Electrical measurement of sediment layer thickness under suspension flows

This paper reports a new technique to measure the thickness of a layer of deposited sediment as a function of time, independent of the flow conditions or presence of suspended sediment above the layer. Small electrodes on the bottom and a reference electrode in the fluid above were used to measure the resistance of the layer with a small AC current and a bridge circuit. Using a multiplexer and an Analog-to-Digital converter the growth of the layer can be accurately monitored at many locations on the tank bottom. In a trial experiment the sedimentation under a stagnant column of a monodisperse suspension was examined. The results show that changes in the sediment layer thickness of less than 0.3% can be measured for layers up to 0.2 g/cm2.