Method and apparatus for detecting a fluorescent area on a sheet

Details Method and apparatus for detecting a fluorescent area on a sheet Method and apparatus for detecting a fluorescent area on a sheet

1979-04-17

1981-06-23

Smith, Alfred E.

Radiant energy

Coded record and readers; invisible radiant energy type

250252, 250461R, G06K 710, G01N 2138

Patent

active

042752990

ABSTRACT:
Method for the detection, on a sheet of paper, of an area which becomes fluorescent when it is exposed to ultraviolet radiation, in which the paper sheet passing in front of a detector is illuminated by means of a source of ultraviolet light modulated by a frequency of between 1 and 10 KHz. The modulated fluorescent radiation is detected, amplified and demodulated by means of an amplification circuit and a demodulation circuit providing a first signal. The intensity of the ultraviolet source is measured by a photo-electric member associated with a detection and demodulation circuit supplying a second signal. This second signal is used to regulate the level of operation of at least one trigger which operates to provide an output, corresponding to the fluorescent radiation, when the level of the first signal supplied to the trigger is at at least the trigger operating level.

REFERENCES:
patent: 3444517 (1969-05-01), Rabinow
patent: 3614430 (1971-10-01), Berler
patent: 3736428 (1973-05-01), Monroe
patent: 3751667 (1973-08-01), Quittner
patent: 3854050 (1975-12-01), Peterson et al.
patent: 3918812 (1975-11-01), Holm
patent: 3935922 (1976-02-01), Cooper et al.
patent: 4158778 (1979-06-01), Gard et al.

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