Pyrometrie

Pyrometrie, or pyrometry, is the science of measuring high temperatures. It covers techniques that estimate temperature from the radiation emitted by hot bodies, often without direct contact. Pyrometry is essential in industrial processes where thermometers cannot withstand or reach the surface being measured.

Principles: Most pyrometry relies on radiative heat transfer. Objects emit radiation according to Planck's law, but real surfaces differ due to emissivity, which ranges from 0 to 1. Pyrometers may measure total emissive power or select specific wavelengths, or use the ratio of two wavelengths. Calibration uses known reference temperatures or blackbody sources to relate detected radiation to temperature.

Types: Non-contact pyrometers include optical or infrared devices such as broadband pyrometers, monochromatic pyrometers, and ratio (two-color) pyrometers. Contact methods include thermocouples and resistance temperature detectors (RTDs) used when direct contact is feasible and within their temperature ranges. Infrared cameras extend pyrometry to temperature mapping of surfaces, a technique known as thermography.

Applications: Pyrometry is widely used in metalworking and foundry operations, glass manufacturing, cement and ceramics, and heat treatment of metals. It supports process control in furnaces, kilns, and reactors. Infrared thermography enables spatial temperature profiling in research and industry.

Limitations: Emissivity variation, target geometry, smoke or dust, and reflections can bias results. Accurate measurements require proper calibration, estimation of surface properties, and awareness of the temperature range and wavelength used. Uncertainty depends on sensor quality, wavelength, and the emissivity of the measured surface.

History: Pyrometry developed alongside advances in radiometry and blackbody theory in the 19th and 20th centuries, with practical instruments evolving throughout the 20th century.