This classical analytical technique determines the average particle size by measuring the pressure drop across a packed powder bed using a water manometer. The pressure drop is a function of the permeability of the packed bed. This is related to the surface area of the particles which is then transformed to an “average size” based upon the assumption that the particles are spherical. The disadvantage of the technique is that it does not report on the statistics of the size distribution.
Fisher Sub-Sieve Sizer - The Fisher Sub-Sieve Sizer tests powders quickly and reproducibly for their Average Particle Diameter - also known as the Air Permeability Diameter.