Patent ID: 6011621
Filing Date: 2000-01-04
Classification: G01J,G01N

Abstract:
A method of measuring the particle size of ultra-small particles suspended in a fluid and experiencing Brownian movement, wherein the concentration of said ultra-small particles in said fluid is low, said method comprising the steps of:irradiating a predetermined measuring volume of said ultra-small particles with a coherent beam of light to cause said light to be scattered by said ultra-small particles into a predetermined scattering angle;detecting the intensity of said light scattered by said ultra-small particles in said predetermined scattering angle, wherein substantial variations in said intensity of said light are a function of said Brownian movement and fluctuations in the number of said ultra-small particles in said measuring volume;generating an electrical measuring signal as a function of said intensity of said light scattered by said ultra-small particles;removing from said electrical measuring signal first signal components with a relatively low characteristic frequency due substantially to said fluctuations in said number of said ultra-small particles in said measuring volume to produce a corrected signal representative of said Brownian movement and substantially free of variations due to said fluctuations in said number of said ultra-small particles in said measuring volume; andcalculating from said corrected signal the size of said ultra-small particles.