A Precision Vacuum Gauge

Abstract

A pressure measuring device of the general type first described by Knudsen has been constructed for obtaining precision measurements of gaseous pressures in the range from 1×10⁻⁵ to 10⁻³ mm of Hg. The instrument has been calibrated, with the aid of a McLeod gauge, in nitrogen, hydrogen, oxygen, methane, ethylene, normal‐butane, and iso‐butane. The mechanical precision of the instrument seems to be better than plus or minus 0.5 percent and the accuracy of the above calibrations is probably of the order of plus or minus 1 percent. Calibration curves for the above gases have been treated analytically and equations for the different gases have been discussed. An empirical method of calibration has been described for calibrating the instrument in condensible gases whose pressures cannot be measured in a McLeod gauge.