Abstract: A sensor (10; 34) for measuring and/or detecting a fouling that forms on one surface of the sensor, includes the following: —a substrate (22) that is used for heat insulation, —at least one heating element (16; 36; 58; 78) arranged on one side on the substrate that is able to diffuse, on command, a homogenous, monitored heat flow from the side opposite the substrate, —a single temperature measuring element (18; 38; 56; 80) with dimensions that are smaller than those of the at least one heating element and positioned above and at the center of the latter, on the side opposite the substrate, in order to be in the most homogeneous part of the heat flow.