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

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.

ionization gage

[‚ī·ə·nə′zā·shən ‚gāj]
(electronics)
An instrument for measuring low gas densities by ionizing the gas and measuring the ion current. Also known as ion gage; ionization vacuum gage.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.