Closed Circuit Television (CCTV) video cameras mounted on small tractor devises or sleds and driven or pulled through the sewer are commonly used to inspect repairs and to assess the condition of sewer systems. The basic CCTV system includes the camera and transport, connecting cables, recording equipment, monitor, and software. The camera begins its survey with the distance counter set at zero corresponding to the point where the camera image records the edge of maintenance hole and pipe interface. As the camera progresses down the pipe, the distance from its launch point is recorded. Other information such as date and time may be recorded and displayed on the video screen. As the camera moves down the pipeline, an operator records defects and other observations using standard methods of coding.
The sewer system should be cleaned to the extent practicable prior to CCTV inspection. The camera should be clean and in good operating condition and capable of producing an accurate image of the condition of the pipe. The camera lens should be positioned along the central axis of round pipes and 2/3 of the vertical distance in egg-shaped pipes. The camera speed should allow all defects to be seen while not causing the operator to become distracted. The ideal speed will depend on the size of the pipe and typically range from 6 m per minute for smaller pipes (200 mm or less) to 12 m per minute for larger pipes (greater than 300 mm). Lighting must be evenly distributed around the surface of the pipe, should illuminate the pipe approximately 2 meters ahead of the camera, and should provide good contrast.
More advanced CCTV systems have pan and tilt cameras that allow closer inspection of defects and lateral connections; fish-eye lenses, which provide full 180 degree view of the pipe walls; laser systems that measure the profile of the pipe; and sonar for assessing pipe conditions in flooded sections and inverts. Advanced software is also available that control the progress of the survey and process incoming data.