These portable "Temperature Guns" can determine temperatures of objects from a distance (non-contact). They are especially useful for quick temperature checks of energized electrical systems.
An infrared thermometer can measure the surface temperature of an object from a distance. An infrared thermometer will only measure one temperature and that temperature is an average value from its circle of measurement. This circle of measurement is determined by the lens in front of the infrared detector. This circle of measurement can be calculated by a common specification which all infrared thermometers should have called D:S (distance to spot ratio). The D:S is going to give the user an idea of how large a measurement circle your thermometer is at any given distance from the target. For example, the distance to spot ratio of 10:1 will allow you to measure a 1" circle at 10" from the target. Higher priced thermometers will typically have a higher D:S which allows measurement of smaller objects at longer distances. When selecting an infrared thermometer, another desirable feature is the ability to adjust emissivity. Emissivity is a value from 0 to 1 which is roughly determined by the reflective nature of a target. When measuring an item, you are trying to capture the infrared energy but in reflective materials some infrared energy is going to be reflected off the surface and included temperature displayed. By changing the emissivity to match the target, you can typically correct this error in all but the most reflective objects.
