Extension of the range of the Moser and Poltz McLeod gauge from 10 −10 to 10 −2 torr

Abstract

Two McLeod gauges of the Moser and Poltz type have been designed, assembled and used in experiments. The primary gauge constants (K) are: low pressure gauge (lpg) 7.66 X 10 −9 medium pressure gauge (mpg) 1.45 × 10 −7. Limits to the smallest practical final volume (8 × 10 −6 cm 3) have been found. Derivation of equations giving the validity of the operating equation as a function of certain simplifying assumptions has been accomplished. It is shown that the optimum shape for the top of the compression capillary is parabolic. Investigation of errors caused by curvature of the mercury surface at the seal off position, adsorption, temperature effects, etc, is described. Experimental results of calibration of several ionization gauges is presented: accuracies of 90% at 3 × 10 −9, 25% at 1 × 10 −8, 8% at 10 −7, and 4% at 10 −6 torr with the lpg or mpg (whichever is appropriate) were obtained.