Present Estimates of the Differences Between Thermodynamic Temperatures and the ITS-90

Abstract

At the request of the Consultative Committee for Thermometry (CCT), Working Group 4 (WG4) has critically reviewed all available measurements of the differences between thermodynamic and ITS-90 temperatures, (T − T 90 ), and documented the conversion of older data to the ITS-90. Particular attention has been given to the uncertainties. Based on this review, we provide consensus estimates of T − T 90 for selected measurements from 0.65 K to 1358 K. We provide two analytic functions for T − T 90 , one for use from 8 K to the triple point of water (T TPW ) and one for use above T TPW . The small discontinuity of the derivative dT 90 /dT at T TPW is discussed.J. Fischer (B) · L. Wolber PTB,We also identify temperature ranges where researchers are encouraged to undertake high-accuracy measurements of T − T 90 .

Progress towards the determination of thermodynamic temperature with ultra-low uncertainty

“…As a whole, these results are mostly consistent with previous (T − T 90 ) determinations obtained with the same technique, where available, and with the WG4 interpolation [4]. This is particularly true for the range above T TPW up to T Ga and the temperature range below 100 K, separately displayed with more detail in figure 3 to ease comparison with older data.…”

“…Working Group 4 (WG4) of the BIPM Consultative Committee of Thermometry recently completed a critical comparative review of the thermodynamic temperature measurements which constituted the backbone for the definition of ITS-90 [4]. Additionally, they considered more recent results (post the inception of the ITS-90) and highlighted some unexplained inconsistencies and the lack, or paucity, of supporting data in particular temperature ranges: notably between 25 K and 255 K; between 550 K and 690 K; and at the copper freezing point.…”

“…Current research in the application of AGTs to primary thermometry aims at a further extension of its useful range to higher and lower temperatures and may finally cover an overall temperature range spanning between the λ-point of 4 He at 2.2 K and the freezing point of copper at 1358 K. The achievement of this goal, while preserving the potential accuracy of AGT, presents a number of technical challenges, recently reviewed with a discussion of possible solutions [2]. At the lowest temperatures, i.e.…”

“…In particular, we consider whether recent measurements may resolve some inconsistencies in previous determinations [4], and prepare the ground for a future revised temperature scale, the so-called ITS-202x.…”

Thermal expansion coefficient of single-crystal silicon from 7 K to 293 K

“…Taking this into account reduces the mismatch of both measurements slightly, but not significantly. The differences between thermodynamic temperatures and the ITS-90 were estimated by Fischer et al 25 and are smaller than 9 mK in the temperature range considered in this work, which is less than half the temperature uncertainty (Sec. II) and thus negligible for our results.…”