METHODS AND APPARATUS FOR DETERMINING CHARACTERISTICS OF PARTICLES

• US 20080221711A1
• Filed: 10/26/2007
• Published: 09/11/2008
• Est. Priority Date: 03/06/2004
• Status: Abandoned Application

• Current Assignee: Michael Trainer
• Original Assignee: Michael Trainer
• Inventors: Trainer, Michael
• Application Number:
  US11/924,702
• Publication Number:
  US 20080221711A1
• Time in Patent Office: Days
• US Class Current: 700/54
• CPC Class Codes: G01N 15/0205 by optical means
• CPC Class Codes: G01N 15/1459 the analysis being performed on a sample stream
• CPC Class Codes: G01N 2015/1486 Counting the particles
• CPC Class Codes: G01N 2015/1493 Particle size
• CPC Class Codes: G01N 2015/1497 Particle shape

Abstract

An instrument for measuring the size distribution of a particle sample by counting and classifying particles into selected size ranges. The particle concentration is reduced to the level where the probability of measuring scattering from multiple particles at one time is reduced to an acceptable level. A light beam is focused or collimated through a sample cell, through which the particles flow. As each particle passes through the beam, it scatters, absorbs, and transmits different amounts of the light, depending upon the particle size. So both the decrease in the beam intensity, due to light removal by the particle, and increase of light, scattered by the particle, may be used to determine the particle size, to classify the particle and count it in a certain size range. If all of the particles pass through a single beam, then many small particles must be counted for each large one because typical distributions are uniform on a particle volume basis, and the number distribution is related to the volume distribution by the particle diameter cubed.

Claims

1. Apparatus for optimizing path length of a light beam through a particle dispersion to improve accuracy of measurement of light scattered from particles, comprising:

a) an optical system for illuminating a particle dispersion,

b) a detection system comprising at least one detector for quantifying light scattered by at least one of said particles,

c) a sample cell, comprising two optical windows, which confine said particle dispersion and pass light, from a light source, through said particle dispersion to produce light scattered by said particle dispersion, and

d) means for adjusting a separation between said optical windows to change a path length of light, from said light source, through said sample cell.

2. The apparatus of claim 1, wherein said path length is optimized to reduce multiple scattering in an ensemble scattering measurement.

3. The apparatus of claim 1, wherein said path length is optimized to reduce coincidence counts in a particle counting measurement.

4. The apparatus of claim 1, wherein said path length is optimized to hold particles in a thin layer of dispersant for particle counting measurements using said optical system and detection system, wherein the particles are scanned over said thin layer to measure scattered light from various locations on said thin layer.

5. The apparatus of claim 4, wherein the particle dispersion has a particle concentration which is adjusted to provide a specified number of particles per unit area in said thin layer.

6. The apparatus of claim 1, wherein the sample cell defines first and second sides, wherein the optical system and detection system are positioned in a vicinity of said first side, and wherein there is a retroreflector positioned in a vicinity of said second side, wherein the retroreflector comprises means for removing angular drift of a light beam caused by drift in position, or drift in optical properties, of said optical system, said sample cell, and/or said detection system.

7. The apparatus of claim 6, wherein the adjusting means comprises means for setting the path length to a fixed value.

8. A method for determining an optimum path length of a light beam passing through a particle dispersion, so as to reduce inaccuracies in particle analysis caused by multiple scattering of light from particles, the method comprising the steps of:

a) determining a specified value of a path length which produces excessive multiple scattering,

b) adjusting said path length to a specified value,

c) measuring first scattered light values at said specified value of path length,

d) reducing said path length to a second value,

e) measuring second scattered light values at said second value of said path length,

f) determining a difference between said second scattered light values and said first scattered light values,

g) if said difference is greater than a specified limit, repeating steps (b) through (f), while setting said specified value of path length, in step (b), to said second value of said path length,

h) if said difference is less than a specified limit, using said second scattered light values to determine particle characteristics.

9. The method of claim 8, further comprising selecting said difference between said second scattered light values and first scattered light values to be a difference in functional shape of the scattered light as a function of scattering angle.

10. The method of claim 8, further comprising the step of removing angular drift of a light beam caused by drift in position, or drift in optical properties, of an optical system and/or a detection system.

11. A method for determining an optimum path length of a light beam passing through a particle dispersion, so as to reduce inaccuracies in particle analysis caused by scattering measurement errors, the method comprising the steps of:

a) adjusting a path length to a specified value,

b) measuring scattered light values at said specified value of said path length,

c) calculating an optimum value of path length based upon said specified value of said path length and said scattered light values,

d) adjusting said path length to said optimum value of path length,

e) measuring scattered light values at said optimum value of path length and using scattered light values to determine particle characteristics.

12. The method of claim 11, further comprising selecting said scattered light values to be based on optical attenuation due to light scattering.

13. Apparatus for measuring scattered light from individual particles which are nearly confined to a plane on a surface or in a thin layer of a dispersant, comprising:

a) an optical system for illuminating said particles,

b) a detection system comprising at least one detector for quantifying light scattered from a specific region on said plane, and

c) mechanical means for moving an interaction volume of said optical system and detection system to various locations on said plane to measure separately light scattered at each location.

14. Apparatus for removing angular drift in a system for analyzing particles, comprising:

a) an optical system for illuminating a particle dispersion,

b) a detection system comprising at least one detector for quantifying light scattered by at least one particle, and

c) a sample cell, comprising two optical windows, wherein the windows confine the particle dispersion and pass light, from a light source, through said particle dispersion to produce light scattered by said particle dispersion,

wherein said optical system and detection system are attached to a first side of said sample cell, and

wherein the apparatus includes a retroreflector positioned in a vicinity of a second side of said sample cell, wherein the retroreflector comprises means for removing angular drift of a light beam caused by drift in position, or drift in optical properties, of said optical system, said sample cell, and/or said detection system.