Magnetic locators

How do handheld magnetic probes work?

Handheld magnetic probes detect changes in the natural geomagnetic field caused by ferromagnetic objects in the subsurface. The measurement principle is based on magnetometry: ferromagnetic materials such as iron, grey cast iron, or steel measurably disturb the local geomagnetic field. Highly sensitive sensors – typically fluxgate or proton precession magnetometers – register these anomalies and output them as a signal.

Unlike inductive metal detectors, magnetic probes respond exclusively to ferromagnetic materials and completely ignore non-ferrous metals such as copper, zinc, or aluminium. The latter produce no interference signals, as they possess no ferromagnetic properties. This is a decisive practical advantage in civil and road construction.

Particular advantage with typical infrastructure installations

Valve caps, manhole covers, valve rods, boundary markers, and survey bolts are as a rule manufactured exclusively from cast iron (grey cast iron EN-GJL, ductile iron EN-GJS) or steel – both strongly ferromagnetic materials. When locating these installations, non-ferrous objects in the surrounding area – such as copper pipes, brass fittings, or aluminium components – generate no interference signal on the magnetic probe whatsoever. The device responds exclusively to the object being sought, which considerably simplifies localisation and minimises misinterpretation in the field.

Note: More recent valve caps are occasionally manufactured from plastic and cannot be detected by magnetic probes. In such cases, the additional use of an inductive metal detector or cable and pipe locator is recommended.

Typical areas of application

Magnetic probes are used to locate valve caps, manhole covers, and valve rods in covered road and pavement areas, to localise boundary markers and steel survey bolts, for pre-investigation before civil engineering works in iron-contaminated areas, and for unexploded ordnance (UXO) clearance and archaeological prospection.

Why procure magnetic search devices from SEMPERDEAL?

SEMPERDEAL specialises in detection technology and buried infrastructure. Our range includes magnetic probes and magnetometers for professional field use – tailored to the requirements of utility companies, civil engineering contractors, municipalities, and public authorities. Expert advice on device selection and individual quotations are available on request. Devices, accessories, and complementary detection technology from a single source.

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