The thermal gas mass flowmeter is an instrument which uses the principle of thermal diffusion to measure the gas flow.

The sensor consists of two reference level RTDS. One is the speed sensor RH, and the other is the temperature sensor RMG to measure the temperature change of gas.

When the two RTDS are placed in the measured gas, the sensor RH is heated and the other sensor RMG is used to sense the temperature of the measured gas.

With the increase of gas flow rate, more heat is carried away by air flow, and the temperature of sensor RH decreases.