Non-invasive, continuous, quantitative detection of powder level and mass holdup in a metal feed tube

We describe a quantitative, non-invasive capacitance detector providing a rapid signal that varies continuously with powder level and/or mass holdup in the metal feed tube of a tablet press. We outline the principle of its processing electronics, provide an algorithm for the accurate interpretation of its signals, pose general design guidelines for embedding the instrument in the tube, and show how the detector can be paired with another non-invasive reference probe to operate with varying powder blend and moisture. We illustrate a control strategy that keeps powder level constant with a process example. [Display omitted] •A new non-invasive capacitance method records powder level and mass in a feed tube.•The design is used in continuous processing of pharmaceutical powders.•This self-calibrating method detects subtle changes in bulk density and moisture.