Lämpötilamittausperiaate

Lämpötilamittausperiaate, or the principle of temperature measurement, refers to the fundamental concepts and physical phenomena that enable the determination of temperature. Temperature is a measure of the average kinetic energy of the particles within a system. Various physical properties of matter change predictably with temperature, and these changes form the basis for different thermometric methods.

One common principle is thermal expansion. Most substances, whether solid, liquid, or gas, expand when heated and contract when cooled. This change in volume or length can be calibrated to indicate temperature. For example, a liquid-in-glass thermometer utilizes the expansion of a liquid, typically mercury or alcohol, within a sealed tube.

Another significant principle is electrical resistance. The electrical resistance of many materials, particularly metals, changes in a well-defined way with temperature. Resistance thermometers, such as platinum resistance thermometers (PRTs), exploit this phenomenon. Thermistors, which are semiconductor-based resistors, also exhibit a strong temperature-dependent resistance.

Thermocouples operate on the Seebeck effect, a thermoelectric phenomenon where a voltage is generated across a junction of two dissimilar metals when there is a temperature difference between the junction and the open ends. This generated voltage is proportional to the temperature difference, allowing for temperature measurement.

Radiation pyrometers measure temperature based on the thermal radiation emitted by an object. All objects above absolute zero emit electromagnetic radiation, and the intensity and spectral distribution of this radiation are dependent on the object's temperature. Infrared thermometers are a common example of devices using this principle. The choice of measurement principle depends on factors such as the required accuracy, temperature range, environmental conditions, and cost.