Influence of the residual gas composition and the Getter-Ion effect on the measurement of the internal pressure in vacuum interrupters

The magnetron method is well established for the internal pressure measurement of vacuum interrupters. Its application during the manufacturing process is essential for the determination of the vacuum quality. The evaluation of the magnetron measurement requires precise knowledge of the residual gas composition and the influence of the metallic surfaces in the vacuum interrupter due to gas binding effects. Leading manufacturers having gained wide experience applying the magnetron method do consider these influences during the production process. However, it is also possible to measure the internal pressure in a vacuum interrupter by means of the magnetron method after a considerable long time in service, e.g. close to the end of the prospective service life. As the residual gas composition in these states is not precisely known, uncertainties in the pressure measurement can arise. Experiments with common residual gases and their typical compositions, which can form inside a vacuum interrupter, show that the uncertainty is less than one decade. In addition experiments performed on vacuum interrupters identify the temporary gas binding due to the Getter-Ion Effect as a factor that considerably limits the repeatability of the magnetron measurement.