COMPARISON OF SOME METROLOGICAL CHARACTERISTICS OF HOT AND COLD CATHODE IONIZATION GAUGES

Three hot cathode gauges and two inverted magnetrons were tested against a primary high vacuum standard over the range 10-7 to 10-3 Pa with gases of N₂, Ar, He and H₂. In a continuous observation for 72 h, hot cathode gauges had better stabilities than inverted magnetrons in N₂, Ar and He, but all gauges behaved similarly in H₂. Repeated calibrations over a period of about 6 months showed that all gauges had similar stabilities in N₂, Ar and He. For H₂ however, the stability of the inverted magnetrons was better than that of the hot cathode gauges. For different gases, the discontinuities of the inverted magnetrons occurred at different pressures. For the hot cathode gauges, the changes in relative sensitivities with pressure were small in a wide pressure range. Nevertheless, for the inverted magnetron gauges the changes were strongly pressure dependent. The starting times of the inverted magnetrons varied with pressures, gases and ionizations sources in the system. For the inverted magnetrons, the outgassing rates were much lower than that of the hot cathode gauges. However, their pumping speeds were similar to that of a hot cathode gauge with an emission current of 10 mA. Some reasons, which influenced the metrological characteristics of the gauges tested, are also discussed.