to be in for the moment. It might be so that you measure heat, which has been con-
ducted over some distance, whereas the ‘real’ hot spot is hidden from you. An example
is shown in the image below.
10717603;a3
Figure 29.4 A hidden hot spot inside a box
Try to choose different angles and make sure that the hot area is seen in its full size,
that is, that it is not disappearing behind something that might hide the hottest spot.
In this image, the hottest spot of what the camera can ‘see’, is +83°C (+181°F), where
the operating temperature on the cables below the box is +60°C (+140°F). However,
the real hot spot is most probably hidden inside the box, see the in yellow encircled
area. This fault is reported as a +23.0°C (+41.4°F) excess temperature, but the real
problem is probably essentially hotter.
Another reason for underestimating the temperature of an object is bad focusing. It
is very important that the hot spot found is in focus. See the example below.
10717403;a2
Figure 29.5 LEFT: A hot spot in focus; RIGHT: A hot spot out of focus
In the left image, the lamp is in focus. Its average temperature is +64°C (+147°F). In
the right image, the lamp is out of focus, which will result in only +51°C (+124°F) as
the average temperature.
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29 – Introduction to thermographic inspections of electrical installations
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