Satisfaction Guaranteed If you're not convinced that this is the best magnetic locator you've ever used we'll refund your money! Lifetime Warranty Separate Power/Volume and Sensitivity Controls Uses 4 - AA batteries LOW Battery Indicator All locators come with a carrying case, users guide, and spare batteries The engineers at Dunham & Morrow Inc. have over 35 years of experience designing and building magnetic sensing equipment for NASA's Hubble Space Telescope and Gamma Ray Observatory, NOAA's GOES weather satellites, the US Military, and the US intelligence community. That is why Dunham & Morrow back their locator with a full LIFETIME warranty. By following the same demanding design principles required of all satellite hardware, the DML2000 magnetic locator is practically indestructible and so easy to use, anyone can operate it. Built "Space tough" right here in the USA, our DML2000 locators are known for their performance and durability. Users relax in the knowledge that our proven shock-mounted sensor technology safeguards the sensor's mechanical integrity in the harshest of conditions. Compare the DML2000 magnetic locator against our competitor's product before you buy. You'll find that the DML2000's performance, light weight, low cost and lifetime warranty make a truly winning combination.   DML2000 The state-of-the-art, DML2000 Magnetic Locator packs all of its sophisticated electronics in an incredibly light 1.6-lb package. Experienced MAG users will appreciate the LOW battery indicator; no more wondering if the batteries are low and you're missing targets. In side-by-side comparison tests with other magnetic locators, the DML2000 outperformed all the competition. Using the DML2000 is the fastest, and easiest way to pinpoint buried survey markers, septic tanks, iron water and gas pipes, water valves, water meters and any other ferrous object buried under dirt, asphalt, water snow or ice. "This locator is well .....FANTASTIC!" Dave Hanley LS, Geneva, NY     DML2000-M The DML2000-M Magnetic Locator has all of the standard features of the DML2000, plus an easily readable Liquid Crystal Display (LCD) panel meter. The DML2000-M with its 3½ digit (0 to ± 1999) Digital Panel Meter, gives the operator a real time, true visual representation of the instrument’s output frequency changes, it also provides the highest resolution display of any Magnetic Locator. The digital display provides an exact numeric readout with a separate polarity indicator that can be even more useful to the experienced professional. When the panel meter peaks and the polarity changes, this normally indicates that you are directly over the end of that pipe section, typically a weld or a "Bell" joint. A polarity change that occurs when the meter readings are at a minimum means you are over the midpoint of that pipe section.   Product Specifications   Dimensions:  42 ½” L x 3 ¾” W x 1 ¾” D (108 cm x 9.5 cm x 4.4 cm)   Low Battery Indicator:  Red, flashing LED Waterproof Length: 36” (91.4 cm), base to tip of sensor tube   Temperature Range: -20°F to 120°F, (-29°C to 50°C) Weight: 1.8 lb. (0.8 Kg)   Audio Output: Variable frequency, 20 to 3,500 hertz Operating Time:  up to 50 hours   LCD Panel Meter: 0 to ± 1999 - DML2000-M only Power: Uses four AA alkaline batteries   Warranty:   Lifetime Pricing   DML2000 Standard Unit Soft-padded (Gun) Case $670 DML2000 Standard Unit Hard Plastic Case $710 DML2000-M Metered Unit Hard Plastic Case $795         Soft Carrying case DML2000 DML2000 DML2000-M Dunham & Morrow, Inc., manufacturers of Quality Magnetic Locators for Surveyors, Hydrologists, Construction Contractors, Septic Tank Services, Public Utilities, Well Drillers and any other professionals desiring to pinpoint buried ferrous metal targets.   Locator with hard case MAG PRO III Sea Pro

Feature: Maximizing Your Magnetic Locator

The capabilities of a magnetic locator are virtually limitless, and an experienced operator will find many uses for this instrument. Utility companies and other services use them to locate water valves, water meters, gas and water pipes, manhole covers, and even septic tanks. It only makes sense that surveyors find them especially useful in their everyday fieldwork as well.

When used properly, a magnetic locator will greatly simplify the task of pinpointing survey markers. Just turn on the power and set the volume control to a comfortable level. Most survey pins can be located quickly and easily with the sensitivity control set on the number 3 setting. Just wave the locator back and forth as you walk along, and you will have no difficulty locating your pin. The locator's audio output idles when there are no ferrous targets nearby, gradually increases in frequency as you approach your target, and finally peaks directly over your survey pin.

But how does this seemingly magic box do this? The primary sensing elements are fluxgate magnetometers that measure the average magnetic field component along their sensitive axis, i.e. along the axis of the sensor tube.

Figure 1 shows a typical magnetic locator with two magnetometer sensors at the lower end of the instrument sensor tube approximately 20 inches apart. The lower sensor measures the positive magnetic field at the tip while the upper sensor measures the negative magnetic field 20 inches away. The electronics combines these two signals, and if there are no ferrous targets near the sensors, the signals will cancel and the instrument will remain at idle. By summing the two output signals, you cancel any field common to both sensors, such as the Earth's magnetic field, and leave only the differential magnetic field. The magnetic field detected by one sensor and not the other becomes the magnetic field of interest.

In figure 2, we show how to hold your magnetic locator while searching for survey markers. To maximize your search operation, hold your locator by the electronics case and reach out at a 45-degree angle. Then sweep your locator back and forth as you walk along. This technique allows you to survey a wide area with just one pass and to probe into bushes and dense vegetation. If you hear an increase in the instrument's output frequency, concentrate on that area. Gradually bring your locator to a vertical position and perform an "X," or "crossing pattern," to pinpoint the source. If you hear a fluctuation or warble in the audio output, BEWARE! A strong warble output from the locator means you are probably over an energized power line, whereas a weak warble output often indicates the presence of a telephone or communications cable.

When working around chain-link fences (figure 3), your task will be greatly simplified if you hold the locator vertically and walk along parallel to the fence approximately eight inches to a foot away. You will hear the magnetic field of the fence as you walk along, including the field from the posts. However, if your target is near or under the fence, there will be a dramatic increase in the instrument frequency as you approach the target, and you will have no difficulty distinguishing your target from the fence.

Buying a Unit

When it comes to purchasing a new locator, there are many items to consider besides the instrument's obvious factors such as performance, cost, reliability, and ruggedness. Ideally, you would like to know something about the manufacturer, i.e. their repair department and the instrument warranty.

By far the most important item listed above is performance; if the locator is poorly designed and poorly calibrated, it will produce false targets as you swing it side-to-side. This can be both frustrating and costly. There are plenty of expensive magnetic locators on the market that perform poorly. The best way to avoid the problem of being strapped with a costly mistake is to test several different locators and select the one with the best performance.

Problem Locates

What happens when you can't locate your survey pin? Most locators have multiple sensitivity settings to help in locating something. Just select a higher sensitivity setting, and if there is a survey pin in the area you will find it.

What happens if the locator produces a higher tone when you swing it in one direction, no matter where you stand? This is called a false target and is usually associated with poor sensor alignment and poor instrument calibration or a combination of the two. The solution is quite simple. The Earth's magnetic field is oriented in a north-south direction. When you are looking for survey pins while traversing in the east-west direction, the magnetic locator's sensors are swinging through a magnetic field range varying from full positive to zero with each swing of the wand. This magnifies the problem of false targets. Fortunately, you can practically eliminate the problem of false targets if you confine your traverses to the north-south direction. When you make north-south traverses, the magnetic locator sensors are nominally in a plane perpendicular to the Earth's magnetic field. This practically eliminates problems associated with sensor alignment, signal channel tracking, and calibration errors. With a well-maintained locator, you should not have this problem, but it always helps to know how to work through the issue should it occur.

A typical manhole cover (figure 4) is actually a combination of two magnetic fields, those of the cover itself and the steel support ring. When both fields are aligned, they add and are easy to detect. When they fall 180 degrees out of alignment, they tend to cancel, and detection becomes more difficult.

The peaking of the Dunn & Morrow model DML2000 output frequency normally indicates you are over the end of a pipe section, which can be either a weld or a "Bell" joint as shown in figure 5. When searching for horizontal gas and water lines, look for a polarity change on the digital panel meter. A polarity change that occurs when the output frequency is low means you are nominally over the midpoint of the pipe section. A polarity change when the output frequency is high typically indicates a pipe joint or weld.

Frequency peaking occurs over service connections and valve boxes—any place the pipe has been cut and a service connection, valve box, or other magnetic anomaly inserted (figure 6).

Historical Notes

Some of the earliest work on fluxgate magnetometers took place at Bell Labs prior to and during World War II. Much of that work was later transferred to the Naval Ordinance Laboratory, where the magnetically triggered torpedo design was perfected. The magnetometer sensors detected the magnetic field of their target and then detonated the torpedo warhead when the signal polarity changed, just as it passed under the keel of the boat. Precision fluxgate magnetometer sensors have been used for decades in earthquake prediction instruments, and they have also been used to monitor solar flare activity, control the attitude (or orientation) of satellites, and guide cruise missiles to their target.

The first practical use of a gradiometer, a system employing two coaxial fluxgate magnetometer sensors arranged in the typical magnetic locator design, occurred during the Vietnam War, where they were used to detect Vietcong tunnels. Commercial use of magnetic locators has expanded greatly since then, and they are now used to pinpoint survey markers and a host of other objects. The FBI has used commercial magnetic locators for years to detect and pinpoint discarded weapons such as handguns and knives in dense shrubbery and shallow waters. The potential uses of magnetic locators are numerous, and in the hands of a skilled operator, they have proven an invaluable tool.

About the Author

With a B.S. degree in electrical engineering from the University of Maryland, Warren Dunham has served as a consultant to NASA, NOAA, and the U.S. intelligence community for over 35 years. His most notable designs include the satellite attitude and control magnetometers for the Hubble Space Telescope, Gamma Ray Observatory, and GOES weather satellites. For 22 years, he worked at the Schonstedt Instrument Company as a principle engineer responsible for satellite magnetometers and magnetic locator products. In 1994, he founded Dunham & Morrow Inc. and for the first five years continued the design and production of satellite magnetometers. In November 1999, Dunham & Morrow introduced its first commercial product, the DML2000 magnetic locator.

The success of locating a buried object depends on your familiarity with the magnetic signature of various targets and the corresponding response of the locator's audio signal. Locator's audio signal responds to the magnetic signature of a survey marker.     As the locator is moved over the target, the waveform depicts the increase in the frequency of the locator's 20 Hz audio idling signal. The highest frequency occurs when the locator is directly over a vertical target, and over both ends of a horizontal target.     The audio signal peaks over identical magnetic signatures at two joints of a cast-iron water line.       Locating a survey marker in close proximity to a steel fence is no problem with the DML2000.     Manhole covers normally appear as short horizontal dipoles with the peak signal level occurring at the perimeter of the manhole cover.   When searching for a Concrete Septic Tank you can expect an increase in the audio output signal as you approach the tank with the strongest signal occurring directly over the two handles on the cover.             Frequency peaking occurs directly over service connections and valve boxes. The depths outlined here are typical responses. There have however been numerous instances where targets have been located at far greater depths. In almost every case the magnetic locator operator used his instrument almost daily and knew how to get the maximum out of his instrument. He was magnetically clean, his search area was well defined and contained a minimum amount of trash metal, he held his instrument in a vertical position and he used the maximum sensitivity setting. Target Depth Iron Marker (3/4” x 18”) 6 - 8 feet Cast-Iron Pipe (4” Pipe) 4 - 5 feet Manhole Cover 3 - 4 feet Well Casing 8 - 10 feet PK Nail (1½”) 6 - 10 inches Iron Valve 4 - 5 feet 55 Gallon drum 5 - 6 feet Septic Tank (Handles) 3 - 5 feet