September 7th 2001, [email protected]
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Radiation thermometry
Uncertainties on measurements on
Tungsten strip-lamps
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Uncertainty budgetPhrase subject into contextSources (alphabetic order)• Base temperature• Current• Drift• Emissivity• Positioning• Quality of polynomial fit• Scale realization• Transmission of window
1. Derive its magnitude2. Find order of importance
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Magnitude - Base temperature
Base temperature has influence on temperatureof strip and needs to be corrected for when deviating from Tref
base (Uncertainty 10%)
• Minimize correction, water-cooled base: Tbase=(20±0.1)°C over entire range of operation
• Magnitude 5 mK at 962°C• Type B evaluation
Tstrip (ºC) 700
800
900
1000
1100
Tstrip / Tbase (mK/ºC)
470
250
110
47 17
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Magnitude - Current
Instruments involved• Current supply (stability I/I 5x10-5)• Zero-flux meter (equivalent I/I 1x10-5)• Voltmeter (equivalent I/I 1x10-4, Keithley
181)
• Magnitude 0.44 mA @ 4 A 54 mK at 962°C
• Type A evaluation
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Magnitude - Drift
Stability test: operate lamp for100 hrs @ 1700°C
Requirement: T/t < 3 mK / hr over 100 hrs
• History provides information on correction• Drift behaviour can be used to give an estimate of drift
during calibration• Traceability route and context of measurement
determines whether this source of uncertainty is relevant
• Magnitude negligible• Type B evaluation
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Magnitude - Emissivity
The emissivity () of Tungsten is involved when
converting Trad from pyrometer to 650 nm.
• Values () of de Vos are used• Only uncertainty in relative change of () is
of importance; estimate 0.5%
• Magnitude 3 mK at 962°C• Type B evaluation
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Magnitude - Positioning-1
• Displacement 2x horizontal, 1x vertical• Rotation around vertical/horizontal
From profile measurements• Determine sensitivity around zero (%/mm, %/°) • Estimate uncertainty in determination of position
• Magnitude 53 mK at 962°C• Type A evaluation
Vert.
Hor.
Hor.
Rot.
Rot.
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Magnitude - Positioning-2
ActionSensitivity
Estimate in
zero
Uncertainty
Left-right 0.1 %/mm 0.1 mm 0.01%
Up-down 0.1 %/mm 0.1 mm 0.01%
Back-forward
0.01 %/mm
0.5 mm 0.005%
Rotate vertical
0.05 %/° 1° 0.05%
Rotate horizontal
0.02 %/° 1° 0.02%
Total 0.06% 53 mK
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Magnitude - Quality of fit
Polynomial fit: t90= ai ln(S), with a=0..5
Least squares residuals result in 26 mK
• Magnitude 26 mK at 962°C• Type A evaluation
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Magnitude - Scale realization
Standard pyrometer@ 650 nm
• Magnitude 51 mK at 962°C
• Type B evaluation
SourceType
Uncertainty (mK)
962°C
1300°C
1700°C
Realization B 8 14 22
Emissivity B 1 1 1
Response A+B 8 9 14
Linearity B 1 2 3
SSE B 2 3 4
Wavelength
B 0 17 45
Drift B 50 82 128
Total 51 86 138
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Magnitude - Trans. window
The transmission () of the window is involved
when converting Trad from pyrometer to 650 nm.
• Values () of Pyrex material are used• Only uncertainty in relative change of () is
of importance; estimate 0.1%
• Magnitude 1 mK at 962°C• Type B evaluation
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Order of importance
SourceType of evaluati
on
Important ?
Magnitude
Current A YES 54 mK
Positioning A YES 53 mK
Scale realization B YES 51 mK
Quality fit A YES/NO 26 mK
Base B NO 5 mK
Emissivity B NO 3 mK
Transmission window
B NO 1 mK
Drift B - -
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EA-4/02 Expression of the uncertainty of Measurement in Calibration
Quantity Estimate
Standarduncertainty
Sensitivitycoefficient
Contribution to the
standard uncertainty
Current 4 A 0.44 mA 8.2 mA/K 54 mK
Positioning
0.06% 1.13 %/K 53 mK
Scale realization
962°C 51 mK 1 51 mK
Quality fit 26 mK
Combined
95 mK
K-factor 2
Expanded
190 mK
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Conclusion
• Uncertainty in measurements associated with Tungsten strip lamps is at NMi-VSL dominated by 4 contributions (1. Current) 2. Positioning 3. Scale realization 4. Quality of the fit
• For NMi-VSL the overall uncertainty is evaluated to values for k=2 and 95% confidence interval:
T90(X)962°C
1300 °C
1700 °C
U(T90(X))
190 mK
280 mK
420 mK