Automated Partial Pressure Estimates from QMA Data

摘要

A Partial Pressure Analyzer (PPA) is the most commonly used instrument to measure the partial pressures of residual gases in any vacuum system. Since, the output of the PPA is a mass spectrum and not the partial pressures of the residual gases, one needs to adopt some procedure to convert the spectrum to obtain the partial pressures. The conventional method of analysis is tedious and time consuming. For each gas species present in the system, one needs to identify a peak in the spectrum which is not due to any other gas species present in the system. This is always not possible and even when possible, makes the procedure complicated. We propose a new approach based on constructing a set of linear equations and solving them using matrix operations. This is a simple method compared to the conventional one and also eliminates the limitations of the conventional method. A Fortran program has been developed which identifies the likely gases present in the vacuum system and calculates their partial pressures from the data of the residual gas analyzers. Application of this method of calculating partial pressures from mass spectra data obtained with a Quadrupole Mass Analyzer (QMA) installed on a vacuum furnace will be discussed in this paper.