A factor applied to gas-dependent gauges (Pirani, convection and ionization types) to correct a reading calibrated for nitrogen. For a Bayard-Alpert gauge the relative sensitivity is about 0.18 for helium, 0.4 to 0.5 for hydrogen and 1.2 to 1.3 for argon, so a helium reading has to be divided by about 0.18. A gas mixture has no single correct factor, which is one reason process control relies on capacitance manometers.
That 1E-5 on the ion gauge is mostly helium, apply the gas correction factor and it's really more like 5.5E-5.
Also heard as
- gas factor
- gas correction
Related terms
Ionization gauge
Gauge that reads high and ultra-high vacuum by ionizing gas molecules and measuring the resulting ion current.
Pirani gauge
Thermal conductivity gauge that reads pressure from how quickly gas carries heat away from a hot wire.
Capacitance manometer
Diaphragm gauge that reads true pressure, regardless of gas type, from the capacitance of a flexing diaphragm.
Convection gauge
Pirani-type gauge that uses gas convection around the heated wire to read from about 10⁻³ mbar up to atmosphere.