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. 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.

Taking the colorimetric pyrometer as an example, the working principle of the photoelectric pyrometer is introduced. The object to be measured is imaged by the objective lens 1, and projected onto the beam splitter 6 through the diaphragm 3 and the light guide rod 4, so that the long-wave (infrared) radiation is transmitted through and the short-wave (visible light) is partially reflected. The radiation transmitted through the spectroscope is filtered by the filter 9 to remove the residual short wave, and then received by the infrared photoelectric element (silicon photoelectric cell) 10, and converted into electric power output.