Vibronic measuring device

A measuring device for determining and/or monitoring a measured variable of a medium, comprising

• a vibronic sensor and a control unit,
• wherein the vibronic sensor includes a mechanically oscillatable unit and an amplifier unit,
• wherein the mechanically oscillatable unit is excitable by an electrical excitation signal having an excitation oscillation frequency and produces a received signal having an oscillation frequency,
• wherein the amplifier unit is designed to produce the electrical excitation signal with a defined phase shift relative to the received signal and to excite the mechanically oscillatable unit therewith,
• wherein the control unit is designed to ascertain the oscillation frequency and/or an amplitude of the received signal and based on the ascertained oscillation frequency and/or the ascertained amplitude of the received signal to determine the measured variable of the medium,
• wherein the control unit is designed to control the amplifier unit for a checking of the measuring device in such a manner that the amplifier unit produces at least two excitation signals with equal signal strength and different predeterminable phase shifts,
• wherein the control unit is designed to judge the sensor relative to its ability to function depending on how the amplitudes and/or oscillation frequencies of the received signals behave as a result of the different phase shifts, and
• wherein the amplifier unit and the mechanically oscillatable unit form a closed oscillatory circuit.