The receiver half of the pair, and how you go from a signal to a mark on the ground.
Quick answer
A locator is a handheld receiver that detects the magnetic field emitted by a sonde in the camera head. You sweep it over the ground until the signal peaks; that peak is directly above the sonde.
Depth is estimated from signal strength. Both the position and the depth are good enough to plan an excavation and not good enough to skip careful digging.
The basic principle
The sonde emits a magnetic field with a predictable shape. As you move the receiver, the strength and orientation of that field change in a way the instrument can interpret.
Directly above the sonde the field has a characteristic signature, which is what the locator is looking for. Most receivers indicate this with a combination of signal strength, a directional arrow and an audible tone.
The procedure in practice
- Push the camera to the point of interest and stop. Note the footage counter, you will want it for the report.
- Switch on the receiver and confirm it is set to 512 Hz, or whatever frequency your sonde uses.
- Sweep in a wide pattern over the expected route until you pick up signal.
- Narrow in on the peak. Work across the signal in two perpendicular directions to find the strongest point.
- Mark the ground at the peak.
- Take a depth reading with the receiver held vertically at the mark.
- Verify by moving the camera a known distance and re-locating. If the mark moves by roughly that distance in a sensible direction, your locate is sound.
That verification step is what separates a reliable locate from a guess, and it is the one people skip.
Where depth readings go wrong
Depth is inferred from field strength, so anything that distorts the field distorts the reading:
- Reinforced concrete, rebar distorts the field and typically produces an inaccurate depth.
- Buried metal, other pipes, tanks and structures interfere.
- Other utilities, live electrical lines can introduce noise.
- Metal host pipe, cast iron shields the sonde, reducing both range and accuracy.
Treat every depth reading as an estimate to plan around, never as a survey measurement.
Before you dig
A locate tells you where your sewer line is. It tells you nothing about the gas, electric, water and telecoms lines that may share the ground.
In the US, contact 811 before excavating. It is free, it is generally a legal requirement, and it exists precisely because locating one utility does not make the others safe.
It is a skill, not just a purchase
The first several locates will be slow and you will second-guess the readings. That is normal.
Practice on a line whose route you already know, a straight run from a cleanout you can see. Compare what the receiver tells you against what you know to be true. That calibration is what makes the instrument trustworthy when you use it on an unknown line.
Common questions
Can I use any locator with any sonde?
Only if the frequencies match. A 512 Hz receiver finds a 512 Hz sonde. Check both halves, a mismatch fails silently, meaning you find nothing and may assume the equipment is faulty.
How accurate is the position?
Position is generally more reliable than depth, since it is based on locating a field peak rather than interpreting its magnitude. Verify by moving the camera a known distance and re-locating.
Do I still need to call 811?
Yes. Locating your sewer line does not identify gas, electric, water or telecoms lines in the same ground. Contact 811 before excavating in the US.
Verified configuration pages
Continue the locating cluster:
Locator ecosystem: Sewer line locators hub · Camera↔locator compatibility · Locator specifications · Locator finder
Common locating mistakes
Most locating errors come from rushing the sweep. Marking on the first strong reading, without crossing it from a second direction, often lands you on a side lobe rather than the true centre. Working next to a parked vehicle, a metal fence, or a buried service pulls the signal and shifts the peak. And forgetting to hold the camera head still while you sweep means you are chasing a moving target.
The fixes are simple. Leave the head in place, sweep slowly until the signal peaks, then confirm from a second angle before you mark. Read the depth only once you are sure of the centre, and repeat the whole check in calm ground away from large metal. A minute spent confirming saves a dig in the wrong place, which is the one mistake a locator is meant to prevent.