A hot cathode ionization gauge in which electrons from a heated filament oscillate through an open helical grid and ionize gas, and a thin wire on the axis collects the ions. The fine collector intercepts little of the soft x-rays produced at the grid, which pushes the lower limit down to about 10⁻¹⁰ to 10⁻¹¹ mbar. Tungsten filaments burn out if air reaches them while hot, whereas oxide-coated iridium filaments usually survive an accidental vent.
Swap in a dual-filament B-A gauge, the last one lost its only filament when somebody vented with it on.
Near its lower limit a B-A gauge reads a floor set by x-ray current rather than gas; an extractor gauge is the next step down.
Also heard as
- B-A gauge
- BA gauge
Related terms
Ionization gauge
Gauge that reads high and ultra-high vacuum by ionizing gas molecules and measuring the resulting ion current.
Degas
To heat a gauge's electrodes hard in vacuum so they release adsorbed gas that would otherwise skew the reading.
Cold cathode gauge
Ionization gauge with no filament that uses a magnetically trapped discharge to read high vacuum pressure.
UHV
Ultra-high vacuum: pressures below about 10⁻⁷ mbar, reached only with baked, metal-sealed systems.