Overview

The aim of this project is to take advantage of the kelvin redefinition using practical primary thermometry approaches for the dissemination of thermodynamic temperature. We progress beyond the state of the art, through: demonstrating dissemination of the kelvin from 4 K to 300 K; developing a robust framework for establishing traceability by primary thermometry; working towards the next generation primary thermometry to 700 K. We will demonstrate how smaller/emerging NMIs can benefit from such dissemination approaches. We will lead the global thermometry community in disseminating the kelvin using primary thermometry ensuring EURAMET remains dominant in this important field of metrology.

Need

The kelvin redefinition in May 2019 initiated a comprehensive research phase for the realisation and dissemination of thermodynamic temperature to replace the ITS-90/PLTS-2000 scales currently in use. The CIPM (International Committee of Weights and Measures) Consultative Committee for Thermometry (CCT) recommendation T1 (2017) stated that member state National Metrology Institutes (NMIs) “take full advantage of the opportunities for the realisation and dissemination of thermodynamic temperature afforded by the kelvin redefinition and the mise en pratique for the definition of the kelvin (MeP-K)”. In addition, the research needs for temperatures above ambient was highlighted by the CCT recommendation T1 (2021) that NMIs establish capability to determine T–T90 above 400 K, and in so doing establish the background capacity for dissemination of thermodynamic temperatures approaching 700 K.

The MeP-K allows for the dissemination of temperature either by thermodynamic means or one of the defined scales. However, many issues remain about how the two approaches interrelate and how to demonstrate the degree of equivalence. To facilitate disseminating thermodynamic temperature these issues need addressing.

The EMPIR 18SIB02 Real-K project began the transition away from defined scales by establishing the capabilities to disseminate thermodynamic temperature at high temperatures >1235 K and low temperatures, particularly <5 K. The research proposed here, building on the achievements of Real-K, addresses the high-level metrology needs stated by CCT, ensuring that thermodynamic temperature can be realised and disseminated to room temperature and beyond.

This research is beyond the capability of a single institute to deliver. We will establish within EURAMET a highly integrated research and metrology infrastructure for disseminating thermodynamic temperature. The project includes a wide range of NMIs ensuring the developed approaches are appropriate for NMIs at different stages of development. This research ensures the EURAMET region retains its globally dominant position in realising and disseminating the redefined kelvin.

Objectives

The overall objective of this project is to establish the capability to disseminate thermodynamic temperature from 4 K to ~300 K, which requires an internationally agreed framework to demonstrate that thermodynamic temperature dissemination is reliable. Additionally, we will build future capability to enable thermodynamic temperature dissemination above 300 K.

The objectives are fully aligned with those documented in SRT-s02. These are:

  1. Demonstrate practical thermodynamic temperature dissemination from 4 K to 25 K using three independent thermodynamic methods to, at least, two NMIs without primary thermometry capabilities using practical temperature sensors as transfer standards. Target uncertainty 0.3 mK (k=1).
  2. Demonstrate practical thermodynamic temperature traceability in the range 25 K to 300 K using two independent thermodynamic methods to, at least, two NMIs without primary thermometry capabilities using practical temperature sensors as transfer standards. Target uncertainty 0.25 mK at 25 K and 0.6 mK at 300 K (k=1).
  3. Develop a coherent framework for thermodynamic temperature dissemination to ensure consistency of dissemination from NMIs to users over the temperature range 4 K to 300 K whether it is by thermodynamic temperature or the defined scale (ITS-90) and develop a recommendation to CCT documenting how to perform the dissemination and uncertainties attainable.
  4. Establish a capability for the realisation and dissemination of thermodynamic temperature between 300 K and 700 K with T–T90 target uncertainty of 0.6 mK at 300 K and 7 mK at 700 K (k=1).
  5. Establish an integrated European temperature metrology infrastructure and facilitate the take up of the developed technology and measurement infrastructure by the measurement supply chain (accredited laboratories, instrument manufacturers), CIPM Consultative Committee for Thermometry (CCT), EURAMET and other RMO TC-Ts and relevant end users (academic and industry).

Progress beyond the state of the art and results

Each objective of this project goes well beyond the state of the art.

We are building on the foundation laid by the EMPIR Real-K project which: 1) Laid the framework for dissemination of thermodynamic temperatures >1300 K. 2) Developed the capability for disseminating the redefined kelvin below 25 K – the effectiveness of which will be demonstrated in this project. 3) Performed theoretical modelling and experimental activities to determine the thermophysical properties of gases required to disseminate thermodynamic temperature to at least 300 K and beyond – here we take advantage of those results to demonstrate practical dissemination of thermodynamic temperature to at least 300 K.

Demonstrating dissemination of thermodynamic temperature from 4 K to 25 K

The current state of the art for temperature realisation and dissemination between 4 K and 25 K is through the defined scale (ITS-90). The situation is complex with different technical approaches and overlapping in ranges; (0.65 K to 5 K 3He/4He vapour pressure thermometry, 3 K to ~24.6 K interpolating He gas thermometer and above ~13.8 K fixed-points and capsule standard platinum resistance thermometer). Because of the complexity there are very few full ITS-90 realisations globally in this temperature range.

We progress the state of the art building on the developments of Real-K, to, for the first time, demonstrate low uncertainty thermodynamic temperature dissemination. We will use three thermodynamic approaches (DCGT, RIGT and AGT) to perform the thermodynamic temperature calibrations. Target uncertainty 0.3 mK (k=1) in the range for the dissemination.

Towards demonstrating dissemination of thermodynamic temperature from 25 K to 300 K

The current state of the art for temperature realisation and dissemination in this temperature region is through calibration of platinum resistance thermometers to the defined scale (ITS-90).

We advance the state of the art building on the developments of Real-K to demonstrate low uncertainty thermodynamic temperature dissemination. We will use two thermodynamic approaches (RIGT and AGT) to perform direct thermodynamic temperature calibrations without reference to ITS-90. Target uncertainty in temperature dissemination of 0.25 mK at 25 K and 0.6 mK at 300 K (k=1).

Development of a coherent framework for thermodynamic temperature dissemination

The current state of the art is that there is no coherent framework for disseminating thermodynamic temperature. The mise en pratique for the definition of the kelvin (MeP-K) states the allowable thermodynamic methods that can be used but does not address the many practical issues such traceable dissemination requires.

We progress the state of the art by developing a coherent framework for disseminating thermodynamic temperature to ensure the reliability of such dissemination, making it accessible in the future to the user community through a recommendation to the CCT.

Establish capability for dissemination of thermodynamic temperature to approximately 700 K

The current state of the art is a few NMIs have made tentative steps towards developing capability for thermodynamic temperature above 300 K.

We progress the state of the art by developing the capability to measure thermodynamic temperature to 700 K and develop values of T–T90 with a target uncertainty of 7 mK at 700 K (k=1).

Outcomes and Impact

Outcomes for industrial and other user communities

Temperature is one of the most measured parameters in industry and by other users (e.g. climate change research). These developments will therefore have outcomes in almost all industrial sectors as well as more widely. However, most impact will be long-term (discussed below).

European accreditation bodies, and calibration laboratories have a long-standing interest in the SI and its development. Links with such bodies have been established and the outcomes of this project with its implications for traceability will be fully communicated.

Temperature sensor manufacturers have signalled their interest in this project both directly and indirectly through trade bodies/learned societies. The outcomes of this project will be communicated to them through an e-newsletter and through the project website. Articles on the project outcomes will be published in trade body journals.

It is known that the introduction of ITS-90 caused significant indirect costs to industry through for example having to update standards, change algorithms and recalibrate reference standards. We anticipate, one of the outcomes of the project is that dissemination of thermodynamic temperature will become widespread, negating the need for a new scale with industry avoiding significant costs. 

In summary because temperature is such a key parameter for industry and over many areas of human endeavour it is anticipated there will be significant outcomes from this project. There will be stimulation of practical primary thermometry per se and the development of practical primary thermometry calibration facilities potentially leading to new products for European companies.

Outcomes for the metrology and scientific communities

The project outcomes for the global thermometry community will be very significant, both through advances in the SI system of units (the kelvin) and contributions to the Consultative Committee of Thermometry.

For the global thermometry community. The realisation and dissemination of thermodynamic temperature, as opposed to defined scales, is a long-term objective. The outcomes here will mark a significant advance towards that long-term objective by using multiple practical primary thermometry approaches to disseminate thermodynamic temperatures.

Specific outcomes will be:

  • Capabilities for the dissemination of thermodynamic temperature demonstrated from 4 K to 25 K and from 25 K to ~300 K, with defined scale level uncertainties
  • Thermodynamic temperature dissemination practicality demonstrated including possibility to supersede the defined scale in these ranges
  • A coherent framework for dissemination of thermodynamic temperature (4 K – 300 K) will be developed and recommended to the CCT
  • The practicality of thermodynamic temperature dissemination at higher temperatures will have been investigated to ~700 K

For the Consultative Committee of Thermometry

Many of the consortium members are members of the CCT, indeed three (PTB, NPL, UL) are chairs of CCT Working Groups. This means the outcomes of DireK-T will be incorporated into CCT advice and recommendations for use by the global thermometry community at the earliest opportunity. Possible outcomes are: revision of the MeP-K, revision of the CCT Strategy and revised consensus values of T–T90. Standards outcomes relating to CCT are given below and more fully in Section B3.c.

The outcomes of this project will be disseminated to the wider scientific community through the following:

  • Research papers (at least 15) in relevant high impact journals
  • Presentations (at least 12) at relevant conferences
  • Dissemination workshop for EURAMET TC-T members
  • Summer school on “Contemporary issues in primary thermometry” for academics and metrologists

Outcomes for relevant standards

This project will have a very significant outcomes for the whole thermometry community. This will be effected chiefly through the CCT, the global authority on temperature, and the relevant standards body for this work.

Key inputs into the CCT, influencing its guides and recommendations are:

  1. Evaluation report on sensors for disseminating thermodynamic temperature from 4 K to 25 K
  2. Practical demonstration of practical thermodynamic temperature dissemination from 4 K to 25 K
  3. Practical demonstration of practical thermodynamic temperature dissemination from 25 K to 300 K
  4. Recommendation report to CCT with framework for thermodynamic temperature dissemination to 300 K
  5. New determinations of T–T90 in the whole range 4 K to 303 K
  6. New determinations of T–T90 in the range 303 K to ~700 K
  7. Report to CCT on approach to disseminating thermodynamic temperature >300 K

In addition, the key international stakeholders, chiefly the RMO TC-Ts, will be kept informed of the progress of DireK-T by annual written reports. There will be an annual oral report to Euramet TC-T.