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Distribution temperature scale realization at NIM-Romania
Author’s name, M. Simionescu and A. Seucan
Affiliation, NIM-Romania
B. Rougie,
LNE-INM, France
Abstract. The closure of the photometric calibration
service of BIPM stirred more national laboratories to
find new SI traceability routes for luminous intensity
and luminous flux calibrations. Therefore, as
reported elsewhere [1], NIM-Romania developed it`s
own, radiometer based, references for luminous
intensity and flux units. To allow units transfer to
secondary standards, a temperature distribution scale
was realized using a multi filtered irradiance meter
traceable to the INM/CNAM-France primary
standard for radiant flux. Theory, design information
and so far obtained results are reported. Key words:
spectral irradiance, distribution temperature.
1 Theory
Secondary standards most frequently used in
photometry are incandescent lamps of special design
that exhibit a quasi Gray Body behaviour in the VIS
and near IR ranges. This also apply to halide lamps
operated in the 2700 K...3300 K range. Assuming a
filtered irradiance meter with two spectral bands,
λ 1 ...λ 2 and λ 3 ...λ 4 , for the range λ 1 ...λ 4 , the
distribution temperature (T 1,4 ) should be the solution
of eq.:
λ 2
∫
s1,2
( λ)
⋅ L0
( λ,
T1,4
) ⋅ dλ
Y1 ,2 λ1
=
(1)
λ 4
Y3,4
s ( λ)
⋅L
( λ,
T ) ⋅ dλ
∫
3,4
λ3
0
where : Y 1,2 and Y 3,4 are the photocurrents generated
by the radiometer in the two different spectral bands;
s(λ) is the (absolute) spectral responsivity of the
filtered radiometer and L 0 (λ 1,4 ) is the spectral
radiance of a Black Body at temperature T 1,4 .
2 Practical realization
A multichanell irradiance meter was developped at
NIM-Romania, covering the wavelength range of
(400…800) nm (Fig. 1).
Figure 1. Filtered irradiance meter basic design
1,4
The definying characteristic of the filtered irradiance
meter is it`s spectral responsivity:
Y ( λ)
R e
( λ)
= = A⋅
s(
λ)
(2)
E(
λ)
10
8
6
4
2
0
Re*E6 [(Axm2)/W]
300 400 500 600 700 800 nm
Figure 2. Spectral responsivity of the irradiance meter in
different spectral bands
3 Characterization
Related to eq. (1), the signals ratios Y 1,2 / Y 3,4 have
an estimated combined uncertainty of 0,15 %. The
spectral responsivity on different measurement
channels (as defined by the different filters) was
measured against the NIM-Romania reference,
traceable to the LNE-INM, France primary standard.
The obtained values were characterised by an
estimated standard uncertainty of 0,50 %.
From eq. (1) it becomes apparent that the estimated
distribution temperature is a function of many
parameters:
T
[ Y / Y , s ( λ),
s ( λ),
c c ]
1 ,4
= f
1,2 3,4 1,2 3,4 1,
so numerical calculation was used troughout for
sensitivity estimations. This approach led to the
uncertainty budget tabulated below :
Quantity
Associated
standard
uncertainty
(%)
Sensitivity
coefficient
(K / %)
Y 1,2 / Y 3-4 0,15 % δT 1,4 /
δ(Y 1,2 /Y 3,4) ≈
50 K / %
s 1,2 (λ) 0,50 % δT 1,4 / δs 1,2 (λ)
≈ 30 K / %
s 3,4 (λ) 0,50 % δT 1,4 / δs 3,4 (λ)
≈ 30 K / %
2
Contribution to
the combined
std. uncertainty
(K)
≈ 7,5 K
≈ 15 K
≈ 15 K
T 1,4
≈ 23 K
Table 1. Temperature distribution measurement uncertainty
budget
Proceedings NEWRAD, 17-19 October 2005, Davos, Switzerland 319