Calibration of a spinning rotor gas friction gauge against a fundamental vacuum pressure standard

The paper reports the direct calibration of a spinning rotor gas friction gauge (RG) against the multiple expansion vacuum pressure standard of the Physikalisch-Technische Bundesanstalt (PTB), Berlin, with HE, Ne, Ar, Kr, Xe, CH4, N2, and, via a membrane micromanometer, with H2, O2, CO, and CO2. It was found that in the pressure range 10−5–10−2 mbar (10−7–10−4 Pa) the macroscopic coefficient of tangential momentum transfer between gas molecules and the rotor surface, σ, is close to unity. The long term reproducibility of the new RG at p≳10−5 mbar as observed over two years with long intermediate periods of air exposure was within the limits of the total uncertainty of 1% for the comparison with the PTB standard. The RG thus seems recommendable for use as a reliable transfer standard, all the more since the only constituent of the new instrument that must be transferred is a small (typically 4.5-mm-diam) steel ball.