The KÖHN analysis according to DIN ISO 11277 is so far the only rational measuring method which provides identical results to the sedimentation analysis with the same dependence on the grain shape. In this method, the sinking velocity of soil particles is investigated at 25 °C on a previously homogenized soil sample separated from carbonates and organic matter. The results are used, for example, to generate grain sum curves, which form the basis for many soil physical investigations.

The fine soil is composed of the fractions coarse silt (gU), medium silt (mU), fine silt (fU) and clay (T). This is illustrated by the grain size triangle. Due to the different grain sizes (<2.0 µm to <63 µm) and grain shapes, the individual fractions have different sinking velocities. By controlled sedimentation of the homogenized soil suspension, the individual fractions are separated on the basis of the different sinking velocities and thus quantified.

The separation of the fractions is done by pipetting analysis. During the sinking process, defined volumes are taken from the suspension at a defined height at defined times, and their mass of solids content is determined afterwards. Due to the high accuracy requirements, the manual test procedure involves many sources of error, such as deviations in the immersion depth of the piepette or the sampling time, and is very tedious due to the slow sinking speed of fine soil particles.