Patent US4099116A successfully refreshed from Google Patents.
US4099116A
Expired / Lapsed
US
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Metal detector with phase related circuit selective discrimination
Assignee: Individual
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Filing: 1977-01-17
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Granted: 1978-07-04
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Expires: 1997-01-17
Abstract
Abstract An improved metal detector circuit with selective discrimination for soil, mineral content or unwanted metal objects is described in which phase related adjustable feedback circuits are utilized to nullify unwanted signals in the receiver detector circuits. A mode switch connects either unwanted metallic object rejection level feedback control or ground mineral rejection controls as desired into the reception coil circuit. By phase relating the transmission and reception coils in a metal detector, all of the mineral content in the soil which produces unwanted signals in the receiver can be nulified so that a practical detector for use in high mineral content areas results.
Inventors
- 👤 Jerry C. Tyndall
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-07 17:42
CPC Classifications
G; G01; G01V; G01V3/00; G01V3/08; G01V3/10; G01V3/104; G01V3/105
Claims Analysis
Total Claims: 25
Claim 1
Independent Claim
307 words
In a metal detector apparatus having inductively coupled and electrically phase and amplitude balanced transmission and reception coils and having a high frequency oscillator connected to said transmission coil and a detector amplifier and high gain and audio amplifiers, respectively, connected in series to one another and to said reception coil for amplifying radiated signals received therein from said transmission coil, the improvement comprising: a plurality of pairs of first variable electrical resistors connected in parallel across the inputs from said high frequency oscillator to said transmission coil to receive signals of opposite phase therefrom; a double pole double throw electrical switch means having its fixed contacts connected to the variable resistance taps of said pairs of first variable electrical resistors and having the movable blade contacts being switchable between at least two positions to selectively connect feedback signals of one or the other phase from two of said fixed contacts to the movable blade contacts of said switch; a second electrical resistance means connected to one of said movable blade contacts of said switch means and to one end input of said reception coil in a series connection; electrical capacitance means connected to the other of said movable blade contacts of said seitch means and to the other end input of said reception coil in an electrical series connection; said pairs of first variable resistances providing, through said switch means for selecting the phase of said feedback selected to be fed to said resistance and capacitance means, respectively, variable electrical feedback input signals of opposite and variable phase and magnitude from said high frequency oscllator to said reception coil for electrically unbalancing said transmission and reception coils by a phase and magnitude amount sufficient to algebraically cancel out unwanted signals of similar but algebraically opposite phase and magnitude which may be received by said reception coil.
Claim 2
Dependent Claim
307 words
In a metal detector apparatus having inductively coupled and electrically phase and amplitude balanced transmission and reception coils and having a high frequency oscillator connected to said transmission coil and a detector amplifier and high gain and audio amplifiers, respectively, connected in series to one another and to said reception coil for amplifying radiated signals received therein from said transmission coil, the improvement comprising: a plurality of pairs of first variable electrical resistors connected in parallel across the inputs from said high frequency oscillator to said transmission coil to receive signals of opposite phase therefrom; a double pole double throw electrical switch means having its fixed contacts connected to the variable resistance taps of said pairs of first variable electrical resistors and having the movable blade contacts being switchable between at least two positions to selectively connect feedback signals of one or the other phase from two of said fixed contacts to the movable blade contacts of said switch; a second electrical resistance means connected to one of said movable blade contacts of said switch means and to one end input of said reception coil in a series connection; electrical capacitance means connected to the other of said movable blade contacts of said seitch means and to the other end input of said reception coil in an electrical series connection; said pairs of first variable resistances providing, through said switch means for selecting the phase of said feedback selected to be fed to said resistance and capacitance means, respectively, variable electrical feedback input signals of opposite and variable phase and magnitude from said high frequency oscllator to said reception coil for electrically unbalancing said transmission and reception coils by a phase and magnitude amount sufficient to algebraically cancel out unwanted signals of similar but algebraically opposite phase and magnitude which may be received by said reception coil.
Claim 3
Dependent Claim
74 words
Apparatus as described in claim 1, wherein: said first variable resistances are switchable in pairs by said switch to be connected to said second resistance means and to said capacitance means individually, said resistance and capacitance means each being connectable to only one of said variable resistances through said switch means; and the effective electrical impedances of said second resistance and capacitance means are selected to present approximately equal AC impedances to incoming signals.
Claim 4
Dependent Claim
104 words
Apparatus as described in claim 2, wherein: pairs of said first variable resistances are individually adjustable to different settings to account for different phases and magnitudes of undesired signals which are to be cancelled out algebraically in said reception coil; and said pairs of first variable resistances are adjusted to electrically cancel unwanted signals from small metal objects or electrically conductive materials generally distributed in the soil, respectively, said switch means being capable of selecting which phase feedback signals and which of said pairs of said first variable resistance is actively connected through said second resistance and capacitance means, respectively, to said reception coil.
Claim 5
Dependent Claim
104 words
Apparatus as described in claim 1, wherein: pairs of said first variable resistances are individually adjustable to different settings to account for different phases and magnitudes of undesired signals which are to be cancelled out algebraically in said reception coil; and said pairs of first variable resistances are adjusted to electrically cancel unwanted signals from small metal objects or electrically conductive materials generally distributed in the soil, respectively, said switch means being capable of selecting which phase feedback signals and which of said pairs of said first variable resistances is actively connected through said second resistance and capacitance means, respectively, to said reception coil.
Claim 6
Dependent Claim
19 words
Apparatus as described in claim 1, wherein: said reception coil in center tapped and grounded at said center tap.
Claim 7
Dependent Claim
19 words
Apparatus as described in claim 2, wherein: said reception coil is center tapped and grounded at said center tap.
Claim 8
Dependent Claim
19 words
Apparatus as described in claim 3, wherein: said reception coil is center tapped and grounded at said center tap.
Claim 9
Dependent Claim
19 words
Apparatus as described in claim 4, wherein: said reception coil is center tapped and grounded at said center tap.
Claim 10
Dependent Claim
16 words
Apparatus as described in claim 1, wherein: said reception coil is end grounded and end tapped.
Claim 11
Dependent Claim
16 words
Apparatus as described in claim 2, wherein: said reception coil is end grounded and end tapped.
Claim 12
Dependent Claim
16 words
Apparatus as described in claim 3, wherein: said reception coil is end grounded and end tapped.
Claim 13
Dependent Claim
16 words
Apparatus as described in claim 4, wherein: said reception coil is end grounded and end tapped.
Claim 14
Dependent Claim
84 words
Apparatus as described in claim 1, and further comprising: an additional pair of variable electrical resistances connected in parallel across the inputs from said oscillator to said transmission coil, the variable tap outputs of said additional resistances being connected through resistance and capacitance means, individually and respectively, to the inputs of said reception coil for establishing preset levels of feed-back to said reception coil for establishing a base level of rejection feedback which is in addition to that provided by said first variable resistance.
Claim 15
Dependent Claim
75 words
Apparatus as described in claim 13, wherein: said first variable resistances are switchable in pairs by said switch to be connected to said second resistance means and to said capacitor means individually, said second resistance and capacitance means each being connectable to only one of said first resistance through said switch means; and the effective electrical impedances of said second resistance and capacitance means are selected to present approximately equal AC impedances to incoming signals.
Claim 16
Dependent Claim
99 words
Apparatus as described in claim 13, wherein: pairs of said first variable resistances are individually adjustable to different settings to account for different phases and magnitudes of undesired signals which are to be cancelled out algebraically in said reception coil; and said pairs of first resistances are adjusted to electrically cancel unwanted signals from small metal objects or electrically conductive material generally distributed in the soil, respectively, said switch means being capable of selecting which phase feedback signals and which of said pairs is actively connected through said second resistance and capacitance means, respectively, to said reception coil, respectively.
Claim 17
Dependent Claim
97 words
Apparatus as described in claim 14, wherein: pairs of said first variable resistances are individually adjustable to different settings to account for different phases and magnitudes of undesired signals which are to be cancelled out algebraically in said reception coil; and said pairs of first resistances are adjusted to electrically cancel unwanted signals from small metal objects or electrically conductive materials generally distributed in the soil, respectively, said switch means being capable of selecting which phase feedback signals and which of said pairs is actively connected through said resistance and capacitance means, respectively, to said reception coil.
Claim 18
Dependent Claim
19 words
Apparatus as described in claim 13, wherein: said reception coil is center tapped and grounded at said center tap.
Claim 19
Dependent Claim
19 words
Apparatus as described in claim 14, wherein: said reception coil is center tapped and grounded at said center tap.
Claim 20
Dependent Claim
19 words
Apparatus as described in claim 15, wherein: said reception coil is center tapped and grounded at said center tap.
Claim 21
Dependent Claim
19 words
Apparatus as described in claim 16, wherein: said reception coil is center tapped and grounded at said center tap.
Claim 22
Dependent Claim
19 words
Apparatus as described in claim 13, wherein: said reception coil is end tapped and grounded at said end tap.
Claim 23
Dependent Claim
19 words
Apparatus as described in claim 14, wherein: said reception coil is end tapped and grounded at said end tap.
Claim 24
Dependent Claim
19 words
Apparatus as described in claim 15, wherein: said reception coil is end tapped and grounded at said end tap.
Claim 25
Dependent Claim
19 words
Apparatus as described in claim 16, wherein: said reception coil is end tapped and grounded at said end tap.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1981-07-03 | 1982-01-02 | 1982-07-04 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1985-07-03 | 1986-01-02 | 1986-07-04 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1989-07-03 | 1990-01-02 | 1990-07-04 | $7700.00 | Window Closed / Lapsed |