Magnetic code reader with adjustable thresholds
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United States of America Patent
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Oct 19, 1993
Grant Date -
N/A
app pub date -
Oct 17, 1991
filing date -
Sep 22, 1989
priority date (Note) -
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status (Latency Note)
Importance
Abstract
A reader for a coded discontinuous security thread in a security document comprises a multiplicity of reading channels each coupled to at least one magnetic transducing means (11, 40) for sensing along a track across the document and including processing circuits for forming a channel signal which exhibits signal excursions in response to the passage of the ends of each length of magnetic material. First and second comparators (55, 56) compare the channel signal with relatively positive and relatively negative thresholds respectively and a bistable switching means (59) is coupled to the comparators to provide a digital signal. A reference comparator (64) controls an analog switch and diode pumps (70, 71) to adjust the thresholds in accordance with the amplitude of a signal excursion.
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