What are the factors that affect the error of infrared thermometer?
1. Radiation rate
Radiance rate is a physical quantity that measures the relative radiation ability of an object to a blackbody. It is not only related to the material shape, surface roughness, and concavity of the object, but also to the direction of the test. If the object has a smooth surface, its directionality is more sensitive. The emissivity of different substances is different, and the amount of radiation energy received by an infrared thermometer from an object is proportional to its emissivity.
(1) The setting of emissivity is based on Kirchhoff's theorem: the hemispherical monochromatic emissivity (ε) of an object's surface is equal to its hemispherical monochromatic absorptivity (α), where ε=α. Under thermal equilibrium conditions, the radiated power of an object is equal to its absorbed power, that is, the sum of absorption rate (α), reflectance (ρ), and transmittance (γ) is 1, that is, α+ρ+γ=1. For opaque (or thick) objects, the transmittance can be seen as γ=0, with only radiation and reflection (α+ρ=1). As the emissivity of the object increases, the reflectance decreases, and the influence of background and reflection decreases, resulting in higher testing accuracy; On the contrary, the higher the background temperature or reflectivity, the greater the impact on the test. From this, it can be seen that in the actual detection process, attention must be paid to the corresponding emissivity of different objects and thermometers, and the setting of emissivity should be as accurate as possible to reduce the error of the measured temperature.
(2) Test angle
The emissivity is related to the testing direction, and the larger the testing angle, the greater the testing error. This is easily overlooked when using infrared for temperature measurement. Generally speaking, the testing angle is best within 30 ° C and should not exceed 45 ° C. If it is necessary to conduct the test at a temperature greater than 45 ° C, the emissivity can be appropriately lowered for correction. If the temperature measurement data of two identical objects need to be analyzed and judged, the testing angle must be the same during testing in order to be more comparable.
2. Distance coefficient
The distance coefficient (K=S: D) is the ratio of the distance S between the thermometer and the target to the diameter D of the temperature measuring target. It has a significant impact on the accuracy of infrared thermometers, with higher K values resulting in higher resolution. Therefore, if the thermometer must be installed far away from the target due to environmental conditions and needs to measure small targets, a high optical resolution thermometer should be selected to reduce measurement errors. In practical use, many people overlook the optical resolution of thermometers. Regardless of the diameter D of the measured target point, turn on the laser beam and aim it at the measurement target to test. In fact, they overlooked the requirement of S: D value for the thermometer, which may result in a certain degree of error in the measured temperature.
