Here - PMOD/WRC

VTBB, BB29Ga, and BB156In with 100 K to 1000K
working temperature range, designed for calibration of
spaceborne IR sensors and high-precision radiometry at
such research organizations as German Aerospace Center
(DLR) and Physikalisch-Technische Bundesanstalt
(Germany), National Physical Laboratory (UK), Space
Dynamics Lab (USA), NIM and IAO (China).
Cavity-type BB100-V1 as a source of thermal radiation
features a series of advantages over any other thermal
sources – such as high reproducibility, low sensitivity of its
effective emissivity to variations and degradation of optical
properties of its cavity inner surface.
Low-temperature and cryogenic BB100-V1 is build up
on the principles of the usage of external liquid-based
thermostat LAUDA Proline PR1845-LCK1891 with
circulating coolant KRYO-51 in a closed loop.
As a material of radiating cavity for low-temperature
and cryogenic BB one can use copper and aluminum alloys.
The necessary value of emissivity was obtained with the
usage of black cover paints, e.g. Chemglaze Z-302 for
BB29gl blackbody or Nextel Velvet 811-21 for BB100 /
BB100-V1 radiation sources. While identifying
appropriate coating for BB-100V1 bottom possessing
emissivity better 0.9 in the spectral range of interest (see
Fig. 1), the Nextel Velvet Coating 811-21 was chosen by
ourselves after comparative analysis of several
comprehensive reviews [e.g., 4] on application and optical
properties of black paints and various coatings to stray
light suppressing, solar energy absorbing, for thermal
detectors of optical radiation, radiation losses control, etc.
Emissivity
0.990
0.985
0.980
0.975
0.970
0.965
0.960
0.955
0.950
0.945
0.940
[10]
[11]
[12]
0.935
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Wavelength (ì m)
Figure 1.
Spectral emissivity of Nextel Velvet Coating 811-21
It is enough to assume that the spectral hemispherical
emissivity of Nextel 811-21 is within 0.935…0.990
interval for wavelength range from 1.5 to 15 μm. The
measurements of reflectance performed for the predecessor
of Nextel 811-21, the 3M Velvet Black, show the presence
of a small specular component, less than 10% from overall
hemispherical reflectance; the diffuse component of
reflectance has the near-Lambertian BRDF.
The drawing of BB100-V1 design performed with the
account of above-mentioned studies is depicted in Fig. 2.
The computations of the normal effective emissivities
of an isothermal cavity depicted in Fig.2 using STEEP3 [5]
software. We have used the limiting values of wall
emissivity (0.935 and 0.990) and 4 values of wall diffusity.
The results of computations are presented in Table 2.
Figure 2. BB100-V1 cross-section.
Cavity dimensions: 200 mm length x 120 mm diameter.
Table 2.
Normal Effective Emissivity of BB100-V1 Isothermal Cavity
Cavity
Cavity Wall Diffusity
Wall
Emissivity
0.7 0.8 0.9 1.0
0.935 0.9972 0.9976 0.9980 0.9983
0.990 0.9996 0.9996 0.9997 0.9997
The BB100-V1 is currently under testing in
cryo-vacuum chamber. The uncertainty of thermodynamic
temperature reproducibility of BB100-V1 within working
temperature ranges did not exceed 0,5K (1). The
temperature non-uniformity and long-term stability
account for less than 0.1K and 0.1% for 1.5 μm to 15 μm
wavelength region under cryo-vacuum conditions of
medium background environment. The results of these
measurements will be presented in the paper.
References
[1] V.I.Sapritsky, S.P.Morozova, B.E.Lisiansky, S.A.Ogarev,
M.K.Sakharov, M.L.Samoylov, A.S.Panfilov, B.B.Khlevnoy,
V.E.Privalsky The Global Earth Observation System of
Systems (GEOSS) and problems of measuring the radiant
properties of objects of observations . Proceedings of
NEWRAD’2005 (in print).
[2] V.I.Sapritsky, S.A.Ogarev, B.B. Khlevnoy, M.L.Samoylov,
V.B.Khromchenko “Blackbody sources for the range 100 K to
3500K for precision measurements in radiometry and
thermometry“ – in Proceedings of the 8th Symposium on
temperature: its measurement and control in science and
industry. Chicago, IL, U.S.A. October 21-24, 2002.
[3] V.I.Sapritsky, V.B.Khromchenko, S.N.Mekhontsev,
M.L.Samoilov, A.V.Prokhorov, S.A.Ogarev, A.Shumway
“Medium Background Blackbody BB1000”. Conference CD
of CALCON’2000. SDL, Utah, USA, 2000.
[4] Hameury J, Hay B, Filtz J R 2003 Measurement of Infrared
Spectral Directional Hemispherical Reflectance and
Emissivity at BNM-LNE – Paper presented at the Fifteen
Symposium on Thermopysical Properties, June 22-27, 2003,
Boulder, CO, USA
[5] STEEP3, version 1.3. User’s Guide. Virial, Inc., NY, 2000
270