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**Temperature and thermal quantities

The works carried out by the different laboratories (LNE-INM at the CNAM, LNE/CMSI and the CETIAT’s hygrometry laboratory) cover the national references as well as the means for transfer to the industry (calibrating benches).

Temperature

1- Temperature references

The projects involving the references, consist in maintaining them at the highest metrology level and making comparisons with the other national references as part of the international comparisons. And this is the everyday work assigned to the National Metrology Institutes (NMIs).

Additionally, it is necessary to make progress in the references through their improvement (means and uncertainties) or via the development of new references (new types, fresh methods). These works can sometimes contribute to the evolution of the definitions of the units or the traditional references at the international level.

Maintaining update the temperature references:

In order to maintain the best materialization of the ITS-90, the LNE-INM compares, for each fixed point, the thermometric cells between themselves and characterises new cells. Regarding the fixed-points blackbodies, the furnaces are undergoing improvement with the aim of allowing interchangeability of the cells, and the luminance comparator is maintained at its best (optical, mechanical and electrical) level.

Conservation bath of the triple point of water at the LNE-INM.
Conservation bath of the triple point of water at the LNE-INM.

Collaborations and international comparisons of references :

As the leading French metrology institute, the LNE participates in several international (or bilateral) comparisons that are organized under the Euromet or the CCT (Consultative Committee for Thermometry of the CIPM): realizations of the ITS-90 between 14 K and 273 K and between 83 K and 693 K, aluminium, silver, ... . LNE participates also in collaboration works focusing on the improvement of the references (measurement of the thermodynamic temperature of the points below water and the blackbodies at high temperature, influence of the isotopic composition of some materials on the values of the fixed points, new materializations of the fixed points between water and silver, new measurements of the Boltzmann constant, ...).

In the thermal area, the LNE’s laboratories are participating in a new project aimed at the development of one European Virtual Institute for Thermal Metrology (evitherm).

European Virtual Institute for Thermal Metrology
European Virtual Institute for Thermal Metrology

This will be materialized by one authorized website, that will provide easily and quickly accessible information and expertise in temperatures and on the thermophysical properties and is meant for supporting the thermal technology needs of the European industry.

We have a keen appetite for any feedback from the users in thermal technology and we invite you to visit the following website www.evitherm.org where you can tell us what Evitherm could bring to further your organization. We look forward to your comments.

Studies on the new references and on thermodynamic temperature :

Cell, with the filling funnel, for the LNE-INM eutectic fixed-points
Cell, with the filling funnel,
for the LNE-INM eutectic fixed-points

Schematic for k measurement through spectroscopy method at the LPL (pdf - 280 Ko).

Sphere for k measurement through acoustical method at the LNE-INM
Sphere for k measurement through acoustical method at the LNE-INM

Studies for the improvement of the current uncertainties :

Assembly of mini cells for the low temperatures.
Assembly of mini cells for the low temperatures.

2- Means of transfer for the temperature references

Calibrating means are all the transfer means of the national references towards the industry, so as to ensure continuous traceability from the national standard up to the references coming from the calibrating laboratories, and the measurement instruments of all types that are used in the industry.

According to the type of instrument and its metrological quality, calibration will be done through different stages that are matching the different connection steps. At the highest metrological level, fixed points, standard platinum resistance thermometers, pyrometers or reference blackbodies are directly connected to the national references. Then the instruments of most common usage in the industry (thermoelectrical couples, pyrometers...) will be calibrated in relation to the working references by using generators/comparators of temperature (furnace, thermostated bath, blackbody at variable temperature,...). And this will build the start of the continuous calibration chain that continues throughout the industry.

Projects involving the means of transfer, generally consist in maintaining at the highest metrology level the calibration means, from the national reference up to the industrial references, to adapt them to the instruments or industrial references, and to develop new benches to widen the calibration possibilities (new range of measurements or new instruments).

Maintaining update the calibrating benches :

Works undertaken in this area are based on the anomalies that have occurred (material break or ageing) and on the needs for improvement in the calibration uncertainties (replacement of the working references, of the measuring instruments, improvement of the measuring benches). And above all, it is essential to ensure the traceability of the measurements by regular calibration of the measuring instruments and the working references to the national temperature references and also to all the other quantities playing a role in the measurements, notably the electrical ones.

International collaborations and comparisons of the transfer means :

The LNE/CMSI participates in works that have led to the development or the improvement of the calibrating means (Pt/Pd couples, IR pyrometers at low and medium temperatures, sensors for temperature ranging from 1 000 °C to 2 000 °C, calibrating means of the couples above the silver point,..).

Studies of the new calibrating means (transfer to the industry) :

Pressure-controlled heat pipe furnaces at the LNE-INM.
Pressure-controlled heat pipe furnaces at the LNE-INM.

Cell for calibrating the thermocouples at the LNE/CMSI.
Cell for calibrating the thermocouples at the LNE/CMSI.

3 000 °C Blackbody furnace at the LNE/CMSI
3 000 °C Blackbody furnace at the LNE/CMSI

Humidity

The study projects are aimed at maintaining at the highest level the two calibrating benches (dew-point temperature and relative humidity) and participating in works that involve international collaborations and comparisons to further the national references.

One specific project, lasting several years, is designed to develop a new reference generator of humid air. Huge digital modeling works have been done and validated through practical experiments in order to demonstrate that the measurement of the dew-point temperature is a primary reference in hygrometry. This new reference will be made up of two humid air generators that allow the calibration of reference condensation hygrometers to cover the dew points ranging from -80 °C to +80 °C.

Thermophysical properties of materials

Thermal conductivity : in addition to the maintenance of the reference bench of the Guarded Hot Plate (GHP) type (large size), its technical improvement and the connection of the different sensors and measuring instruments, a new bench is under development to widen the range of the thermal conductivities.

This bench, which is smaller than the first one but of identical type, should allow measuring medium conductivities ranging from 0,2 W·m-1·K-1 to 10 W·m-1·K-1, for temperatures comprised between 20 °C and 200 °C.

Scheme of measurement stacking for of thermal conductivity.
Scheme of measurement stacking for of thermal conductivity.

Prototype of the guarded hot plate  for the medium thermal conductivities at the LNE.
Prototype of the guarded hot plate for the medium thermal conductivities at the LNE.

  • Thermal diffusivity : The projects currently launched are designed to extend the possibilities of measurements in two areas :
    - In temperature for the homogeneous and good conductor materials; the bench will allow calibrations up to 1 500 °C ;
    -- In material types; the bench will be adapted to the dual-layer materials by allowing measurement via the “laser flash” method on front face.

Optical system and detector on the “front face” diffusivity bench of the LNE/CMSI.
Optical system and detector on the “front face” diffusivity bench of the LNE/CMSI.

  • Specific heat capacity : mplementation of one measurement instrument up to 1 500 °C in order to characterize in the longer term the reference materials designed for the calibration of calorimetry and thermal analysis equipment. The means chosen is a drop calorimeter.
  • Gas calorific value : The LNE/CMSI is constructing one reference calorimeter for absolute measurement of gases in order to have a reference instrument to qualify and calibrate the calorimeters and chromatographs used in the gas industry. For natural gas specifically, the focus is on making the transactions in energy value (kW·h) and not in volume (m3)any more. The financial stakes are considerable because of the different origins and qualities of natural gas.
    The objective is to measure the Gas calorific value (GCV) of the different components of natural gas with one uncertainty of 0,05 %. The isoperibolic calorimeter, which is under development, associated with the reference gases realized by the LNE/CMSI’s laboratories of chemistry should allow connecting the different measuring instruments of the GCV and redefining the 1960 ISO standard stating the values for the calorific power of each component of natural gas.

Burner and exchanger of the gas calorimeter at the LNE/CMSI. Burner and exchanger of the gas calorimeter at the LNE/CMSI.
Burner and exchanger of the gas calorimeter at the LNE/CMSI.

Thermoradiative properties of materials

  • Maintain update the measuring benches for emissivity : dIn this area, the calibrations of the different measuring chains have been made and some equipment has been replaced for the three reference measuring benches.
  • Improvement of emissivity measurements at low temperature : It is about improving the uncertainty in the measurement of the directional hemispherical reflectance and validating the measurements and the uncertainties by comparison with other foreign national references. In addition, due to the limitation in the improvement of the current bench, a novel method is under development for the measurement of the spectral reflectance. The possibility to perform measurements at the highest wavelengths (beyond 14 µm, and up to 25 µm at 50 µm) is also anticipated.