A family of gauges covering roughly 10⁻² down to 10⁻¹¹ mbar, in which electrons ionize gas molecules and the collected ion current is proportional to gas density. Hot cathode types use a heated filament as the electron source, while cold cathode types use a magnetically confined discharge. Each gas ionizes with a different efficiency, so these gauges are calibrated for nitrogen and corrected with gas factors for anything else.
Don't switch the ion gauge on till the convection gauge has bottomed out, or you'll fry the filament.
Also heard as
- ion gauge
- IG
Related terms
Bayard-Alpert gauge
Hot cathode ionization gauge with a fine central collector wire, the standard gauge for high and ultra-high vacuum.
Cold cathode gauge
Ionization gauge with no filament that uses a magnetically trapped discharge to read high vacuum pressure.
Gas correction factor
Multiplier that converts a gauge reading calibrated for nitrogen into the true pressure of another gas.
Degas
To heat a gauge's electrodes hard in vacuum so they release adsorbed gas that would otherwise skew the reading.
High vacuum
The range from about 10⁻³ down to 10⁻⁷ mbar, where molecules mostly hit the walls rather than each other.