Method and apparatus for determining the air rate

摘要

In the determination of the air rate by means of a measuring bridge, the current flowing through the air-current measuring resistor at bridge balance is normally taken as a measure for the air rate. If, in critical working ranges, especially when beginning at low temperatures, there is not a sufficient reserve in the bridge supply voltage available for the measuring bridge and thus a bridge balance is not achievable, considerable measurement errors result. These can be avoided in that the bridge differential voltage is compared with a threshold value and that, in the case of overshoot of the threshold value, there follows a switching-over to an evaluation at constant supply voltage. In this way, a different evaluation or assessment of the measured value corresponding to the current is carried out when the bridge differential voltage is smaller than or greater than the threshold value. It is furthermore possible not only to evaluate the current flowing through the air-current measuring resistor as a measured value, but also to form, from this and from the bridge differential voltage, a corrected measured value which is then evaluated or assessed differently, depending on whether the bridge differential voltage undershoots or overshoots the threshold value. In this way it is possible to measure the air current sufficiently accurately, even if the voltage reserve for balancing the measuring bridge is no longer sufficient.