Long-term stability of two types of hot cathode ionization gauges

Abstract

We have monitored the nitrogen sensitivity of four gauges each of two selected types of hot cathode ion gauges over a 500-day test period. Gauges of one type, a tungsten filament conventional triode, changed by about 12% during this time, with most of the decrease caused by ‘‘high’’ pressure operation. Gauges of the second type, a twin tungsten filament Bayard–Alpert gauge, changed by no more than 6% and with no obvious correlation between sensitivity changes and ‘‘high’’ pressure operation or exposure to air. There were no significant differences in the sensitivity changes for the two filaments in a given Bayard–Alpert gauge, although their operating times differed by a factor of 10.