REALIZATION OF THE ITS-90 AT THE NRLM USING ~(4)He VAPOR-PRESSURE THERMOMETRY

摘要

The ~(4)He vapor-pressure temperature scale is realized in the range of 2.2 K to 4.3 K as part of the realization of the International Temperature Scale of 1990 at the National Research Laboratory of Metrology (NRLM), Japan. The vapor pressure is measured using an absolute pressure gauge set at room temperature. The sensing element of the gauge is a silicon resonant sensor attached to a diaphragm. The temperature distribution along the pressure-sensing tube is measured using five thin-film Rh-Fe resistance thermometers. Three capsule-type Rh-Fe resistance thermometers are calibrated against the scale and the measurement uncertainties in the realization and the calibration are estimated. The combined standard uncertainty of the fitted equation is less than 0.1 mK from 2.25 K to 4.25 K for each thermometer. The present realization is compared with the ~(4)He vapor-pressure scale realized in 1976 at the NRLM by calibrating the same Rh-Fe thermometers against both scales. The difference between the two scales is within 0.2 mK from 2.25 K to 4.25 K and is less than the combined standard uncertainty of measurement.