In-line measuring device, particularly a Coriolis mass flowmeter, density meter and/or a viscosity meter, designed to measure at least one physical measured variable x, particularly a mass flow, m, a density, ρ, and/or a viscosity, η, of a medium conducted through a pipe, said in-line measuring device comprising a vibronic-type sensor and a measuring device electronics unit electrically coupled to the sensor, - wherein the sensor comprises: -- at least one measuring tube, which is essentially straight, said tube serving to conduct the medium to be measured and communicating with the connected pipe, -- an exciter arrangement acting on the measuring tube, said arrangement being designed to make the at least one measuring tube vibrate, causing the measuring tube to produce torsional vibrations, during operation, at least temporarily and/or at least partially around an axis of torsional vibration connecting, in an imaginary manner, an inlet end of the measuring tube and an outlet end of the measuring tube, as well as -- a sensor arrangement designed to measure vibrations of the at least one measuring tube, which supplies at least one vibration measuring signal (s 1, s 2) representing vibrations of the measuring tube, wherein the measuring device electronics unit at least temporarily delivers an excitation signal (i exc) that drives the exciter arrangement, and, using the at least one vibration measuring signal (s 1, s 2) and/or the excitation signal (i exc), at least temporarily generates at least one measured value (X x), which represents the at least one physical measured variable to be measured, particularly the mass flow, m, the density, ρ, or the viscosity, η, of the medium, characterized in that the measuring device electronics unit is designed to recurrently determine, on the basis of the at least one vibration measuring signal (s 1, s 2) and/or on the basis of the excitation signal (i exc), a vibration frequency, f excT, of the torsional vibrations of the measuring tube and to monitor, on the basis of the vibration frequency, f excT, of the torsional vibrations, changes to the wall of the at least one measuring tube. - wherein the sensor comprises: -- at least one measuring tube, which is essentially straight, said tube serving to conduct the medium to be measured and communicating with the connected pipe, -- an exciter arrangement acting on the measuring tube, said arrangement being designed to make the at least one measuring tube vibrate, causing the measuring tube to produce torsional vibrations, during operation, at least temporarily and/or at least partially around an axis of torsional vibration connecting, in an imaginary manner, an inlet end of the measuring tube and an outlet end of the measuring tube, as well as -- a sensor arrangement designed to measure vibrations of the at least one measuring tube, which supplies at least one vibration measuring signal (s 1, s 2) representing vibrations of the measuring tube, wherein the measuring device electronics unit at least temporarily delivers an excitation signal (i exc) that drives the exciter arrangement, and, using the at least one vibration measuring signal (s 1, s 2) and/or the excitation signal (i exc), at least temporarily generates at least one measured value (X x), which represents the at least one physical measured variable to be measured, particularly the mass flow, m, the density, ρ, or the viscosity, η, of the medium, -- at least one measuring tube, which is essentially straight, said tube serving to conduct the medium to be measured and communicating with the connected pipe, -- an exciter arrangement acting on the measuring tube, said arrangement being designed to make the at least one measuring tube vibrate, causing the measuring tube to produce torsional vibrations, during operation, at least temporarily and/or at least partially around an axis of torsional vibration connecting, in an imaginary manner, an inlet end of the measuring tube and an outlet end of the measuring tube, as well as -- a sensor arrangement designed to measure vibrations of the at least one measuring tube, which supplies at least one vibration measuring signal (s 1, s 2) representing vibrations of the measuring tube, wherein the measuring device electronics unit at least temporarily delivers an excitation signal (i exc) that drives the exciter arrangement, and, using the at least one vibration measuring signal (s 1, s 2) and/or the excitation signal (i exc), at least temporarily generates at least one measured value (X x), which represents the at least one physical measured variable to be measured, particularly the mass flow, m, the density, ρ, or the viscosity, η, of the medium,