| 摘要 |
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.
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