Thermometry

Thermometry is the science and practice of measuring temperature, a fundamental physical quantity that reflects the thermal state of matter. Temperature measurement relies on properties that vary with temperature, such as liquid expansion, electrical resistance, or emitted radiation, and it encompasses a range of devices and methods from simple glass thermometers to advanced electronic sensors.

Common instruments include liquid-in-glass thermometers, which use the expansion of mercury or alcohol in a capillary; bimetallic thermometers; and electronic sensors such as resistance temperature detectors (RTDs), thermistors, and thermocouples. Non-contact methods detect infrared radiation emitted by objects. Modern thermometers often provide digital readouts, data logging, and wireless transmission, with measurements traceable to standard references.

Temperature scales organize measured values. The kelvin (K) is the SI base unit for thermodynamic temperature, while Celsius (°C) and Fahrenheit (°F) are widely used in daily and industrial contexts. Reference points such as absolute zero and the triple point of water underpin scale definitions, with practical realizations provided by standards like the ITS-90 and older scales such as IPTS-68. Calibration against primary standards ensures traceability and comparability across instruments and laboratories.

Calibration and uncertainty are central to thermometry. Instruments are calibrated against known references, and measurements are accompanied by uncertainty budgets that account for sensor response, environmental conditions, drift, and measurement procedures.

Applications span science and industry: laboratory research, process control in manufacturing, medical and clinical thermometry, environmental monitoring, meteorology, and food safety. Thermometry thus supports both fundamental science and everyday decision making.