We describe measurements of thermodynamic temperature in the range 5 K to 24.5561 K (the triple point of neon) using single-pressure refractive-index gas thermometry (SPRIGT) with ⁴He. In the wake of the May 2019 re-definition of the kelvin and its associated mise en pratique, the main purpose of the work is to provide values of T–T ₉₀, the discrepancy between thermodynamic temperature and that of the International Temperature Scale of 1990 (ITS-90). The link to ITS-90 is made via calibrated rhodium-iron resistance thermometers. Innovations required to reach the level of accuracy required for meaningful measurements (uncertainty in T–T ₉₀ less than the expected deviation) include the suppression of temperature oscillations in a cryogen-free cryostat, a pressure stabilization scheme based on a non-rotating piston balance, modelling of the hydrostatic head correction and refinements of the measurement of microwave resonances in a quasi-spherical copper resonator. The accuracy of measurements varies from 0.05 mK to 0.17 mK and is competitive with that of all previous ones in this temperature range using other techniques. The improvement stems partly from the new techniques used for the new definition of the kelvin as well as ab initio calculations of the thermophysical properties ofgaseous ⁴He. In addition to confirming the validity of SPRIGT as an accurate, easier-to-implement alternative to other low-temperature primary thermometry techniques (e.g. acoustic gas thermometry) yet with scope for improvement, the results should provide important input data for any future revision of ITS-90.

我们描述了使用单压折射率气体温度计 (SPRIGT) 和⁴ He测量 5 K 到 24.5561 K（氖三相点）范围内的热力学温度。在 2019 年 5 月重新定义开尔文及其相关的实践之后，这项工作的主要目的是提供T – T _{90 的}值，即热力学温度与 1990 年国际温标之间的差异(ITS-90)。与 ITS-90 的链接是通过校准的铑-铁电阻温度计实现的。达到有意义测量所需的准确度水平所需的创新（T – T _{90 中的}不确定性）小于预期偏差）包括抑制无冷冻剂低温恒温器中的温度振荡、基于非旋转活塞平衡的压力稳定方案、静水压头校正建模和准微波共振测量的改进。球形铜谐振器。测量精度从 0.05 mK 到 0.17 mK 不等，在此温度范围内使用其他技术与所有以前的测量精度相媲美。改进部分源于用于开尔文的新定义的新技术以及气体⁴的热物理性质的从头计算他。除了确认 SPRIGT 作为其他低温主要测温技术（例如声学气体测温法）的准确、更易于实施的替代方案的有效性外，还有改进的余地，结果应为未来的任何修订提供重要的输入数据ITS-90。