Small Corrections to 1989 NIST Constant-Volume Gas Thermometry Data

Area of Science:

• Thermodynamics
• Metrology
• Thermometry

Background:

• Constant-volume gas thermometry provides data on thermodynamic temperature.
• The International Practical Temperature Scale of 1968 (IPTS-68) is a consensus scale.
• Previous data from 1989 required refinement due to new scientific understanding.

Purpose of the Study:

• To correct previously published constant-volume gas thermometry data.
• To refine the difference between thermodynamic temperature and IPTS-68.
• To assess the impact of updated physical property data on temperature scale comparisons.

Main Methods:

• Revising gas thermometry data using a refined estimate of gas bulb material thermal expansivity (published 1990).
• Improving corrections for helium gas nonideality based on better knowledge.
• Analyzing the net effect of these corrections on thermodynamic temperature measurements.

Main Results:

• Refined thermal expansivity increased thermodynamic temperature by 1-3 mK.
• Improved nonideality corrections decreased thermodynamic temperature by 0.1-0.5 mK.
• The net effect resulted in a small increase in thermodynamic temperature, ranging from 0.5 mK to 3 mK across the measured temperature range (505 K to 933 K).

Conclusions:

• The corrected thermodynamic temperatures are slightly higher than previously reported.
• These corrections, while smaller than experimental uncertainties, are significant for future temperature scale recommendations.
• The findings refine the relationship between thermodynamic temperature and consensus scales in the high-temperature range.