Pumping speed measurement of turbomolecular pumps by a quasi-stationary pump-down method

The pumping speed of a turbomolecular pump is usually measured by injecting a stationary known gas flow via a standardized test dome into the pump and measuring the equilibrium pressure in the test dome. The ratio of gas throughput and pressure is just the pumping speed. In practice, the pressure can be conveniently and accurately measured, whereas the convenient and accurate throughput measurement is a challenging experimental problem. The present paper reports on a new method for measuring the pumping speed in which the throughput is generated by the pumping down of a vessel via an orifice. From the decrease of vessel pressure with time, and from known vessel volume, the throughput can be directly and accurately derived. Exploring measurements by the new method in fact give high accuracy, systematical error sources are practically negligible.