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Techniques for Sewer Condition Assessment

Sewer Condition Assessment
  • Zoom cameras
  • Closed-circuit television
  • Digital scanners
  • Laser profilers
  • Remote sensing diagnostic techniques

Zoom cameras

  • Cost and time saving preliminary inspections 

  • Main premise is that most of sewer problems occur at or near maintenance holes 

  • Provide good quality imagery up to 20-75 m pipe length
  • Able to survey 150 to 1525 mm diameter sewers 

  • Colour videos and digital images saved on optical storage devices

Closed-circuit television (CCTV)

  • Most widely used technology for sewers in past 35 years 

  • Depend on expertise, alertness and judgment of field technicians or camera operators for identification and classification of defects 

  • Advances in coloured image enhancements, pan-and-tilt camera heads, steerable crawler systems
  • A video camera along with a lighting unit mounted on a crawler 

  • A cable drum with a counter to measure distance inside sewers connects camera to the surface 

  • A computerized control unit for controlling camera, lighting, and crawler movement usually hosted in a van accompanies the CCTV system

Digital scanners

Flash Cameras

  • Two high resolution cameras with 186 degrees wide-angle lenses are integrated at the front and rear ends of the system 

  • Hemispherical digital images are put together to form a 360-degree spherical image 

  • Defects and objects can be measured on unfolded images 

  • Camera works in pipes of dia 200mm & up, operates at a speed of 20 metres per minute

Laser Profiler

  • Employed in combination with CCTV camera to determine internal condition and measurement of defects and other features for sewers 

  • A ring of laser light is projected onto the internal pipe surface, and laser image is captured by the CCTV camera
  • Ring of light is analyzed using the laser profiler software and digital profile of pipe is produced

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