Dynamic extension - A new principle for a vacuum primary standard for UHV-range (10^(-6)-10^(-10) Pa) calibration of hot cathode ionisation gauges
Abstrakt
The main obstacle in the construction of primary vacuum standards for very low pressures - ultra-high vacuum (UHV) - is outgassing from the walls of the apparatus. Thus, principles utilising a higher pumping rate in the calibration chamber, e.g., the pressure ratio technique, seem to be more useful for this range.
However, a serious problem is inherent in this method, namely, that the gas in the calibration chamber is not in equilibrium and thus cannot be characterised by a single scalar pressure value, although such a value is then used to evaluate the measurement. This discrepancy can be overcome by using a hot cathode ionisation gauge as a transfer standard calibrated by the dynamic extension method.
The dynamic extension method is explained and compared with the pressure ratio technique. The basic conditions for achieving acceptable uncertainty values are considered.