Laser Surveys

Topographical Surveys, Land Surveys, Building Surveys And Underground Drainage Surveying

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A Practical Guide For Underground Services Location and CCTV Drainage Surveys

Radiodetection

The purpose of electronic tracing is to locate, identify and trace buried services. Contrary to popular belief this is not like “metal detecting”. The site is first scanned for passive signals. They are called “passive” because they already exist on buried cables and pipes and are there for us to detect. There are two types of passive signal either a power signal (50Hz or 60 Hz) or radio signal emitted by power cables or telephone cables respectively. Secondly an “active” signal can be applied by a transmitter to a pipe or cable via a fire hydrant/stopcock/gas valve etc. and then this unique signal is traced above ground using a receiver and the ground is marked up with paint at about 5 metre centres or change in direction. The route is then surveyed in.

If only it was that simple - a number of circumstances, as listed below, can occur that degrades the information.
A. Fractured Service
B. Service comes into close contact with other services or Rebar
C. Electrical field from other services degrades signal.

We hope to achieve an accuracy of ± 10% of depth. E.g. service 2 metre deep = positional accuracy ± 200 millimetres/ depth accuracy ± 200 millimetres.

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Last Updated Monday, August 8, 2005 15:52