MASS-FLOW SENSING WITH HEAT WAVES - THE EFFECT OF GAS-PRESSURE

Two conceptual examples are given of mass flow sensors based on heat w aves that have exact gas pressure self-compensation in uniform flow: o ne with a plane heat source through which the flow passes, and one wit h a line source. Both sensors ratio the heat wave amplitudes detected at equal distances upstream and downstream from the source. Heat wave fronts from either source expand symmetrically upstream and downstream . An automotive air flow sensor based on heat waves is also described and modeled. It is a microelectronic device on silicon. This sensor is approximately, but not exactly, self-compensated for pressure change.