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Determination of spectral responsivity in radiation thermometry. J. Fischer, Physikalisch-Technische Bundesanstalt, Berlin, Germany. theoretical background design of interference filters measurement of spectral responsivity blocking problems stability polarisation scattered light - PowerPoint PPT Presentation
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• theoretical background• design of interference filters• measurement of spectral responsivity• blocking problems• stability• polarisation• scattered light • references• summary
Determination of spectral responsivity in radiation thermometry
J. Fischer, Physikalisch-Technische Bundesanstalt, Berlin, Germany
Basic theory of radiation thermometry
0
0
)(),(
)(),(
dsTL
dsTL
i
iQ
refs
s
ref
0
0
)(),(
)(),(
1
dsTL
dsTL
s
s
eff
ratio Q of spectral radiance :
limiting effective wavelength ( Tref T), (Wien´s approximation) :
Propagation of uncertainties
ref
ref
refref T
dT
T
Td
T
T
Q
dQ
c
T
T
dT
12
measurement of photocurrent ratio
determination of wavelength
realisation of reference temperature
Influence of wavelength uncertainty
-0,05
0,00
0,05
0,10
0,15
0,20
0,25
0,30
0,35
0,40
1000 1500 2000 2500 3000
T / K
T
/ K
Tref = 1337,33 K
Tref = 2300 K
Tref = 1800 K
= 650 nm = 0.05 nm
Determination of spectral responsivity
refref i
iss
Measurement by comparison to reference detector :
sref () : spectrally flat responsivity (thermopile, pyroelectric detector)
sref () : calibrated responsivity (silicon photodiode, trap detector)
: monochromator with wavelength calibration, tunable laser
i (iref (: sensitive to out-of-band radiation, scattered light, etc.
Spectral comparator (IMGC)
Interference filters
10-6
10-5
10-4
10-3
10-2
10-1
100
900 940 980 1020 1060Wavelength
nm
Transm
itta
nce
10-6
10-5
10-4
10-3
10-2
10-1
100
580 620 660 700Tr
ansm
itta
nce
Wavelength
740nm
Spectral transmittance of the interference filter with effective wavelength 974 nm and halfwidth 41 nm
Spectral transmittance of the interference filter with effective wavelength 653 nm and halfwidth 39 nm
Out-of-band error without blocking
Error in silver-gold ratio of 2.1 K
Additional Schott glass KG3
Error in silver-gold ratio reduced to 3.9 mK
Confirmation by sharp-cut filter
Out-of-band signal of 1.4x10-4 measured
Stability, definitions
For monitoring the stability of the calibration, two quantities areused:
Integral of the spectral responsivity ( 1, 2 bandpass limits)
dsI s 2
1
Center wavelength
SSP I
ds
2
1
800 nm filter radiometer
0,0E+00
5,0E-04
1,0E-03
1,5E-03
2,0E-03
2,5E-03
3,0E-03
19
94
-12
-07
19
95
-12
-07
19
96
-12
-06
19
97
-12
-06
19
98
-12
-06
19
99
-12
-06
20
00
-12
-05
20
01
-12
-05
date of calibration
rel.
ch
an
ge
of
inte
gra
l sp
ec
tra
l re
sp
on
siv
ity
0
0,05
0,1
0,15
0,2
0,25
0,3
dri
ft o
f c
en
ter
wa
ve
len
gth
/ n
m
1 year
Stability of filter 800 nm
900 nm filter radiometer
-4,0E-03
-3,5E-03
-3,0E-03
-2,5E-03
-2,0E-03
-1,5E-03
-1,0E-03
-5,0E-04
0,0E+00
19
99
-02
-27
19
99
-08
-28
20
00
-02
-26
20
00
-08
-26
20
01
-02
-24
20
01
-08
-25
date of calibration
rel.
chan
ge
of
inte
gra
l sp
ectr
al
resp
on
sivi
ty
0
0,05
0,1
dri
ft o
f c
en
ter
wa
ve
len
gth
/ n
m
1 year
Stability of filter 900 nm
Measurement of filters
1,0E-12
1,0E-10
1,0E-08
1,0E-06
1,0E-04
1,0E-02
1,0E+00
1,0E+02
400 600 800 1000 1200 1400 1600
wavelength / nm
spec
tral
res
po
nsi
vity
/ A
W-1
800 nm
900 nm
1000 nm
Line above responsivity curve indicates the bandpassfrequently calibrated, covering four orders of magnitude
Polarisation
||2
1sssunpol
Monochromator system emits partly polarised light
radiation thermometer and reference detectors sensitive to polarisation
required : calibration for use at randomly polarisedblack body sources
polariser behind exit slit, 2 measurements :
Scattered light in monochromator
0,996
0,997
0,998
0,999
1,000
1,001
1,002
1,003
4 9 4 9 9 9 2
grating
inte
gra
l of
spec
tral
res
po
nsi
vity
, n
orm
alis
ed
0°
90°
with pre-disperser
with pre-disperser
Calculatedfor randomlypolarisedlight
Principle of spectral comparator
TUNGSTENHALOGEN
LAMP GLAN-THOMPSON
PRISM
GRATING MONOCHROMATORZEISS SPM2 (f=400 mm)
TRANSLATION UNIT
TRAP-DETECTOR
FILTERRADIOMETER
f=450 mm
f=300 mm
FILTER WHEEL(SUPPRESSION OFHIGHER ORDERS)
SPECTRAL ORTUNGSTEN HALOGEN LAMP
LEISS PRISMMONOCHROMATOR
f=150 mm
LIGHTTIGHT ENCLOSURE
SPECTRAL LAMP
Example for uncertainty
Source of uncertainty explanatory note TAu (mK)
Spectral Transmittance of interferencefilter (passband)
= 14 pm 2.9
Blocking of interference filter OBS(TAu)=1.5•10-4 6.0
Relative spectral response of photodiode = 25 pm 5.1
Non-linearity of photodiode NL = 5•10-5 2.9
Impurity of silver sample 6N 3.0
Impurity of gold sample 5N 6.0
Random uncertainty includingrealization of freezes
see table I 4.8
Addition in quadrature 12.1
uncertainty contributions (k=1) for measurement of thesilver-gold interval :
• Battuello M., Girard F., Ugur S., Aytekin S.H.,. Measurements of spectral responsivity at IMGC (Italy) and UME (Turkey). a bilateral comparison,to be published in Proceedings of TEMPMEKO 2001
• Battuello M., Uncertainty budgets for realisation of scales by radiation thermometry, CCT-WG5 working paper, 2001
• Fischer J., Hartmann J., Calibration of tungsten strip lamps as transfer standards for temperature, In Proceedings of TEMPMEKO ‘99, edited by M. de Groot and J. Dubbeldam, Delft 1999, pp 561...566
• Fischer, J., Jung, H.J., Friedrich, R., A new determination of the freezing temperature of gold relative to that of silver by radiation thermometry, Proceedings of Temperature, Its Measurements and Control in Science and Technology, Vol. 6, edited by J.F. Schooley, New York, 1992, pp 53..57
• Gibson, C.E., Tsai, B.K., Parr, A.C., Radiance temperature calibrations, Natl. Inst. Stand. Technol. Spec. Pub. 250-43, 1998
• Sakuma F., Kobayashi M., Interpolation equations of scales of radiation thermometers, In Proceedings of TEMPMEKO ‘96, edited by P. Marcarino, Torino 1997, pp 305...310
• Saunders P., General interpolation equations for the calibration of radiation thermometers, Metrologia 1997, 34, pp 201...210
References
• Uncertainty depends crucially on effort for calibration
• re-calibration interval• main contributions :• monochromator wavelength calibration• calibration of reference detector• scattered light (single/double monochromator)• out-of-band blocking of filters• stability of filters and detectors• temperature coefficient of thermometer
Conclusions