Infrared Thermography, thermal imaging, or thermal video, is a type of
infrared imaging science. Thermographic cameras detect radiation in the infraredrange 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 bodyradiation 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 insulationbecomes faulty, building constructiontechnicians 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. [ [http://www.sadcom.com/night/night1.htm Thermal imaging lights up darkened highways] ]
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 the 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, HgCdTeand QWIPFPA. 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 such as InSb require cryogenic cooling, usually by a miniature Stirling cyclerefrigerator or liquid nitrogen.
It is important to note that while thermal imaging displays the amount of infrared energy emitted by an object, it is quite difficult to get an accurate temperature reading of a specific subject using this method. The energy displayed in a thermal image represents three types of energy: Emitted Energy, Transmitted Energy, and Reflected Energy.
Thus, Incident Energy = Emitted Energy + Transmitted Energy + Reflected Energy
where Incident Energy is the energy profile when viewed through a thermal imaging device, Emitted Energy is generally what is intended to be measured, Transmitted Energy is the energy that passes through the subject from a remote thermal source, and Reflected Energy is the amount of energy that reflects off the surface of the object from a remote thermal source.
thermographic cameradoes not record the actual temperature of the object in question. Instead the camera records the infrared radiation emitted by the object. If the object is radiating at a higher temperature than its surroundings, then power transfer will be taking place and power will be radiating from warm to cold following the principle stated in the Second Law of Thermodynamics. So if there is a cool area in the thermograph, that object will be absorbing the radiation emitted by the warm object. The ability of both objects to emit or absorb this radiation is called "emissivity" (see below). In outdoor environments, convective cooling from wind may also need to be considered when trying to get an accurate temperature reading.
The thermographic camera would next employ a series of mathematical algorithms. Since the camera is only able to 'see' the electromagnetic radiation that is impossible to see in real life, it will build a picture in the viewer and record a visible picture, usually in a JPG format. In order to perform the role of noncontact temperature recorder, it will change the temperature of the object being viewed with its emissivity setting. Other algorithms can be used to affect the measurement, including the transmission ability of the transmitting medium (usually air), temperature of that transmitting medium and others. All these settings will affect the ultimate output for the temperature of the object being viewed.
This makes the thermographic camera an excellent tool for maintenance of electrical and mechanical systems in industry and commerce. By using the camera settings and by being careful when capturing the image, electrical systems can be scanned and problems can be found. Faults with steam traps in steam heating systems are easy to locate.
Please click on the image to see the description.
In the energy savings area, the thermographic camera can do more. Because it can see the radiating temperature of an object as well as what that object is radiating at, the product of the radiation can be calculated using the Stefan-Boltzmann equation.
Emissivity is a term representing a material's ability to emit thermal radiation. Each material has a different emissivity and it can be quite a task to determine the appropriate emissivity for a subject. A material's emissivity can range from 0.00 (completely not-emitting) to 1.00 (completely emitting); the emissivity often varies with temperature.
Black Bodyis a theoretical object which will radiate Infrared Radiation at its Contact Temperature. If a thermocouple on a Black Body Radiator reads 50 degrees Celsius, the radiation the Black Body will give up will also be 50 degrees Celsius. Therefore a true Black Body will have an emissivity of 1.
Since there is no such thing as a Black Body, the Infrared Radiation of normal objects will appear to be less than the Contact Temperature. The rate of transmission of Infrared Radiation will thus be a fraction of the true Contact Temperature. This fraction is called Emissivity.
A table of the Emissivity of many materials and the temperatures that correspond to them are listed in this link. [http://www.monarchserver.com/TableofEmissivity.pdf] You will note in the table that some objects will have different emissivities in long wave as compared to mid wave emissions. As well emissivites may also change when some materials are at a different temperature.
To make a temperature measurement of an object, the thermographer will refer to the emissivity table to choose the emissivity value of the object which is then entered into the camera. The camera's algorithm will correct the temperature by referring to the emissivity percent and calculate a temperature that would more closely match the actual Contact Temperature of the object.
If possible the thermographer would try to test the emissivity of the object in question. This would be more accurate than attempting to determine the emissivity of the object via a table. The usual method of testing the emissivity is to place a material of known, high emissivity, in contact with the surface of the object. The material of known emissivity can be as complex as industrial emissivity spray which is produced specifically for this purpose or it can be as simple as standard black insulation tape, emissivity 0.97. A temperature reading can then be taken of the object with the emissivity level on the imager set to the value of the test material. This will give an accurate value of the temperature of the object. The temperature can then be read on a part of the object not covered with the test material. If the temperature reading is different, the emissivity level on the imager can be adjusted until the object reads the same temperature. This will give the thermographer a much more accurate emissivity reading. There are times however when an emissivity test is not possible due to dangerous or inaccessible conditions. In these situations the thermographer must rely on tables.
Difference between IR film and thermography
IR film is sensitive to infrared radiation in the 250-500 °C range, while the range of thermography is approximately -50 °C to over 2,000 °C. So for an IR film to show something it must be over 250 °C or be reflecting infrared radiation from something that is at least that hot. Night vision infrared devices image in the non-thermal range of infrared (Near IR) just beyond the visual spectrum, and can see emitted or reflected NIR in complete visual darkness. Starlight-type night vision devices generally only magnify ambient light.
Passive vs active thermography
All objects above the absolute zero temperature will emit
infrared radiation. Hence, an excellent way to measure thermal variations is to use an infrared visiondevice, usually a focal plane array(FPA) infrared cameracapable of detecting radiationin the mid (3to 5 μm) and long (7 to 14 μm) wave infrared bands, denoted as MWIR and LWIR, corresponding to two of the high transmittance infrared windows. Abnormal temperature profiles at the surface of an object are an indication of a potential problem. [Maldague X. P. V., Jones T. S., Kaplan H., Marinetti S. and Prystay M. “Chapter 2: Fundamentals of Infrared and Thermal Testing: Part 1. Principles of Infrared and Thermal Testing,” in Nondestructive Handbook, Infrared and Thermal Testing, Volume 3, X. Maldague technical ed., P. O. Moore ed., 3rd edition, Columbus, Ohio, ASNT Press, 2001, 718 p.]
In passive thermography, the features of interest are naturally at a higher or lower temperature than the background. Passive thermography has many applications such as
surveillanceof people on a scene, and medical diagnosis. In active thermography on the other hand, an energy source is required to produce a thermal contrast between the feature of interest and the background. The active approach is necessary in many cases given that the inspected parts are usually in equilibrium with the surroundings.
Advantages of Thermography
* It shows a visual picture so temperatures over a large area can be compared
* It is capable of catching moving targets in real time
* It is able to find deteriorating (i.e. at higher temperature) components prior to their failure
* It can be used to measure or observe in areas inaccessible or hazardous for other methodsFact|date=April 2008
* It is a non-destructive test method
* It can be used to find defects in shafts and other metal partsFact|date=April 2008
Limitations and disadvantages of thermography
* Due to the low volume of thermal cameras, quality cameras often have a high price range (often $6,000 USD or above)Fact|date=April 2008
* Images can be hard to interpret accurately even with experienceFact|date=April 2008
* Accurate temperature measurements are hindered by differing emissivities and reflections from other surfaces Fact|date=April 2008
* Most cameras have ±2% accuracy or worse and are not as accurate as contact methodsFact|date=April 2008
* Only able to directly detect surface temperatures
* Process control
* Surveillance in security, law enforcement and defense
Thermal infrared imagers convert the
energyin the infrared wavelength into a visible light videodisplay. All objects above 0 kelvins 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 -50 °C.
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
emissivityof 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 absorptionof the atmosphere.
Infrared and thermal testing
Thermal imaging camera
* [http://www.goinfrared.com/success/image_gallery.asp Good examples of FLIR thermographic images broken down by industry application]
* [http://www.thermograph.net/ Infrared Thermograph, Thermography and Infrared Thermal Imaging Application Resources]
* [http://www.irinfo.org/ IrInfo.org, online resource for infrared thermography]
* [http://www.infratec.de/en/infratec/submenu/theory/basics.html Physical basics]
* [http://www.radio101.info/thermographie/pictures.htm various examples of thermographic images]
* [http://vzone.virgin.net/ljmayes.mal/pubs/uncooled.htm Uncooled Thermal Imaging]
* [http://www.meditherm.com/thermography_page1.htm Some uses of thermographic images in medicine]
* [http://www.compix.com/articles.npconint.html Some uses of thermographic images in electronics]
* [http://www.thermalconsultancy.com/gallery/ More examples of Thermographic Images]
* [http://mivim.gel.ulaval.ca/index.php Canada Research Chair in Multipolar Infrared Vision – MiViM ]
History of thermal imager manufacturers
* [http://www.aim-ir.com/pages/unternehmen/historie.php?lan=en History of AIM thermal imaging]
* [http://www.compix.com/about.htm History of Compix Incorporated thermal imaging]
* [http://www.drsinfrared.com/company/history.html History of Texas Instruments/DRS Thermal imaging]
* [http://www.thermal-eye.com/default.asp?nodeid=15 History of Raytheon Commercial Infrared/L-3 Communications thermal imaging]
Wikimedia Foundation. 2010.
Look at other dictionaries:
Thermography — Ther*mog ra*phy, n. [Thermo + graphy.] Any process of writing involving the use of heat. [Webster 1913 Suppl.] … The Collaborative International Dictionary of English
thermography — [thər mäg′rə fē] n. [ THERMO + GRAPHY] 1. the recording of temperature variations by means of a thermograph 2. a process for imitating copperplate engraving, as on calling cards, by dusting the freshly printed surface with a resinous powder which … English World dictionary
thermography — termografija statusas T sritis Standartizacija ir metrologija apibrėžtis Šiluminės spinduliuotės matavimo ir užrašymo metodų visuma. atitikmenys: angl. thermography vok. Thermographie, f rus. термография, f pranc. thermographie, f … Penkiakalbis aiškinamasis metrologijos terminų žodynas
thermography — termografija statusas T sritis chemija apibrėžtis Šiluminės spinduliuotės matavimo ir užrašymo metodų visuma. atitikmenys: angl. thermography rus. термография … Chemijos terminų aiškinamasis žodynas
thermography — termografija statusas T sritis fizika atitikmenys: angl. thermography vok. Thermographie, f rus. термография, f pranc. thermographie, f … Fizikos terminų žodynas
thermography — In medicine, a procedure in which a heat sensing infrared camera is used to record the surface heat produced by different parts of the body. Abnormal tissue growth can cause temperature changes, which may show up on the thermogram. Thermography… … English dictionary of cancer terms
thermography — noun Date: 1840 1. a process of writing or printing involving the use of heat; especially a raised printing process in which matter printed by letterpress is dusted with powder and heated to make the lettering rise 2. a technique for detecting… … New Collegiate Dictionary
thermography — thermographer, n. thermographic /therr meuh graf ik/, adj. thermographically, adv. /theuhr mog reuh fee/, n. 1. a technique for imitating an embossed appearance, as on business cards, stationery, or the like, by dusting printed areas with a… … Universalium
thermography — noun Any of several techniques for the remote measurement of the temperature variations of a body, especially by creating images produced by infrared radiation … Wiktionary
thermography — The technique for making a thermogram. infrared t. measurement of the regional skin temperature with an infrared sensing device. liquid crystal … Medical dictionary