A mass airflow sensor (MAF) determines the mass of air flowing through a conduit. This is generally achieved by using heated wires in the airstream. By knowing the temperature of the air (generally through an intake air temperature sensor) and the resistance in the wire, the MAF can determine how much mass is flowing. Mass is a property of physical objects that, roughly speaking, measures the amount of matter they contain. ... Layers of Atmosphere (NOAA) Earths atmosphere is a layer of gases surrounding the planet Earth and retained by the Earths gravity. ... A wire is a single, usually cylindrical, elongated strand of drawn metal. ... Mass flow rate is the movement of mass per time. ...

The wires in the airstream are commonly heated by passing a fixed electrical current through them. Because a metal wire's electrical resistance increases with temperature, by passing a fixed current and knowing the temperature and thus electrical resistance the wire should reach, one has a laboratory-established baseline. If, however, a mass flow of air is passing over the wire a cooling effect takes place. This reduction in temperature provides a reduction in electrical resistance from the laboratory-established baseline, which can be interpreted as a specific amount of airflow. A wire is a single, usually cylindrical, elongated strand of drawn metal. ... In electricity, current refers to electric current, which is the flow of electric charge. ... Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ... Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ... Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ... Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ... Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ... Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ...

The cooling effect is, of course, slightly dependent on the current air temperature, and the wires themselves don't always hold to their baseline (dirt, for instance, changes the result). Thus, an initial condition prior to the airflow is generally established, and an intake air temperature sensor is generally used to sense the airflow temperature.

Another sensing principle utilizes a very thin membrane over which the air passes. The membrane has a thin film temperature sensor printed on the upstream side and one on the downstream side. A heater is integrated in the center of the membrane and maintained at a fixed temperature above ambient by an ASIC. Without any airflow, the temperature profile across the membrane is uniform. When air flows across the membrane, the upstream side is cooled while the downstream side remain more or less the same. The difference between the upstream and downstream temperature sensors then becomes the direct measure of the mass airflow. With such a layout, the mass airflow sensor is also capable of measuring flow in both directions.

A MAF is commonly used in automobiles with modern fuel injection systems to measure the ingested aircharge. This in conjunction with the exhaust gas oxygen sensor, provide the closed loop fueling system need to operate the engine at the stoichiometric air/fuel ratio. Fuel Injection is a method or system for metering fuel into an internal combustion engine. ... In chemistry, stoichiometry is the study of the combination of elements in chemical reactions. ...