Comparison of the Pressure Indication of a Bayard–Alpert and an Extractor Gauge

Previous measurements by Redhead have shown that a main advantage of the extractor gauge (EG) in comparison with the Bayard–Alpert gauge (BAG) is the very much reduced influence of electronic desorption on the pressure indication. Detailed comparative measurements were made and have shown: (1) When pumping a UHV system for the first time, or switching off for a period and re-energizing, the pressure indicated by the EG is 3 to 5 times lower than that indicated by the BAG. (2) After degassing the gauges the pressure readings are almost the same, but higher because of increased gas desorption. The influence of the electronic desorption effect has been quantitatively investigated. The measurements confirmed that the reading of the EG is lower and more correct than the BAG reading under similar conditions.