Radiation thermometry

September 7th 2001, [email protected]

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Radiation thermometry

Uncertainties on measurements on

Tungsten strip-lamps


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Subject of interest

Base

Strip


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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%



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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%



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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

Radiation thermometry

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