Light barrier utilizing two radiation branches each having diffe

Details Light barrier utilizing two radiation branches each having diffe Light barrier utilizing two radiation branches each having diffe

1986-04-28

1988-03-29

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

340555, 250225, G01V 904

Patent

active

047345756

ABSTRACT:
In a light barrier, especially for outside application and long distances monitored, insensitivity to interfering light and scattering through fumes or fog and an increased range and sensitivity to objects passing through the light barrier are achieved by subdividing radiation from a source into two radiation branches which are offset relative to each other and differently polarized, e.g., by means of a polarization filter divided into two parts, with different linear or oppositely circular polarization of the filter part surfaces. By means of an analogously subdivided polarization filter, the radiation of each of the two radiation branches is focused on a different individual sensor element. The two sensor elements are connected in a differential circuit which triggers an alarm signal in response to signals arriving from both radiation branches in short succession but does not trigger an alarm signal if both sensor elements are equally irradiated.

REFERENCES:
patent: 2457502 (1948-12-01), Shepherd
patent: 3440427 (1969-04-01), Kammer
patent: 4171908 (1979-10-01), Robert et al.
patent: 4333008 (1982-07-01), Misek
patent: 4339660 (1982-08-01), Buchholz et al.
patent: 4342987 (1982-08-01), Rossin

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