Abstract: A capacitance type material level detector for a hopper for particulate solid materials has a support that extends through an opening in a hopper sidewall to carry a detector unit for which it provides a hood. An electrically conductive sensor member of the detector unit is protected from contact with material in the hopper by a dielectric shield, and is sealed in a chamber defined by the shield and a mounting plate. A manually slidable and rotatable paddle hangs alongside the shield where it may be swung in front of the shield to check operativeness of the detector unit; and by moving the paddle rearwardly it may be used to break accumulated material off the face of the shield.