Procedure for the determination of particle size distribution in particle mixtures

A method for determination of particle size distribution of a particle mixture comprising opto-electronic scanning a particle stream separated from the particle mixture, wherein the particle stream is transported in a transparent fluid or gaseous medium vertically to a parallel ray of light, the chord lengths of particles are measured and assigned to certain length categories, wherein the particles stream for each linear scan by the ray of light is exposed to an exposure time less than the quotient d.sub.min /(2 v.sub.min), wherein d.sub.min stands for the diameter of the smallest particle to be measured and v.sub.min stands for the velocity of the smallest particle to be measured, and wherein the number of particles per particle size category is ascertained beginning with the particle size category of the largest particle diameter proceeding to the category with the smallest particle diameter from the quotient of the number of recorded chord lengths in a respective lengths category and the appearance probability of said lengths category for this particular particle size category, whereby after each determination of number of particles in a particle size category the number of chord lengths for those lengths categories which correspond to the not yet determined particle sizes is corrected by the number of those chord lengths, which, according to the appearance probabilities are to be assigned to the particles of the already determined particle size categories.