Method and system for detection of the presence, removal, or abs

Details Method and system for detection of the presence, removal, or abs Method and system for detection of the presence, removal, or abs

1981-10-19

1984-11-20

Swann, III, Glen R.

Communications: electrical

Condition responsive indicating system

Specific condition

340539, 340545, G08B 1326

Patent

active

044841833

ABSTRACT:
An oscillator circuit includes electromagnetic feedback which is interrupted by the presence of a metal body within the field of electromagnetic radiation. Thus, when the metal body is present, the circuit does not oscillate. Removal of the metal body causes the circuit to oscillate with a first characteristic, such as a first modulation period of off and on switching of the oscillator. Once the metal body has been absent for a preset time, the oscillation assumes a second characteristic, such as second modulation period of off and on switching. A receiver circuit monitors the oscillations, and a decoder determines which characteristic of the oscillation is present and provides a corresponding output indication. Among other uses, the system can be utilized as a security system to monitor the state of doors and windows.

REFERENCES:
patent: 3706982 (1971-12-01), Gehman
patent: 4095211 (1978-06-01), Shaughnessy
patent: 4101872 (1978-07-01), Pappas
patent: 4257038 (1981-03-01), Rounds et al.

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