COMPARISON OF THE STABILITY OF HOT AND COLD CATHODE IONIZATION GAUGES

The stabilities are most important features when ionization gauges are used as reference or secondary standards. Generally, only hot cathode gauges are used as reference or secondary standards in calibration services. Some reasons preventing the use of cold cathode gauges are the presence of discontinuities in the current versus pressure characteristic, the ignition delay at very low pressures, and the poor stability especially under contaminating vacuum environments. Though modern inverted magnetron designs are believed to avoid some of these problems at least under clean conditions, no "hard facts" have been published to support this believe. The experimental results of calibrations of three hot cathode gauges and two inverted magnetrons against a primary high-vacuum standard over the range 10^-7 to 10^-3 Pa with gases of N₂, Ar, He and H₂ are presented respectively. During a continuous observation period of 72 h at a constant pressure of about 1×10^-4 Pa, hot cathode gauges showed better stabilities than inverted magnetrons in N₂, Ar and He, but all gauges behaved similar in H₂. Repeated calibrations over a period of about 6 months showed that all gauges had similar long-term stabilities in N₂, Ar and He. For H₂, however, the stability of inverted magnetrons was better than that of hot cathode gauges. Toward different gases, the discontinuities of inverted magnetrons occurred at different pressures, making their calibrations more elaborate.