Sensitivity variation of Bayard–Alpert gauges with and without closed grids from 10−4 to 1 Pa

Abstract

Since the accurate range of the spinning rotor gauge (SRG) does not extend below 10−4 Pa, constant sensitivity of high vacuum gauges for at least one decade above this value is important for their calibration when using an SRG. Two pairs of nude Bayard–Alpert (BA) gauges were compared with an SRG over the range 10−4–1 Pa. One pair was made from two identical, commercial, nude ultrahigh vacuum (UHV) BA gauges by removing the grid caps from one gauge. At 1.0 mA emission, the sensitivity of the gauge with closed grid started to decrease at 10−3 Pa, falling from 0.18/Pa to 0.047/Pa at 1.6 Pa. With open grid, the sensitivity was constant at 0.096/Pa to 10−3 Pa, increased slightly, and then fell to 0.047/Pa at 1.6 Pa. A pair of nude gauges was built with grids 16 mm in diameter by 26 mm long, identical except that one had a closed grid and the other did not. The sensitivity of the gauge with closed grid was nearly constant at 0.069/Pa to 1.3×10−2 Pa, decreasing to 0.033/Pa at 1.6 Pa, and with open grid was constant at 0.049/Pa to 4×10−1 Pa, falling to 0.033/Pa at 1.6 Pa. At an emission current of 0.10 mA, constant sensitivity extended to higher pressures for all gauges.