AVS 49th International Symposium
    Vacuum Technology Tuesday Sessions
       Session VT-TuP

Paper VT-TuP7
Influence of Temperature on the Sensitivity Coefficient of a Hot Cathode Ionization Gauge

Tuesday, November 5, 2002, 5:30 pm, Room Exhibit Hall B2

Session: Poster Session
Presenter: H. Akimichi, National Institute of Advanced Industrial Science and Technology, Japan
Authors: H. Akimichi, National Institute of Advanced Industrial Science and Technology, Japan
M. Hirata, National Institute of Advanced Industrial Science and Technology, Japan
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Hot cathode ionization gauges, such as a triode gauge and a Bayard-Alpert type gauge are used as reference, secondary and transfer standards in high and ultrahigh vacuum. For these applications, the stability of the sensitivity coefficient (S) of the gauge is very important. Under ideal conditions, the coefficient may be kept within 1%. It is well known, however, that the indication of the gauge is strongly affected by temperature. We studied the influence of temperature on the indication of the gauge. By cooling an ionization gauge with an electric fan, the indication at pressure lower than about 10@super -4@ Pa decreased with temperature, which dues to the decrease in the outgassing from the gauge itself. Typically, the indicated pressure at 6x10@super -6@ Pa decreases about 30 % by the decrease in the temperature (Tg) of the gauge head from 40 to 27 °C. In contrast, at pressure higher than about 10@super -4@ Pa, the decrease in the temperature caused an increment of the indicated pressure at about 2 %. The shift in the indicated pressure was explained by the thermal transpiration effect S'/S = @sr@(Tg/Tg'). Change in room temperature (Tr) from 22 to 32 °C, on the other hand, the sensitivity coefficient of the gauge changed from 0.128 to 0.125 Pa@super -1@. This result was also explained by the relations S'/S = Tr/Tr', since the temperature change in vacuum chamber and in gauge head are much the same. These results mean that compensation of the temperature for the sensitivity coefficient is important for a precious pressure measurement using an ionization gauge.