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Background Compensation for Optical Read Systems

IP.com Disclosure Number: IPCOM000080287D
Original Publication Date: 1973-Nov-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Dunik, SL: AUTHOR

Abstract

In transmittance and reflectance systems for reading data marks on moving cards, it is necessary to vary the intensity of the light source to compensate for gradual variations in detected card material transmittance and reflectance. However, brief variations in detected light intensity, such as those caused by the marks themselves, should be ignored. For this purpose, the light source is selected to have a response time which is both short enough to respond to slow variations in detected light intensity, and long enough to ignore rapid variations in detected light intensity caused by the marks themselves.

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Background Compensation for Optical Read Systems

In transmittance and reflectance systems for reading data marks on moving cards, it is necessary to vary the intensity of the light source to compensate for gradual variations in detected card material transmittance and reflectance. However, brief variations in detected light intensity, such as those caused by the marks themselves, should be ignored. For this purpose, the light source is selected to have a response time which is both short enough to respond to slow variations in detected light intensity, and long enough to ignore rapid variations in detected light intensity caused by the marks themselves.

Card 1, which is moving out of the page, has both data marks and gradual variations in material density. As card 1 moves, photocell 2 detects both brief variations in transmitted light intensity and those caused by gradual variations in material density.

Both brief and slow-current variations from photocell 2 are amplified by power amplifier 3, and act to increase the current passing through filament 5 of light source 4. Because of the thermal lag of filament 5, the intensity of light which it emits does not change rapidly enough to accommodate the short-duration changes in filament current caused by data marks on card 1. Filament 5 does, however, respond to long-duration changes caused by variations in card material transmittance. In this way, source 4 provides an increased light intensity only when a gradual var...