Further Estimates of 
                
                  
                
                $$(T-T_{90})$$
                
                  
                    
                      (
                      T
                      -
                      
                        T
                        90
                      
                      )
                    
                  
                
               Close to the Triple Point of Water

We report new developments in instrumentation and techniques for both acoustic (speed of sound) and radiometric primary thermometry methods. These include both new cylindrical resonators for extending acoustic gas thermometry to higher temperatures and absolute radiation thermometers incorporating InGaAs detectors to extend primary radiometry to lower temperatures than can be achieved using Si-detector based instruments. These new approaches have been established in order to determine the difference between thermodynamic temperature, T, and the International Temperature Scale of 1990 (the ITS-90), T90, over the temperature range from 430 K to 1358 K as part of the three-year EMPIR project 'Implementing the new kelvin 2' (InK2). This paper describes the facilities and measurement methodologies for measuring T -T90 at each of the different institutes, along with an assessment of the target uncertainties. The work is ongoing, but we anticipate that the results of these measurements will ultimately be pooled to provide consensus values of T -T90 with associated estimated uncertainties. These consensus values will initially feed into the technical annex of the mise en pratique for the definition of the kelvin (MeP-K-19) and, if required, will be used to help to provide a foundation for any future temperature scale.

Section: Equipment and Methodologymentioning

confidence: 99%

Methodologies and uncertainty estimates for T – T ₉₀ measurements over the temperature range from 430 K to 1358 K under the auspices of the EMPIR InK2 project

McEvoy¹,

Lowe²,

Underwood³

et al. 2020

“…A [14], and thermodynamic temperature values from that project are still being published (e.g. [50][51][52][53][54]). New low uncertainty values of T − T 90 were obtained in the temperature region ~25 K-303 K, by two primary thermometry methods, namely AGT and DCGT.…”

Section: Determining New Low Uncertainty Values Of T − T 90 T − T 2000mentioning

confidence: 99%

The kelvin redefined

Machin

2018

On 20 May 2019 it is anticipated that the most radical revision of the International System of Units (the SI), since its inception, will come into force. From that point, all the SI units will be based on defined values of fundamental constants of nature. In this paper the redefinition of the kelvin and its implications are considered. The topic will be introduced by discussing how the wording of the new definition of the kelvin developed. The kelvin redefinition is reliant on a secure low-uncertainty value of the Boltzmann constant; its determination by different physical methods and how the final definitive value for the kelvin redefinition was arrived at is discussed. The redefined kelvin will be implemented through a document known as the mise en pratique (i.e. the ‘practical realisation’) for the definition of the kelvin (MeP-K). The development and contents of the MeP-K will be described. There follows a discussion of contemporary primary thermometry, which is the bedrock on which a secure kelvin redefinition will be founded. Finally the paper ends with a discussion of the implications of the redefinition, for traceability, and, more widely, the practice of thermometry in general.

“…In this work we have compared the measurement uncertainty achieved using a VNA costing less than 10% of the cost of the Agilent VNAs used previously at the NPL [1,10,11]. Corbellini and Gavioso previously reported on the design and performance of a custom-made, low-cost microwave analyser [12] for the determination of the S 21 transmission parameter.…”

Section: Investigating the Adequacy Of A Low-cost Vector Network Anal...mentioning

confidence: 99%

“…We used the NPL-Cranfield (NPL-C) QSR for this work. This QSR was used for NPL's Boltzmann constant determination [1] and also for thermodynamic temper ature measurements by means of AGT at the NPL [10,11]. The nominal radius along the shortest axis of the QSR was 62 mm at 0.01 °C.…”

Section: Resonator and Thermostatmentioning

confidence: 99%

Investigating the adequacy of a low-cost vector network analyser for microwave measurements in quasispherical resonators

Yang

Underwood

Podesta

2018

Microwave measurements in quasispherical resonators (QSRs) have enabled remarkable improvements in primary gas thermometry, but the expense of vector network analysers (VNAs) restricts wider use of the technique. In this work we compare the performance of a commercially available, low-cost VNA with a fully-featured VNA in microwave resonance measurements in a QSR. For acoustic gas thermometry (AGT) where a relative uncertainty in frequency measurement in an order of 10−7 is required, we have found that the accuracy of the low-cost VNA is easily sufficient. The use of a +20 dB amplifier was also tested for both VNAs and allowed statistical uncertainties to be reduced by a factor of 5 to 12. The two VNAs showed agreement within 20 × 10−9 of the absolute frequency of microwave resonances. However, when the low-cost VNA was used with the amplifier, some spurious systematic effects were found which biased the measured resonance frequency at levels below 20 × 10−9. These effects were apparent only when the amplifier was used with the low-cost VNA, because, when the amplifier was not used, the statistical uncertainty was much larger than the magnitude of these effects. While the physical cause of these systematic effects is not investigated in the present work, we made observations that could help to estimate their magnitudes. The comparison showed that the low-cost VNA, although being perfectly suitable for the AGT, may not be sufficiently accurate for applications where the required relative uncertainty in the frequency determination is of an order of 10−9.