mass airflow sensor

The mass airflow sensor’s purpose is to measure the mass amount of air entering the engine. The mass sensor is usually located on the intake inlet running to the intake manifold. Sometimes if there is a problem with it you can tap on it gently in the electronics area, and the engine should surge. There are multiple types of mass airflow sensors. Hot wire airflow meters use a current to keep a wire at a constant temp. The heat is carried away from the wire dependent on the airflow and temp. The ptc resistor varies with temperature change, as the temp drops so does the resistance. As the resistance changes the current has to increase to keep balance. This is sent to the ecu in a form of a voltage change. Another system is the hot film. It is very similar to the hot wire mass airflow meter. It heats a wheatstone bridge board, The air moves across the board and is measured on the back of the board. The thermistor measures the change in temp and thus the airflow change. The intake air temperature sensor also contributes to this equation being that humidity can slightly throw off the density reading. A vane airflow sensor simply rotates a flap as air comes in.

 

The vane airflow flap has resistance, so that as more air comes in it forces the gate open more. The angle that it’s at gives a voltage number that has a predetermined airflow value. This meter has an obvious air restriction for power purposes. Also heating the air in the hot wire meter causes negative power results. Obviously volume of air being used by the engine is the major objective of the air flow meter, as other sensors can read temp and density. One last design has definite advantages the cost must be high as I’ve never seen one used in production. This meter sends ultrasonic waves across the meter that bounce back. Dependant on the time the wave takes to bounce back to the sensor, is how it calculates the density of the fluid (air) it passes through. This is similar to how radar works. The major advantage to this system is that it doesn’t have to heat air, losing density to heat. Also because it is perfectly smooth on the inside it has no restriction to the air flow passing through it.