Pyrometer

A pyrometer, also called a radiation thermometer, is a remote-sensing thermometer that measures the temperature of a distant object by detecting the thermal radiation it emits, so it never needs to touch the surface being measured. It works from the Stefan-Boltzmann law: an optical system focuses the incoming radiation onto a detector, and the measured irradiance is used to infer the object temperature once its emissivity is known. In energy and industrial settings, pyrometers read the operating temperature of metallurgical and salt bath furnaces so fuel use and smelting can be controlled, measure steam temperature in the superheater of steam boilers, and monitor the surface temperature of turbine blades inside operating gas turbine engines. Because they need no contact with the object, they are also used on moving parts and on surfaces too hot to touch, such as the envelope of a hot air balloon. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/