Coriolis mass flow meter

A Coriolis mass flow meter for measuring a mass flow and density of a fluid to be measured, wherein the fluid is a gas, a liquid or a dispersion, the flow meter comprising:

• a measuring transducer including at least one vibration element, an exciter assembly, and a sensor assembly, the measuring transducer configured to conduct the fluid to be measured such that the fluid flows through the measuring transducer at least temporarily;
• and
• an electronic transformer circuit that is electrically coupled to the measuring transducer, including to both the exciter assembly and the sensor assembly, the transformer circuit including at least one microprocessor,
• wherein the at least one vibration element is configured to be contacted by the flowing fluid to be measured and to be vibrated at the same time,
• wherein the exciter assembly is configured to convert electrical power fed to the exciter assembly into mechanical power that produces forced mechanical vibrations of the at least one vibration element,
• wherein the transformer circuit is configured to generate an electrical driver signal and to feed electric power to the exciter assembly via the driver signal such that the at least one vibration element produces forced mechanical vibrations at a vibration frequency, which is determined by the driver signal such that the forced mechanical vibrations generate Coriolis forces based on the mass flow of the flowing fluid to be measured,
• wherein to detect the forced mechanical vibrations of the at least one vibration element, the sensor assembly includes an electrodynamic first vibration sensor and an electrodynamic second vibration sensor structurally identical to the first vibration sensor, wherein the first vibration sensor is configured to convert vibration movements of the at least one vibration element at a first measurement point into an electrical first vibration measurement signal such that the first vibration measurement signal includes:
• a first signal component, which is an alternating current voltage component at a frequency corresponding to the vibration frequency with an amplitude dependent on the vibration frequency and a first magnetic flux through the first vibration sensor;
• and
• a first harmonic component, which is an alternating current voltage component at a frequency corresponding to a whole-number multiple of the vibration frequency with an amplitude dependent on the first magnetic flux,
• wherein the second vibration sensor is configured to convert vibration movements of the at least one vibration element at a second measurement point remote from the first measurement point into an electrical second vibration measurement signal such that the second vibration measurement signal includes:
• a second signal component, which is an alternating current voltage component at a frequency corresponding to the vibration frequency with an amplitude dependent on the vibration frequency and a second magnetic flux through the second vibration sensor;
• and
• a second harmonic component, which is an alternating current voltage component at a frequency corresponding to a whole-number multiple of the vibration frequency with an amplitude dependent on the second magnetic flux, and
• wherein the transformer circuit is configured to receive and evaluate the first and second vibration measurement signals and to:
• determine and output mass flow measurement values representing the mass flow of the fluid based on the first and second vibration measurement signals;
• and
• determine characteristic number values of a sensor characteristic number based on at least one of the first and second vibration measurement signals, wherein the sensor characteristic number defines a change behavior of the first and second vibration sensors in the presence of an external magnetic field and depends on the amplitude of at least one of the first and second harmonic components, and
• wherein the transformer circuit is further configured to compare one or more characteristic number values of the sensor characteristic number with one or more corresponding reference values for the sensor characteristic number so as to determine whether the one or more characteristic number values are greater than the corresponding one or more reference values and, when the one or more characteristic number values are greater than the corresponding one or more reference values, to at least one of:
• output a message indicating that the one or more characteristic number values are greater than the corresponding one or more reference values;
• and
• output no mass flow measurement values.