ionization gage

Ionization gage

An instrument for measuring vacuum by ionizing the gas present and measuring the ion current. There are two types of ionization gages.

In the hot-filament ionization gage (see illustration), electrons emitted by a filament are attracted toward a positively charged grid electrode. Collisions of electrons with gas molecules produce ions, which are then attracted to a negatively charged electrode. The current measured at this electrode is directly proportional to the pressure or gas density.

Hot-filament ionization gageenlarge picture
Hot-filament ionization gage

In the cold-cathode (Philips or Penning) ionization gage, a high voltage is applied between two electrodes. Fewer electrons are emitted, but a strong magnetic field deflects the electron stream, increasing the length of the electron path which increases the chance for ionizing collisions of electrons with gas molecules. See Vacuum measurement

ionization gage

[‚ī·ə·nə′zā·shən ‚gāj]
An instrument for measuring low gas densities by ionizing the gas and measuring the ion current. Also known as ion gage; ionization vacuum gage.