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Optical Mark Sensing

IP.com Disclosure Number: IPCOM000098386D
Original Publication Date: 1960-Sep-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Johnson, JR: AUTHOR

Abstract

When small neon bulbs are used as the light source in a reflected light mark detecting system, the variations in light output due to aging and drift of the neon may be as great as the difference in reflection between the record card and a mark on the card. This condition requires constant attention to keep the light output within acceptable limits. If the D. C. voltage is modulated with a small A. C. voltage, the change in light output due to the A.C. is substantially constant and over a considerable range is independent of the average output due to the D.C.

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Optical Mark Sensing

When small neon bulbs are used as the light source in a reflected light mark detecting system, the variations in light output due to aging and drift of the neon may be as great as the difference in reflection between the record card and a mark on the card. This condition requires constant attention to keep the light output within acceptable limits. If the D. C. voltage is modulated with a small A.
C. voltage, the change in light output due to the A.C. is substantially constant and over a considerable range is independent of the average output due to the D.C.

In the system, the initial light output of neon bulb 1 is adjusted by rheostat 2. A transformer 3 fed by an A. C. voltage of about 25 KC modulates the light output. The light, after reflection from the record 4, is detected by a photocell 5 whose output is amplified in amplifier 6. The amplifier output is passed through a frequency sensitive filter 7 to another amplifier 8 whose A. C. output is rectified by a full-wave rectifier 9. The output voltage of rectifier 9 is proportional to the reflected A. C. portion of the light only and indicates the presence or absence of a mark on record 4.

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