Patent ID: 8316711

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, wherein the mechanically oscillatable unit is an oscillatory fork, a single rod or a membrane oscillator; 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; and 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, wherein: a control unit; at least one input amplifier, and at least one output amplifier are provided in said electronics unit, said electronics unit has a total amplification factor; the amplification factor of said output amplifier is tunable, the amplification factor of said input amplifier is tunable, said control unit tunes the amplification factor of said output amplifier, as a function of damping of said mechanically oscillatable unit by the medium, in such a manner that the amplitude of the electrical, input signal lies essentially within a predeterminable amplitude band and that the amplification factor of said output amplifier decreases in the case of lessened damping by the medium and increases in the case of greater damping by the medium; and said control unit tunes the amplification factor of said output amplifier and corresponding to said timing of said output amplifier tunes the amplification factor of said input amplifier in such a manner that the total amplification factor of said electronics unit is essentially equal to a predeterminable value.