Knudsenmätare

A Knudsenmätare, often translated as Knudsen gauge or Knudsen number meter, is a scientific instrument used to measure gas pressure, particularly in low-pressure environments. It is based on the principle of the Knudsen effect, which describes the behavior of gases at very low pressures where the mean free path of gas molecules is comparable to or larger than the characteristic dimensions of the container.

In such conditions, the gas molecules collide more frequently with the container walls than with each other, leading to a pressure dependence on the momentum transfer between molecules and the walls. The Knudsenmätare typically utilizes this phenomenon by measuring the force exerted by gas molecules impinging on a suspended vane or surface. This force is then related to the pressure of the gas.

Different designs of Knudsenmätare exist, but a common type involves a torsion balance. A lightweight vane is suspended by a fine fiber. When gas molecules strike the vane, they transfer momentum, causing a slight deflection. This deflection is detected and calibrated to represent a specific pressure reading. These instruments are valuable in vacuum technology, thin-film deposition, and research involving rarefied gases where traditional pressure measurement methods may not be accurate. They are particularly useful for measuring pressures in the molecular flow regime.