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Realisation of ITS-90 fixed points and associated uncertainties. Bernard ROUGIE, Mohamed SADLI ( BNM-INM). Introduction. Black body and furnace technology Sources of uncertainty Uncertainty budget : ITS-90 and beyond. Furnace characteristics.

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slide1

Realisation of ITS-90 fixed pointsand associated uncertainties

Bernard ROUGIE, Mohamed SADLI (BNM-INM)

Workshop on uncertainties in radiation thermometry

Paris,September 7, 2001

introduction
Introduction
  • Black body and furnace technology
  • Sources of uncertainty
  • Uncertainty budget : ITS-90 and beyond

Workshop on uncertainties in radiation thermometry

Paris,September 7, 2001

furnace characteristics
Furnace characteristics

Heating element : Ni-Cr-Al (Kanthal), max. temperature 1300 °CTechnology : 3-zone furnace associated to three temperature controllersTemperature sensors : 3 Type S thermocouples Temperature stability < 0.1 °CTemperature uniformity < 0.3 °C over 80 mm (in the central region of the furnace)

Workshop on uncertainties in radiation thermometry

Paris,September 7, 2001

crucible dimentions
Crucible dimentions

90 mm

75 mm

35 mm

1 mm

8 mm

Material : High-purity (5N) graphite.Machining by especially dedicated tools (in order to minimize pollution)Dimensions :

Solidity ensured by a “rounded” design of the inner edges of the most fragile parts.Additional parts (screw or ring) to support the cavity well from hydrostatic force.Wall thickness of the cavity is 0.9 mm.

Workshop on uncertainties in radiation thermometry

Paris,September 7, 2001

realisation of its 90
Realisation of ITS-90

43 mm

700 mm

Copper, gold or siver

Workshop on uncertainties in radiation thermometry

Paris,September 7, 2001

crucible filling up set up
Crucible filling-up set-up

Silver 0.515 kg

Gold 0.952 kg

Copper 0.422 kg

Workshop on uncertainties in radiation thermometry

Paris,September 7, 2001

radiance comparator

Black body

Other source

Sources bench

Aperture stop

Field stop

Grating

Detectors

Radiance comparator

Workshop on uncertainties in radiation thermometry

Paris,September 7, 2001

analysis of gold test piece
Analysis of gold test piece

Global purity : 0.99985

Measured from a spark spectrum

Workshop on uncertainties in radiation thermometry

Paris,September 7, 2001

impurities
Impurities

State of the art estimate for the uncertainty components caused by impurities and isotopes

B. Fellmuth, J. Fischer, E..Tegeler

  • Basis of the estimates:
      • Standard deviations of the results near (CCT-k2) or at fixed points (CCT-K3, CCT K4) of the CIPM Key comparisons

Fixed pointsGa InSnZnAlAg

Estimate (mK) 0.2 0.8 0.5 0.7 1.5 4

Proposal: These guideline estimates should be used for uncertainty budgets if State-of-the-art high purity materials are used and no individual information on the impurity content is available.

Workshop on uncertainties in radiation thermometry

Paris,September 7, 2001

emissivity parameters and uncertainty
Emissivity :Parameters and uncertainty

Workshop on uncertainties in radiation thermometry

Paris,September 7, 2001

temperature gradient through crucible wall

Metal at uniform temperature

Sint :internal surface

Sout =8 mm or 1 mm

=0.05 sr

9 mm

75 mm

Temperature gradient through crucible wall
  • Heat flow is constant at each point : wall thickness, inner temperature and outer temperature are uniform; radiation loss is uniform at each point
  • The solid angle of emission is determined by the output diaphragm of the cavity and the first diaphragm in front of it which is almost at the same temperature
  • Heat loss through output diaphragm is only due to radiation (no convection). It is computed by Stefan law.

Workshop on uncertainties in radiation thermometry

Paris,September 7, 2001

computation of temperature drop
through cavity wallComputation of temperature drop

Sout : output surface

Sint : internal surface

e : wall thickness

Rth : thermal resistivity

0 : flux lost

Workshop on uncertainties in radiation thermometry

Paris,September 7, 2001

value and uncertainty of temperature drop
Value and uncertainty of temperature drop

Workshop on uncertainties in radiation thermometry

Paris,September 7, 2001

temperature uniformity
Temperature uniformity

Workshop on uncertainties in radiation thermometry

Paris,September 7, 2001

freezing and melting plateau
Freezing and melting plateau

Workshop on uncertainties in radiation thermometry

Paris,September 7, 2001

uncertainty budget
Uncertainty budget

ITS-90 fixed points

Workshop on uncertainties in radiation thermometry

Paris,September 7, 2001

uncertainty budget1
Uncertainty budget

Future High temperature fixed points T=2600 K

Workshop on uncertainties in radiation thermometry

Paris,September 7, 2001

conclusion
Conclusion

The major component of ITS-90 fixed points uncertainty is due to the plateau determination and its reproducibility.

Improvements of temperature uniformity can reduce this term to 10 mK.

The influence of metal purity is not easy to evaluate but not negligible.

For the higher temperature fixed points, the gradient of temperature through cavity wall will be to evaluate accurately.

Workshop on uncertainties in radiation thermometry

Paris,September 7, 2001

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