×

Metal object locator including frequency shift detector

  • US 4,439,734 A
  • Filed: 06/23/1980
  • Issued: 03/27/1984
  • Est. Priority Date: 06/23/1980
  • Status: Expired due to Term
First Claim
Patent Images

1. A metal detector apparatus, including in combination:

  • a. inducer means effective for producing an extensive electromagnetic field couplable with a metal object;

    b. sense oscillator means having a first frequency determining means effectively coupled with said inducer means whereby a first signal is produced thereby having an instant frequency variably determined in part by the change in reactance of the inducer means wrought by the presence of the metal object;

    c. frequency shift detector means coupled with said sense oscillator means, effective for receiving a said first signal produced therefrom and coupling same through a frequency responsive detector means including a tuned element means which is maintained resonant near a predetermined second frequency value;

    wherefrom an error signal is produced having a first level error signal when said first frequency and said second frequency are about the same, and a different second level error signal which is variously proportional to the magnitude of any variation of the said first frequency relative with the said second frequency as bounded by the difference between the resonant and off resonance responses substantially determined by the effective "Q" factor of the second frequency tuned element means;

    d. frequency control means coupled with said sense oscillator means and said frequency shift detector means and effective in combination with said error signal to continuously retune said first frequency signal determining means to decrease the magnitude of any proportional difference between the said first and second frequency signals shown by the relative increase of any effective difference between the error signal first and second levels;

    e. indicant means coupled with said error signal effective to produce a telltale signal proportional to the instant error signal level; and

    ,f. source of d.c. power coupled at least with said several means comprising the apparatus for the operation thereof.

View all claims
  • 0 Assignments
Timeline View
Assignment View
    ×
    ×