Accuracy, repeatability and reproducibility of PSA

This application report provides a better insight into the requirements of the ISO13320 for laser diffraction regarding accuracy, repeatability and reproducibility and shows how the PSA is capable of fulfilling them.

Importance of the accuracy and repeatability

Laser diffraction technique describes a three-dimensional object with a single value of length, the ‘equivalent spherical diameter (laser diffraction)’ based on the assumption that particles are spherical (1).
Therefore, in case of a collection of irregularly shaped particles laser diffraction instruments calculate the particle size distributions by comparing the diffraction patterns deduced for spheres to those measured for irregular particles. Consequently, the measurement result is a distribution of spherical particles that ‘fit’ to the light scattered from the “irregularly shaped objects” (1). Each irregular particle may present itself in different orientations and, those different resulting cross-sections will have different scattering features. For this reason, the equivalent spherical diameters reported for non-spherical particles depend on the correct operation of the instrument which has to be confirmed by a qualification procedure.

For laser diffraction the type of certified materials and qualification procedures based on the accuracy and repeatability determination are described by the ISO 13320.

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