The camera head carries a small transmitter called a sonde, usually at 512 Hz. A handheld receiver above ground finds the strongest signal, marks the spot and shows an estimated depth. That tells the plumber where a defect sits and how deep it is. It is not a substitute for calling Arizona 811 before digging.
How does a sonde work?
A sonde is a small transmitter that sits in or just behind the camera head. Powerwill describes it as a device that, when active, "emits an electromagnetic signal at its specified frequency, such as 512 Hz." It does not send back coordinates or a map. It just puts out a signal that can be found through the ground.
The plumber above ground carries a receiver tuned to that frequency. RIDGID, which makes both push cameras and locators, says its NaviTrack Scout receiver detects the inline 512 Hz sonde in compatible SeeSnake camera reels. The Scout's product page says "Depth is automatically calculated and displayed when over the target." The operator walks the surface, watches the signal grow and fade, and marks the spot where it is strongest. Where the head sits, the receiver shows an estimated depth.
Put together, the crew gets three numbers for every defect: how many feet of cable the camera has traveled, where that spot is on the surface, and roughly how deep the pipe is.
Why not just use the cable footage?
Cable footage measures how far the cable has gone, not how far the pipe travels in a straight line. Powerwill gives an example: a camera may show roots after 60 feet of cable travel, but that reading "does not tell you the straight-line distance from the access point, the direction of the pipe, or its burial depth."
That is why a good crew uses both. The footage counter tells you where the defect is on the video. The locator tells you where to stand.
How accurate is the depth reading?
It is an estimate, and it depends on the equipment and the conditions. Powerwill lists what a locate should record: the position, the estimated depth, the access point and "any uncertain readings." It also says a sonde "locates the camera head, not every utility or the full extent of a defect."
The sonde’s depth estimate also differs from a sewer camera’s slope or pitch display. Ask which measurement was taken and what equipment and conditions qualify it.
Powerwill advises checking signal shape and consistency "rather than relying on a single peak," so one reading on the receiver is not proof. RIDGID's own pitch for the Scout is that its antenna sees the whole signal, so there are no "nulls or false peaks to complicate the locate," which tells you those are the traps a locate can fall into. Before a trench, ask the crew how they confirmed the mark, and whether they will expose the pipe by hand at that spot first.
Are there other ways to locate a buried pipe?
Yes, but the sonde is the standard for a pipe you are already inspecting. NASSCO's assessment page mentions ground penetrating radar as a geophysical method that images the subsurface and is typically used to detect buried utilities and potential voids. It is a different tool for a different job. It can help find things around a pipe, but it does not replace the camera.
Does locating my sewer replace calling Arizona 811?
No. A camera sonde locates the camera head in the pipe being inspected. It does not locate every buried facility near a proposed excavation. Private lateral locating is not automatically included in a utility’s normal 811 marks; confirm who is responsible for the particular line. Apartment-community landlords also have statutory duties for facilities they operate under A.R.S. 40-360.22. A camera sonde locate does not replace those duties or the required one-call request.
Under A.R.S. 40-360.22, an underground facility operator generally has two working days to respond to an excavation inquiry; an apartment-community or mobile-home-park landlord has ten working days. The law prohibits starting covered excavation until required marking is complete or the excavator is told it is unnecessary, subject to the law’s specific procedures and exceptions. Have the excavator arrange the required notices and private locating before planning a dig.
What should you ask for?
- The footage marker and the surface mark. Ask that both are written down or photographed, so the spot can be found again.
- The estimated depth. Ask what it was measured at and how it was confirmed.
- The route. For a long run, ask for a rough sketch or a marked line on the ground, not just one dot.
- How the repair will be planned. Depth and route decide whether a trenchless method is on the table. See our page on trenchless repair versus digging.
If you need a camera inspection with line locating, HQ is licensed and insured, runs 24/7 emergency service, and gives free estimates and upfront pricing on repairs. See sewer repair.
For the current inspection service, see HQ’s sewer camera inspections.
When planning inspection work, see how long does a sewer camera inspection take.