EP0096568A1
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Metal detection system
Assignee: Deere and Co
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Filing: 1983-06-06
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Granted: —
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Expires: 2003-06-06
Abstract
Abstract A housing 10 is open at both ends for the flow of material therethrough. Extending around the housing are a central primary coil 18 flanked by two secondary coils 20, 22 connected in series opposition. The primary coil is excited with an oscillatory signal which also provides a reference signal to a phase detector which detects a component of the signal across the secondary coils generated when there is conductive metal in the housing. The detected signal is differentiated to provide an indication only when there is moving metal. Conductive straps 12 and 14 are disposed either side of the coils to shield them from moving metal outside the housing.
Inventors
- 👤 Keith Ronald Baker
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-03 09:38
CPC Classifications
G; G01; G01V; G01V3/00; G01V3/08; G01V3/10; G01V3/104; G01V3/105; G01V3/107
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
117 words
A metal detection system for detecting metal in material flowing along a path through a housing (10) and comprising two secondary coils (20, 22) extending around the housing so that the material also flows through the coils, the coils being connected in series opposition, characterised in that the secondary coils (20, 22) are disposed on either side of a primary coil (18) excited with an oscillatory signal and by a phase detector (42) responsive to a reference signal having a fixed phase relative to the exciting signal and the output signal (Vt) of the series- connected secondary coils to provide a detection signal (X(t)), and by a differentiator (46) providing an output signal from the detection signal.
Claim 2
Dependent Claim
117 words
A metal detection system for detecting metal in material flowing along a path through a housing (10) and comprising two secondary coils (20, 22) extending around the housing so that the material also flows through the coils, the coils being connected in series opposition, characterised in that the secondary coils (20, 22) are disposed on either side of a primary coil (18) excited with an oscillatory signal and by a phase detector (42) responsive to a reference signal having a fixed phase relative to the exciting signal and the output signal (Vt) of the series- connected secondary coils to provide a detection signal (X(t)), and by a differentiator (46) providing an output signal from the detection signal.
Claim 3
Dependent Claim
59 words
A system according to claim 1, characterised by two shorting straps (12, 14) also extending around the housing one on either side of the coils (18, 20, 22) so that the material flows in turn through one shorting strap (12), one secondary coil (20), the primary coil (18), the second secondary coil (22) and the second shorting strap (14).
Claim 4
Dependent Claim
28 words
A system according to claim 1 or 2, characterised in that the reference signal is a square-wave signal and the phase detector (42) is a switching synchronous detector.
Claim 5
Dependent Claim
35 words
A system according to claim 1, 2 or 3, characterised by a source (30) of a sine-wave excitation signal and a voltage-to-current converter (36) driving the primary coil (18) in response to this excitation signal.
Claim 6
Dependent Claim
31 words
A system according to claim 4, characterised in that the reference signal is a square-wave signal derived from the excitation signal by a trigger circuit (40) producing a square wave output.
Claim 7
Independent Claim
25 words
A system according to any of claims 1 to 5, characterised by a low-pass filter (44) between the phase detector (42) and the differentiator (46).
Claim 8
Dependent Claim
19 words
A system according to claim 6, characterised in that the low-pass filter (44) is an active seven-pole Chebyshev filter.
Claim 9
Independent Claim
34 words
A system according to any of claims 1 to 7, characterised by a comparator (48) connected to the differentiator (46) to provide an output signal when the differentiator output signal exceeds a predetermined level.
References Cited (Backward Citations)
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