this zone convection in the gas until reaching the saturation zone, beyond
400 Pa. The third part is above 400 Pa. The heat transfers by Joule
effect do not increase sufficiently the wires temperature because
the intensity of the heat convection which cools the wires. Then,
the temperature difference between the gas and the wires is no
longer sufficient to start the frequency oscillation. In this third
part, the sensor response is independent of the pressure.