Transparency sensors

Details Transparency sensors Transparency sensors

1997-11-20

2000-01-25

Le, Que T.

Radiant energy

Photocells; circuits and apparatus

With circuit for evaluating a web, strand, strip, or sheet

3562391, G01N 2186

Patent

active

060181648

ABSTRACT:
An improved transparency sensor (10) uses Brewster's Law to detect the presence of sheets of transparency material (20). The sensor (10) includes a light emitting diode (LED) (12) and two photodiodes (14, 16) arranged to receive light reflected from the material (20). The LED (12) supplies incident light at an angle (.theta.) which is related to the refractive index of the transparency material (20) to be detected. A polarizing filter (18) is associated with one of the photodetectors (16) and is oriented to cut out substantially reflected polarized light entering that photodiode (16). Output signals from the photodetectors (14, 16) are processed in a comparator (40) which provides an output signal (42) indicating the presence or not of a transparency material (20).

REFERENCES:
patent: 4459023 (1984-07-01), Reich et al.
patent: 5139339 (1992-08-01), Courtney et al.

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