Novel techniques for traceable temperature dissemination

Accurate and consistent temperature measurement underpins manufacturing, health and safety as well as the development of new science and technology. Temperature measurement devices are calibrated using well-defined ‘fixed points’ (specific temperatures at which certain substances freeze or melt) on the International Temperature Scale of 1990 (ITS-90). However, measurements in some regions of the ITS-90 scale have larger uncertainties than others. Reducing these uncertainties will ensure that the ITS-90 can more effectively meet user needs, whilst new and emerging temperature measurement methods offer the potential for direct thermodynamic temperature measurements without using a defined temperature scale.

The EMRP project Novel techniques for traceable temperature dissemination (NOTED) improved the accuracy of some regions in the ITS-90 scale, and developed direct temperature measurement methods to provide a link to thermodynamic temperature, so removing reliance on the ITS-90.

The project:

• Improved the accuracy of a number of ITS-90 fixed temperature points by developing methods to address key sources of measurement uncertainty, including impurities in the fixed points and temperature fluctuations in furnaces.
• Developed four new fixed temperature point cells to address gaps in the ITS-90 scale.
• Improved calibration procedures for two commonly used types of standard platinum resistance thermometers, to account for a range of environmental and internal influences that had not previously been considered or thoroughly studied (such as self-heating effects).
• Developed temperature measurement methods independent of ITS-90 as the basis for new thermodynamic temperature standards. These methods are based on near infra-red radiation thermometry, vapour pressure temperatures, and acoustic thermometry.

This EMRP project focused on improving the ITS-90 scale by plugging gaps through developing new fixed temperature points so reducing interpolation uncertainties and contributing to a more robust scale. In addition, the project’s new CO2 fixed temperature point may eventually provide an alternative to the mercury fixed point, overcoming issues associated with toxicity and transportation. The project’s new temperature amplifier system has potential to address the lack of calibration points between 660 ºC and 960 ºC. Infrared radiation thermometry has undergone a significant step forward with the development of new methods and facilities for the absolute calibration of infrared thermometers and the new tuneable wavelength thermometer.

Dedicated electronics for temperature control of thermometry instrumentation and practical acoustic thermometry technology, developed by the project, are being incorporated into new commercially available devices. For the first time, users in industry and research will be able to make direct SI traceable thermodynamic temperature measurements outside NMI facilities.