Triple Point of Water Cells

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Triple Point of Water Cells (197.49 KB)

An improved technique for manufacturing triple point of water (TPW) cells is reported. The im-provements focus primarily on two points: (1) keeping the gas pressure in the cell as low as pos-sible, and (2) achieving the highest possible water purity in the cell. Two cells manufactured with the new technique were certificated at NIST, and the differences from the NIST reference TPW cell were within 0.01 mK. Five designs of TPW cells (with different sizes and shell materi-als such as Pyrex and stainless steel) are described. Many TPW cells were intercompared with each other in the laboratory. The effects of the isotopic composition of the water on the TPW equilibrium temperature are also discussed.