District heating systems distribute hot water or steam heat generated in a centralized location to residential and commercial properties through an underground network of pipes. But inspecting and maintaining a large district heating network can be a difficult task.
To aid the inspection process, engineers at Termisk Systemteknik (Linköping, Sweden; www.termisksystemteknik.se) mounted an SC7600 infrared (IR) camera from FLIR Systems (Wilsonville, OR, USA) on the bottom of a small plane. By flying over Scandinavian cities, recording the thermal images, and then geo-referencing them, they can produce thermal maps of the cities.
The SC7600 thermal imaging camera contains a cooled indium antimonide (InSb) IR detector that produces 640 × 512-pixel thermal images at a thermal sensitivity of 20 mK (0.02°C).
"It is useful for this application because it can capture the full resolution at a frame rate of 100 Hz. Such acquisition is indispensable when you are flying over a city at moderate speed and want sharp and clear images," says Stefan Sjökvist, director of Termisk Systemteknik.
Once the images have been captured, they are compared with maps and satellite images, and where necessary, the images are modified to compensate for any differences in the viewing angle due to nonlinear motion.
For the system to automatically point out leaks of hot water or steam to a user, any potential false alarms that could be created from thermal signatures of vehicles, pedestrians, animals, or insulation faults in roofs are first eliminated. The system then produces a map showing the location of district heating pipework and the location of the leaks, enabling maintenance teams to rectify any problems.