HGF-3000 series of thermal gas mass flow meter is the use of the principle of thermal conductivity measurement of gas mass flow meter. The instrument's sensor consists of two benchmark grade thermal resistance (platinum RTD) components. One is the mass velocity sensor T1, a temperature change is measured gas temperature sensor T2. When these two RTD into gas to be measured, wherein the sensor T1 is heated to a constant temperature difference between the gas temperature or above, another sensor for sensing measured gas temperature T2. With increasing gas mass flow rate, air flow away more heat, the temperature sensors T1 decrease to maintain T1, T2 constant temperature difference, T1 heating power would increase. According to the law of thermal effects Kim, heating power P, the temperature difference △ T (T1-T2) and the mass flow rate Q has a definite mathematical relationship. P / △ T = K1 + K2 f (Q) K3 K1, K2, K3 are related to the physical properties of the gas constants.