Abstract: An Apparatus for determining and/or monitoring at least one process variable of a medium in a container, comprising: a mechanically oscillatable unit a driving/receiving unit for exciting the mechanically oscillatable unit to execute mechanical oscillations by means of an electrical, exciting signal and for receiving and transducing the mechanical oscillations into an electrical, received signal a control unit, which is embodied to produce the exciter signal starting from the received signal and to set a predeterminable phase shift between the exciter signal and the received signal, an electromagnetically oscillatable unit, an active element for producing and/or maintaining electromagnetic oscillations in the electromagnetically oscillatable unit, which active element forms together with the electromagnetically oscillatable unit an oscillator, a coupling unit, which is embodied to tap an output signal from the active element, and an evaluation unit, which evaluation unit is embodied to determine the at least