What are the reasons for the inaccurate measurement of infrared thermometers?
Infrared thermometers are inaccurate in measuring reflective objects because reflective objects reflect. After reflection, the infrared thermometer not only measures the infrared radiation of the target, but also measures other infrared radiation energy such as the reflective surface, ambient temperature and even sunlight sensed by the thermometer, so it will be inaccurate.
First, the temperature measurement distance is too far
According to the principle, external thermometers can be divided into single-color thermometers and two-color thermometers (radiation colorimetric thermometers). For monochromatic thermometers, when measuring temperature, the target area to be measured should fill the field of view of the thermometer. It is recommended that the size of the target to be measured should 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 photoacoustic branch of the pyrometer, which will interfere with the temperature measurement reading and cause 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
The effective diameter of the measurable target is different at different distances, so pay attention to the target distance when measuring small targets. The distance coefficient k of the infrared thermometer is defined as the ratio of the distance l of the measured target to the diameter d of the measured target, that is, k=l/d.
Second, select the emissivity of the measured substance
1. Infrared thermometers generally use a black body scale (emissivity = 1.00), but in fact the emissivity of the substance 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 materials can be found in "Data about emissivity of objects in radiation thermometry".
2. Infrared thermometers cannot measure temperature through glass. Glass has special reflective and transmissive properties, so infrared temperature measurement is not allowed. But the temperature can be measured through the infrared window. Infrared thermometers should not be used to measure the temperature of shiny or polished metal surfaces (stainless steel, aluminum, etc.). ).
Third, the measurement of the target under the strong light background
If the measured target has bright background light (especially sunlight or strong light), it will affect the accuracy of the measurement. Therefore, objects can be used to block the strong light directly hitting the target to eliminate the interference of background light.
Fourth, 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 or higher, the instrument can adjust to the new ambient temperature within 20 minutes.
2. Steam, dust, smoke, etc. It can block the optics of the instrument and affect temperature measurements. To avoid damaging the infrared thermometer, 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, soak the cloth with water and a little mild soap. In addition, after use, please put the infrared thermometer on the lens cover as soon as possible, and put it in the carrying case for storage.
