An Ionization Gauge of Simple Construction

A-new ionization gauge is described for measuring pressures from 10
^-4
to less than 10
^-8
millimeters of mercury. Except for a multiplying factor of 10, it gives a direct reading of residual air pressure. The gauge employs two plates, as the electron and ion collector, respectively. They are located on opposite sides of the filament, but equidistant from it. This allows easy outgassing of parts, either by electron bombardment or by radio-frequency heating. A protective shield in front of the ion collector aids in reducing the electrical leakage to that element. Danger of filament burnout due to vacuum leaks has been removed by the choice of an oxide-coated filament.