Method and apparatus for detecting liquid presence on a reflecti

Details Method and apparatus for detecting liquid presence on a reflecti Method and apparatus for detecting liquid presence on a reflecti

1994-12-05

1996-04-16

Westin, Edward P.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

250576, 2503418, 25033911, 2505594, G01N 1506, G01N 2149, G01N 2185

Patent

active

055085210

ABSTRACT:
The invention is a Method and Apparatus for detecting the application of a liquid drop into a transparent reaction chamber or other reflecting surface in the presence of ambient light and transient motion of the chamber. A light source is modulated into two or more discrete levels at a fixed or variable modulation rate. These levels include an off level where there is no light from the optical source. Light from the source is specularly reflected into an optical detector which is sampled at least once for each modulated light level. Differences between modulated levels and the off level represent the amount of reflectivity of the surface or chamber. When liquid enters the chamber or is applied to the surface, the reflectivity changes. This leads to detectable changes between the modulated levels and the off level. Ambient light simply shifts the absolute values of the levels. The amplitude differences are compared against thresholds to determine if the reflectivity has changed sufficiently to indicate the presence of liquid. If such a detection occurs for three or more complete modulation cycles, the presence of liquid is reported.

REFERENCES:
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patent: 4591710 (1986-05-01), Komadina et al.
patent: 4723319 (1988-02-01), Stricker
patent: 4849340 (1989-07-01), Oberhardt
patent: 5110727 (1992-05-01), Oberhardt
patent: 5117099 (1992-05-01), Schmidt
patent: 5177565 (1993-01-01), Stoughton
patent: 5406082 (1995-04-01), Pearson et al.

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