US3697972A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Metal detection and alarm systems
Assignee: Individual
•
Filing: 1970-06-22
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Granted: 1972-10-10
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Expires: 1990-06-22
Abstract
Abstract A metal detection alarm system detects the presence of an article of a particular metal in a given region by measuring the disturbance of two oscillating electromagnetic fields, one oscillating at from 5 to 20 kHz., the other at from 16 Hz. to 5 kHz., and also of the disturbance of a magnetic field established by D.C. pulses produced at a rate of 0 to 16 pulses per second. Receivers tuned to respond to the electromagnetic and magnetic fields established in the region produce a different response when a metal is present, the change in responses depending upon different parameters of the metal article. The outputs from the receivers are compared with the transmitted signals or in a logic circuit with standard signals and if at least two of the receiver outputs indicate the presence of the particular metal, an alarm is actuated. Applied to revolving doors, apparatus to prevent a person carrying a firearm into a bank or other building, or from entering an aircraft, is obtained. The system can also be used in conjunction with conventional non-revolving doors or with windows. A temperature controller utilizing the change of resistance with temperature of a thermistor is also described. The thermistor is located in the base circuit of a transistor which, in turn, is in a control circuit which determines the length of pulses applied to the gates of two thyristors or silicon controlled rectifiers. The time of switching the thyristors or S.C.R.s and length of pulse controls the supply of power to a heater.
Inventors
- 👤 Yull Brown
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 13:30
CPC Classifications
G; G08; G08B; G08B13/00; G08B13/22; G08B13/24; G01; G01V; G01V3/00; G01V3/08; G01V3/10; G01V3/104; G01V3/105
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
243 words
A metal detection and alarm system comprising a region through or over which a person carrying a metallic object must pass; a first and second oscillator coupled, respectively, to a first and second transmitting coil, each said coil being adapted to produce signals within said region; a first and second receiving coil each responsive to signals within said region and coupled to a first and second receiver, respectively; said first oscillator being adapted to produce a low audio-frequency signal, said second oscillator being adapted to produce a high audiofrequency signal, said first and second receivers being tuned to the frequency of the signals of said first and second oscillators, respectively; a pulse generator adapted to supply D.C. pulses to a magnetic field producing coil to produce a magnetic field within said region, and a third receiving coil coupled to a magnetic flux detector; each of said receivers and said magnetic flux detector being adapted to produce an output signal to be either fed into a logic circuit capable of comparing each said output signal with a respective reference signal or used to actuate a switching device; said logic circuit producing a signal when there is a departure of at least two of said output signals from their respective reference signals or said switching devices providing an output signal on actuation of at least two of said switching devices, said signal from said logic circuit or said switching devices causing actuation of an alarm.
Claim 2
Dependent Claim
243 words
A metal detection and alarm system comprising a region through or over which a person carrying a metallic object must pass; a first and second oscillator coupled, respectively, to a first and second transmitting coil, each said coil being adapted to produce signals within said region; a first and second receiving coil each responsive to signals within said region and coupled to a first and second receiver, respectively; said first oscillator being adapted to produce a low audio-frequency signal, said second oscillator being adapted to produce a high audiofrequency signal, said first and second receivers being tuned to the frequency of the signals of said first and second oscillators, respectively; a pulse generator adapted to supply D.C. pulses to a magnetic field producing coil to produce a magnetic field within said region, and a third receiving coil coupled to a magnetic flux detector; each of said receivers and said magnetic flux detector being adapted to produce an output signal to be either fed into a logic circuit capable of comparing each said output signal with a respective reference signal or used to actuate a switching device; said logic circuit producing a signal when there is a departure of at least two of said output signals from their respective reference signals or said switching devices providing an output signal on actuation of at least two of said switching devices, said signal from said logic circuit or said switching devices causing actuation of an alarm.
Claim 3
Dependent Claim
52 words
A system as claimed in claim 1, in which said low audio-frequency is a frequency in the range 16 Hz. to 5,000 Hz., said high audio-frequency is in the range 5,000 Hz. to 20,000 Hz., and said D.C. pulses are generated at a rate of from one to 16 pulses per second.
Claim 4
Dependent Claim
48 words
A system as claimed in claim 2, in which said third receiving coil is disconnected from said magnetic flux detector while one of said D.C. pulses is applied to said magnetic field producing coil and is re-connected to said magnetic flux detector on the termination of the pulse.
Claim 5
Dependent Claim
14 words
A system as claimed in claim 3, in which said region comprises a doorway.
Claim 6
Dependent Claim
65 words
A system as claimed in claim 4 in which said doorway comprises an entrance including a revolving door having transparent, bullet-proof panels, said revolving door being located between curved side walls, actuation of said alarm being effective to lock said revolving door in a position where a person carrying said metallic object is trapped between two of said panels and one of said side walls.
Claim 7
Dependent Claim
66 words
A system as claimed in claim 5, in which said revolving door can rotate in a single direction and the side wall alongside which a person must pass on leaving through side doorway is terminated short of its normal termination point to enable a person locked in the opposite quadrant to a person trapped on actuation of said alarm to leave the proximity of said doorway.
Claim 8
Dependent Claim
53 words
A system as claimed in claim 5 in which said side walls each extend around more than one quarter the circumference of the area swept out by said revolving door and each contain a small door therein which is openable when a person is trapped in the quadrant including said other side wall.
Claim 9
Dependent Claim
48 words
A system as claimed in claim 6, in which the side wall alongside which a Person entering through said doorway must pass has therein a small openable region through which a person trapped by actuation of said alarm can pass the metal object which has actuated said alarm.
Claim 10
Dependent Claim
38 words
A system as claimed in claim 7, in which said side walls each have a small openable region through which a person trapped by actuation of said alarm can pass the metal object which has actuated the alarm.
Claim 11
Dependent Claim
18 words
A system as claimed in claim 5, in which said revolving door and said side walls are non-metallic.
Claim 12
Dependent Claim
42 words
A system as claimed in claim 5, in which at least one of said coils is formed in a vertical plane and has one side located in the center of a spindle upon which the panels of said revolving door are mounted.
Claim 13
Dependent Claim
29 words
A system as claimed in claim 1 in which said coils, said oscillators, said pulse generator and said magnetic flux detector are all located within a constant temperature enclosure.
Claim 14
Dependent Claim
83 words
A system as claimed in claim 1, in which said region includes a first revolving door located in a first passageway, a second revolving door being located adjacent said first revolving door in or at the end of a second passageway, said second revolving door being normally locked, actuation of said alarm causing said first revolving door to be locked and said second revolving door to be unlocked so that a person carrying said metal object is forced to enter said second passageway.
Claim 15
Dependent Claim
29 words
A system as claimed in claim 1, in which said metallic object comprises an object made of high carbon content steel of the type of which firearms are made.
References Cited (Backward Citations)
US3582931A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-10-10 | 1976-04-10 | 1976-10-10 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-10-10 | 1980-04-10 | 1980-10-10 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-10-10 | 1984-04-10 | 1984-10-10 | $7700.00 | Window Closed / Lapsed |