An infrared thermometer has a measurement range.
If the measured object is smaller than the measurement range,
accurate temperature measurement cannot be achieved.
This is because the measurement includes the surroundings of the measured object,
resulting in a field of view deficiency.
The minimum measurement range (determined by the size of the lens) is specific to each product.
Objects smaller than the minimum measurement range cannot be measured for temperature.
When measuring with an infrared thermometer, it is also important to consider the D:S ratio.
In the example shown above, the minimum measurement range is 2.5cm,
which means that the diameter of the target object must be at least 2.5cm.
Even if the distance is within 1.5m, the measurement range will still be 2.5cm.
At A&D, we offer infrared thermometers with a minimum measurement range of 10mm.
（Reference: How to choose an infrared thermometer ）