Performance of infrared thermometers
In order to obtain accurate temperature readings, the distance between the thermometer and the test target must be within a suitable range. The so-called "spot size" is the area of the measurement point of the thermometer. The further away you are from the target, the larger the spot size. The ratio of distance to spot size, or D:S. On laser sight thermometers, the laser spot is above the center of the target with a 12mm (0.47 in) offset.
When determining the measurement distance, make sure that the target diameter is equal to or larger than the size of the spot being measured. The distance between "object 1" and the measuring instrument is positive because the target is slightly larger than the spot size being measured. And "object 2" is too far away, because the target is smaller than the size of the light spot being measured, that is, the thermometer is also measuring the background object, thereby reducing the accuracy of the reading. [2]
