Apparatus for measuring total pressure and partial pressure with common electron beam

An apparatus for determining a total pressure of a gas, comprising:

• an ionization chamber;
• said ionization chamber having adjacent first and second ionization regions, wherein a boundary between said regions is defined by one of an aperture and an anode grid;
• a filament for producing a plurality of electrons;
• a repeller;
• said repeller and anode operatively associated to focus said plurality of electrons into an electron beam passing through each of said first and second ionization regions, whereby an interaction between said electron beam and molecules of said gas within said ionization chamber produces first and second ion streams from a same gas density;
• a focus plate biased such that said first ion stream is directed from said first ionization region to an analyzer, wherein said analyzer includes means for calculating at least one partial pressure of said gas within said ionization chamber;
• an ion collector biased such that said second ion stream is directed from said second ionization region to an ion collector;
• means for measuring a reference current produced by said second ion stream at said ion collector;
• and
• means, using said reference current, for calculating said total pressure of said gas within said ionization chamber.

A method for determining a total pressure of a gas, comprising the steps of:

• providing an ionization chamber, said ionization chamber having adjacent first and second ionization regions, wherein a boundary between said adjacent ionization regions is defined by one of an aperture and an anode grid;
• producing an electron beam passing through each of said adjacent first and second ionization regions, whereby an interaction between said electron beam and molecules of said gas within said ionization chamber produces first and second ion streams from a same gas density;
• directing said first ion stream from said first ionization region to an analyzer;
• and
• directing said second ion stream from said second adjacent ionization region to an ion collector.