The Ultimate Guide to Magnetic Locators

What is a magnetic locator?

Magnetic locators are devices designed for finding ferromagnetic items or structures buried in the ground. Ferromagnetic items can include those made of iron, steel, cast iron, or stainless steel or basically any item that a refrigerator magnet will stick to.

What can magnetic locators find?

• Steel or iron survey markers
• PK Nails (surveyors nails)
• Firearms
• Manhole covers
• Cast Iron Valves
• Pipeline joints
• Septic tanks
• Well Casings
• Unexploded Military Ordinance
• Any buried iron or steel object

How do magnetic locators work

To understand magnetic locators, we must first review a few aspects of magnetics.

First: All magnetic items have two poles, a north and a south.

Second: Magnetic fields can induce complementary magnetic fields in other iron or steel objects. For example, if you move a refrigerator magnet near a paperclip, you can then use the paper clip to pick up a staple, even though the clip itself is not normally a magnet. This is due to the “induced” magnetic field in the paperclip.

Third: This bipolar nature, and ability to induce a magnetic field works at all scales. Thus, due to the Earth’s magnetic field, each piece of iron or steel buried underground will have a weak induced magnetic field, just like the paperclip near the refrigerator magnet.

Now we can address how magnetic locators work. These devices are used to read variations in the Earth’s magnetic field caused by nearby ferromagnetic (iron or steel) objects. Magnetic locators contain two sensors. The first sensor reads the magnetic field of the Earth in the general work area. This reading acts as a baseline and is generally fairly weak.

The second sensor interprets the magnetic field of the ground directly below the device. If there is an iron or steel item buried in the ground, it will have an induced magnetic field from the Earth. Depending on the size and shape of the item, this induced field can be relatively strong compared to the weak field of the Earth. The locator will then detect the difference between the expected weak magnetic field of the earth and the stronger induced magnetic field on the buried object.

Magnetic Locators VS Metal Detectors

Magnetic locators are often compared to metal detectors, however the way that they function is very different. This gives magnetic locators an advantage in some areas of detection and metal detectors an advantage in others.

Where magnetic locators work by detecting differences in magnetic fields, metal detectors work through electromagnetic induction.

Metal detectors have two coils in the search head. An electric current is run through the first coil. This creates an electromagnetic field in the shape of a cone on either side of the coil. As the operator swings the metal detector, this field is projected into the ground.

If a conductive piece of metal is within this moving electromagnetic field, a separate field is induced around the buried object. This induced field can then be read by the second coil in the search head.

Strengths and Weaknesses of a Magnetic Locator

Magnetic locators are excellent at finding ferromagnetic materials such as iron, steel, or cast iron. Due to the sensitivity of the device, a magnetic locator can often read these ferromagnetic items at greater depths than a traditional metal detector.

However, since magnetic locators work by reading differences between magnetic fields, they will not read non-metallic metals such as brass, copper, gold, or silver. This limits the targets that magnetic locators can be used on, but it also means that they can be used in extremely trashy environments where small, non-ferrous debris items can be ignored.

In addition, differently shaped ferromagnetic items will have differently shaped magnetic fields. A skilled magnetic locator operator can often identify the size, shape, and depth of an item before digging. This can help eliminate unnecessary excavation and can save time on projects where only specific items are being searched for.

Strengths and Weaknesses of a Metal Detector

Metal detectors are able to detect any material that can conduct electricity. This means that almost every type of metal and even some non-metallic items can be detected. Metal detectors can also read the difference in conductivity of the item that they are detecting, meaning that they can be equipped with “discrimination” settings to remove unwanted signals. However, metal detectors are not as sensitive as magnetic locators and can have trouble reading iron or steel items at extreme depths.

How deep will magnetic locators detect?

The depth at which an item can be located by a magnetic locator will vary depending on factors such as the shape of the item, the size of the item, the soil type, and the amount of electromagnetic interference (EMF) in the surrounding environment. The model and brand of the magnetic locator will also be a factor as well as the skill of the operator.

Generally speaking, a magnetic locator should be able to find the following items at the marked depths.

What are magnetic locators used for?

Magnetic locators are used by a variety of professionals in the course of their jobs. Many of these workers will also use metal detectors in the course of their duties, however the magnetic locator often remains the tool of choice for work that require the location of iron or steel items.

Magnetic Locators for Survey

Surveyors of all types employ magnetic locators, primarily to re-locate survey pins, PK nails (magnetic nails), or other iron and steel survey markers. In locations where old boundary lines were marked with steel pipes or old fence lines, a magnetic locator can also come in handy for general boundary location.

Magnetic Locators for Utility Location

Magnetic locators are used by utility professionals to locate steel or iron pipe joints, valves, buried manholes, or other metal fixtures. They are especially useful in locating items buried by asphalt, concrete, or years of soil accumulation. While magnetic locators will not aid in the location of copper, plastic, or ceramic pipelines, the ability to find fixtures and valves associated with these utilities is often enough to give operators a good idea of their location.

Magnetic Locators for UXO Survey

Magnetic locators are an essential tool for technicians working to remove unexploded military ordinance. Since many artillery shells, land mines, and other explosive rounds contain steel and iron, the magnetic locator is an ideal tool for the location of these dangerous materials. The additional detection depth compared to a traditional metal detector also allows UXO technicians to find items that would otherwise be missed and provides an extra amount of separation between the operator and a potentially hazardous munition.

Magnetic Locators for Law Enforcement

Law enforcement professionals use magnetic locators on crime scenes to locate evidence such as discarded firearms or steel shell casings. In addition, waterproof magnetic locators such as the ML-3 by Subsurface Instruments can be used in underwater operations to recover evidence that has been hidden in rivers or lakes.

Magnetic Locators in Construction

Magnetic locators are useful in construction activities where PK nails (magnetic nails) have been placed in masonry, concrete, or other foundation materials. They can also be used to locate or trace rebar or other iron supports that might be hidden in concrete or walls.

Magnetic Locators in Timber Operations and Lumber Mills

Magnetic locators may be used by lumberjacks, wildland firefighters, or lumber mill workers to scan trunks for nails and wire before using a chainsaw on the wood. This can help prevent chainsaw kickback and dangerous flying metal debris.

Magnetic Locator Features

Manufacturers have added an array of features to increase the usefulness of their magnetic locator products.

Ergonomic Handles: Some professionals will use their locators for more than just a few minutes at a time. For jobs that require more than a few minutes of survey, an ergonomic handle can help increase the ease of the operator, especially over a long work shift.

Extra Length: Magnetic locators can vary significantly in length. Shorter lengths work for people with smaller stature and can reduce the weight of the device. Longer lengths can increase swing arc and therefore survey efficiency. Longer lengths can also be useful for surveying thick vegetation or for UXO operations where more distance is preferred between the operator and the items being searched for.

Digital Meters: digital meters can convey information from signal strength to battery life. They can also be used to display the sensitivity setting of the device.

Aircraft Aluminum Housings: Magnetic locators are often used in tough outdoor conditions. Aircraft aluminum housings are not only light enough to swing throughout the day, but they can take a beating. In addition, aluminum is non-magnetic, so it will not interfere with the accuracy of the locator.

Waterproof Housings: Most magnetic locators will be used in outdoor environments where they can be exposed to the elements. Many models are waterproof or water resistant along the shaft, while some, such as the ML-3 by Subsurface Instruments are completely waterproof and are capable of being used for long periods in deep water.

Choosing the best magnetic locator

Magnetic locators can be valuable tools for anyone looking to find buried iron or steel objects. If you are considering purchasing a magnetic locator, we would be glad to hear from you. Precision Outdoor Tech carries a variety of different locators from various manufacturers. Please feel free to reach out to us through our contact page and we will be glad to help you find the magnetic locator that best meets your needs.