Principle and distance coefficient analysis of infrared thermometers
According to the principle, external thermometers can be divided into single-color thermometers and two-color thermometers (radiation colorimetric thermometers). For a monochromatic thermometer, when measuring temperature, the measured target area should fill the field of view of the thermometer. It is recommended that the size of the measured target exceeds 50% of the field of view. If the target size is smaller than the field of view, the background radiation energy will enter the visual and acoustic signals of the thermometer and interfere with the temperature measurement reading, causing errors. In contrast, if the target is larger than the thermometer's field of view, the thermometer will not be affected by the background outside the measurement area. For colorimetric thermometers, the temperature is determined by the ratio of radiated energy in two independent wavelength bands. Therefore, when the measured target is small, does not fill the field of view, and there are smoke, dust, and obstructions on the measurement path, which attenuate the radiation energy, it will not have a significant impact on the measurement results. For small targets that are in motion or vibrating, colorimetric thermometers are the best choice. This is due to the small diameter and flexibility of light, which can transmit optical radiation energy in curved, blocked and folded channels.
Analysis of infrared thermometer based on principle and distance coefficient
What is the distance coefficient of infrared thermometer? The distance coefficient is determined by the ratio D:S, which is the ratio of the distance D between the infrared thermometer 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 small targets need to be measured, a thermometer with high optical resolution should be selected.
The higher the optical resolution, that is, the higher the D:S ratio, the higher the cost of the thermometer. Infrared thermometer D:S ranges from 2:1 (low distance factor) to over 300:1 (high distance factor). If the thermometer is far away from the target and the target is small, you should choose an infrared thermometer with a high distance coefficient.
For a thermometer with a fixed focal length, the focus of the optical system is a small light spot. The light spot will increase both near and far from the focus. There are two distance coefficients. Therefore, in order to accurately measure temperature at distances close to and away from the focus, the size of the target to be measured should be larger than the spot size at the focus;
Zoom thermometers have a small focus position that adjusts based on the distance to the target. Increasing D:S will reduce the received energy. If the receiving aperture is not increased, it will be difficult to increase the distance coefficient D:S, which will increase the cost of the instrument.
