Measuring temperature

Heat and temperature are both measures of the energy possessed by molecules of a substance. Heat refers to total kinetic and potential energy; temperature refers to average kinetic energy. The coldest predicted temperature is absolute zero. The triple point defines the unique temperature and pressure at which the solid, liquid and vapour phases of a pure substance coexist. The international temperature scale of 1990 attempts to standardize temperature measurement by defining various fixed points. Temperature may be measured mechanically by the expansion of solids, liquids or gases. Electrical measurement methods include thermocouples, thermistors, semiconductors and resistance thermometers. Liquid crystal and electromagnetic radiation thermometers are also used. Measuring body temperature is important as it tends to fall during anaesthesia. Core temperature measurements are more useful than peripheral temperature measurements. Active warming devices are often used to prevent perioperative hypothermia. For safety reasons the temperature of these should always be monitored.