Here - PMOD/WRC
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Here - PMOD/WRC
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Comparing curves 5 and 6 shows that the graphite holder<br />
does not improve the uniformity.<br />
Another holder we used was a 3 mm thick CC tube of<br />
150 mm length rapped with 4 layers of graphite cloth.<br />
Such a holder, in distinction from the graphite one,<br />
improves the uniformity, which is shown on Fig.3.<br />
Temperature Difference, C<br />
Figure 2. Temperature distributions measured by thermocouple<br />
at T=1500 o C for BB3500YY with a graphite holder<br />
Temperature Difference, C<br />
40<br />
20<br />
0<br />
-20<br />
-40<br />
-60<br />
-80<br />
-100<br />
20<br />
0<br />
-20<br />
-40<br />
-60<br />
-80<br />
1. All baffles+felt<br />
2. No outer baffles<br />
3. No inner baffles<br />
4. No felt<br />
5. Hot rings at rear end<br />
6. Hot rings+graphite holder<br />
-100 -80 -60 -40 -20 0 20 40 60 80 100 120 140<br />
Distance from Holder centre, mm<br />
1. Hot ring s. CC tube<br />
2. Hot ring s. No tube<br />
3. Hot ring s. CC tube+cloth<br />
4. No tube<br />
5. CC tube+cloth<br />
6. NEW heater. CC tube+cloth<br />
-100<br />
-120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120<br />
Distance from Holder centre, m m<br />
Figure 3. Temperature distributions measured by thermocouple<br />
at T=1500 o C for BB3500YY with a CC-tube holder<br />
Distribution measured first for the arrangement with<br />
some high resistance rings at the rear end of the cell<br />
position but without any holder (curve 2), then for the<br />
same arrangement but with the CC-tube (curve 1), and<br />
then with the tube wrapped in the cloth (curve 3).<br />
Comparison of the curves shows that the cloth has more<br />
significant effect than the tube itself. Curves 4 and 5<br />
represent distributions measured without and with the tube<br />
wrapped with cloth respectively but for arrangement with<br />
low resistance rings around the rear end of the cell position.<br />
Finally a new set of rings was arranged, which showed (in<br />
combination with CC holder) the uniformity (curve 6)<br />
within 5 degrees along the distance of 110 mm.<br />
Temperature uniformity at 2500 o C<br />
Two radiation thermometers were used for temperature<br />
distribution measurement at higher temperatures. One of<br />
them, narrow-beam fiber radiation thermometer looked<br />
through the rear channel of the furnace to a blind baffle<br />
placed at the rear end of the CC-tube holder and used for<br />
furnace temperature control. The second thermometer<br />
looked through the front opening to a movable target<br />
inside the holder. The target was a 10 mm length graphite<br />
tube with soot-blackened bottom at one end and 5 mm<br />
aperture at another one.<br />
At the beginning the target was placed inside the CC<br />
tube near its front end, the furnace was brought to the<br />
desired temperature of 2500 °C, and the temperature of the<br />
target was measured by means of the second radiation<br />
thermometer. Then the furnace was brought to the<br />
temperature of 1500 o C, the target was pushed by an<br />
alumina rod to be moved by one step of 10 to 20 mm, the<br />
furnace was brought back to the temperature of 2500 °C<br />
and the second point of the temperature distribution<br />
measurement was taken. This was repeated to cover the<br />
length of the CC tube.<br />
As a test of the validity of this method, the temperature<br />
distribution was measured at 1500 o C and was compared<br />
with measurement with the thermocouple with the same<br />
furnace arrangement. Both methods agreed within one<br />
degree. Then the method was applied to measure the<br />
temperature distribution at 2500 o C. The measurements<br />
showed that the hottest point was just in the center of the<br />
CC tube and temperature gradually decreased towards its<br />
ends. The central 40 mm and 80 mm parts of the tube were<br />
uniform within 2 and 5 degrees respectively.<br />
Work with eutectics cell<br />
The NMIJ Re-C cell of 45 mm length, 24 mm outer<br />
diameter and 3 mm aperture cavity was heated in<br />
BB3500YY furnace to observe melting and freezing<br />
plateaus. The same cell was then used for observing the<br />
plateaus in VR10-A23 furnace [6], which has operation<br />
temperature limited to 2500 o C. The former showed better<br />
melting plateau shapes.<br />
BB3500YY was used for filling one Re-C and one<br />
TiC-C cells. The Re-C cell was compared with a similar<br />
one but filled in VR10-A10 furnace (vertical variant of<br />
VR10-A23). The TiC-C cell was compared with a cell<br />
manufactured by VNIIOFI. The results of these<br />
comparisons will be presented in the paper.<br />
References<br />
[1] Yamada Y., Advances in High-temperature Standards above<br />
1000 o C, MAPAN - Journal of Metrology Society of India, v.20,<br />
No 2, 2005, pp.183-191.<br />
[2] Sapritsky, V., Ogarev, S., Khlevnoy, B., Samoylov, M., and<br />
Khromchenko, V., Metrologia 40 (2003), S128-S131. 2003<br />
[3] N. Sasajima, M. K. Sakharov, B. B. Khlevnoy, Y. Yamada, M.<br />
L. Samoylov, S. A. Ogarev, P. Bloembergen and V. I. Sapritsky.<br />
'A comparison of Re-C and TiC-C eutectic fixed-point cells<br />
among VNIIOFI, NMIJ and BIPM'. in 9th International<br />
Symposium on Temperature and Thermal Measurements in<br />
Industry and Science (TEMPMEKO). 2004. Dubrovnik.<br />
[4] Woolliams E., Khlevnoy B., Sakharov M., Samoylov M.,<br />
Sapritsky V., Investigation of TiC-C and ZrC-C eutectic<br />
fixed-point blackbodies., Submitted to Metrologia.<br />
[5] Sapritsky V. and others, Applied Optics, 36, 5403-5408, 1997.<br />
[6] Y. Yamada, N. Sasajima, H. Gomi, and T. Sugai, in<br />
Temperature: Its Measurement and Control in Science and<br />
Industry, 7 (Ripple et al ed.), AIP Conference Proceedings,<br />
Melville, New York (2003) 965-990.<br />
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