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In a recent research paper co-authored by colleagues from the National Institute of Standards and Technology, the National Research Council of Canada and I, we presented an overview of emerging thermometry technologies which although in an early stage of development (some) have the potential of providing reliable, indeed traceable, temperatures in the measurement setting.
The reliable measurement of temperature is vital for a whole host of human activities, including healthcare to ensure reliable diagnosis, meteorology for accurate weather forecasting, scientific 
research e.g. for determining the extent and progress of climate change and industry to ensure optimum process control and therefore minimising the impact on the environment.
Moreover, there is a vast range of temperatures and applications to be covered, from low temperatures below 25 K (-248 °C) vital for e.g. for the emerging hydrogen economy and quantum computing, to high temperatures well above 1500 °C for e.g. in metals processing, glass and energy production.
To reliably measure and control temperature requires the use of practical sensors. In the case of contact thermometers these are usually thermocouples, or resistance thermometers. To ensure these sensors yield low uncertainty measurements they need to be traceably calibrated by an accredited laboratory. Unfortunately, all sensors drift in use, and in an unpredictable manner. To overcome this problem, the thermometers need to be either periodically replaced with new calibrated thermometers or the old ones removed and recalibrated before being reinstalled. If this is not done the output of the thermometers departs increasingly from the true value of the temperature which has the potential for many unfortunate consequences such as loss of process control in an industrial process which can increase scrappage rate and energy use.
One approach to deal with the issue of sensor drift is to introduce traceability “at the point-of-measurement”. This has two main approaches. Firstly, the incorporation of known fixed points within the thermometer itself, then through detecting the phase transition the sensor can be calibrated at that temperature and so run optimally. A more radical approach, discussed in our paper, is through the establishment of practical primary thermometry where the sensor itself requires no calibration but uses fundamental physics from which to obtain temperature.
Both these approaches are currently at different stages of development at NPL. Self-validating thermometers are in the process of being commercialised; whilst research is underway in the two areas of practical primary thermometry.
The provision of traceability at-the-point-of-measurement is potentially a disruptive change to the current approach to thermometry. Instead of temperature sensors requiring calibration in an accredited laboratory before use they can be deployed directly within the measurement setting and can be relied upon to provide reliable traceable temperatures from installation until they fail. Such developments are essential to facilitate true autonomy in industrial production. In addition, such sensors are required to validate the performance of temperature sensor networks that require such “points-of-truth” to ensure the reliable performance of the whole network.
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19 Oct 2022