LASER PARTICLE SIZE MEASURING INSTRUMENTS FOR THE DETERMINATION OF PARTICLE SIZE DISTRIBUTIONS
Laser diffraction - for quick and reliable determination of the particle size is almost an indispensable method in modern quality control. Areas of application cover practically all branches of industry. For example, laser diffraction can be found in the receiving, but also in the pre-delivery inspection of base materials, in which their particle size is significant for the processability or for the quality and directly related end product; or for controlling individual process steps, where the size distribution of intermediate products is determined.
The underlying principle of laser diffraction is very simple: Diffraction, respectively scattering of light on a particle produces behind the particle an angle-dependent intensity distribution, which consists of a ring system with light and dark areas. Depending on the particle size, the intervals of the light and dark areas vary, whereas the small particles generate large ring intervals and large particles lead to intensity distributions with closely bordering rings. With the aid of the Mie-theory the distances of the rings can be exactly calculated, whereas with sufficiently large particle diameters the so called Fraunhofer- approximation can be utilized.