The Model 17402B Gallium Apparatus is not an adaption from general purpose equipment, but is designed specifically to realize and maintain the Gallium Cell on the melt plateau, for calibration of thermometers on the International Temperature Scale of 1990.
The apparatus permits the gallium to melt coaxially over 12 to 16 hours. It is also uniquely designed to freeze the cell from bottom up, which eliminates the danger of damage from the expansion of gallium during freezing.
1. The Model 17401 Gallium Cell may be used, without the thermal environment provided by Model 17402B Gallium Apparatus, in a well-controlled bath. However, the advantages of automatic operation, convenience and cell protection, recommend the use of the Model 1742B environment in most cases.
2. No external connections other than the power are required.
3. A completely automatic electronic control system provides a precise means for realization and maintenance of the plateau. The Apparatus can be turned on by a timer an hour before the laboratory day begins, the plateau utilized throughout the working day, and the system recycled overnight. A thermal sink is provided, which forces the gallium to refreeze upwards from the bottom (see second paragraph).
4. Confidence is a major requirement in a standard. The Isothermal Gallium Cell and Apparatus have a long (20 year) history, and have been successfully used in most National and Primary Laboratories world-wide. This is one of the main reasons for choosing the Isothermal Cell and Apparatus.
5. The Cell and Apparatus are manufactured to the strict requirements of BS 5750 and ISO 9000. Each finished unit becomes part of the Isotech UKAS working Calibration Laboratory for two weeks or more, during which use the control circuits are set and checked for optimum performance. It is released only when Isotech is entirely satisfied with its performance.