Understanding the Origin of Uncertainty in Thermometer
Calibration  Jonathan Pearce National Physical Laboratory
Thermometers have widespread application and like any
measurement device, they must be calibrated. Many do this with
the International Temperature Scale of 1990 (ITS-90), which is a
platinum resistance thermometer that calibrates using a fixed
point cell, which is a container with a well running through its
center for insertion of the thermometer. The container has a
material of 99.9999% purity. The central well allows a
thermometer to be inserted so that the sensing element at its
bottom is completely immersed in the fixed point metal. The
container is then placed in a furnace to allow controlled
melting and solidification of the metal.  To better understand
the microscopic behavior of the phase change processes,
researchers at the National Physical Laboratory turned to
simulation. They were able to identify specific behavior in a
system that is difficult to observe experimentally and yet
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