Search for Accuracy in Absolute Calibration

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Abstract
The need for an absolute calibration facility in metrological studies has resulted in the design and construction of a variable conductance apparatus whose precision has been determined by statistical methods. Absolute manometers have been compared with this apparatus. Particular attention has been given to the exact determination of the error bars, both for the apparatus and for the reference manometers: this comparison yields increased accuracy. The Monte Carlo method appears well adapted to problems of molecular flow in the system and indicates that the diamagnetic suspension molecular gauge (MSD) may be considered absolute between 10−3 and 10−6 Torr. Fruitful comparisons in the 10−4 Torr range have also been made with another absolute device: the differential interferometric manometer (MDI). For instance for absolute pressure differences across the adjustable conductance, calculated value by Monte-Carlo simulation and experimental values measured by MDI and MSD yield a result of 2.25±0.01×10−4 Torr. In the above range of pressure there are now two absolute gauges which renew the calibration method by direct comparison and allows one to avoid the need of a pressure reference transfer, as it is often necessary by using, for instance, a MacLeod gauge.

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