thermal mass flowmeter is to measurement of fluid flow in closed conduits. The flow meter with two sensors mounted on a probe, inserted through the process conduit wall, into the gas stream. An amount of heating power P is applied to one of the sensors, causing its temeprature to raise to a measured value T2, the other sensor measures the gas temperature T1. The gas mass flowrate can be determined from the temperature difference between the heated sensor and the gas(T=T2-T1), and the amount of heating power P applied.  thermal mass flowmeter is to measurement of fluid flow in closed conduits. The flow meter with two sensors mounted on a probe, inserted through the process conduit wall, into the gas stream. An amount of heating power P is applied to one of the sensors, causing its temeprature to raise to a measured value T2, the other sensor measures the gas temperature T1. The gas mass flowrate can be determined from the temperature difference between the heated sensor and the gas(△T=T2-T1), and the amount of heating power P applied.  Constant heating current which is to heat the Tv RTD with consistent current and analyze the temperature difference between Tv and Ta= △T. Flow rate is computed based on the heated velocity sensor and the temperature sensor △T. Constant temperature differential which is to heat the Tv RTD with changing current, to keep the temperature difference between Tv and Ta consistent. Flow rate is computed based on the amount of electrical power added to heat the velocity sensor.