Optical pyrometer is one of the earliest and most widely used non-contact thermometers. It has a simple structure, is easy to use, and has a wide temperature measurement range (700-3200°C), which can generally meet the accuracy requirements of industrial temperature measurement. Optical pyrometers are currently widely used for temperature measurement of high-temperature melts and furnaces, and are very important high-temperature instruments in metallurgy, ceramics and other industrial sectors. The optical pyrometer is made by using the principle that the monochromatic radiation intensity of the heated object increases with the increase of temperature. It is also called a monochromatic radiation thermometer because a single wavelength is used for brightness comparison.

The disadvantage of the optical pyrometer is that it is observed by the human eye and needs to be manually balanced, so it cannot achieve fast measurement and automatic recording, and the measurement results are subjective. Recently, due to the development of photodetectors, interference filters and monochromators, the position of optical pyrometers in industrial measurement has gradually declined, and is being replaced by more sensitive and accurate photoelectric pyrometers. The photoelectric pyrometer is developed on the basis of the optical pyrometer. It replaces the human eye with a photosensitive element to realize photoelectric automatic measurement.