Adjusting the Emissivity of Infrared Thermometers
Infrared radiation is ubiquitous and never-ending, and the greater the temperature difference between objects, the more obvious the radiation phenomenon will be. The vacuum can transmit the infrared radiant energy emitted by the sun to the earth through 93 million miles of space and time, where it is absorbed by us and warms us. When we stand in front of a food freezer in a shopping mall, the infrared radiation heat emitted by our body is absorbed by the frozen food, making us feel very cool. In both examples, the radiation effect is very obvious, we can clearly feel the change and feel its existence.
When we need to quantify the effect of infrared radiation, we need to measure the temperature of infrared radiation, and an infrared thermometer is used at this time. Different materials have different infrared radiation characteristics. Before using the infrared thermometer to read the temperature, we must first understand the basic principle of infrared radiation measurement and the infrared radiation characteristics of the specific material to be tested.
Infrared Radiation = Absorption + Reflection + Transmittance
No matter what kind of infrared radiation is emitted, it will be absorbed, so absorption rate = emissivity. What the infrared thermometer reads is the infrared radiation energy emitted by the surface of the object. The infrared radiation meter cannot read the infrared radiation energy lost in the air. Therefore, in the actual measurement work, we can ignore the transmittance, so that we can get a Basic infrared radiation measurement formula:
Infrared radiance = emissivity - reflectivity
The reflectivity is inversely proportional to the emissivity, the stronger the object's ability to reflect infrared radiation, the weaker its own infrared radiation ability. Usually the visual method can be used to roughly judge the reflectivity of the object. The new copper has a higher reflectivity and a lower emissivity (0.07-0.2), and the oxidized copper has a lower reflectivity and a higher emissivity (0.6-0.7). ), the reflectance of copper blackened by heavy oxidation is even lower, and the emissivity is correspondingly higher (0.88). The vast majority of painted surfaces have very high emissivity (0.9-0.95) and negligible reflectance.
For most infrared thermometers, all that needs to be set is the rated emissivity of the material being measured, which is usually preset to 0.95, which is sufficient for measuring organic materials or painted surfaces.
By adjusting the emissivity of the thermometer, the problem of insufficient infrared radiation energy on the surface of some materials, especially metal materials, can be compensated. The influence of reflectivity on the measurement only needs to be considered when there is a source of high-temperature infrared radiation near the surface of the measured object and reflects it.
