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The camera view of a sewer pipe is valuable for showing the overall condition of the pipe, the nature of obstructions etc. However for many applications this information is useless without also knowing the specific location of the problem being viewed, i.e the exact location of the camera head. Since sewer pipes practically always have one or more bends (sweeps) in their layouts, it is impossible to know the exact location of the camera head simply from a measurement of the length of the camera push cable that has been inserted into the pipe. About the only exception to this is the manhole-to-manhole pipe of sewer mains. To locate the exact position of the camera head, It is necessary to have a remote transmitter (sometimes called sonde) in or near the camera head. This transmitter will then emit a signal which can be detected by a "receiver" unit located above the ground. It is thus possible to accurately locate the point on the ground directly above the transmitter and to determine the depth of the camera head. A small hole can then be dug down to the pipe to do the repair, minimizing the damage to the slab/ground surface and the amount of labor needed.
It is best to have the transmitter within the camera head, rather than behind the camera head in the flex lead, so that the head position can be more accurately determined and also so the transmitter electronics are protected against the sewer chemical environment. Since transmitters and locators are quite difficult to design, most companies that manufacture video inspection systems, or acquire them througn a private label arrangement, have to also acquire other companies transmitters and receivers. This leads to most systems having the transmitters external to the camera head. MicroEngineering, one of the few companies that develops and manufactures both pipe locater systems and sewer video inspection systems, have the camera and transmitter both included in the stainless steel camera head.
Sometimes it is desired to trace the sewer line but not of interest to do a video inspection. Pipe locators have been widely used by both plumbing contractors and municipalities for more than twenty years while push-cable sewer cameras have been in widespread use for about five years. While some of these pre-camera applications also involved tracing and digging up the lines for the purpose of finding a blockage, pipe damage etc, many of them involved line location so that a new drain line could be tied into the sewer system as additions were made to residential and industrial facilities. For this purpose, the transmitter is a battery powered stand-alone unit that can be taped near the end of the cable, even near the cutting head.
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