BEHAVIOR OF COMMERCIAL SPINNING ROTOR GAUGES IN THE TRANSITION REGIME

We have investigated the accuracy of commercial Spinning Rotor Gages ( SRG) in the transitional regime between 0. 1 and 133 Pa. We have found that commerical SRGs which have been calibrated at low pressure (10(- 2) Pa) are in good agreement with our standard for pressures up to 1.0 Pa. Above 1.0 Pa, we found that the SRG readings are systematically i n error and are gas and rotor diameter dependent. The best performance was found with the lighter gases, H-2 and He. Errors as large as a fa ctor of 2 were observed for the heavier gases, Ar and N2. We also have found that different linearization schemes have been implemented in t he two brands of SRGs. For one brand of SRG controller, the best perfo rmance with the heavier gases was for Ar and 4.76 mm rotors without te mperature compensating for gage heating effects. For the other brand o f SRG, errors are significantly reduced by temperature compensating fo r gage heating effects.