APPLICATIONS OF THERMOGRAPHY
Thermography finds very wide applications in both engineering and medicine. Let us see few of the practical applications.
Medical thermography is a non invasive, non control tool which uses the heat for human body for diagnostic purposes. One of the most exiting is digital infrared thermal imaging (DITI). Thermography is completely safe and uses no radiation. The heat from the body is processed using accurate thermal imaging cameras and recorded in the computer as an image map which can be then analyzed. These, include, the screening of the breast cancer, extra cranial (head and neck vessel), neuro-musculo-skelatal disorder and vascular disease of the lower extremities. The concept is quite simple. For example in breast thermography excess heat generated due to the metabolic activity of the tumor tissue in diseased breast is compared with heat radiation from normal breast of the patient. Thus normal heat signatures associated with metabolism of the tumor can be detected easily. In a similar way, a variety of conditions which relate to flow of blood through the vessel s of the neck and head are readily accessed with thermal imaging. Thus the use of themography in the field of medicine is most appealing since it is a non contact and non-invasive method.
Electrical wiring involves many discrete physical connections between connectors and mounting studs on equipment. The hallmark of a high-quality electrical connection is very low electrical resistance between the items joined by the connection. Continued electrical efficiency depends on this low contact resistance. Passing a current through an electrical resistor of any sort dissipates some of the electrical power. The dissipated power manifests itself as heat. If the quality of the connection degrades, it becomes in effect, an energy dissipating device as its electrical resistance increases. With increased resistance, the connector or joint exhibits ohmic resistance. Electrician and maintenance technicians use the thermographic camera to locate these hot spots in electrical panel s and wirings. The heated electrical components appear as bright spots on a thermogram of the electrical panel. Three-phase electrical equipment connects to the power supply through three wires. The current through each wire of the circuit should be equal in magnitude. However, it is possible to have an unbalance in the phases. In this case, the current is one of the phases differs significantly from the others. Consequently, there exists a temperature difference among the three connections. Thermographic cameras can illustrate this imbalance quite easily and dramatically. Thermographer can easily and safely inspects overhead electrical connections or pole mounted transformers from a remote, safe place on the ground.
Thermography also finds use in inspecting the building envelope. It can locate sections of wall that have insufficient insulation. It can also spot differences in temperatures that indicates air leaks around window and door frames. Thermal imaging is useful for inspecting roofs as well. If a defect in the outermost in the outermost roof membrane admits rain water that gets trapped between the layers making up the roofs, the thermal conductivity of the water logged section of roofs is greater than that of the surrounding areas. Because the thermal conductivity differs, so does the temperature of the outer roof membrane. An infrared camera can easily detect such roof problems. A thermal scan of the roof is all that is needed to identify possible roof defects for a roofing contractor to repair.
Because thermography is a non contact measurement method, it makes possible the inspection of mechanical system and component in real time without shutting down the underlying production line. Thermography lend itself to eliminating the energy loss related to defective steam traps. If steam is leaking through a steam trap, it heats the downstream return piping. The heat section of piping is clearly visible to an infrared imager.
Thermography finds further use in the inspection of concrete bridge decks and other paved surfaces. The defects in question are voids and delamination in and among the various layers of paved materials. The air or water contained within the interlaminar spaces of the pavement slab affects its overall thermal conductivity. The IR images can detect the defects.
Painted surfaces become multilayer composites when a bridge or storage tank has been repainted numerous times during its service life. Here, too, the possibility of hidden rust, blistering, cracking, and other delamination defects between adjacent paint layers make visual inspection difficult. A technique called transient thermography helps in evaluating a costly repainting project. During transient thermography the surface under study is heated from behind for a short period of time. Because the imager detects temperature differentials of less than a degree, voids and delaminations become apparent. Forestry department use thermography to monitor the scope and range of forest fires. Semiconductors manufacturers use it to analyze operational failure in computer chips.
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