The Science Behind Thermal Imaging

From: TI Blog – everything you need to know about Thermal Imaging

A useful set of articles despite not being very precise about the science.
describe the image

“On this blog, we spend a lot of time discussing the benefits of thermal imaging; we thought it would be interesting to actually understand how the technology actually works.

“As technology has advanced and costs of thermal imaging cameras have declined, thermal imaging has become more and more accessible to a variety of industries – including manufacturing, retail, security, transportation and domestic services. But how does thermal imaging work?

Thermal energy makes up one part of the electromagnetic spectrum. The naked eye cannot see thermal energy, because it is emitted from objects as heat, not reflected as light. The hotter an object, the more thermal energy it emits. All objects, even inanimate ones such as electronic components, emit some form of thermal energy.

Infrared thermal imaging cameras are detectors and precision optics platforms, which provide a visual representation of infrared energy emissions. A thermal imaging camera transforms thermal energy into visible light and processes that information through these basic steps:

A specialized camera lens focuses infrared radiation that is given off from all objects;
Infrared detectors detect and measure this focused radiation to create a thermogram, also known as a temperature map;

The camera then translates the thermogram into electric impulses;

The electric impulses are sent to a signal-processing unit where they are translated into usable data;
Once translated, the signal-processing unit sends the data to a display where thermal emissions are visible to a viewer;

Where quantitative information is required, the thermal camera can also provide accurate temperature values of the surface being viewed; and
Images can be saved for later analysis and report generation.

ED Notes:

  1. The above is a syndicated post, which originally appeared at TI Blog – everything you need to know about Thermal Imaging. View original post
  2. We have to take strong issue with several of the “Science” statements made in this blog post lest people get an incorrect idea of thermal energy and the workings of thermal imaging cameras, otherwise we applaud their informative efforts. To wit:
    • First: We are able to see some radiated thermal energy from an object if it is hot enough, just not all of it – we cannot see the infrared portion. This is a common enough experience of everyone who has seen a flame or an opaque object heated to ‘Incandescence”. Heck, the Sun is a the equivalent of a thermal radiation source with a thermal radiation temperature of about 6270 °C, and it lights up the whole world plus the Moon! We see the Sun by emission and the Moon by reflection.
    • Second: Thermal radiation covers a very significant portion of the electromagnetic spectrum, far more than just the infrared or the visible portions. For a pretty good science explanation about thermal radiation see the Wikipedia article at: http://en.wikipedia.org/wiki/Thermal_radiation.
    • Third: Not to confuse people, but the map of the image created inside a thermal camera is a “Radiance” map. The electronics in the imager converts the radiance map into a radiance-temperature map via the functional relationship first described by the Nobel Prize winning German Physicist Max Planck in 1899 (it’s not very new science).
    • Fourth: The true temperature map of a surface is related to the radiance temperature map by a series of correction factors, which factors are key to successful uses of the imagers.
    • Fifth: In some uses, precise temperatures are not needed, just enough contrast in the radiance temperatures for an object to be recognized visually on the displayed image in the accompanying screen.
    • Sixth:  In other uses, such as sensitive maintenance situations and process temperature monitoring and control, the corrections need to be performed by a specialist who understands them and how they are to be applied given the measurement situation and the imager’s properties.
    • Seventh: That’s why makers of these cameras and many third parties provide training courses for users. Thermal imaging is not an off-the-shelf exercise as some  would like the uninformed to believe – it is easy in some cases, but can be extremely complex and difficult in others, especially where one seeks temperatures within a repeatable uncertainty of  better than about 5 or 10 °C.

grp@mrpyro.com


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