by James Caviness
Detecting utilities underground can be an important and difficult job; with so many different types of underground cables and pipes, it can be difficult to make sure you are using the right tool for the right job. One of the simplest but most effective tools in locating underground iron or steel targets is a magnetic locator.
What Is a Magnetic Pipe Locator?
Magnetic Pipe Locator vs. Cable Locator
A magnetic pipe locator is a metal detector that uses a strong magnetic field to detect the presence of any iron or steel targets nearby. The Schonstedt GA 92xtd Magnetic Locator is a ferrous object locator that will easily locate deep tanks and other objects such as a buried pipe. This model is a featured product for this application.
These units use a magnetic field to be able to detect very small targets, like nails in a log, or very large targets, like a manhole cover under the pavement. The depth of a magnetic locator is impressive when compared to other metal detectors. Another benefit to a magnetic locator is the ability to ignore any nearby targets that are not iron or steel- this eliminates digging for trash or undesired targets in the vicinity.
Rebar, galvanized pipe, and any other iron or steel targets would be well within the capabilities of a magnetic pipe locator. Magnetism is a double-edged sword in that while it can certainly find iron or steel if that is what you're after, it will NOT be able to detect any other type of metal or target; if you are looking for copper wire or underground pipes, for example, you would need a different type of location setup.
If the desired target is an underground cable, a different tool would need to be implemented in order to find the target effectively. An underground cable locator would be an easy to use option for locating any nearby, non ferrous metal targets. An underground utility locator typically comes equipped with a range of tools used to locate underground electrical cables and utilities and iron pipes. So while a magnetic locator may not be able to find a non ferrous metal object like aluminum cans.
Types of Magnetic Pipe Locators
There are a number of different options out there for magnetic pipe locators, but they will each use a similar type of technology in order to locate the desired targets. Some of the more basic options will offer a turn-on-and-go approach to locating targets, other systems will be able to provide more information on the target, as well as provide an interface to navigate the functions of the unit itself. The application and the frequency of use will likely be the driving factors in choosing the right magnetic locator.
When searching for ferrous metal objects like septic tanks and valve boxes, a pistol grip magnetic locator like the Fisher FML-3 would be able to find iron or steel pipes. To locate a plastic pipe, a special plastic pipe locator would be required. Power lines can be located with a special device called a power line locator. The final type of locator is a Ground Penetrating Radar. While it is more complicated and has several limitations, a GPR system is capable of detecting targets that other utility locating systems would not be able to detect.
What Are Magnetic Locators Used For?
Magnetic locators are some of the most versatile options when looking to locate iron or steel targets. While most magnetic locators find themselves searching for property markers or septic covers, they can be effective tools for finding lost parts of machinery in a field or pulling metal nails or chains out of logs before processing. Of course, magnetic locators are terrific options when searching for buried utilities as well, so long as they are composed of iron or steel. A magnetic locator would be the best option to find a broken underground galvanized water pipe, which could save a ton of time and money! If you suspect a water leak in a pipe, you would need a leak detection locator.
How Do You Use a Magnetic Pipe Locator?
Magnetic pipe and cable locators are fortunately some of the easiest locators to operate, some of the most popular options, like the Schonstedt locator devices, only have one or two buttons or knobs for very simple operation. Like a traditional metal detector, this unit would be swept along the ground until a signal is found. The signal strength produced by the target is based on adjusting the audio gain of the device to maximize the depth. Setup is similarly pretty straightforward: once the unit is powered on, the only significant adjustment is the gain or sensitivity. Setting the gain determines how much signal the detector will take in or how sensitive it would be to metallic pipe or other targets; deeper targets require a more sensitive setting than targets closer to the surface. Similarly, smaller targets like nails or stakes will require a high sensitivity setting than a 3-foot pipe. The signal from the pipe cable locator will become more intense as you get closer to the target. Once detected, pivoting and hitting the same target from a 90-degree angle can help pinpoint the exact location.
Methods for Locating Buried Utilities
As you can see from the infographic above, locating buried utilities can be accomplished using either a direct connection method or a clamp connection method. The two methods are shown visually in this graphic.
Direct Connection Method
This first method is also referred to as conduction. Locating metallic utility lines is best done this way. This is one of the most accurate methods of locating underground utilities.
The transmitter is placed at a point where there is direct access to the target line such as a utility box. A connection from the transmitter is connected to the target line. Next, a second lead is connected to the ground.
A transmitter's frequency and power output are adjusted to match the properties of the target line.
The target line is traced and marked on the surface by setting the receiver to the same frequency as the transmitter. This will allow the two to communicate with one another. Be sure to adjust the audio gain control as well.
Clamp Connection Method
This method is also referred to as the induction method. Clamps come in a variety of sizes for different applications. It is sometimes necessary to use a clamp to create a signal in a metallic cable when a direct connection is not possible.
In place of the connection leads, a clamp is connected to the transmitter and clamped around the metal pipe or exposed cable. A coil within the clamp transmits the signal to the target line.
It is necessary to set the receiver to the same frequency as the transmitter to trace the target line with a direct connection.
Copyright 2021 Detector Electronics Corp. - Revised August 2022