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A metal detector for detecting and distinguishing between ferrous and non-ferrous objects in an area which may contain a ferrous, mineralized soil background is disclosed. The hysteresis effect is used to distinguish between ferrous and non-ferrous objects by generating groups of transmit current pu

A metal detector for detecting and distinguishing between ferrous and non-ferrous objects in an area which may contain a ferrous, mineralized soil background is disclosed. The hysteresis effect is used to distinguish between ferrous and non-ferrous objects by generating groups of transmit current pulses, each group including a polarizing pulse of one polarity followed by a pair of read pulses of the opposite polarity and less magnitude. The transmit pulses are applied to a transmit coil to induce corresponding receive voltage pulses in a receive coil. A pair of receive pulses corresponding to the read transmit pulses are fed through a low pass filter and thereafter sampled to produce a sample output signal corresponding to the difference between the sampled voltage levels of the pair of receive pulses. Control means are provided to adjust the sampling times such that when the metal detector is placed over an area containing a ferrous, mineralized soil background and no metallic objects, the sample output signal will be a constant D.C. voltage. This eliminates the effect of mineralized soil, which otherwise tends to prevent the detection of metallic objects. Thereafter, as the metal detector is moved around and used to search for metallic objects, it will indicate the presence of a ferrous object by a first polarity sample output signal and will indicate the presence of a non-ferrous object by an opposite polarity sample output signal. Demodulator means, such as a balanced synchronous demodulator, is provided to generate detector outputs corresponding to the ferrous or non-ferrous sample output signals and to nullify the effect of relative motion between the metal detector and the objects being detected.

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