METHOD AND APPARATUS FOR DETECTING LIQUID PRESENCE ON A REFLECTING SURFACE USING MODULATED LIGHT

摘要

PURPOSE: A method and apparatus for detecting liquid presence on a reflecting surface using modulated light is provided to detect 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. CONSTITUTION: A light source (4) is modulated into two or more discrete levels at a fixed or variable modulation rate by modulator (3). These levels include an off level where there is no light from the optical source. Light from the source is reflected into an optical detector (5) 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.