Magnetic field detection by differential phase lag

摘要

Magnetic field detection apparatus including means for supplying a periodic excitation signal to a rod of magnetic material having high permeability (whether or not it has hysteresis due to retentivity of the core or eddy currents) and means for sensing the external field wherein the material is situated. When the material has retentive properties and there is an external field being detected the flux lag (or lead) relative to the periodic excitation is longer for one flux direction that the other. The difference in these lags provides an indication of the field to be detected. When the material does not have retentive properties, an external field can still be detected by logic circuitry in an embodiment similar to the last mentioned embodiment.