Laws about infrared thermometers

Infrared thermometer is an essential tool for detecting internal structural faults of power transformers, and is also an important means of product quality control and monitoring. It is mainly composed of optical systems, photodetectors, signal amplifiers, signal processing, display output, etc.

In nature, when the temperature of any object is higher than zero, it will continuously emit infrared radiation energy to the surrounding space, and the size and distribution of the radiation energy are related to the surface temperature of the object. Therefore, we can measure the infrared radiation energy of the object. Infrared energy is used to determine the temperature of its surface. This is the objective basis on which infrared radiation temperature measurement is based.

Let’s look at another law about infrared thermometers.

Blackbody radiation law: A blackbody is an idealized radiator. It absorbs radiant energy of all wavelengths and has no energy reflection or transmission. Its surface emissivity is 1. It should be pointed out that there is no real black body in nature, but in order to clarify and obtain the distribution law of infrared radiation, an appropriate model must be selected in theoretical research. This is the quantized oscillator model of body cavity radiation proposed by Planck, thus deriving Planck's law of black body radiation, that is, the black body spectral radiance expressed in wavelength, is the starting point of all infrared radiation theories, so it is called the black body radiation law.

The influence of object emissivity on radiation thermometry: Almost all actual objects existing in nature are not black bodies. The radiation amount of all actual objects depends not only on the radiation wavelength and the temperature of the object, but also on factors such as the type of material, preparation method, thermal process, surface state and environmental conditions of the object. Therefore, in order to make the black body radiation law applicable to all real objects, a proportional coefficient related to the material properties and surface state must be introduced, that is, the emissivity. This coefficient represents how close the thermal radiation of an actual object is to blackbody radiation, and its value is between zero and a value less than 1. According to the radiation law, as long as the emissivity of the material is known, the infrared radiation characteristics of any object can be known. The main factors that affect emissivity are: material type, surface roughness, physical and chemical structure, and material thickness.

When using an infrared thermometer to measure the temperature of a target, the infrared radiation of the target within its band range must first be measured, and then the temperature of the measured target is calculated by the thermometer. A single-color thermometer is proportional to the amount of radiation within the band; a two-color thermometer is proportional to the ratio of the amount of radiation in the two bands.