Thermal imaging or thermography is a technique of scanning the infrared radiation emitted from an object. The collected information is processed and a graphical output showing the temperature distribution across the object is provided. It is possible to measure temperature which lies between – 20° C to +1500° C. The elements of the thermal imaging system are shown in figure 1.
Figure 1: Thermal Imaging System
Working Principle of Thermal Imaging
The principle of operation of radiation detector is same as that of radiation pyrometer. Due to scanning mode of operation of thermal imager, it is required that radiation detector must have very quick response. Therefore, photoconductive or photovoltaic sensors are preferred. These sensors are sensitive to the section of infrared radiation present between wavelengths of 2 μm and 14 μm. The other simple version of thermal imager (thermal imaging instrument) includes hand-held viewers which are aimed at the object of interest. The output from a series of infrared detectors is targeted on an assembly of red light-emitting diodes placed behind a glass screen. The output display contains various intensities of red on a black background, these different intensities correspond to different temperatures. Since, the temperature variations are identified as small as 0.1° C, the resolution of measurement is high.
More complicated thermal imaging systems consist of tripod-mounted detector which is linked to a desktop computer and display system. Such systems use multi-colour displays in which up to 16 colours show different bands of temperature in the entire measured range. Therefore, the heat distribution around the measured body is shown graphically as a set of contours comprising of coloured bands that represent different temperature levels.
Applications of Thermal Imaging
The following are the applications of thermal imaging.
- Monitoring flow of product through pipeline.
- Identifying insulation faults.
- Recognizing hotspots in furnace linings, electrical machines, bearings etc.
- Scanning electrical transmission lines for faults.
- Searching for lost or injured people during disasters.
- Detecting the pattern of spreading of forest fires.
- Examining electronic circuit boards and monitoring the process of production by colour-thermography.
- Medical applications such as body scanning.