An apparatus including: a mechanically oscillatable unit; an exciting/receiving unit; and an electronics unit having an input amplifier and an output amplifier. The amplification factors of the output amplifier and the input amplifier are tunable. The control unit tunes the amplification factor of the output amplifier as a function of damping of the mechanically oscillatable unit in such a manner that the amplitude of the electrical, input signal lies within an amplitude band and that the amplification factor of the output amplifier decreases in the case of lessened damping by the medium and increases in the case of greater damping by the medium, and the control unit tunes the amplification factor of the output amplifier and the amplification factor of the input amplifier in such a manner that the total amplification factor of the electronics unit equals a predeterminable value.