Magnetic-inductive flow meter

A magnetic-inductive flow meter for detecting a flow velocity-dependent measurement variable of a flowable medium, the flow meter comprising:

• a device configured to generate a magnetic field, which includes a coil arrangement;
• a device configured to tap a measuring voltage induced in the flowable medium, which includes at least two diametrically arranged measuring electrodes;
• an operating circuit configured to supply electrical power to the magnetic field-generating device by an electrical operating signal including a variable coil voltage and a variable coil current,
• wherein the operating signal has a time-varying coil voltage curve, which is divided into time intervals,
• wherein the time intervals each have a first time subinterval in which a first voltage of the variable coil voltage is applied to the magnetic field-generating device over the first time subinterval, wherein the first voltage is a constant voltage;
• a control circuit configured to control at least the first voltage such that a deviation of a control function from a predetermined control setpoint is minimal, wherein the control setpoint includes a quantity proportional to a magnetic flux;
• and
• a diagnostic circuit configured to monitor at least one diagnostic value.

A method for operating a magnetic-inductive flow meter for determining a flow rate-dependent measured variable of a flowable medium, wherein the magnetic-inductive flow meter comprises a device configured to generate a magnetic field and a device configured to tap a measurement voltage in the medium, the method comprising:

• applying an electrical operating signal including a variable coil voltage and a variable coil current to the magnetic field-generating device, which operating signal supplies electrical power to the magnetic field-generating device,
• wherein the operating signal has a time-varying coil voltage curve, which is divided into time intervals,
• wherein the time intervals each have a first time subinterval, in which a first voltage is applied to the magnetic field-generating device over the first time subinterval, and
• wherein the first voltage is controlled such that a deviation of a control function from the control setpoint is minimized;
• and
• monitoring a diagnostic value.