Electronic monitoring of events within dynamic particulate beds: conductance and capacitance measurements

Methods for monitoring mechanical events occurring within particulate solids systems in a dynamic state are described. The electrical conductance and capacitance characteristics of such systems, as they relate to the degree of bed dilation or expansion, extent of interparticulate contact, and intensity of particle motion, were studied and are discussed. To establish the potential of this approach, harmonically vibrated beds of monodispersed conducting spheres were used. A technique, based on the frequency modulation of standard FM broadcast frequency carrier signals, was developed to measure low and high frequency fluctuations in bed capacitance. The electrical conductance of these systems also was determined by both voltage drop and current flow methods. The experimental techniques developed are broadly applicable to various materials and modes of agitation or flow. They permit the evaluation of the time courses of both bed dilation and particle motion which, in turn, are known to determine of modify critically powder flow and mixing behavior.