Abstract: A measuring device (1) is provided for measuring the flow rate of a medium (5) flowing through measuring tube (3). The measuring device (1) contains means for generating a constant magnetic field (B) perpendicular to the flow direction (v) of the medium (5) and at least two decoupling regions (7, 7?) which are disposed in a plane (E) perpendicular to the flow direction (v) of the medium (5) on the wall (9) of the measuring tube (3). Each decoupling region (7, 7?) comprises an electrode (13, 13?) which has a non-metal porous layer (11) on the side facing the medium (5) and a measuring unit (19) for detecting a measuring signal. In the measuring device (1), the porous layer (11, 11?) comprises an oxidic and/or non-oxidic ceramic material.