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Thermal Testing
What is Thermal Testing? Is it considered form of nondestructive testing? What is its
history and how does it work? While researching I was able to find a vast amount of information
on the topic. Hopefully within this paper I will be able to explain all of the above questions
along with providing specific examples to support my findings.
To achieve this goal, I have structured my paper into four sections. In the first section I
will go over a brief history of thermal testing and provide information to as how it was
developed and how discovered it. The second section will concentrate on the scientific side of
things. Third section will go over the equipment used to both detect along with produce the
images you can see when doing thermal testing. The fourth and final section will provide
examples of techniques and applications that thermal testing is used.
The nerve endings of your skin can respond to temperatures as low as .0009 C. While
very impressive, that is not enough for a thermal nondestructive evaluation. Throughout history
several discoveries have been made by many different people to form what we know today as
Thermal Testing.
Sir William Herschel in 1800 is the man responsible for the beginnings of thermography.
Sir William Herschel knew that sunlight consisted of colors. Wanting to explore more into detail
of how the colors had a relationship to the heat, Sir William Herschel came up with a trial where
he would use a prism to spread the light. Using thermometers with blackened blubs to test the
various temperatures of the varying colors, He witnessing the increased temperature which
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caused the color to move from violet to red he also noted that the hottest of them was beyond red
light. Sir Herschel’s discovery that calorific rays when the heating beyond the visible red range
is what we refer today as “infrared” energy.
Twenty years later, Thomas Johann Seebeck would discover the thermoelectric effect.
He found that a simple device made of two dissimilar metals when come in contact would have
response changes in a predictable manner with a change in temperature. Soon after this Nobil
would invent the thermocouple in 1829. With the thermocouple technology Melloni would then
produce the thermopile. The thermopile is simply thermocouples put together in conjunction and
connected in series. This device would focus thermal radiation and in turn allow a person to be
detected by up to 30 ft. away. 40 years later a device very similar was developed called the
bolometer. The main difference with this device was that instead of measuring voltage
