David A Bach

US Patent:

55085210, Apr 16, 1996

Filed:

Dec 5, 1994

Appl. No.:

8/349411

Inventors:

Clifford H. Kraft - Naperville IL
Gregory S. Godlevski - Raleigh NC
David T. Bach - Raleigh NC

Assignee:

Cardiovascular Diagnostics Inc. - Raleigh NC

International Classification:

G01N 1506
G01N 2149
G01N 2185

US Classification:

250574

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.