The generic name for mass air flow meters is "hot wire aenemometer". The principal is that a variable current source heats a wire (or grid of wires) to a specified temperature, but the wire(s) is constantly cooled by the air flow. The difference in current required to keep the wire at the predetermined temperature between some non-zero air flow value and zero flow rate is proportional to the mass flow rate, so the wire current is an analog for the mass flow. This analog value is then digitized by the engine control electronics and used to calculate base fuel flow, which is then constantly adjusted by the O2 sensor and associated control system.

The system also needs to detect and correct for inlet air temperature since cool air will cool the wire(s) more than warm air.

Duke