A gauge with a heated filament forming one arm of a bridge circuit; the power needed to hold the wire at constant temperature depends on how much heat the gas conducts away, which depends on pressure in the medium vacuum range. Useful readings run from about 10⁻³ mbar up to some tens of mbar, extended to atmosphere in convection-enhanced versions. The reading depends on gas type because each gas conducts heat differently, so the gauge is calibrated for nitrogen or air.
Pirani says 2E-2 on the foreline, that's fine for the turbo, leave it alone.
The thermocouple gauge, or TC gauge, common on US furnaces and coaters, works on the same principle with a cruder readout, so it shares the same blind spots on helium and argon.
Also heard as
- Pirani
- thermal conductivity gauge
Related terms
Convection gauge
Pirani-type gauge that uses gas convection around the heated wire to read from about 10⁻³ mbar up to atmosphere.
Gas correction factor
Multiplier that converts a gauge reading calibrated for nitrogen into the true pressure of another gas.
Capacitance manometer
Diaphragm gauge that reads true pressure, regardless of gas type, from the capacitance of a flexing diaphragm.
Medium vacuum
The band between about 1 and 10⁻³ mbar, where gas flow shifts from fluid-like to molecule-by-molecule.