How Does a Magnetic Locator Work?

Homeowners use magnetic locators to find property pins, cast iron or galvanized pipes, and septic tanks. They’re used by surveyors to find magnetic surveying nails and property pins. Construction workers and excavators use these versatile tools to locate manhole covers, fuel tanks, steel drums, and lost wells.

A magnetic locator is a specialized type of metal detector. It's used to find buried objects made from iron or steel. It can reach depths of up to 16’ (4.8 m). But how does it work?

How a Magnetic Locator Works

Unlike an ordinary metal detector, magnetic locators don’t transmit a signal into the ground. Rather, they measure distortion in the earth’s magnetic field caused by buried iron or steel objects.

Earth’s magnetic field produces smaller secondary magnetic fields in any magnetic object. Magnetic objects include property pins, cast iron pipes, septic tanks, and buried well casings. These objects' small magnetic fields cause distortion in the measured strength of the earth’s magnetic field.

A magnetic locator uses two sensors along its length to measure the earth’s magnetic field. If the measurement is the same to both sensors, the locator emits a low hum.

If the measurement differs between sensors, this indicates that a buried magnetic object is in the ground. The locator will emit an increasingly high-pitched tone as it nears a buried object.