Offset scatter reduction of spinning rotor gauges by vibration isolation

The spinning rotor gauge is an accurate vacuum gauge of good long-term stability. Many efforts have been aimed at the reduction of the uncertainties of this device. Here we examine the possibility of reducing the uncertainty in the low-pressure range caused by the scatter of the pressure-independent residual drag (offset). Random vibrations exposed to the system produce random eddy currents and lead to an additional scatter of the offset value. We tested different configurations, where the suspension head only was isolated from vibration or where both suspension head and stainless steel thimble were isolated. Data sets containing time, frequency of the rotor, relative deceleration rate and temperature were taken at residual pressure conditions. It was found that vibration isolation of the suspension head alone does not cause a significant reduction of the offset scatter, while vibration isolation of suspension head and thimble reduces the scatter by a factor of down to 130. Surprisingly, it was found that the size of the reduction depends on the controller suspension head unit used for the measurement.