Working Principle

Thermal gas mass flow meter is designed on the basis of thermal dispersion, and adopts method of constant differential temperature to measuring gas flow.

The thermal sensor part consists of two reference platinum resistance. When the flow meter is running, a temperature sensor continuously measures the temperature T1 of the medium,  and the other sensor will be heated to a temperature T2.  T2 is greater than T1.

This temperature difference △T=T2-T1, when there is a gas flow going, the gas molecules in the process will take away heat, so that the value of T2 decreased. If you want to make sure △T unchanged, it must increase the T1 sensor power supply current. The greater the velocity of the medium, the greater the power supply current of the T1 sensor.

There is a specific functional relationship between the velocity of the medium and the increased heat.

V=[K（Q/△T)^1.87]/ρg  …………（1）

In the formula：ρg — specific gravity of fluid (related to medium density)

V — Flow rate

K – equilibrium coefficient

Q — heat added (related to specific heat)

△T — temperature difference

Since the sensor temperature keeps about 30 ° C higher than the medium (ambient) temperature automatically, the thermal gas mass flow meter does not need temperature compensation in principle.

The thermal gas mass flow meter is suitable for the medium temperature range of -40℃ ~ 220℃.

ρ=ρn*[（101.325+P）/101.325]*[(273.15+20)/(273.15+T)]……（2）

In the formula：ρ — medium density under working conditions (kg/m3)

ρn — medium density under standard conditions (101.325kPa, 20℃) (kg/m3)

P — Operating pressure (kPa)

T — Operating temperature (℃)

It can be seen from equation (1) and (2), the function of gas flow rate and operating pressure, density and operating temperature has been determined.