Hot and cold: defining and measuring temperature

Abstract

Despite the economic importance of temperature measurement and 300 years of scientific research into thermal phenomena, temperature remains one of the least understood and most difficult to measure of all physical quantities. Indeed, our current ability to measure temperature in accordance with thermodynamics fails to meet our needs. This review paints a broad overview of temperature measurement, with insights into the evolution and meaning of the concept of temperature, the structure of different temperature scales and their limitations, the most accurate primary measurement techniques, the International Temperature Scale of 1990, and speculations on future developments.

KEYWORDS:

• Temperature
• measurement
• primary thermometers
• temperature scales

Acknowledgements

The author gratefully acknowledges comments and suggestions from colleagues Patrick Rourke, Peter Saunders, and Andrea Peruzzi. Figure 5 is provided courtesy of the National Physical laboratory (NPL).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Notes on contributors

D. R. White

Rod White is a metrologist, now retired, from the Measurement Standards Laboratory of New Zealand. He has worked on many aspects of temperature measurement but has specialised in Johnson noise thermometry, resistance thermometry, the nature of measurement, and measurement uncertainty. He was awarded the Silver Medal and Cooper Medal of the New Zealand Royal Society, and a D.Sc. from the University of Waikato for his contributions to temperature metrology. He has served as the New Zealand representative on the BIPM’s Consultative Committee for Thermometry for many years and has chaired and been an active member of several of its working groups.