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Photocell Filter Combination

IP.com Disclosure Number: IPCOM000097584D
Original Publication Date: 1961-Mar-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Durbeck, RC: AUTHOR

Abstract

In magnetic tape recording, the beginning and end of the tape is marked by scrapping portions of oxide from a tape having a plastic backing, such as Mylar. The resulting windows are detected by means of a light source and photocell positioned on opposite sides of the tape.

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Photocell Filter Combination

In magnetic tape recording, the beginning and end of the tape is marked by scrapping portions of oxide from a tape having a plastic backing, such as Mylar. The resulting windows are detected by means of a light source and photocell positioned on opposite sides of the tape.

Oxide tape, however, transmits red and infrared radiation through areas of the tape where the oxide becomes thin. Hence, false end of tape indications can result unless the photocells are made insensitive to the red and infrared radiation bands. Photocells having this characteristic are not readily available.

A filter is provided in line with the light to block red and infrared radiation but to pass visible light spectra. Such filters are readily available. Thus, false indications are eliminated.

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