Effect of measuring conditions on the accuracy of a spinning rotor gauge

Abstract

The performance of a spinning rotor gauge was measured for nitrogen under various conditions. The effective accommodation coefficient was determined to be 1.05 by comparison with the standard McLeod gauge. The ratio of the reading of the gauge to that of a diaphragm gauge showed a variation ±1% at pressures from 0.1 to 10 Pa. The deviation of the ratio at 0.3 Pa was within ±1% for 7 months. The lower limit of the measuring pressure of the gauge was affected by fluctuations of its offset. The angular deviation of gauge positioning changed the offset up to 10−3 Pa (nitrogen equivalent). Just after starting the operation of the gauge at pressures less than 10−5 Pa, the offset changed by ±3×10−5 Pa from its final value. This was revealed to be due to a temperature variation of the rotor. And the offset depended not only on the amplitude of vibration but also on its frequency.