Construction and theoretical analysis of a direct-reading hot-wire vacuum gauge with zero point control

Summary

A hot-wire vacuum gauge connected to a special bridge (fig. 2), indifferent to voltage fluctuations or changes in the temperature of the surroundings, is described. The balance point of the bridge can be controlled independently of the actual gas pressure in the vacuum system. The heating current is adjusted in the region of maximum sensitivity for very low pressures. The instrument has been calibrated from 10⁻⁵ up to 0.1 mm Hg. Calibration curves for air, hydrogen, helium and argon are shown (fig. 6 and 7).

A theoretical analysis of the gauge-bridge assembly is given. The calculated total sensitivity at very low pressures as a function of the heating current appeared to be in fair agreement with the experimental results (fig. 5). The calibration curve for air could be computed on the basis of a theoretical formula, assuming that the thermal conductivity of air remains directly proportional to the pressure in the whole region investigated. Factors, determining the pressure sensitivity of a gauge-bridge combination, are discussed.