Progress beyond the state of the art
This project will use primary thermometry for temperature realisation and dissemination at temperatures <25 K and >1300 K. The project will target reducing non-uniqueness uncertainties in the realisation of the ITS-90 by 30 % and identify a replacement for the mercury triple point.
1. Realisation and dissemination of the redefined kelvin >1300 K.
The current state of the art for temperature realisation and dissemination >1300 K is through the ITS-90. We will progress the state of the art through:
- Assigning definitive thermodynamic temperatures to the HTFPs: Fe-C (1426 K), Pd-C (1765 K), Ru-C (2226 K) and WC-C (3020 K); target standard uncertainty from 0.1 K to 0.4 K.
- Demonstrate the first practical outworking of the Mise en Pratique by indirect primary radiometry (>1300 K).
2. Realisation and dissemination of the redefined kelvin <25 K.
The current state of the art for the temperature scale <25 K is complex. Traceable temperatures are referenced to ITS-90 or PLTS-2000 and scale realisation requires different sophisticated, time-consuming, experimental methods only available in a few National Metrology Institutes. We will progress the state of the art through:
- Developing primary thermometers covering the entire range from 1 K to 25 K significantly reducing the complexity of realisation and dissemination of temperature (target uncertainty <1 %)
- Greatly improved reliability in scale realisation and dissemination by enabling a direct check of different realisation techniques of the currently used temperature scales.
3. Extending the life of the International Temperature Scale of 1990.
The current state of the art leaves Type 1 and 3 non-uniqueness among the dominant uncertainties in ITS-90 calibrations. However significant data to support uncertainty contribution assignment is only available in limited sub-ranges e.g. 0 °C to 420 °C. There are three candidates for replacing the hazardous mercury triple point, namely Xe, CO2 or SF6. To date only limited investigations have been performed. We will progress the state of the art through:
- Substantially increasing the knowledge of Type 1 and 3 non-uniqueness in ITS-90 calibrations (target 30 % uncertainty reduction)
- Identifying and characterising a suitable replacement for the mercury triple point.
4. Facilitating full range primary thermometry.
The current state of the art in establishing traceable temperatures is through calibration to, e.g. the ITS-90. In this project the ITS-90, at the extremes of temperature, will be challenged through demonstrating direct linkage to the redefined kelvin. However for primary thermometry to become usable for kelvin dissemination between 25 K and 1300 K, gas-based methods, i.e. AGT, DCGT and RIGT, need to be substantially simplified. We progress the state of the art through:
- Reducing the ab initio calculation uncertainty of the thermodynamic non-ideality of monatomic gases. Target uncertainty reduction (factor 10) in these properties for Ar and Ne. Validation of calculations through low-uncertainty thermodynamic measurements over wide ranges of temperature (10 K to 350 K) and pressures (up to 100 MPa).
- Demonstrating traceability to thermodynamic temperature through trial calibration of thermometers.
 Type 1 non-uniqueness – arises from the use of different equations in overlapping ranges, using the same thermometer
 Type 3 non-uniqueness – arises from the use of different interpolating thermometers of the same kind in the same range