Extra points for thermometry
Jonathan Pearce explains the impact of the National Physical Laboratory's (NPL) work on temperature measurement in an invited article for Nature Physics.
Jonathan's article covers more than 400 years of advances in temperature measurement – from one of the first temperature scales, traced back to 1612, based on the expansion of a gas; through the development of the centigrade (later Celsius) scale in the 18th century; to the first modern temperature scale, introduced in 1887, linked to absolute temperature.
Today, almost every technological process depends in some way on temperature measurement and control – from intercontinental flights to reliable electricity. They all depend on a sophisticated measurement infrastructure that allows temperature measurements to be traced back to the SI unit of temperature, the kelvin, via the International Temperature Scale of 1990 (ITS-90).
But for temperatures above around 1000 °C, ITS-90 relies on extrapolation from a reference value, the melting temperature of silver (962 °C), which makes temperature measurements in this range subject to large uncertainties. To overcome this problem, NPL is at the forefront of current efforts to develop high-temperature fixed points, based on the melting temperatures of metal–carbon eutectic alloys at temperatures up to almost 3,200 °C.
High-temperature fixed points have proven to be extremely reproducible and NPL is coordinating a global research programme to introduce these reference standards for better temperature measurements. The significant improvements in temperature control they bring have already been used in a wide range of situations, for example, to improve manufacturing processes for high-efficiency gas turbines, develop new temperature sensors and characterise nuclear accident conditions. After the upcoming redefinition of the kelvin, high-temperature fixed points will be introduced as a standardised method of realising temperature.
Read the full article in Nature Physics
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