Q. What is the role of distance-to-spot ration (D:S) in temperature measurement?

Answer

The distance-to-spot ratio (D:S) is the ratio of the distance to the measurement surface and the diameter of the temperature measurement area. For example if the D:S ratio is 12:1 the diameter of the measurement area is one-twelfth of the distance to the object. An infrared thermometer with a higher ratio of D to S is able to sense a more-specific narrower surface at a greater distance than one with a lower ratio. A 12:1 rated device can sense a 1-inch circle at a distance of one foot.