measured temperature will be displayed on the LCD,
along with the
icon on the top line.
When you make temperature measurements, be sure
to get close enough to the target to ensure that you are
reading its temperature alone, rather than the average
temperature of the target and objects behind or near it
within the IRT’s field of view.
The IRT in the VR40 has a distance-to-spot (D:S) ratio
of 4:1. This means that the target area (spot) whose
infrared radiation (temperature) is being measured
increases in diameter by 1 inch for every 4 inches you
move away from the target. Conversely, the diameter of
the target area measured decreases by 1 inch for every
4 inches you move closer to the target.
All IRTs, including the one in the VR40, take the average
temperature of all objects within a circular target area
(spot). Although the distance “D” in the D:S ratio is
defined as a linear value and the “S” defines the
diameter of the spot (see figure at top of next page), the
critical parameter is the target area. Depending on the
distance to the target, the target area may include both
the target and background objects near or behind the
thermometer’s field of view, which defines the target
area or spot.
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