Accuracy and applicability of the spinning rotor gauge to calibration in gas mixture environments

Abstract

The spinning rotor gas friction gauge (SRG) is being used increasingly for measurement and calibration of gauges in cases where a single gas type environment is not achievable. This may involve gas mixtures composed of molecules with differing mass values and surface interaction characteristics. Since the molecular momentum transfer and hence rate of rotational decay of the spinning rotor depend on molecular mass and accommodation coefficient, the calibration of the pressure indication must reflect the gas mixture ratio. The theoretical expression for the calibration factor is derived and compared with experimental data in the molecular flow regime. Agreement to within 5% is typical with inert gas mixtures. The proper application of this method allows the SRG to accurately calibrate other high vacuum gauges for use with known gas mixtures encountered in processing conditions.