Surveyors Magnetic Locator Theory of Operation

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 Theory of Operation

All magnetic locators operate on the same basic principle; two fluxgate magnetometer sensors, securely mounted inside a rigid sensor support tube, measure the local magnetic field.

The two-magnetometer sensors are vector sensors, mounted 20” apart and each measures the average magnetic field component along their sensitive axis, i.e. the magnetic field component along the longitudinal axis of the sensor tube.

For a magnetic locator to work properly, the magnetometer sensors are aligned opposing so that the magnetic field measured by one sensor is the negative of the magnetic field measured by the other. The locator then sums the output of the two sensors. 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 differential magnetic field, the magnetic field detected by one sensor and not the other, is the magnetic field of interest and hopefully represents the magnetic field of your target and not the field of your pocketknife, watch or the steel arch support in your shoes. The drawing on the right shows the construction of a typical magnetic locator and the location of the two sensing elements.

Field Operation

Good instrument performance goes hand-in-hand with proper operation.  When searching for survey benchmarks or underground ferrous targets, the magnetic locator should be held in the vertical or near vertical position.  In this position the instrument audio output is facing the operator and the controls are readily accessible. The picture at the top of this page shows how to hold the instrument for optimum operation.

To pinpoint your target, rotate the instrument to the vertical and use and “X” or crossing pattern.  The audio output will peak directly over your target.

All Weather Operation

The sensor housing is waterproof and the electronics water-resistant.  Moreover, the circuit design and component selection ensures proper operation whether the ambient temperature is -20^oF or 120^oF.

Unparalleled Reliability

For added strength and reliability, the electronics package is made of impact resistant ABS plastic, while the sensor tube and base plate are made of 6061-T6 aluminum, welded together. Moreover, the two sensing elements are shock-mounted on there own individual support tube, inside the yellow sensor tube.  This added sensor isolation guarantees that the sensor alignment and overall instrument performance will withstand normal physical abuse and harsh weather conditions. In addition, all electronic components have been carefully selected for long life and harsh environment operation. 

With normal handling, this combination of quality electronic components, shock-mounted sensors, and robust package design, should ensure a lifetime of maintenance free operation from your DML2000 magnetic locator.

 

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.

• 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
  Covers Everything!
• Unsurpassed Performance
• Separate Power/Volume and Sensitivity Controls
• Uses 4 - AA batteries
• LOW Battery Indicator
• All locators come with a, Carrying case, an Instruction Manual, and a spare set of Batteries.

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 100 hours	LCD Panel Meter:	0 to ± 1999 - DML2000-M only
Power:	Uses four AA alkaline batteries

 

     

 

			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.             Frequency peaking occurs directly over service connections and valve boxes.     Target Depth Iron Marker (3/4” x 18”) Up to 9 feet Cast-Iron Pipe (4” Pipe) Up to 10 feet Manhole Cover Up to 10 feet Well Casing Up to 18 feet PK Nail (1½”) Up to 12 inches Iron Valve Up to 10 feet 55 Gallon drum Up to 10 feet Septic Tank (Handles) Up to 5 feet