GB1112796A - Vacuum gauge - Google Patents

Abstract

1,112,796. Ionization manometers. VARIAN ASSOCIATES. 7 March, 1966 [5 March, 1965], No. 9934/66. Heading H1D. An ionization gauge comprises an emitter 12, a high-voltage electron accelerator 13, a separate low-voltage electron collector 14 and an ion collector 15. The gauge functions in the presence of a magnetic field which constrains the electrons to move so that they do not strike the accelerator 13 but have a high probability of being collected by the low-voltage collector 14 which reduces the number of X-rays produced. The magnetic field may also be such that any photoelectrons emitted from ion collector 15 due to impinging stray X-rays are constrained to return to the ion collector. As shown, the cylindrical filamentary thermionic emitter 12 is disposed coaxially about one end of the elongated accelerator 13, which has a relatively small surface area, and the low-voltage collector 14 is placed coaxially about the opposite end, and all three are encompassed by coaxial tubular ion collector 15, which also forms part of the envelope. Coaxially outside the ion collector 15, and insulated from it by ring 29, is permanent or electromagnetic means 16, which produces the required field. One end of the envelope is sealed by an insulating glass or ceramic header assembly 21 through which the lead-in wires pass. The opposite end of the gauge is connected via ring 22 to vacuum flange 24 which is secured to mating flange 25 in the wall of the system whose pressure is to be measured, so that the gauge forms an evacuable appendage in the wall 26 of the system. To eliminate a residual current in the ion collector due to ion emission from the filament 12, a cylindrical electrostatic shield 30 may be provided. The accelerating electrode may be provided with an outwardly extending disc-like member to aid in drawing off electrons from the filament, Fig. 3 (not shown).