Comparison of various outgassing rate measurements for UHV systems

Outgassing rate is one of the most important criteria for vacuum acceptance of various components used in ultra-high vacuum (UHV) systems. There are numerous methods to measure the outgassing rate of UHV components. One of the most common techniques is the so called ‘pressure-rise’ method. In this method the component under test is enclosed in a system and disconnected from the pump. The outgassing rate is calculated from the pressure rise that occurs due to the outgassing of the component. Comparing this with other techniques, the pressure-rise method is more straightforward and allows easier analysis of the data. Nevertheless, the outgassing rate obtained from the pressure-rise method tends to be much lower than the actual outgassing rate. This paper presents an investigation of another approach to analysing the data obtained from the pressure-rise method. The objective of this approach is to provide a greater accuracy in the outgassing rate measurement, as well as to understand the reason behind the large error obtained using the pressure-rise method. The new approach of calculating the outgassing rate from the ‘pressure-rise’ method is then compared to other methods.