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Thermography_______________________________________________________________ |
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Thermography, thermal imaging,
or thermal video, is a type of infrared imaging.
Thermographic cameras detect radiation in the infrared range
of the electromagnetic spectrum (roughly 900–14,000
nanometers or 0.9–14 µm) and produce images of that
radiation. Since infrared radiation is emitted by all
objects based on their temperatures, according to the black
body radiation law, thermography makes it possible to "see"
one's environment with or without visible illumination. The
amount of radiation emitted by an object increases with
temperature, therefore thermography allows one to see
variations in temperature (hence the name). |
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When viewed by thermographic camera, warm objects stand out well
against cooler backgrounds; humans and other warm-blooded
animals become easily visible against the environment, day or
night. As a result, thermography's extensive use can
historically be ascribed to the military and security services. |
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Thermal imaging photography finds
many other uses. For example, firefighters use it to see through
smoke, find persons, and localize the base of a fire. With
thermal imaging, power lines maintenance technicians locate
overheating joints and parts, a telltale sign of their failure,
to eliminate potential hazards. Where thermal insulation becomes
faulty, building construction technicians can see heat leaks to
improve the efficiencies of cooling or heating air-conditioning.
Thermal imaging cameras are also installed in some luxury cars
to aid the driver, the first being the 2000 Cadillac DeVille. |
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Some physiological
activities, particularly responses, in human beings and other
warm-blooded animals can also be monitored with thermographic
imaging. |
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The appearance and operation of a
modern thermographic camera is often similar to a camcorder.
Enabling the user to see in the infrared spectrum is a function
so useful that ability to record their output is often optional.
A recording module is therefore not always built-in. |
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Instead of CCD sensors, most
thermal imaging cameras use CMOS Focal Plane Array (FPA).
The most common types are InSb, InGaAs, QWIP FPA. The newest
technologies are using low cost and uncooled microbolometers
FPA sensors. Their resolution is considerably lower than of
optical cameras, mostly 160x120 or 320x240 pixels, up to
640x512 for the most expensive models. Thermographic cameras
are much more expensive than their visible-spectrum
counterparts, and higher-end models are often
export-restricted. Older bolometers or more sensitive models
as InSB require cryogenic cooling, usually by a miniature
Stirling cycle refrigerator or liquid nitrogen. |
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Advantages
of Thermography |
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You get a visual picture so that you can compare
temperatures over a large area |
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It is real time capable of catching moving targets
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Able to find deteriorating components prior to failure
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Measurement in areas inaccessible or hazardous for other
methods |
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Benefits |
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Reduction
of production losses due to unplanned downtime |
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Reduced
maintenance and repair costs |
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Increased
equipment life |
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Increased
Mean-Time-Between-Failures (MTBF) |
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Increased
productivity and profitability |
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Reduced
insurance premiums |
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Applications |
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Condition monitoring |
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Medical imaging |
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Research |
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Process control |
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Non destructive testing |
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Thermal
infrared imagers convert the energy in the infrared
wavelength into a visible light video display. All objects
above 0 degrees Kelvin emit thermal infrared energy so
thermal imagers can passively see all objects regardless of
ambient light. However, most thermal imagers only see
objects warmer than -50C
The spectrum and amount of thermal radiation depend strongly
on an object's surface temperature. This makes it possible
for a thermal camera to display an object's temperature.
However, other factors also influence the radiation, which
limits the accuracy of this technique. For example, the
radiation depends not only on the temperature of the object,
but is also a function of the emissivity of the object.
Also, radiation also originates from the surroundings and is
reflected in the object, and the radiation from the object
and the reflected radiation will also be influenced by the
absorption of the atmosphere. |
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