Thermal measuring and testing – Thermal calibration system
Reexamination Certificate
2000-01-11
2001-09-25
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Thermal calibration system
C374S003000
Reexamination Certificate
active
06293695
ABSTRACT:
BACKGROUND OF THE INVENTION
A triple point of water is the temperature at which water, water vapor, and ice are in thermal equilibrium. Water triple point cells are used as an ITS-90 primary standard for calibrating thermometers; for this purpose, the triple point of pure water has an assigned value of exactly +0.01 degrees C.
There are commercially-available water triple point cells. A typical such cell sold by Hart Scientific has concentric cylindrical glass vessels. Both the inner and outer vessels are closed at the bottom. At the top, the vessels are joined together, thus sealing off an annular volume between the two cylinders. The annular volume is partially filled with water at the factory, and a vacuum is drawn (also at the factory) such that the remaining of the sealed-off volume is occupied by water vapor. When some of the water is cooled to become ice, there will be water, water vapor and ice inside the cell, and when they come to thermal equilibrium, the triple point is reached.
The Hart water triple point cells are quite expensive (currently they sell for around one thousand dollars each). Because the cells are filled and sealed at the factory. Water in the cells may slosh around during transportation, without air inside to dampen the water motion, a “water hammer” effect is generated, and breakage of the glass by action of water hammer is a common problem.
An object of the present invention is to provide a much less expensive water triple point cell.
Another objective of the invention is to provide a more rugged triple point cell, one that is not so susceptible to breakage during transportation.
SUMMARY OF THE INVENTION
One preferred embodiment of the invention provides a triple point cell comprising: 1) An outer vessel and an inner vessel; 2) an elastomeric stopper that fits inside the open end of the outer vessel; the elastomeric stopper has two holes, one through which the inner vessel is tightly fitted, and a second through which unwanted gasses is allowed to escape; 3) water in the volume between the outer and inner vessels. 4) a vent plug for plugging up the second hole after all the unwanted gases has been driven out of the triple point cell by water vapor that has been generated by boiling the water. Triple point is reached by freezing some of the water in the cell, and then letting the ice, water, and water vapor come to thermal equilibrium.
REFERENCES:
patent: 3216236 (1965-11-01), Rohrbach
patent: 3308646 (1967-03-01), Singleton
patent: 3348408 (1967-10-01), Engborg
patent: 3844894 (1974-10-01), Kronick et al.
patent: 5219225 (1993-06-01), Ball
patent: 2590981-A1 (1987-06-01), None
The National Bureau of Standards, Heat demonstrations Book 1, Figure 21-1, “Triple Point Cell” (no date).*
Isothermal Technology Ltd, “Jarret Water Triple Point Cell” (no date).*
S. Carlson, “Trackling the triple point”, Scientific American, vol. 280, Issue 2, pp. 98-99, Feb. 1999.*
1998-1999 Hart Scientific Temperature Calibration Equipment.
De Jesus Lydia M.
Gutierrez Diego
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