A vibronic sensor for measuring the mass flow of a flowable medium, comprising: - A line inlet section; - a line outlet section; - a measuring pipe capable of oscillating for conducting the medium, wherein the measuring pipe is bent in one pipe plane in its idle position, wherein the measuring pipe connects to the line inlet section on the inlet side and to the line outlet section on the outlet side, and can be connected to a pipeline by means of the line outlet section; - a sensor housing, wherein the line inlet section and the line outlet section are both securely connected to the sensor housing; - at least one oscillation exciter for exciting bending oscillations of the measuring pipe in a bending oscillation useful mode; and - at least two oscillation sensors (51, 52) for detecting oscillations of the measuring pipe, wherein the at least one oscillation exciter comprises an excitation coil and/or the at least two oscillation sensors (51, 52) each comprise one sensor coil, wherein the at least one oscillation exciter comprises an excitation magnet and/or the at least two oscillation sensors (51, 52) each comprise a sensor magnet, wherein the excitation magnet and/or the sensor magnet is/are arranged on the measuring pipe, wherein the excitation magnet extends through a coil opening in the excitation coil and/or the sensor magnet extends through a coil opening in the sensor coil, characterized in that the coil opening has an elongated basic shape, wherein the basic shape has a center of mass through which a largest diameter with a length d1 and a smallest diameter with a length d2 pass, wherein the excitation coil and/or the sensor coil has/have a first coil axis and a second coil axis in a cross-sectional plane, wherein the largest diameter d 1 is located in the first coil axis, wherein the smallest diameter d 2 is located in the second coil axis, wherein the following applies for a quotient d 1 l d 2: 1.15 ≤ d 1 / d 2, in particular 1.5 ≤ d 1 / d 2, and preferably 2 ≤ d 1 / d 2, wherein the measuring pipe is configured in such a way that, when the measuring pipe oscillates in an in-plane mode, in particular the lowest in-plate mode, a deflection direction of the measuring pipe is oriented in an area of the excitation magnet and/or the sensor magnet parallel to the first coil axis. - A line inlet section; - a line outlet section; - a measuring pipe capable of oscillating for conducting the medium, wherein the measuring pipe is bent in one pipe plane in its idle position, wherein the measuring pipe connects to the line inlet section on the inlet side and to the line outlet section on the outlet side, and can be connected to a pipeline by means of the line outlet section; wherein the measuring pipe is bent in one pipe plane in its idle position, wherein the measuring pipe connects to the line inlet section on the inlet side and to the line outlet section on the outlet side, and can be connected to a pipeline by means of the line outlet section; - a sensor housing, wherein the line inlet section and the line outlet section are both securely connected to the sensor housing; - at least one oscillation exciter for exciting bending oscillations of the measuring pipe in a bending oscillation useful mode; and - at least two oscillation sensors (51, 52) for detecting oscillations of the measuring pipe, wherein the at least one oscillation exciter comprises an excitation coil and/or the at least two oscillation sensors (51, 52) each comprise one sensor coil, wherein the at least one oscillation exciter comprises an excitation magnet and/or the at least two oscillation sensors (51, 52) each comprise a sensor magnet, wherein the excitation magnet and/or the sensor magnet is/are arranged on the measuring pipe, wherein the excitation magnet extends through a coil opening in the excitation coil and/or the sensor magnet extends through a coil opening in the sensor coil, characterized in that the coil opening has an elongated basic shape, wherein the basic shape has a center of mass through which a largest diameter with a length d1 and a smallest diameter with a length d2 pass, wherein the excitation coil and/or the sensor coil has/have a first coil axis and a second coil axis in a cross-sectional plane, wherein the largest diameter d 1 is located in the first coil axis, wherein the smallest diameter d 2 is located in the second coil axis, wherein the following applies for a quotient d 1 l d 2: 1.15 ≤ d 1 / d 2, in particular 1.5 ≤ d 1 / d 2, and preferably 2 ≤ d 1 / d 2, wherein the measuring pipe is configured in such a way that, when the measuring pipe oscillates in an in-plane mode, in particular the lowest in-plate mode, a deflection direction of the measuring pipe is oriented in an area of the excitation magnet and/or the sensor magnet parallel to the first coil axis.