Ferrous target identification system with magnetic field polarity and gradient indication

A target identification system for a gradiometer for detecting a desired ferrous object concealed beneath a surface, said system comprising:

• (a) a first sensor for detecting a magnetic field at a first point above the surface;
• (b) a second sensor for detecting said magnetic field at a second point above the surface, said second point located above said first point;
• (c) means for providing drive signals for the sensors, connected the first and second sensors, to generate sensor output signals proportional to the magnetic fields sensed by the sensors;
• (d) circuit means connected to the first and second sensors and including means for generating a difference signal at an output thereof, said difference signal being the difference between the output signals of the sensors and being proportional to the detected gradient of the magnetic field between said first point and said second point, the circuit means also generating a polarity signal indicative of the magnetic field polarity at the first sensor;
• and
• (e) interface means for producing an indication signal when both said polarity signal has a selected value, indicative that said magnetic field has a selected polarity and when said difference signal has a magnitude that exceeds a set value, indicative that the magnitude of the detected magnetic field gradient exceeds a set value, the interface means being connected to the circuit means.