Commercial spinning rotor gages (SRGs) use a special linearization procedures to compensate for a vanishing pressure dependence of the rotor deceleration rate in the transition regime from 0.1 to 100 Pa. These procedures have been found to have large errors above 10 Pa,@footnote 1@ but can be significantly improved. An extensive set of experimental data of rotor deceleration rate versus gas pressure up to 130Pa was acquired. A group of six SRGs and four gases (N@sub 2@, Ar, He and H@sub 2@) were used in the study. Temperature measurements where also included to account for heating effects. The data shows that the differences between rotor/thimble combinations are large enough to cause differences of several % if one uses the linearization functions currently in use without adjustable parameters. To get the best accuracy, one parameter is left in our linearization procedure to be determined by calibration. We call it the Knudsen length of the rotor/thimble assembly. This is the second calibration constant of SRG that needs to be determined for accurate pressure measurements above 1Pa. The method to determine the second calibration constant at 100Pa will be proposed. The first calibration constant is the already well-known rotor accommodation coefficient and is determined in molecular regime below 0.01Pa. Achievable accuracy of the new linearization procedure with the two calibration parameters is better than 1% over the entire range from molecular regime up to 130Pa. The effect of thimble temperature on this linearization procedure will also be discussed.
@FootnoteText@
@footnote 1@J.Setina and J.P.Looney, Vacuum, 44,1993, p.577