Apparatus for detecting presence of metal strand in paper

Details Apparatus for detecting presence of metal strand in paper Apparatus for detecting presence of metal strand in paper

1979-03-30

1984-09-25

Strecker, Gerard R.

Electricity: measuring and testing

Magnetic

Combined

324236, G01N 2772, G01R 3312

Patent

active

044737998

ABSTRACT:
Apparatus for detecting the presence of a metal strand in paper, for example in a document or bank note of which one wishes to check the authenticity, comprises means for moving the paper in front of a detection head comprising a coil a resonance circuit supplied by a high frequency source, the frequency of which is close to the resonance frequency of the circuit. The high frequency voltage is modulated by variation of the current in the resonance circuit when the strand passes the detection head. After filtering and amplification, the demodulated signal is applied to a trigger circuit to obtain a digital signal. Delivery of the digital signal to an output terminal is checked by means of a reading window, the opening of which is controlled by the means for moving the paper. The output of the detection head is also applied to a second trigger for checking maintenance of a continuous component in the signal from the resonance to verify continuity of the coil circuit.

REFERENCES:
patent: 2587631 (1952-03-01), Kuehne
patent: 3319160 (1967-05-01), Wood et al.
patent: 3381217 (1968-04-01), Williamson et al.
patent: 3602643 (1971-08-01), Wright, Jr.
patent: 3966047 (1976-06-01), Steiner
patent: 4013894 (1977-03-01), Foote et al.
patent: 4130792 (1978-12-01), Sullivan

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