Comtest explains the importance of high-quality thermal images and how to spot a quality thermal image.
Thermography is the science of seeing heat patterns using special electronic cameras. Thermal imagers measure infrared energy and convert the data to images in order to create pictures of temperature, but how can professionals in the design and construction industry spot a high-quality thermal image from a low-quality one?
Thermal images that are of a high quality are characterised by the detail resolution called thermal sensitivity and spatial resolution, which is a reliable way to see various temperatures in an image. Other factors that point to thermal image quality (and can help to interpret the temperature) include visual image, blending of the thermal and the visual image as well as the display of the image.
Spatial resolution IFOV (instantaneous field of view)
Thermal cameras have “detectors” and these detectors have a certain number of pixels. The Fluke Ti400 camera, for example, offers 320×240 pixels, which equal 70,800 pixels. The number of pixels, however, doesn’t define the quality of the measurement; it’s the IFOV, the field of view of a single pixel. A camera that offers a large number of pixels, for example, won’t necessarily create a good thermal image if the pixel quality is poor.
A wide angle lens will have worse pixel quality in comparison to a telelens on the same camera with the same amount of pixels. This can result in measurement errors when you are inspecting small objects such as electrical cables and connectors.
Thermal resolution or NETD (noise-equivalent temperature difference)
Temperature differences are portrayed by showing the viewer different colours. In a black and white image, there will be various shades of grey (as opposed to colours).
If the total difference between the lowest and the highest temperature on the object is 10ᵒC and the thermal camera can see differences of 0,1ᵒC, there are 100 true shades of grey with which to compose the thermal image. A good image is one where the human eye cannot see the difference between the grey tones. In the majority of industrial applications the difference between maximum and minimum temperatures on the scene is well above 10ᵒC.
If a thermal image is needed for reporting purposes, then it is advised to invest in a good visual image with a resolution up to 5Mp. The image is also easier to interpret if the thermal image and the visual image are combined into a single aligned image. Two images can be blended in order to enhance the visual image and provide as much information as possible.
A good quality display with 640×480 pixels will not only enhance the image, it will also be more comfortable and ergonomic to watch in variable light conditions which usually occur in the field.
Comtest offers a range of training courses that will help attendees to think “thermally”, including an “Introduction to thermography – Basic thermography practices” course and a course entitled “How to kick-start your business with thermography”. The company is also certified to teach Level I certified thermography, where students will learn the principles of how to think thermally, basic heat transfer theory, electrical applications, mechanical equipment, building systems, roof inspections, use of thermal imaging equipment and proper image acquisition, and receive the international Snell Certification Standard. For more information about thermography, contact Val Verwer on 011 608 8520.
Tel: 011 608 8520
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