4 Reasons Why Infrared Thermometers Are Inaccurate
1. The relationship between the temperature measurement target size and the temperature measurement distance
External 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
At different distances, the effective diameter of the measurable target is different, so pay attention to the target distance when measuring small targets. The definition of the distance coefficient K of the infrared thermometer is: the ratio of the distance L of the measured target to the diameter D of the measured target, that is, K=L/D.
2. Select the emissivity of the measured substance
1. Infrared thermometers are generally graduated according to black bodies (emissivity ε=1.00), but in fact, the emissivity of substances is less than 1.00. Therefore, when the real temperature of the target needs to be measured, the emissivity value must be set. The emissivity of matter can be found from "Data on emissivity of objects in radiation thermometry".
2. Infrared thermometers cannot measure temperature through glass. Glass has very special reflection and transmission characteristics, and infrared temperature readings are not allowed. But the temperature can be measured through the infrared window. Infrared thermometers are best not used for temperature measurement on bright or polished metal surfaces (stainless steel, aluminum, etc.).
3. Measurement of targets in strong light background
If the measured target has a bright background light (especially when it is directly illuminated by sunlight or strong lights), the accuracy of the measurement will be affected. Therefore, objects can be used to block the strong light directly hitting the target to eliminate background light interference.
4. Other reasons
1. Only the surface temperature is measured, and the infrared thermometer cannot measure the internal temperature. Ambient temperature, if the thermometer is suddenly exposed to an ambient temperature difference of 20°C or higher, allow the instrument to adjust to the new ambient temperature within 20 minutes.
2. Steam, dust, smoke, etc. It blocks the optical system of the instrument and affects temperature measurement. To avoid damaging the infrared thermometer, first remove large particles and dust with compressed air, then wipe with a cloth. Gently wipe the thermometer body with a clean slightly damp cloth. If necessary, dampen the cloth with a solution of water and a little mild soap. In addition, after use, please cover the infrared thermometer with the lens cap as soon as possible, and put it in the carrying case for storage.
