Traceable Temperatures: An introduction to temperature measurement and calibration, 2nd edn

Abstract

This is the second edition of a text first published in 1994, which had its origin in a volume of course notes published for a series of workshops on temperature measurement and calibration that took place in the 1980s in New Zealand. In the first edition, the authors set out to cater particularly for `the beginner with modest experience who wishes to acquire expertise and knowledge quickly'. The text, in fact, was much broader than this and was written for a wide readership that extended from the beginner to experienced scientists and engineers who need a ready reference covering many aspects of temperature measurement and calibration. The authors succeeded admirably in their aim and the first edition provided a welcome addition to the relatively small body of literature devoted to temperature measurement. In the second edition, the main body of the text treating the principal methods of temperature measurement remains largely unchanged. The new version, however, reflects the much greater importance now placed on the formal requirements for traceability and statements of uncertainty. The excellent chapter on uncertainties in measurement has been revised to make it fully consistent with the ISO Guide to the Expression of Uncertainty in Measurement. The chapter on calibration gives essential advice on the application of ISO 17025 General Requirements for the Competence of Testing and Calibration Laboratories. For those engaged in running or setting up a calibration laboratory for temperature measurement, the text is now a mine of useful information. The second edition also contains a new chapter entitled `Use of thermometers'. This is essentially a summary of all the reasons why a thermometer is not giving the right answer! It includes a good discussion on the various mechanisms of heat transfer to and from the thermometer, immersion errors, settling response errors, and the effects of thermal radiation and temperature measurements in non-equilibrium situations. All users of thermometers will find this chapter useful as it brings together material that otherwise is widely dispersed. For the rest, there are chapters on the International Temperature Scale of 1990 (ITS-90), platinum resistance thermometry, liquid-in-glass thermometry, thermocouple thermometry and radiation thermometry. The chapter on thermocouples now includes an extensive account of how a thermocouple works. It is emphasized that the measured thermoelectric potential difference between the ends of a pair of thermocouple wires is developed along those parts of the wires that are in the temperature gradient and that it has nothing to do with the junction provided that there is electrical contact and the junction itself is not in a temperature gradient. The authors quite rightly stress that, unless this is understood, the correct use of thermocouples and an appreciation of their likely source of error are much more difficult. The authors point out that the so-called `laws of thermoelectricity', although perfectly correct, do not lead to an understanding of how a thermocouple works and have given generations of users the false idea that somehow the junction of a thermocouple is the critical element, when it is not. The one chapter where the revisions in the second edition have, in my view, been less successful is the first one on `Measurement and Traceability'. The authors have chosen to present the basis of measurement wholly in terms of scales and scale units rather than the conventional quantities and units to be found in the official SI Brochure and in the ISO 31 Standards Handbook Quantities and Units. This is unfortunate, since it leads to the SI being presented as a system of units corresponding to the `SI scales' of length, mass, etc. One can multiply, divide, add and subtract quantities, but not scales. However, this is a minor criticism of what is otherwise an excellent book. I recommend everyone interested in or having responsibility for accurate and reliable temperature measurements to have a copy on their shelves. Terry Quinn