Realization at IMGC of the ITS-90 Fixed Points from the Argon Triple Point Upwards

Refractive index gas thermometry between 13.8 K and 161.4 K

“…Both cSPRTs were calibrated in 2018 and in 2020, with slightly different procedures, before and after the RIGT measurements which took place in 2019 over the course of nearly one year. The reader is referred to [28] for a detailed account of the apparatus and the calibration procedures available at INRiM for the realization of ITS-90 between 13 K and 273 K. Both the 2018 and the 2020 calibration procedures involved the direct realization of the triple points of neon (T 90 = 24.5561 K), oxygen (T 90 = 54.3584 K) and argon (T 90 = 83.8058 K) in an adiabatic cryostat with the calorimetric method [29], and the insertion of the cSPRTs into the standard cells for the realization of the triple points of mercury (T 90 = 234.3156 K) and water (T 90 = 273.1600 K) realized using the continuous heating method [30,31]. In order to fit the capsule thermometers into the water and mercury standard sealed cells, which are conceived for the calibration of long-stem SPRTs, suitable custom adapters designed at INRiM were used.…”

Determination of the thermodynamic temperature between 236 K and 430 K from speed of sound measurements in helium

“…Stability at the TPW was an important requisite for the sake of an accurate determination of the Boltzmann constant, but is not affecting T 90 determinations obtained by relative AGT where only the stability of W = R(T)/R(273.16 K) matters, as it is further commented below. All three cSPRTs were calibrated at the INRiM facility maintaining the ITS-90 fixed points for long-stem SPRTs [45]. For that purpose the cSPRTs were mounted, one at a time, within a copper sleeve embedded into a hollow stainless steel adaptor designed to reproduce the exterior dimensions of long-stem thermometers.…”

Acoustic measurements of the thermodynamic temperature between the triple point of mercury and 380 K

“…The complete features and the performance of this improved temperature system, which have been partially described in an earlier publication [13], are described in section 4. Before the first preliminary tests for this experiment were started, the SPRTs were calibrated at the ITS-90 fixed points, between the mercury triple point and the indium freezing point, as maintained at IMGC [14].…”

“…A casual inspection of the inset resonance curves in figure 2 shows that all the TM1n modes appeared as doublets, suggesting an axisymmetric deformation of the sphere. Evidence of the presence of a third very weakly excited component was obtained by comparing the results of a fit to the experimental data when including two or three terms in the sum of (14). Summing over just two complex resonance frequencies (12 adjustable parameters) gave unsatisfactory high and systematic residuals as shown for the mode TM11 at 234 K in the middle part of figure 3.…”

“…Summing over just two complex resonance frequencies (12 adjustable parameters) gave unsatisfactory high and systematic residuals as shown for the mode TM11 at 234 K in the middle part of figure 3. Including a third resonance in the summation (14) (which takes the number of adjustable parameters to 16), the deviations were substantially reduced and became more random (see the lower part of figure 3). A comparison of the precision achieved in fitting with the sum of either two or three complex functions the same recorded data, for modes TM11, TM12, TM13 and TM15 near 273.16 K, is shown in table 1, which reports the standard deviation of the fit, expressed as a fraction of the maximum measured amplitude, and the relative fractional uncertainty of the different frequency components, which has been estimated by computing the error matrix for (14) with the appropriate generalization for complex fitting functions [19,20].…”