Study of an infrared thermometer based on distance coefficient and theory
Infrared thermometers can be divided into single-color thermometers and two-color thermometers (radiation colorimetric thermometers) according to the principle. For a monochromatic thermometer, when measuring temperature, the area of the target to be measured should fill the field of view of the thermometer. It is recommended that the measured target size exceed 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 symbols of the thermometer and interfere with the temperature measurement readings, causing errors. Conversely, if the target is larger than the pyrometer's field of view, the pyrometer will not be affected by background outside the measurement area. For colorimetric thermometers, the temperature is determined by the ratio of radiant energy in two independent wavelength bands. Therefore, when the target to be measured is small and does not fill the field of view, there is smoke, dust, and obstructions on the measurement path, and the radiation energy is attenuated, it will not have a significant impact on the measurement results. For small targets that are moving or vibrating, colorimetric thermometers are the best choice. This is due to the small diameter of the light rays and their flexibility to transport light radiant energy over 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 of D:S, that is, the ratio of the distance D between the infrared thermometer probe to the target and the diameter of the measured target. If the thermometer must be installed far away from the target due to environmental conditions, and a small target must be measured, a thermometer with high optical resolution should be selected.
The higher the optical resolution, i.e. increasing the D:S ratio, the higher the cost of the pyrometer. Infrared thermometers D:S range 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, an infrared thermometer with a high distance coefficient should be selected.
For a pyrometer with a fixed focal length, the spot at the focal point of the optical system is a small spot, and the spot near and far from the focal point will increase, and there are two distance coefficients. Therefore, in order to measure temperature accurately at a distance close to and far from the focus, the size of the measured target should be larger than the spot size at the focus;
Zoom thermometers have a small focus position that can be adjusted according to the distance to the target. If D:S is increased, the received energy will decrease. If the receiving aperture is not increased, the distance coefficient D:S will be difficult to increase, which will increase the cost of the instrument.
