An improved settling tube system

In this report a settling tube system is described for the measurement of the settling velocity distribution of sand samples with particle diameters ranging from 0.1 to 2 mm and sample weights ranging from 0.1 to 20 gf(10^-3 to 0.2 N). The time of arrival of the particles is detected by means of an underwater balance. The response, stability and accuracy of this balance are greatly improved by utilizing the well-known principle of feedback (Slot & Geldof, 1979). The accuracy (systematic part of the error) of the measurenlent of the settling velocity turns out to be better than 2%, i.e. with the exception of the error due to the concentration effect. The error due to the concentration effect is dependent on the sample weight and particle size. It is possible to choose a sample weight (for sand particles in the range from 0.1 to 2 mm) for which the error due to the concentration effect is less than 1% and the signal-noise ratio is better than 72 dB (~4000). This means that the overall accuracy is better than 3%. The precision (random part of the error) of the measurements turns out to be better than 4% (95% confidence). A rapid analysis of the samples is accomplished by connecting the settling to be to a micro computer. Results are presented by means of a hard copy yielding plots of the cumulative distribution and the calculated moments (mean, standard deviation and skewness) of the settling velocity as well as the sedimentation diameter