CALIBRATION OF A SPINNING ROTOR GAS FRICTION GAUGE AGAINST A FUNDAMENTAL VACUUM PRESSURE STANDARD

This study reports the direct calibration of a spinning rotor gas friction gage (RG) against the multiple expansion vacuum pressure standard of the Physikalisch-Technische Bundesanstalt (PTB), Berlin, West Germany, with HE, Ne, Ar, Kr, Xe, CH//4, N//2, and, via a membrane micromanometer, with H//2, O//2, CO, and CO//2. It is shown that in the pressure range 10** minus **5-10** minus **2 mbar (10** minus **7-10** minus **4 Pa) the macroscopic coefficient of tangential momentum transfer between gas molecules and the rotor surface, sigma , is close to unity. The long term reproducibility of the new RG at p greater than 10** minus **5 mbar as observed over two years with long intermediate periods of air exposure is within the limits of the total uncertainty of 1% for the comparison with the PTB standard.