Four factors affecting the inaccurate measurement of infrared thermometers
Infrared temperature measurement technology plays an important role in product quality control and monitoring, equipment online fault diagnosis and safety protection, and energy conservation during the production process. In the past 20 years, non-contact infrared human body thermometers have rapidly developed in technology, with continuously improved performance, enhanced functionality, an increasing variety, and an expanding range of applications.
1, The relationship between the size of temperature measurement targets and the measurement distance
External thermometers can be divided into monochromatic thermometers and two-color thermometers (radiation colorimetric thermometers) based on their principles. For monochromatic thermometers, the area of the measured target should fill the field of view of the thermometer during temperature measurement. It is recommended that the size of the tested target 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 optoacoustic symbol of the thermometer to interfere with the temperature measurement 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
The effective diameter of measurable targets varies at different distances, so attention should be paid to the target distance when measuring small targets. The distance coefficient K of an infrared thermometer is defined as the ratio of the distance L of the measured target to the diameter D of the measured target, i.e. K=L/D.
2, Select the emissivity of the tested substance
1) Infrared thermometers are generally divided by blackbody (emissivity ε=1.00), but in reality, the emissivity of substances is less than 1.00. Therefore, when measuring the true temperature of the target, the emissivity value must be set. The material emissivity can be obtained from the data on the emissivity of objects in radiation thermometry.
2) Infrared thermometer cannot measure temperature through glass, which has special reflection and transmission characteristics and does not allow infrared temperature readings. But temperature can be measured through an infrared window. It is best not to use infrared thermometers for temperature measurement on bright or polished metal surfaces (such as stainless steel, aluminum, etc.).
3, Measurement of targets in strong light backgrounds
If the target being tested has a bright background light (especially when exposed to sunlight or strong light), the accuracy of the measurement will be affected. Therefore, objects can be used to block the strong light of the target directly to eliminate background light interference.
4, Other reasons
1) Only measuring surface temperature, infrared thermometer cannot measure internal temperature. The ambient temperature, if the thermometer is suddenly exposed to an ambient temperature difference of 20 ℃ or higher, allows the instrument to adjust to the new ambient temperature within 20 minutes.
2) Steam, dust, smoke, etc. It obstructs the optical system of the instrument and affects temperature measurement. To avoid damaging the infrared thermometer, first use compressed air to remove large particles and dust, and then wipe with a cloth. Gently wipe the body of the thermometer with a clean and slightly damp cloth. If necessary, a solution made of water and a small amount of mild soap can be used to wet the cloth. Additionally, after use, please cover the infrared thermometer with the lens cover as soon as possible and store it in a carrying case.
