System determining throughput of flowing medium with substrate exposed to medium

摘要

The determining system has a substrate (10) exposable to the flowing medium, on which a first resistance system, as a part of the heat regulating circuit (HK) is arranged. With at least one resistance, heatable to a specified excess temperature. Also a second resistance system, which is wired as a bridge, with a diagonal lying between a supply voltage and earth. It includes at least two temperature dependent resistances, which are arranged related to the flow direction of the medium to be determined, above and below the heating resistance. So that they are uniformly heated by these, whilst they are cooled at differing strengths by the flowing medium, and which due to temperature difference adjusts the measuring voltage at the other bridge diagonal, and is evaluated for determining the throughput. The measuring voltage is supplied to a voltage/frequency converter (UFW) circuit, which delivers an output signal, the frequency of which is a measure for the flowing medium.