Air Mass Measurement

OPERATION
During operation, a heated platinum wire is subjected to the flow of intake air in the inner tube of the hot-wire Mass Air Flow Sensor (HLM). Heat is dissipated from the hot wire by the flow of air. This heat is compensated by controlling the heating current. At the same time, the supplied current also flows via a precision resistor whose voltage drop represents a direct measure for the air mass which is drawn in. Air-temperature fluctuations are detected by way of a compensation resistor and taken into account in the measurement. After switching off the engine, an increased current surge is applied to the hot wire for approx. 1 second in order to burn the wire clean of impurities.

The advantages offered by the air mass meter can be found in the fact that, in this case, the air mass is measured and not the air flow (volume). Fluctuations in the air density (different air pressure due to differences in altitude and weather situation) are already taken into account during initial measurement. In addition, less resistance is offered to the flow of air in the air mass meter since it is not equipped with an air sensor plate which needs to be pressed down.

The voltage value of the air mass meter in conjunction with the engine speed is a direct measure for the engine load.