Reduced uncertainty radiation thermometer calibration serviceNew fixed points offer improved temperature measurementThe National Physical Laboratory (NPL) is a world leader of research into high temperature fixed points based on eutectic alloys of metal and carbon that extend the temperature range for practical and stable references up to 2750 °C. These references have been shown to agree to within 0.1 °C, even at the highest temperatures.

NPL now uniquely offer a UKAS-accredited radiation thermometer calibration service based on these references with traceability to national standards. For suitable radiation thermometers this has the potential for much reduced calibration uncertainties. Comparison has shown that calibration laboratories can achieve a level of uncertainty in scale realisation comparable to using a standard calibrated as a primary ITS-90 realisation.

Novel fixed point materials have expanded the options for high temperature calibration

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NPL has been extensively involved in researching high temperature fixed points (HTFPs). We maintain a set of standard HTFPs with very precisely known ITS-90 temperatures. These can be used to calibrate a suitable radiation thermometer†, readily achieving a calibration uncertainty of 0.05 % (k = 2)*(1.25 °C at 2500 °C) traceable to national standards. In practice this has been shown to make it possible for a calibration laboratory using such a secondary standard to achieve scale realisation uncertainties previously requiring a primary realisation of ITS-90** Any temperature range can be covered using a combination of ITS-90 defined fixed points and ITS-90 traceable high temperature fixed points, but the biggest benefit is expected to be from 1200 °C to 2800 °C.

This is a specialised service intended to give the lowest possible uncertainties in a cost effective manner. Please contact NPL to discuss details.

For further reading1. ** Reducing uncertainty in practical radiation thermometer

calibration based on proposed changes to the mise en pratique of the definition of the kelvin, David Lowe, Mick Broughton, Jon R Willmott, International Congress of Metrology 15010 (2013). http://dx.doi.org/10.1051 metrology/201315010

2. D Lowe 2013 Meas. Sci. Technol. 24 01590 http://doi:10.1088/0957-0233/24/1/015901

Contact details Further information

National Physical LaboratoryHampton RoadTeddingtonMiddlesexUnited KingdomTW11 0LW

Switchboard: 020 8977 3222Website: www.npl.co.uk

For further information please contact: David Lowe dave.lowe@npl.co.uk

The National Physical Laboratory is operated on behalf of the National Measurement Office by NPL Management Limited, a wholly owned subsidiary of Serco Group plc

Fixed point metal-carbon Nominal temperature / °CIron 1153

Cobalt 1324

Platinum 1738

Ruthenium 1954

Rhenium 2474

Tungsten carbide 2748

Example of the possible reduction in uncertainty in assigning a temperature to a blackbody source when changing to a radiation thermometer calibrated with HTFPs

† The requirements for a suitable thermometer are: target size < 1.5 mm, low size-of-source effect and non-linearised output. NPL can supply a suitable radiation thermometer with UKAS accredited calibration certificate.

* subject to the performance of the instrument being calibrated

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