Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1980-05-15
1982-07-13
Punter, William H.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250225, G01V 904
Patent
active
043396607
ABSTRACT:
A light transmitter directs light via a first polarizing filter, so that it is polarized in one plane, to a retro-reflecting device across a region to be monitored and the retro-reflector produces depolarization, or rotates the plane of polarization of the light, prior to directing it to a light receiver positioned adjacent the light transmitter. A second polarizing filter crossed relative to the first is positioned in front of the light receiver so that the light receiver will only recognize light whose plane of polarization has been appropriately rotated by the retro-reflector but not light reflected from a strongly reflecting object which interrupts the light barrier. Threshold circuitry evaluates whether a signal from a photoelectric convertor embodied in the receiver lies above or below a given threshold. Weakly reflecting objects are not recognized, because light reflected therefrom will be too weak to generate a signal above the required threshold. Various polarizing arrangements are described.
REFERENCES:
patent: 3631254 (1971-12-01), Covault
patent: 3715165 (1973-02-01), Smith
patent: 4224608 (1980-09-01), Lederer
Buchholz Karl-Otto
Erdmann Jurgen
Fetzer Gunter
Erwin Sick GmbH - Optik-Elektronik
Punter William H.
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