Browse Prior Art Database

Capacitive Tape Loop Position Detector

IP.com Disclosure Number: IPCOM000075791D
Original Publication Date: 1971-Nov-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Fraeunfelder, LS: AUTHOR

Abstract

This tape loop position detector develops a variable magnitude, reversible polarity direct-current output voltage as the loop of tape in the vacuum column moves above or below a nominal position.

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Capacitive Tape Loop Position Detector

This tape loop position detector develops a variable magnitude, reversible polarity direct-current output voltage as the loop of tape in the vacuum column moves above or below a nominal position.

Magnetic tape 1 is buffered by vacuum column 2 as it moves between reel 3 and capstan 4. The position of the bottom of the tape loop is sensed by a capacitance column sensor, represented by variable capacitors C1 and C2. As the loop moves from the nominal midposition, the capacitance values of these two capacitors differentially vary.

On the positive half-cycle of the alternating-current source, diode 5 is forward biased and diode 6 is reverse biased. Capacitor 7 then charges, its upper terminal becoming positive with respect to ground, and the magnitude of the charge being determined by the capacitance value of C1. On the negative half- cycle, diode 5 is reverse biased and diode 6 is forward biased. Capacitor 7 now tends to discharge in accordance with the value of C2.

The average DC value of output voltage 8 is determined by the relative values of C1 and C2 and thus by the tape loop position. When the tape loop is at the nominal midposition, C1 equals C2 and the output voltage is zero. The output voltage changes polarity as the loop moves above or below this nominal position, and the magnitude of the output voltage indicates the extent of this movement.

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