The air quality sensor contains a conventional two-electrode fuel cell sensor inside. The working electrode discharges electrons to the counter electrode through an external circuit and is consumed as the oxygen is reduced at the counter electrode end, and the internal circuit is realized by the ion current in the electrolyte.
When the air quality sensor is energized, the 2 diaphragms are heated, the temperature rises linearly, and the linearity is uniform. When there is no airflow, the temperature difference between the two diaphragms is 0. When the airflow passes, the airflow is blown through the 2 diaphragms. The order of the two causes different temperature changes of the diaphragm (dashed line), and the difference between the temperature of the two diaphragms is an important parameter for the ECU to calculate the mass of the intake air.