Application of precise heat-capacity data to the analysis of the temperature intervals of the NBS (1955) and the International Practical Temperature Scales in the region of 90 °K

Abstract

A method is presented for analyzing the temperature intervals of the NBS (1955) temperature scale and the International Practical Temperature Scale (IPTS). Values of dT/dR as a function of resistance are derived from equations of dQ/dR and dQ/dT, obtained from precise heat-capacity data (better than ± 0.02 percent) by the method of least squares. An adjusted temperature scale is obtained by integration of the values of dT/dR relative to a reference temperature and the corresponding resistance of the thermometer. The results of the adjusting process in the neighborhood of the oxygen point (90.18 °K) are discussed and compared with the existing temperature scales. The derived temperature scale was found to be similar to the scales maintained by the Pennsylvania State University (PSU), the Physico-Technical and Radio-Technical Measurements Institute (PRMI), and the National Physical Laboratory (NPL) from the upper limits of these scales, near 90 °K, down to 50 °K. The adjusting method presented is limited by the uncertainty of formulation of dQ/dR and dQ/dT and the derived temperature scale is limited by the accumulated uncertainty in the integral of dT/dR.