Infrared thermometer analysis based on principle and distance coefficient
Infrared thermometers can be divided into monochrome thermometers and two-color thermometers (radiation colorimetric thermometers) based on their principles. For monochrome thermometers, the area of the measured target should fill the thermometer's field of view during temperature measurement. It is recommended that the size of the target being tested exceed 50% of the field of view size. If the target size is smaller than the field of view, the background radiation energy will enter the visual and acoustic symbols of the thermometer and interfere with the temperature reading, causing errors. On the contrary, if the target is larger than the field of view of the thermometer, the thermometer will not be affected by the background outside the measurement area. For a colorimetric thermometer, its temperature is determined by the ratio of the radiated energy within two independent wavelength bands. Therefore, when the target being measured is small, does not fill the field of view, and there is smoke, dust, or obstruction on the measurement path, which attenuates the radiation energy, it does not have a significant impact on the measurement results. For small targets that are in motion or vibration, a colorimetric thermometer is the best choice. This is due to the small diameter and flexibility of light rays, which can transmit light radiation energy through curved, obstructed, and folded channels.
Infrared thermometer analysis based on principle and distance coefficient
What is the distance coefficient of an infrared thermometer? The distance coefficient is determined by the ratio of D: S, which is the ratio of the distance D between the infrared thermometer probe and the target to the diameter of the measured target. 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.
The higher the optical resolution, i.e. increasing the D: S ratio, the higher the cost of the thermometer. The range of infrared thermometer D: S ranges from 2:1 (low distance coefficient) to over 300:1 (high distance coefficient). If the thermometer is far away from the target and the target is small, a high distance coefficient infrared thermometer should be selected.
For a fixed focal length thermometer, the spot size is small at the focal point of the optical system, and the spot size increases near and far from the focal point, resulting in two distance coefficients. Therefore, in order to accurately measure temperature at distances close to and far from the focal point, the size of the measured target should be larger than the size of the light spot at the focal point;
The zoom thermometer has a small focal point position that can be adjusted based on the distance to the target. Increasing D: S reduces the received energy. Without increasing the receiving aperture, it is difficult to increase the distance coefficient D: S, which increases the instrument cost.
