Disclosed is an apparatus for determining a process variable of a medium in a containment, comprising first and second oscillatory elements, first and second driving/receiving units, and electronics. The first driving/receiving unit is embodied to excite the first oscillatory element using a first electrical excitation signal to execute mechanical oscillations, and to receive the mechanical oscillations of the first oscillatory element and to convert such into a first electrical, received signal, wherein the second driving/receiving unit is embodied to excite the second oscillatory element by means of a second electrical excitation signal to execute mechanical oscillations, and to receive the mechanical oscillations of the second oscillatory element and to convert such into a second electrical, received signal, and wherein the electronics is embodied to determine the process variable from the first received signal and/or the second received signal.