Ionization Gauge Calibration System Using a Porous Plug and Orifice

Abstract

A calibration facility in which reproducible pressures are conveniently generated for ionization gauge calibration is described. The method uses two conductances in series, both operating in the molecular flow region, to produce low pressures at the test gauge. These low pressures are referenced to higher pressures whose measurement can been accomplished by convenient methods. The test pressure is proportional to the ratio of the two conductances. By using a porous material and a thin plate orifice, the reference pressure is reduced by a factor of approximately one million. A convenient feature of the system is the fact that once the ratio of the conductances has been determined, it can be used for many gases. Experimental results obtained using this method over the range from 10−3 to 10−9 Torr are presented.