Utility Locating Equipment: What Is Actually on the Truck

The workhorse. A transmitter puts a signal on a conductive line and a receiver traces the field radiating from it. Signal is applied three ways: direct connection by clipping to a meter, valve, riser, pedestal, or panel; inductive clamp around an exposed cable or pipe, which is how energized cable and gas services are handled; and induction from a transmitter set on the ground when no access point exists.

Direct connection is the cleanest and most selective. Induction is the least, because it couples onto everything nearby, which is why bleedover is so common when there is nothing to clip to.

Most transmitters offer a range of frequencies, and the choice matters more than the brand. Lower frequencies stay on the target line and bleed over less but need a good connection. Higher frequencies couple onto almost anything, which rescues a marginal connection and creates ghost traces in a congested corridor. Watching an operator choose, and change, frequency is a decent proxy for whether they know what they are doing.

A wheeled antenna that images the subsurface from reflected radio pulses, and the only tool on the truck that finds targets carrying no signal at all: plastic pipe, clay tile, concrete, tanks, vaults, voids. Handheld higher-frequency units do the same job against slabs and decks, which is concrete scanning. Its limit is soil — high-conductivity ground attenuates the pulse and can cut usable depth to a foot or two.

A small transmitter on a push rod or camera head, fed into a non-metallic line and tracked from the surface. This is how a plastic water service, a sewer lateral, or an empty conduit gets traced when there is nothing conductive to energize. It works point by point rather than as a continuous trace, and it needs an accessible open end and a reasonably clear line.

Ground microphones, listening sticks, correlators, and hydrophones. Used to pinpoint a pressurised leak from the sound it makes in the pipe wall. Correlators solve for position from the difference in arrival time between two contact points, which works under pavement where surface listening does not. Plastic pipe absorbs the useful frequencies, so hydrophones that couple into the water column, or tracer gas, take over there.

What turns a locate into a record. An RTK rover or robotic total station captures each mark as a coordinate rather than a paint dot, so the result can be issued as CAD, GIS, or a point file and re-staked later from survey control. A total station covers the ground where canopy or buildings block satellites. Without this on the truck, the deliverable is paint, and paint is temporary.

Not a locating instrument, but the one piece of equipment that converts a locate into a measurement. Compressed air or water breaks the soil and an industrial vacuum lifts it out, exposing the line intact so depth, material, and diameter can be recorded. Some locating companies run their own unit; others bring in a crew that does. Ask which, because it changes how a test hole gets scheduled and quoted.