Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Frequency of cyclic current or voltage
Patent
1975-04-29
1977-03-15
Corcoran, Robert J.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Frequency of cyclic current or voltage
340258C, G01R 3312
Patent
active
040126900
ABSTRACT:
A portable support structure is provided with coils mounted therein in spaced parallel relationship to each other. One of the coils is connected to an oscillator and serves as a transmitting coil. The other coils are receiving coils. A detector is connected to the receiving coils. Means are provided for introducing a fixed bias voltage in the receiving coils and for introducing a substantial phase change between the voltage in the transmitting coil and the voltage in the receiving coils so that no usefully shaped ferrous or non-ferrous metal target above a pre-determined size could move through the station without disturbing the voltage and phase angle induced in the receiving coils and thus deceive the station operator. The coils are shielded so that ferrous or non-ferrous metal objects moving outside the station near the coils do not affect the voltage in the receiving coils and provide a spurious indication of a target moving through the station. The phase difference between the voltage in the transmitting coil and the voltage in the receiving coils can be adjusted to maximize the sensitivity of the station to a pre-determined metal or metal alloy.
REFERENCES:
patent: 2237254 (1941-04-01), Broekhuysen
patent: 2513745 (1950-07-01), Reynolds
patent: 2549567 (1951-04-01), Berman
patent: 2609530 (1952-09-01), Tricebock et al.
patent: 2753520 (1956-07-01), Doll
patent: 2869074 (1959-01-01), Clapp
patent: 2888026 (1959-05-01), Henderson et al.
patent: 2958037 (1960-10-01), Riede et al.
patent: 3665298 (1972-05-01), Geiger
Luck et al.; The Prison Gun Detector; Radio World; Dec. 1936; pp. 50-56.
Brockheysen; A Practical Metal Detector; Electronics; Apr. 1938; pp. 17-19.
Industrial Metal Detectors; ASEA Journal; 1954; pp. 55-64.
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