Patent ID: 8322194

Claim:
An apparatus for ascertaining and/or monitoring at least one process variable of a medium in a container, comprising: at least one mechanically oscillatable unit; at least one exciting/receiving unit, which excites said mechanically oscillatable unit to execute mechanical oscillations and which receives the mechanical oscillations of said mechanically oscillatable unit; at least one electronics unit, which supplies said exciting/receiving unit with an electrical, output signal, and which receives from said exciting/receiving unit an electrical, input signal, said electronics unit includes at least one amplifier unit, which amplifies the electrical, input signal to an amplified signal; at least one tunable phase shifter, which changes the phase of the amplified signal; and at least one control unit, which controls said phase shifter, wherein: said control unit is embodied in such a manner that it measures at least the frequency of the amplified signal; said control unit controls said phase shifter at least starting from stored data concerning frequency-phase dependence of said at least one amplifier unit, said control unit evaluates the output signal at least with regard to phase and compares the phase of the output signal with a predetermined value; and said control unit controls the phase shifter starting from the comparison.