THEORY OF EDDY CURRENTS IN ELECTROMAGNETIC FLOWMETERS

The problem of calculating eddy currents and transformer signals in electromagnetic flowmeters is considered and a procedure for solving this is given. In this way Wyatt's theory relating base-line error to contact impedance effects at the electrodes is confirmed on the basis of the full field equations. A simple relation is shown to exist between the axial component E(z) of the eddy current E field in the liquid and the potential U induced by a flat profile flow. Using this relation it is proved that there is no way of reducing base-line error by magnetic field shaping. The same relation between E(z) and U provides the basis of a new technique for sensitivity measurement or self calibration of electromagnetic flowmeters.