Recent clarifications[1] issued by the Consultative Committee on Thermometry (CCT) for the definitions of the equilibrium hydrogen (e-H2) triple point (TP) and vapor-pressure points (VPs) have resulted in adjustments to the NIST-disseminated ITS-90 (T90) in the range of the interpolating constant vo...
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.621.3908 http://www.bipm.org/cc/CCT/Allowed/24/D09_NIST_ICVGT_Adjustment_Tew.pdf |
| Summary: | Recent clarifications[1] issued by the Consultative Committee on Thermometry (CCT) for the definitions of the equilibrium hydrogen (e-H2) triple point (TP) and vapor-pressure points (VPs) have resulted in adjustments to the NIST-disseminated ITS-90 (T90) in the range of the interpolating constant volume gas thermometer (ICVGT) from 5 K to 24.56 K. The NIST-disseminated ITS-90 is derived from capsule standard platinum resistance thermometers (SPRTs) calibrated over their lowest-defined sub-range of 13.8 K to 273.16 K and from realization of the ICVGT from 5 K to 24.556 K[2]. The SPRT subrange-1 uses e-H2 VPs and both definitions use the e-H2 TP as a calibration points. These calibrations are traceable to NIST realizations of the e-H2 TP and VPs which were performed using highly-depleted hydrogen gas. The revised CCT definitions for all e-H2 fixed points now call for a less-depleted composition equivalent to that of Standard Light Antarctic Precipitation (SLAP). This has necessitated adjustments in both the ICVGT range and the SPRT subrange-1. One effect of this adjustment has been changes in the observed non-uniqueness in the overlap range from 13.8 K to 24.556 K. Another effect has been a larger difference between the ICVGT and NPL-75 temperatures in the region from ~ 10 K to 20 K. The differences T-T90 reported by Pitre et. al.[3] in the range of the ICVGT have likewise been adjusted. |
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