Heat and Thermodynamics

7.12 Measurement of Low Temperature

The normal hydrogen pressure thermometer can be used for measurement of low temperature down to −259°C. For measurement of low temperatures down to −270°C, normal helium thermometers are used. To convert the readings to absolute scale, the readings of these thermometers must be extrapolated to vanishingly small pressures. For measurement of still lower temperatures—4.2 K to 0.9 K—the zero point pressure of 10 cm to 0.2 cm of mercury is employed and the mercury manometer is replaced by the Pirani or the hot wire manometer. Some uncertainty arises on account of thermal molecular pressure at such low temperatures.

7.12.1 Secondary Thermometers

For measurement of low temperatures, secondary thermometers such as ...