Thermometry

Abstract

In experiments on matter at low temperatures, some means of accurate temperature measurement is necessary to quantify the results fully so that they can be compared with the appropriate theoretical models. Thermometers have some property, preferably one that is easily measured, which changes with temperature in a known or predictable way. The basic requirements for thermometers, the need for good thermal contact to the apparatus or sample under investigation, low self-heating and fast response to changes in temperature etc. are essentially the same at low temperatures as at higher temperatures. However, some of the technical difficulties in fulfilling these requirements increase as temperatures are reduced. Quite a large number of different types of thermometer are used at low temperatures, depending on temperature range, the required accuracy, size and cost. However, all thermometers fall into one of two categories: (1) primary or absolute thermometers or (2) secondary thermometers.