Abstract: For supervising the filling level in an elongated space, such as hoppers, shafts, silos and the like, for miscellaneous granular material, the movement of the material is transformed into vibrations and the vibrations are converted into indicating signals which indicate the filling level. This may be accomplished by a plurality of rods which extend through the wall of the space and are subjected to the vibrations produced by solid materials falling through the space. This may be done by providing rods which extend beyond the wall into the space, and by accelerometers or the like which detect the vibrations and convert them into electrical signals which may control the discharge from the shaft.