Thermography
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Thermography can refer to a printing process and an imaging process. A thermogram is an image produced by thermography.
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[edit] Thermographic imaging
Thermography, or thermal imaging, 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 temperature, 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). 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.
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. Some physiological activities, particularly responses, in human beings and other warm-blooded animals can also be monitored with thermographic imaging. [1]
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.
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.
See also: infrared camera, infrared detector
[edit] Thermographer training
Aside from test equipment, training is the most important investment a company will make in an infrared inspection program. Advances in technology have provided infrared equipment that is user-friendly; however, infrared thermography is not a “simply point and shoot” technology. In addition to understanding the object or system being inspected, thermographers must also understand common error sources that can influence observed thermal data. Typically, infrared training courses should cover the topics of infrared theory, heat transfer concepts, equipment selection and operation, how to eliminate or overcome common error sources, and specific applications.
[edit] Thermographic printing
Thermographic printing refers to two types of printing, both of which rely on heat to create the letters or images on a sheet of paper.
The simplest type is where the paper has been coated with a material that changes colour on heating. This is called thermal printing and was used in older model fax machines and is used in most shop till receipt printers. This is called direct thermal.
More complex is thermographic printing that melts print off a ribbon and onto the sheet of paper (thermal ink transfer printing). This is called thermal transfer.
Thermography printing is also a post print process done immediately after printing. It can be done inline or offline as long as the ink is wet. Thermography powder is applied to the sheet of paper after it leaves the printing press. The sheet is then vacuumed or shaken to remove excess powder. This leaves powder only where there is wet ink. The sheet then travels through a heat tunnel; there the heat causes the powder to melt which leaves a raised effect.
It is commonly used on letterheads, business cards, greetings cards, gift wrap, packaging and can also be used to print braille text.
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