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Metal detector with two magnetic field transducers connected in opposing relationship and their sensing directions orthogonal to the magnetic field

  • US 4,990,850 A
  • Filed: 07/17/1987
  • Issued: 02/05/1991
  • Est. Priority Date: 07/17/1987
  • Status: Expired due to Fees
First Claim
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1. Apparatus for detecting the presence of ferromagnetic material in a predetermined detection zone comprising:

  • magnetic field producing means for providing a detection magnetic field extending through said detection zone;

    transducer means including first and second transducers disposed adjacent one another for producing, respectively, a first signal directly related to the magnetic field component in a first sensing direction and a second signal directly related to the magnetic field component in a second sensing direction opposite to said first sensing direction, whereby an increase in magnetic field component in said first sensing direction will increase said first signal and decrease said second signal and whereby said first and second transducers will be exposed to substantially the same environmental conditions;

    signal processing means for providing an output signal related to the difference between said signals, said signal processing means including means for amplifying said first and second signals, said output signal or both;

    means for mounting said transducers so that said sensing directions are substantially orthogonal to the direction of a magnetic field prevailing in the vicinity of said transducers while said magnetic field is in a predetermined rest state, said mounting means including means for mounting said transducers so that said sensing directions are substantially orthogonal to said detection magnetic field in the absence of ferromagnetic material within said detection zone; and

    nuling means for adjusting said output signal to a predetermined null value when there is no ferromagnetic material in said detection zone, whereby a change in said output signal from said null value will indicate the presence of ferromagnetic material in said detection zone, said nulling means including means for adjusting said output signal to substantially a zero value and for adjusting the relative orientation of said transducers and said detection magnetic field.

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