When the infrared thermometer measures the temperature, the infrared energy emitted by the measured object is converted into an electrical signal on the detector through the optical system of the infrared thermometer. The important factors are the emissivity, the field of view, the distance to the light spot, and the position of the light spot.

Emissivity. All objects reflect, transmit, and emit energy. Only the emitted energy can indicate the temperature of the object. When the infrared thermometer measures the surface temperature, the instrument can receive all three kinds of energy. Therefore, all infrared thermometers must be adjusted to read only the emitted energy. Measurement errors are usually caused by infrared energy reflected from other light sources. Some infrared thermometers can change the emissivity. Emissivity values for a variety of materials can be found in published emissivity tables. Other instruments have a fixed pre-set emissivity of 0.95. The emissivity value is the surface temperature of most organic materials, paints or oxidized surfaces, which is compensated by applying a tape or flat black paint to the measured surface. When the tape or lacquer reaches the same temperature as the base material, measure the temperature of the surface of the tape or lacquer, which is its true temperature.

The ratio of distance to light spot. The optical system of the infrared thermometer collects energy from a circular measuring spot and focuses it on the detector. The optical resolution is defined as the ratio of the distance from the infrared thermometer to the object to the measured spot size (D : S). The larger the ratio, the better the resolution of the infrared thermometer and the smaller the spot size to be measured.

Laser aiming to help aim at the measurement point. A new improvement in infrared optics is the addition of close focus characteristics, which can provide accurate measurements on small target areas and prevent the effects of background temperature.

Field of view, make sure the target is larger than the spot size of the infrared thermometer. The smaller the target, the closer it should be. When accuracy is particularly important, make sure the target is at least 2 times the spot size.