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NPL Makes Hot Christmas Pudding


More Than Time Signals

Heat With A Purpose

PL does not just send out a time signal by radio (at 60kHz). The temperature experts at the National Physical Laboratory (NPL) created a Christmas pudding, complete with sprigs of holly, from various forms of graphite. The pudding was placed in a high-temperature furnace and heated to 2,200 °C, (or 2,473 K, where K is kelvin, the SI unit of temperature).

When the pudding was heated, its parts glowed with differing levels of brightness due to the contrasting emissivity of each form of graphite used. NPL then took pictures with a standard SLR camera and a thermal imager. NPL’s temperature and humidity team use the high-temperature furnace to calibrate non-contact thermometers and thermal imagers, from around 1000 °C to about 3000 °C, to the international temperature scale of 1990 (the ITS-90).

It is also used to compare temperature calibration capability with other national measurement institutes around the world. In the future, the furnace will be used with high-temperature fixed-point cells to realise the kelvin with very low uncertainties, from around 1000 °C and above, and then disseminate it to accredited calibration laboratories and other users. You probably have some graphite at home as it is what is commonly known as ’pencil lead’.

However, graphite is not lead at all, it is a form of carbon. Graphite is a good conductor of heat and electricity and has an incredibly high melting (sublimation) temperature of around 3,700 °C. A layer of graphite one atom thick is called graphene which has some incredible properties that NPL exploits. Reliable temperature measurement is required in areas as diverse as healthcare, manufacturing, meteorology, defence and energy production, and is a key indicator of climate change across the world. Temperature measurement touches on most areas of human endeavour in modern society.

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For example, although widespread fever screening was not recommended for COVID-19, the pandemic highlighted the requirement for reliable fever screening as a first line of defence to control the spread of infection.

(Source & Picture-Credit: NPL; [email protected])

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