In what pressure range does the Extorr work?
The Extorr systems are really three vacuum measuring devices all housed on a single probe. The Useful range of the Pirani gauge section is from atmospheric pressure to 10-2 torr. At 10-2 torr the ion gauge filament starts to turn on with a reduced electron current. The ion gauge operates at this reduced emission until 10-4 torr. At this point the filament turns fully on and quadrupole partial pressure readings become available. The total pressure is still determined by the ion gauge all the way down to about 10-9 torr where the x-ray limit of the gauge is approached. Partial pressures give useful qualitative information at pressures between 10-4 and 10-5 torr and become more quantitative all the way to partial pressure readings in the 10-12 torr range.With the addition of the optional multiplier, some partial pressures may be observed to below 10-14 torr.
