Eddy-current effects in an electromagnetic flowmeter

A new two-dimensional analytical model is developed for the effect of eddy currents in the metal parts of an electromagnetic flowmeter under ac excitation. This model considers the influence of both the inner stainless-steel meter tube and the outer iron magnet core, treating them as thin sheets. Appropriate boundary conditions are derived across these sheets. The model predicts the coil impedance ZZ and the magnetic field BB as complex numbers (magnitude and phase) for a given frequency ff. The model is validated by extensive experiments on a commercial 2 inch meter using excitation frequencies in the range 10 Hz to 1 kHz. After first fitting some unknown physical parameters from the data, such as the effective core permeability μμ and the conductivity σσ of each metal component, the resulting model has a typical accuracy of better than 1% for the magnitude and phase of ZZ and BB.