A microcomputer-based sensing system for measuring the erosive disposition of clay and silt sized soil particles

Accurate knowledge of particle size distribution plays an important role in controlling soil erosion from farm lands, construction sites, tropical areas, channel beds, and forest lands. The concept of the vortical particle size distribution system (VPSDS) was developed by Burcham (1989) for determining particle size and concentration in soil-water mixtures on a real-time or near real-time basis. The VPSDS has three main components; (1) the VPSDS vortex chamber and sensing zone, (2) a laser light detection system, and (3) the data acquisition and control system.

Experiments were developed to determine relationships between the output of the VPSDS (voltage) and actual particle concentration in the 4 to 63 micron range using eight soils from four unified soil classifications (CL, CH, ML, MH). A modified pipette method was developed to collect soil-water mixture samples from the VPSDS sensing zone. The light blocked by soil particles in the sensing zone is detected by a logarithmic light extinction circuit, which produces voltage relative to the mass of particles blocking the laser light. The experiment compared recorded voltage with measured particle concentration at various computed particle sizes from 4 to 63 microns.

A computer control and data acquisition system was developed to operate the VPSDS and record data. The control program stores the instrument's voltage response, impeller speed, and elapsed time for each experiment.

Results related the VPSDS voltage response to actual particle size and sample concentration for the 4 to 63 micron particle size range. Regression analyses of the data indicated a good correlation between the VPSDS voltage response and sample concentration. The mass-voltage relationship for the eight soils tested in this study was described with one equation having r² values ranging 0.98 to 0.99. Voltage as an independent variable to predict mass was statistically significant (α = 0.01).