the current through said one exterior coil when the first portion of magnetic material switches state;
measuring, with the second portion of the magnetic material and the other of said coils, both within the sensed magnetic field, the intensity of which is to be indicated, the value of the current through said other coil at the instant when the second portion of magnetic material switches state, and over a period of time substantially shorter than the cycle time of said alternating voltage wave;
comparing the measured values of current;
and
indicating, in accordance with the difference in the compared values of the current, the intensity of the measured magnetic field.

3 more elements

Apparatus for testing the strength of a magnetic field comprising:

first conductive coil means;
a magnetic material element having substantially a square hysteresis loop and located within the magnetic influence of the first conductive coil and the magnetic field under test;
second conductive coil means located within the magnetic influence of the magnetic material element;
means for applying an alternating signal to the first conductive coil means, said signal being of sufficient intensity to switch the magnetic material element;
means for sensing a voltage generated in the second conductive coil means at the instant at which the magnetic material element switches magnetic state;
means responsive to the sensing means for sampling the alternating signal applied to the first conductive coil means over a period of time substantially shorter than the cycle time of said alternating signal;
and
means for averaging over time a predetermined succession of the sampled portions of the signal applied to the first conductive coil means.

5 more elements

Dependencies are inferred from the claim text.

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

Life of this patent

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

Life of this patent

Abstract

Claims12