Nitrogen sensitivities of a sample of commercial hot cathode ionization gage tubes

Abstract

In order to help assess the magnitude of errors that might arise from the use of uncalibrated ionization gage tubes and help select the best type of tube when accurate measurements are required we have determined the nitrogen sensitivities from 10−5 to 10−2 Pa for lots of from two to four each of five different types of commerical hot cathode gage tubes. Included were conventional triodes and B‐A structures of four distinct types. Two types with tungsten filaments—the triodes and tubulated B‐A structures—were markedly superior to the others with respect to agreement with manufacturer’s sensitivity, linearity, and uniformity of sensitivity within a type. The least satisfactory results were obtained from the nude B‐A structures, which showed significant nonlinearities, sensitivities ranging from 70%–110% of the manufacturer’s value, and typical 25% differences in sensitivity between the two filaments of a dual‐filament structure.