Method and apparatus for detecting liquid presence on a reflecting surface using modulated light

• US 5,508,521 A
• Filed: 12/05/1994
• Issued: 04/16/1996
• Est. Priority Date: 12/05/1994
• Status: Expired due to Term

• Current Assignee: Cardiovascular Diagnostics, Inc. (PharmaNetics, Inc.)
• Original Assignee: Cardiovascular Diagnostics, Inc. (PharmaNetics, Inc.)
• Inventors: Bach, David T., Godlevski, Gregory S., Kraft, Clifford H.
• Primary Examiner(s): Westin, Edward P.
• Assistant Examiner(s): Steady, Jacqueline M.
• Application Number:
  US08/349,411
• Time in Patent Office: 498 Days
• Field of Search: 250/574, 250/576, 250/341.8, 250/339.11, 250/559.4
• US Class Current: 250/574
• CPC Class Codes: G01N 21/8483 Investigating reagent band test-element handling not specific to a test method G01N33/4875; analytical elements specific to chemical analysis of biological material G01N33/52; autometer with reagent band G01N35/04

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.

Claims

1. An apparatus for detecting the application of liquid to an optical reflecting surface in the presence of ambient light, the invention comprising, in combination:

a light source;

electronic modulation means controlling the current to said light source to produce a plurality of intensity levels including one off level having no intensity;

an optical detector for producing electrical signals proportional to light intensity;

a reaction chamber containing a reflecting surface capable of receiving liquid, said surface positioned so that some light from the source reflects into the optical detector;

conversion means coupled to the optical detector, and synchronized to the modulation means, for producing at least one intensity sample for each of said intensity levels;

processing means for computing differences between intensity samples representing light levels and intensity samples representing the off level, said differences being proportional to reflectivity of the reflecting surface in the presence of ambient light;

reporting means for reporting the presence of liquid on the reflecting surface when said differences change by a predetermined amount.

2. The apparatus of claim 1 wherein the conversion means is an A/D converter.

3. The apparatus of claim 1 wherein the conversion means is an intensity to frequency converter.

4. The apparatus of claim 1 wherein the processing means determines ambient light intensity from intensity samples representing said off level.

5. The apparatus of claim 1 wherein the light source is a light emitting diode.

6. The apparatus of claim 5 wherein the light emitting diode emits infrared light.

7. The apparatus of claim 1 wherein the processing means is a microprocessor.

8. An apparatus for detecting the application of liquid to an optical reflecting surface in the presence of ambient light, said reflecting surface of the type used to perform coagulation assays, the invention comprising:

an optical source current modulated to at least one on amplitude level and one off level, said levels occurring at predetermined times;

a reaction chamber containing a reflecting surface and optical detector positioned so that light from the source reflects into the detector;

processing means responsive to amplitude levels from the optical detector for computing differences between the on amplitude levels and the off level, said differences representing reflectivity of the reflecting surface, and the off level representing ambient light, whereby said processor reports the application of liquid to the reflecting surface when said differences change by predetermined amounts.

9. An apparatus for detecting the application of liquid to a reflecting surface that is insensitive to ambient light and transient motion of the surface comprising:

an optical source producing light modulated to three different levels, an off level, a midrange level, and a bright level in sequence, each level being held for a predetermined duration;

an optical detector;

a reflecting surface capable of receiving liquid positioned such that light from the optical source reflects from the surface into the optical detector;

an A/D converter coupled to the optical detector and synchronized with the optical source producing one sample value for each modulated level in sequence;

processor means for determining an amount of ambient light from sample values of the off level, and surface reflectivity from a first difference of sample values of the bright level and sample values of the off level, and a second difference of the midrange level and the off level, the surface reflectivity being proportional to said differences;

a reporting means for reporting the application of liquid to the surface when said first difference and second difference change by predetermined amounts.

10. The apparatus of claim 9 wherein the processor means is a microcontroller.

11. The apparatus of claim 9 wherein the optical source is a light emitting diode.

12. The apparatus of claim 9 wherein the optical detector is a PIN diode.

13. The apparatus of claim 9 wherein the optical detector is an intensity to frequency converter.

14. A method of detecting the application of a liquid to a reflecting surface, said method being insensitive to ambient light and transient motion of the surface comprising, in combination:

current modulating an optical source at predetermined times to produce discrete amplitude levels with one level being an off level;

reflecting light from the optical source on a reflecting surface in a reaction chamber capable of receiving liquid, said light reflected into an optical detector with signal output;

sampling the signal output of said optical detector at least once for each different modulated level;

comparing differences between the modulated levels with the off level to determine an amount of ambient light and a change in reflectivity of the reflecting surface that can indicate application of liquid to the reaction chamber.