The sensor part consists of two temperature sensors of platinum resistance.
When the meter is in operation, one sensor continuously measures the temperature of the medium(T1), and the other sensor automatically heats to a temperature higher than that of the medium(T2). It is used for sensing the flow velocity of the flow body and is called the velocity sensor. △T=T2-T1(T2＞T1)
As the fluid flows through, the temperature of T2 drops as the gas molecules collide with the sensor and take away the heat. To keep △T constant, the power supply current of T2 needs to be increased. The faster the gas flows, the more heat is taken away.
There is a fixed functional relations of the flow rate of gas and the amount of heat added, which is called the thermostatic difference principle.