Heat-type gas mass flowmeter is a meter that uses the principle of thermal diffusion to measure gas flow. The sensor consists of two base-level thermal resistors (RTD). One is the speed sensor RH, one is the temperature sensor measuring the gas temperature change RMG. When the two RTD is placed in the measured gas, the sensor RH is heated and the other sensor is RMG for sensing the measured gas temperature. As the gas flow rate increases, the airflow takes more heat and the temperature of the sensor RH decreases.