Airflow Measurement

During operation a heated platinum filament is subjected to the flow of intake air in the inner tube of the heating filament of the airflow meter (HLM). Heat is dissipated from the heating filament by the flow of air. This heat loss is compensated by controlling the heating current. At the same time, the power supply also flows via a precision resistor whose voltage drop represents a direct measure for the volume of intake air. Air temperature fluctuations are registered by a compensation resistor and taken into account during the measurement procedure. After switching off the engine, the healing filament is subjected to an increased current surge for approximately one second in order to burn off any impurities on the filament.