Metal object locator including frequency shift detector
First Claim
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.
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Abstract
A frequency shift responsive metal detector having a sense oscillator coupled with an inducer loop. When the inducer nears a metal object, the effective inductance is changed which correspondingly shifts the natural frequency of the sense oscillator. The sense oscillator couples with a frequency shift detector. The detector produces a d.c. feedback signal which is proportional to the sense oscillator shift and acts therewith to re-establish the oscillator to it'"'"'s original natural frequency by way of a voltage controlled reactance. The detector also produces a d.c. output that serves to drive an audio frequency rate voltage controlled oscillator wherein the pitch, or resultant frequency therefrom produced is proportional to the effect of the metal object on the inducer loop. A d.c. signal from the detector also serves to drive a visual indicator, such as a meter. The change in the loop inductance may be either positive or negative, resulting in a unique indication distinction between diamagnetic materials, and those which are ferromagnetic or paramagnetic. The use of a dual channel, stereo-like apparatus also provides the operator with directivity, which may be coupled with an enhancement gate signal which alternates the stereo-response back and forth between the earphones of a stereo-headset, thereby improving operator acuity.
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Citations
18 Claims
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1. A metal detector apparatus, including in combination:
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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 Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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Specification