realisation of its-90 fixed points and associated uncertainties

Workshop on uncertainties in radiation thermometryParis,September 7, 2001

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


Heating element : Ni-Cr-Al (Kanthal), max. temperature 1300 °C

Technology : 3-zone furnace associated to three temperature controllers

Temperature sensors : 3 Type S thermocouples

Temperature stability < 0.1 °C Temperature uniformity < 0.3 °C over 80 mm (in the central region of the furnace)

Furnace characteristics


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.

1 mm 8 mm

90 mm

35 mm

75 mm

Crucible dimentions


43 mm

700 mm

Copper, gold or siver

Realisation of ITS-90


Crucible filling-up

set-up

Silver 0.515 kg

Gold 0.952 kg

Copper 0.422 kg


Radiance comparator

Aperture stop

Detectors

Field stop

Grating

Other sourceBlack body

Sources bench


Analysis of gold test pieceAl Ag B Ba Bi Ca 4 25 0.07 0.1 0.2 2.5

Cr Cu Fe Ga Hg In 0.4 14 60 4 0.2 1.4 Ir K Mg Mn Na Ni

0.1 1 3 0.8 2.5 4 Pb Pd Pt Sb Si Sn 19 0.8 0.8 0.1 1.2 0.1 Ti V Zn O2 N2 CO 0.2 0.6 1 0.6 0.2 0.0

Measured from a spark spectrum

Global purity : 0.99985


ImpuritiesState of the art estimate for the uncertainty

components caused by impurities and isotopesB. 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 points Ga In Sn Zn Al Ag

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.


Temperature Wavelength Material Length Inner diameter

Output diameter

1300 K 650 nm Graphite 75 mm 9 mm 1 mm

Value Uncertainty

Emissivity of cavity

uncertainty

Temperature uncertainty

mK

Reflectivity of material (graphite)

0.128 0.006 8.4 10-4

5.0 10-6 0.4

Reflectivity of cavity:

Monte Carlo computation

0.0000143 0.0000038 1 3.8 10-6 0.2

Cavity emissivity .0999986 6.3 10-6 5.2

Emissivity : Parameters and uncertainty


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.

Metal at uniform temperature

75 mm

=0.05 sr9 mm Sout =8 mm or 1 mmSint :internal surface


Computation of temperature drop

0

2 Sout T4

Sout : output surface

Sint : internal surface

e : wall thickness

Rth : thermal resistivity

0 : flux lost T e

0

S int R th

through cavity wall


Value and uncertainty of temperature drop

Output diameter

Loss of thermal flux

Temperature drop from metal to cavity through crucible wall

Uncertainty of temperature drop

1 mm 1,2 mW 0.06 mK 0.06 mK

8 mm 77mW 4.3 mK 4.3 mK


Temperature uniformity

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

-50 0 50 100 150

Distance from exit diaphragm of black body (mm)

Deg

rees

Internal TC

External TC


Freezing and melting plateauMelting plateau 30/11/2001

1357.70

1357.72

1357.741357.76

1357.78

1357.80

1357.82

1357.84

12:00 12:28 12:57 13:26 13:55 14:24 14:52

Freezing plateau 30/11/2000

1357.701357.721357.741357.761357.781357.801357.821357.84

18:00 18:28 18:57 19:26 19:55 20:24 20:52


Uncertainty budget

Exit aperture 1 mm Exit aperture 8 mm Correction Uncertainty Correction Uncertainty Emissivity

1.2 mK 0.52 mK 49 mK 3.5 mK

Temperature drop through cavity wall

0.06 mK 0.06 mK 4.2 mK 4.2 mK

Impurities effect

4 mK 4 mK

Plateau determination

25 mK 25 mK

Combined uncertainties

25 mK 25 mK

ITS-90 fixed points


Future High temperature fixed points T=2600 K

Uncertainty budget

Exit aperture 1 mm Exit aperture 8 mm Correction Uncertainty Correction Uncertainty Emissivity

4.4 mK 1.9 mK 180 mK 13 mK

Temperature drop through cavity wall

0.96 mK 0.96 mK 66 mK 66 mK

Impurities effect

No data No data

Plateau determination

100 mK ? 100 mK ?


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.

realisation of its-90 fixed points and associated uncertainties

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