A System Of Pressure Sensors To Characterize Duration And Area Of Avalanches On A Conical Bead Pile

A system of pressure sensors is used to measure the area of avalanches on a conical bead pile. The bead pile is a slowly driven critical system of 3 mm steel beads. The pile comprises roughly 20,000 steel spheres atop a circular base; it is driven by adding one bead at a time to the apex of the pile. Avalanches are recorded by the change in mass as beads fall off the pile. To create cohesion between beads, a pair of Helmholtz coils is used to apply a uniform magnetic field and induce magnetization of the beads. As cohesion is added, the size and number of the largest avalanches in the system increase. To more fully compare the experiment to models, we want to characterize the fraction of the pile involved in a given avalanche to determine which avalanches are system-spanning. Thus we added a set of eight pressure sensors at the edge of the base of the pile to detect dynamic changes in the pile during an avalanche. The signals from the force-sensitive resistors are amplified through a custom circuit board and each signal is read via Arduino. The sensors provide a sensitive response to changes in the force chains within the pile, and allow us to characterize the fraction of the pile involved in an avalanche at any time during the avalanche.