Workshop on uncertainties in radiation thermometry Paris,September 7, 2001 Realisation of ITS-90...
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Transcript of Workshop on uncertainties in radiation thermometry Paris,September 7, 2001 Realisation of ITS-90...
Workshop on uncertainties in radiation thermometryParis,September 7, 2001
Realisation of ITS-90 fixed points
and associated uncertainties
Bernard ROUGIE, Mohamed SADLI (BNM-INM)
Workshop on uncertainties in radiation thermometryParis,September 7, 2001
Introduction
• Black body and furnace technology
• Sources of uncertainty
• Uncertainty budget : ITS-90 and beyond
Workshop on uncertainties in radiation thermometryParis,September 7, 2001
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
Workshop on uncertainties in radiation thermometryParis,September 7, 2001
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
Workshop on uncertainties in radiation thermometryParis,September 7, 2001
43 mm
700 mm
Copper, gold or siver
Realisation of ITS-90
Workshop on uncertainties in radiation thermometryParis,September 7, 2001
Crucible filling-up
set-up
Silver 0.515 kg
Gold 0.952 kg
Copper 0.422 kg
Workshop on uncertainties in radiation thermometryParis,September 7, 2001
Radiance comparator
Aperture stop
Detectors
Field stop
Grating
Other sourceBlack body
Sources bench
Workshop on uncertainties in radiation thermometryParis,September 7, 2001
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
Workshop on uncertainties in radiation thermometryParis,September 7, 2001
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.
Workshop on uncertainties in radiation thermometryParis,September 7, 2001
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
Workshop on uncertainties in radiation thermometryParis,September 7, 2001
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
Workshop on uncertainties in radiation thermometryParis,September 7, 2001
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
Workshop on uncertainties in radiation thermometryParis,September 7, 2001
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
Workshop on uncertainties in radiation thermometryParis,September 7, 2001
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
Workshop on uncertainties in radiation thermometryParis,September 7, 2001
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
Workshop on uncertainties in radiation thermometryParis,September 7, 2001
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
Workshop on uncertainties in radiation thermometryParis,September 7, 2001
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 ?
Workshop on uncertainties in radiation thermometryParis,September 7, 2001
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.