Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1986-04-11
1988-03-08
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
2502221, 242188, G01V 904
Patent
active
047301082
ABSTRACT:
An optical sensing circuit useful for detecting the end of a moving tape in a tape transport includes a light source and a light sensor which are closely spaced across a gap. The radiation output of the light source is modulated at a selected frequency which is determined by the operating frequency of a frequency detector. In the absence of a light obstruction, such as passage of the tape in the optical path between the light source and the light sensor, the modulated output from the light source is detected by the sensor. The processed signal from the sensor, which is characterized by the modulation frequency, is applied to the frequency detector. The detector recognizes only those signals having the modulated frequency, and does not respond to signals of different frequencies, which may result from impingement of other radiation than that from the light source on the photosensor.
REFERENCES:
patent: 3596006 (1971-07-01), Lawhon
patent: 3861622 (1975-01-01), Wakami et al.
patent: 3889118 (1975-06-01), Walker
patent: 4029957 (1977-06-01), Betz et al.
patent: 4068222 (1978-01-01), Treviranus
patent: 4570075 (1986-02-01), Spiero
Osborn Nathan W.
Rodal David R.
Almeida George B.
Ampex Corporation
Kallman Nat
Lange Richard P.
Nelms David C.
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