Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1974-09-23
1976-01-06
Lieberman, Eli
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
250209, 250214E, 250557, 250561, 315151, G01J 132
Patent
active
039315134
ABSTRACT:
A circuit for sensing beginning of tape (BOT) and end of tape (EOT) tape position markers on digital magnetic tape includes an illumination source disposed to emit controlled illumination onto a marker sense position along the length of a tape path, a pair of photosensors disposed to sense illumination from the illumination source which is reflected from different positions across the width of a tape lying in the tape path, a control circuit coupled to control the illumination intensity emitted by the illumination source to maintain a predetermined illumination intensity at the photosensor receiving the least intense illumination, and a comparator connected to sense and indicate substantial differences in light intensities received by the two photosensors. The utilization of a feedback signal dependent on actually sensed illumination intensity permits the controlled illumination source to drive the photosensors with a predetermined reflected illumination intensity irrespective of the reflective characteristics of the magnetic tape over wide temperature variations. Adjustment of the gain for at least one photosensor amplifier readily permits compensation at the time of manufacture for deviations from symmetry in positioning the illumination source and photosensors as well as compensation for tolerance variations in circuit components.
REFERENCES:
patent: 3436553 (1969-04-01), Bevis
patent: 3566132 (1971-02-01), Walker
Ampex Corporation
LaRoche E. R.
Lieberman Eli
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