Laser Diffraction: Particle size determination according to ISO 13320


CILAS 1090, CILAS 1090D, CILAS 1090LD
CILAS 1190, CILAS 1190D, CILAS 1190LD

Particle size

To state completely the size of a particle is only possible at spheric particles with a single dimension number. As most particles deviate from such idealized particle shape the so called equivalent  diameters are focussed upon at many analysis methods for particle size distribution. Depending on the analysis method particle sizes of sphere-equivalent particles are evaluated which e.g. have the same mass, projection surface, volume. The conversion to spheric particles result at the laser diffraction method out of the diffraction intensity of the laser.

Analysis method

Particles diffract the light of a monochrome laser beam. Particles with a large diameter diffract the laser beam only a bit, e.g. in a small angle. The light spectra of the small particles though have to be taken in larger angles against the laser beam because of a stronger diffraction. The detectors of the analyzers as a whole take an intensity picture of the diffracted laser beam. The particle size distribution gets calculated by complex mathematics out of the angle-dependent light intensities on the basis of the MIE-theory or the so-called Fraunhofer approximation.


CILAS invented the commercial use of the laser diffraction method more than 40 years ago. The laser diffraction as a means for particle size analysis has prevailed in many fields against more traditional methods since then because of its time economy, wide measurement range and high flexibility towards most different material systems.

The CILAS laser diffraction granulometers excel by high reproducibility, robustness and durability as well as by outstanding ease of use. The combination of the CILAS analyzers with the EXPERT SHAPE-option as latest development offers additional particle shape analysis at an unrivalled price-performance ratio. Measurements are possible in liquid- as well as in dry-mode – combination models allow the change between modes with a simple mouse-click. The illustration above shows the CILAS 1090 LD with the EXPERT SHAPE-Option as well as particles which were visualized and evaluated with the EXPERT SHAPE Option of the CILAS 1090 (image analysis according ISO 13322).


1. Mixtures of BCR-standards 66 and 67 were analyzed with the CILAS 1090L, the share of BCR66 was in percentage: 100, 98, 95, 90, 85, 75, 50, 25, 15, 10, 5 and 2. The illustration highlights the exact reproduction of the mixture ratio.


ISO 13320