Investigations of the long-term measuring stability of cold-cathode gauges

Abstract

Cold-cathode ionization gauges (CCGs) are used widely for pressure reading in vacuum systems due to large measuring range, robustness and relative low cost. Amongst the many advantages of CCGs, however, these instruments are restricted in use by decreasing measuring accuracy over operating time as internal electrodes become contaminated. Thus, to guarantee a consistently high measuring accuracy, this gauge type needs to be calibrated regularly after a fixed operating time period. With the aim of quantifying the useful lifetime of CCGs we investigated the measuring behavior of different commercial CCGs in several long-term-operation tests. After a first calibration, the gauges were operated in a vacuum atmosphere with a high fraction of hydrocarbons for several thousand hours at varying high-vacuum pressures. After use, the gauges were re-calibrated and changes in their characteristics analyzed. To compare the operating states of the used CCGs a new basic quantity was introduced: the so-called pressure dose. Using this quantity it should be possible to verify roughly the effective lifetime of CCGs until their pressure readings become erroneous due to contamination effects. It was found that the pressure reading of all tested CCGs become inaccurate after a pressure dose of about 1 mbar h.