IMPROVEMENTS RELATING TO THE CALIBRATION OF THERMOMETERS Abstract:

ITS-90 specifies a series of temperatures which are used to define the scale. Supplementary Information to ITS-90 describes how these substances can be embodied into structures, known as fixed point cells that are useful to thermometrists. At present, fixed point cells are used with apparatus such as cryostats, baths and furnaces. However, current furnaces for example are expensive. The ideal furnace employs a heat siphon which has thermal conductance 200 times better than copper to create isothermal conditions during phase transitions. It may not be possible for a furnace to use the working fluid of choice for safety reasons. There is often poor thermal conductance between the furnace and the fixed point cell such that a series of furnaces are required to enable the required temperature range to be achieved. A patent application filed during September 2007 describes a combined metal clad fixed point cell and heat siphon, which when heated provides an isothermal environment for the metal within to change state. The outer wall of the cell becomes the inner wall of the heat siphon with cost as well as performance benefits. The device is called a “Siphonic Cell”. Siphonic Cells can be of Indium, Tin, Zinc, Aluminium, Silver