A magnetic flowmeter comprises a pipe section for process flow, a coil for generating a magnetic field across the pipe section, a current source for energizing the coil to generate the magnetic field at a coil drive frequency, and electrodes for sensing voltage induced across the process flow by the magnetic field. A processor calculates a function of the sensed voltage and generates a flow output based on the function. The processor adjusts an operating parameter of the flowmeter, such as electrode voltage sampling period, the coil drive frequency, or a phase shift, as a function of a sensed electrode-to-electrode or electrode-to-ground complex impedance.