Sensitivity factor of the axial-symmetric transmission gauge: Deviation and long-term variation

The deviation of the sensitivity factors for about 50 sensors of the axial-symmetric transmission gauge (ATG) was examined. The deviation has been compared with that for about 30 sensors of the B-A gauge and for about 30 sensors of the extractor gauge. Almost the same deviations are found for the above three types of gauges. The long-term variations of the sensitivity factors for two sensors of the ATG were also measured during four years. After the initial change with operating time, the sensitivity factor stabilized after long-term operation. The room temperature effect of the sensitivity factor plays an important role on the total pressure measurement by an ionization gauge, but the change of the sensitivity factor was larger than the room temperature effect. The reason for the change of the factor is estimated in connection with the annealing and the alignment of the filament and with the deviation of the place of electron emission on the filament.