FLIR DM166 USER MANUAL Document Identifier: DM166-en-US_AA
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7.4 Infrared Energy and Thermal Imaging Overview
A thermal imager generates an image based on temperature differences. In a thermal image, the
hottest item in the scene appears as white and the coldest item as black. All other items are
represented as a gray scale value between white and black. The DM166 also offers color images
to simulate hot (lighter colors) and cold (darker colors) temperatures.
It may take some time to get used to the thermal imagery. Having a basic understanding of the
differences between thermal and daylight cameras can help with getting the best performance
from the DM166.
One difference between thermal and daylight cameras has to do with where the energy comes
from to create an image. When viewing an image with an ordinary camera, there has to be some
source of visible light (something hot, such as the sun or other lighting) that reflects off the
objects in the scene to the camera. The same is true with human eyesight; the vast majority of
what people see is based on reflected light energy. On the other hand, the thermal imager
detects energy that is directly radiated from objects in the scene.
This is why hot objects such as parts on engines and exhaust pipes appear white, while the sky,
puddles of water and other cold objects appear dark (or cool). Scenes with familiar objects will
be easy to interpret with some experience.
Infrared energy is part of a complete range of radiation called the electromagnetic spectrum.
The electromagnetic spectrum includes gamma rays, X-rays, ultraviolet, visible, infrared,
microwaves (RADAR), and radio waves. The only difference is their wavelength or frequency. All
of these forms of radiation travel at the speed of light. Infrared radiation lies between the visible
and RADAR portions of the electromagnetic spectrum.
The primary source of infrared radiation is heat or thermal radiation. Any object that has a
temperature radiates in the infrared portion of the electromagnetic spectrum. Even objects that
are very cold, such as an ice cube, emit infrared. When an object is not quite hot enough to
radiate visible light, it will emit most of its energy in the infrared. For example, hot charcoal may
not give off light, but it does emit infrared radiation, which we feel as heat. The warmer the
object, the more infrared radiation it emits.
Infrared imaging devices produce an image of invisible infrared or “heat” radiation that is
unseen by the human eye. There are no colors or “shades” of gray in infrared, only varying
intensities of radiated energy. The infrared imager converts this energy into an image that we
can interpret.
The FLIR Infrared Training center offers training (including online training) and certification in all
aspects of thermography:
http://www.infraredtraining.com/
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