TOC

GA-72Cd
Magnetic Locator

Operations Manual
Last modified 02/02/2017
Locating with a Schonstedt GA-72Cd Versatile Magnetic Locator

Table of Contents

Operation

Intro

 

The GA-72Cd Magnetic Locator detects the magnetic field of ferromagnetic objects.  It responds to the difference in the magnetic field between two sensors that are spaced approximately 14 inches apart.  This difference is referred to as the “signal strength” throughout this manual and is represented in the instrument by an audio tone and visual indication of both signal strength and polarity.  While most objects can be located using either the audio or visual indication, simultaneous use of both will help you pinpoint a target and determine its orientation.

The below image illustrates an application in which the locator is used to detect an iron marker used for property line identification.  As shown, the magnetic field of the iron marker is stronger at Sensor A than it is at Sensor B.  As a result, the frequency of the audio signal is higher than the idling frequency, 40 Hz, which exists when the field strength is the same at both sensors.  This stronger signal also causes the digital indication to peak in either the positive or the negative direction when the audio signal is at its highest frequency.

 

When shipped, the locator is set to provide an audio signal that is heard as long as the instrument is turned on.  If desired, you can change this setting to an audio signal that is heard only when the instrument is within detection range of an object.

 

Schonstedt GA-72Cd Detect Iron Marker Property Corner Iron Pin

Detecting Magnetic Field of Iron Marker

 

Turn-On, Sensitivity, & Volume Settings

 

Turn on the GA-72Cd by rotating the On/Off-Sensitivity control knob clockwise to position 1.  This sets the sensitivity to what is referred to as the Normal Range (the L meter indication).  Sensitivity can be increased by rotating the Sensitivity control clockwise to select M, H, or XH settings (as indicated on the meter’s GAIN display).  Adjust the Volume control for the desired audio output level.

 

Schonstedt GA-72Cd Control and Meter Indications

 

Battery Level Indication

 

The meter’s BATT indication displays the batteries’ voltage level.  When all four segments are black, the voltage level is between 100% and 25% (up to 60 hours of operation with intermittent usage).  As the voltage decreases, the number of black segments decreases.  Battery life varies with usage and the ambient temperature.  Cold temperatures reduce battery life.  Low temperatures may result in only two or three segments being black; this could be temporary and all segments will change back to black as the temperature increases.

 

 

Audio Output Selection

 

All GA-72Cds are shipped from the factory with the Audio Output Switch set to “B”; this setting provides an audio signal that is always present.  If you prefer to not hear a signal until the locator is within detection range of a target, set the switch to “A”.

Audio Signal with Output Switch set to “A”

No audio signal is heard until the GA-72Cd comes within detection range of a ferromagnetic object.  The locator will increase in volume over the object. It will decreases in volume and turn off when the locator is moved out of range.

NOTE:  If you put the GA-72Cd down without turning the Sensitivity/Power switch to Off, the “power-on monitoring feature” (designed to conserve battery life) will initiate a beeping audio-alert signal after 15 seconds.

Audio Signal with Audio Output Switch set to “B”

As you move the GA-72Cd across a ferromagnetic object, the 40 Hz idling signal, which is always present, increases in frequency, peaks when the locator is directly over the object and then decreases to 40 Hz.

Regardless of which switch setting, the indication of signal strength and the polarity on the meter will always peak (positive or negative) when the locator is directly over a ferromagnetic object. The cover must be removed to change the setting of the Audio Output Switch.

 

Audio Output Switch Schonstedt GA-72Cd

 

Search Procedure

 

Set the On/Off-Sensitivity control for L and grasp the locator as illustrated in Figure 5.  Because the upper sensor is located near where the locator is usually held, wristwatches may produce unwanted changes in the audio signal and in the meter indications. Remove your wristwatch or hold the locator in the other hand.  Keep the locator away from your shoes; shows may contain magnetic material.

 

To obtain the maximum area of coverage, the locator should be swept from side to side.  When the locator comes within range of an iron object, the audio signal will peak, the bar graph will expand positive or negative, and the digital readout will peak.

 

Searching with Schonstedt GA-72Cd

 

Locating & Detecting Buried Iron Objects

Determining Target’s Orientation

When the GA-72Cd is positioned directly over a vertical pipe, the audio and digital indications will peak.  The expanding bar graph and digital readout may display either a positive or a negative level.

The audio signal, bar graph and digital indications peak over each end of a horizontal pipe.  One end is positive; the other end is negative.  This will help you to distinguish between two vertical pipes or one horizontal pipe.  Usually two vertical pipes buried in close proximity will produce digital indications with the same polarity.

 

Schonstedt GA-72Cd Meter's Polarity Indicators Help Determine Orientation of Iron Target

The Meter’s Polarity Indications Help to Determine Target’s Orientation

 

Basic Signal Patterns

Schonstedt GA-72Cd Signals Peak over Vertical and Horizontal Targets

Signals from Vertical and Horizontal Buried Iron Objects

 

After you have detected the presence of a target, hold the locator vertically and slowly move it back and forth in an “X” pattern while observing the digital readout.  The value of the number will be highest when the locator is directly over a vertical target or over the ends of a horizontal target.  The “X” pattern is ideal for pinpointing small objects.  By using this technique, a 1-1/4 inch PK nail buried up to 8 inches can be precisely located.

 

Precise Location of Buried Iron Objects

“X” Pattern provides precision locating

 

If you are looking for a corner marker and detect two more signals in the same general area, raise the locator several inches above the ground or reduce the sensitivity setting.  Any signal that disappears when the locator is held higher or when the sensitivity is decreased is probably coming from a shallow target.  As shown in Figure 9, the signal from a rusty bolt or other small item decreases much faster with distance than the signal from a larger target, such as a 18-inch length of 3/4 rebar that can be located at depths up to 7 feet.

 

Schonstedt Magnetic Locators - Raising the Locator Eliminates Unwanted Signals

Raising the Locator Eliminates Unwanted Signals

 

Strongly Magnetized Markers

 

A strongly magnetized marker that is at or near the surface will provide a weaker indication on both sides of the marker, and this can be mistaken for the actual marker.

 

The heavy line in the below illustration represents the increase and decrease in the audio and digital indications as you move the locator over a marker.  Between points A and B, the signals increase slightly and then decrease.  Just beyond B, the signals increase rapidly, peak directly over the marker, and then decrease at point C.  From C to D, the signals increase and decrease again.  Therefore, if you do not move the locator completely across the marker, you may assume that the weaker indication on either side of the marker is its location.

 

Schonstedt GA-52Cx Signal Pattern from a Strongly Magnetized Marker

Signal Pattern from a Strongly Magnetized Marker

 

The two weaker indications on both sides of the actual marker occur because the locator is extremely sensitive to the magnetic field components parallel to its long axis.  At point B and C, the field is perpendicular to the locator so no peak audio or digital indications are produced.

 

When Placing Stakes, Correct Orientation is Important

For checking purposes, the orientation of the pin relative to the locator is shown in the below illustration.  Check the pin with one orientation.  Then rotate the pin 180°.  The orientation that gives the largest reading is the one that should be used.  This reading will be positive in the Northern Hemisphere and negative in the Southern Hemisphere (Australia, New Zealand, etc.)

 

An iron pin has two types of magnetization.  One is the magnetization induced by the Earth’s magnetic field.  The induced magnetization is always downward in the Northern Magnetic Hemisphere and produces a positive output no matter which end of the stake is driven into the ground.  The other type of field is the permanent magnetization that is fixed to the pin.  For maximum detection, the stake should be driven into the ground so that the permanent magnetization is in the same direction as the induced magnetization.

Checking a Stakes Orientation with Schonstedt's GA-72Cd

Checking a stake’s orientation

 

Locating Manholes, Septic Tanks, & Well Casings

 

The magnetic field is strongest at the edge of a shallow manhole cover.  You can easily trace the edges of covers near the surface.  The locating depth for manhole covers ranges up to 8 feet.

Detect Manhole Covers Under Pavement with Schonstedt GA-72Cd

Locating Manhole Covers

 

The great length of a well casing provides a strong field at the surface that makes it easy to locate casings buried up to 15 feet deep.

Find Buried Water Well Casings with Schonstedt GA-72Cd

Locating Water Well Casings

 

The GA-72Cd can precisely locate the metal handles, or reinforcing bars, on septic tank covers at depths up to 4 feet.

 

Schonstedt GA-72Cd detects buried septic tank metal handles

Signal Patterns Provided by Septic Tank Covers

 

 

Locating Objects under Snow or Water and Tracing Barbed Wire

 

The locator can be used in snow or in flooded areas – just keep the electronic unit out of the snow or water.

 

Schonstedt Magnetic Locators Find Iron Objects Under Snow or Water

Locating under snow or water

 

Locating and Tracing Barbed Wire

 

You can often trace barbed wire from old fence lines buried just beneath the surface.  Even if the wire is only a trail of rust, it can still be detected near the surface.  Tip the locator a little lower than usual (but not parallel with the ground).

 

Examine trees for benchmarks and bits of embedded barbed wire.  Then hold the locator parallel to the direction of the wire.

 

Tracing Barbed Wire From Old Fences with a Schonstedt GA-72Cd

Locating & Tracing Barbed Wire

 

Searching Areas along a Chain Link Fence

 

Searching in the vicinity of a chain link fence requires a reduced sensitivity setting and some control over the orientation of the locator.  As illustrated in the below graphic, position the locator horizontally with its long axis perpendicular to the fence.  This ensures that the upper sensor is kept away from the fence.

Perform the search by slowly moving the locator forward along the fence while also moving it to the right and to the left.  As you move forward, this technique will allow you to search an area several feet wide.  Listen for an abrupt drop in the signal that will occur when the lower sensor, located 1-5/8 inches from the end of the locator, is directly over the stake.  Any variation in the position of the locator will produce an abrupt rise in the frequency of the signal.

Searching for iron objects near a chain linked fence with a Schonstedt GA-72Cd

 

Locating Along a Chain Link Fence with a Schonstedt GA-72Cd

Placement of Locator while Searching along a Chain Link Fence

 

Locating Valve Boxes

 

Both the valve and its casing, when iron, provide strong magnetic fields that make them easy to locate.  Plastic enclosures containing magnets are easily located at depths of 6 feet or more.

Locating Valve Boxes and Casings with a Schonstedt GA-72Cd Magnetic Locator

 

Locating Cast-Iron Pipe Joints

 

Cast-iron pipes produce the strongest magnetic signals at their joints. The initial search should be performed as follows:

 

  1. Set the Sensitivity control for maximum (XH indication).
  2. Hold the locator vertically and approximately 1 to 1-1/2 feet above the surface.
  3. Walk without turning or tilting the locator.
  4. Mark the locations where the maximum signal levels occur.
  5. Return to an area of maximum signal strength and hold the locator several inches above the surface. The sensitivity will probably have to be reduced during this second pass.  Four-inch pipes can be located at depths up to 8 feet.

 

Find Cast-Iron Pipe Joints with a Schonstedt Magnetic Locator

 

 

 

Locating Steel Drums

 

The GA-72Cd’s signal pattern will vary depending on the vertical or horizontal orientation of the drum and how deep it is buried.  A 55 gallon drum can be located at depths up to 8 feet.

 

Find Buried Steel Drums with a Schonstedt Magnetic Locator

 

Locating Ordnance & Weapons

 

The versatile, lightweight, cost-effective GA-72Cd is designed to aid EOD technicians, UXO Deminers, and law enforcement officers during area search operations.

 

Locating Ammunition with a Schonstedt Magnetic Locator

 

 

  • A 175mm Projectile can be located up to 4 feet deep.
  • An 81mm Mortar can be located up to 12 inches deep.
  • MK81 Low Drag Bombs can be located up to 7 feet deep.
  • A hunting knife under water can be located in up to 16 inches of silt.
  • A discarded hand gun can be located up to 12 inches deep.

 

 

Additional Applications

 

  1. The military and many local and state police departments use the GA-72Cd to detect buried ordnance and discarded weapons.
  2. People drilling in an area where hazardous materials might be encountered should use the GA-72Cd to search the area prior to drilling.

 

 

Other Notes

 

  1. A burbling sound indicates the presence of an energized power line. This will not influence the meter indication unless associated with a magnetic structure.
  2. The instrument will not respond to non-ferrous metals such as gold, silver, copper, brass and aluminum.

Data Logger Output

The headset jack also provides an analog output signal for input to a data logger.  This +/-4 volt signal varies in proportion to signal strength and is accessible by wiring a standard stereo plug.

 

Stereo Plug Connections for Analog Output Signals

 

 

Maintenance

The GA-72Cd is designed and built to give trouble-free operation.  Normally, maintenance is limited to the occasional replacement of the batteries.  In the event a malfunction does occur, refer to the Troubleshooting Guide.

 

Replacement of Batteries

 

The GA-72Cd is powered by two 9-Volt lithium batteries that have a shelf life of ten years and provide twice the operating life of alkaline batteries.  Access to the batteries is obtained by loosening the four captive screws and removing the electronics cover. It is recommended that you purchase spare batteries for this unit.  When you use the spare batteries, replace them as soon as possible so that you will never be without batteries in the field.
CAUTION Schonstedt recommends lithium batteries in this unit.  Alkaline batteries produce magnetic fields that will impact performance of the locator (especially when set to the H or XH sensitivity range).

 

Sc

Exploded View of Electronic Unit Cover

 

 

Troubleshooting Guide

 

SymptomPossible CauseHow to CheckHow to Fix
DeadDead BatteriesReplace--
Batteries not making contactCheck for contact corrosionClean contacts
Battery LeakageRemoveReturn unit to factory for repair
IntermittentBatteries not making good contactCheck for corrosionClean contacts
Uncontrollable ScreamingWeak batteriesReplace--

Service & Repairs

If your locator needs service, please return it to the Schonstedt factory (in its case) and complete a Repair Form with the following information:

  • Name
  • Address
  • Telephone and Fax Numbers
  • Email Address
  • Where Purchased
  • Date of Purchase
  • Description of Problem(s)
  • If unit is out of warranty, an estimate will be provided prior to service work being done.

 

For Service or Repairs, Ship locator to: 

Schonstedt Instrument Company

100 Edmond Road

Kearneysville, WV 25430

 

Specifications

Audio OutputSwitch at “A” Signal increases or decreases in volume with gradient-field intensity
Switch at “B” Signal increases or decreases in frequency with gradient-field intensity.
Video OutputDigital readout and expanding bar graphs indicate polarity (+ or-) and relative
strength of the magnetic field.
Input PowerSupplied by two 9V batteries
Battery Life40 Hours (intermittent usage)
Battery Check4-segment LCD BATT indicator
OutputApproximately 40 Hz audio tone on speaker.
Tone frequency increases or decreases with gradient-field intensity.
WeightApproximately 2.5 lb (1.14 kg)
Operating Temp-13° to 140°F (-25° to 60°C)
Overall Length34.5" (87.6 cm)
Waterproof Length21" (53.3 cm)
Nominal Sensor Spacing14" (35.6 cm)
ConstructionRugged, all solid state, polycarbonate & ABS casing

 

This device complies with part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) this device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation.

 

Application of Council Directive(s):

2004/108/EC

Standard(s) to which Conformity is Declared:

EN 61000-6-1:2001, EN61000-4-2, EN61000-4-3, EN 61000-6-3:2004, EN55022:1998  with Amendment A1:2000 (CISPR-22)

Warranty

Schonstedt Instrument Company (Schonstedt) warrants each product of its manufacture to be free from defects in material and workmanship subject to the following terms and conditions.  The warranty is effective for 7 years* after the shipment by Schonstedt to the original purchaser.  Please complete the warranty registration card and send back to Schonstedt Instrument Company.

 

Schonstedt’s obligation under the warranty is limited to servicing or adjusting any product returned to the factory for this purpose and to replacing any defective part thereof. Such product must be returned by the original purchaser, transportation charges prepaid, with a description of the defect in writing. If the fault has been caused by misuse or abnormal conditions of operation, repairs will be billed. Specifically, this warranty does not cover product that has been subject to inundation by fire, water or other liquid intrusion, or units that have been damaged or compromised due to repair, alteration or modification by anyone other than an authorized repair representative.  Prior to a repair being performed by Schonstedt, a cost estimate will be submitted and no work will be completed until authorized by the customer. Batteries are specifically excluded under the warranty and should be addressed to the manufacturer of batteries in question.

 

Schonstedt shall not be liable for any injury to persons or property or for any other special or consequential damages sustained or expenses incurred by reason of the use of any Schonstedt product.

 

* For Military & EOD applications, the warranty is 1 year.

Parts Diagram

Schonstedt GA-72Cd Parts Diagram Exploded
Item #Part NumberDescription
1K20015Knob, Pointer
2K20013Knob, Round
3208306Battery Board Assembly
4208282Captive Screw (4 required)
5SS208195Tip, Crutch
6208345Potentiometer Assembly
7208323Gasket, Base
8302376LCD - Satellite Board Assembly
9302372Main Board Assembly
10208317Battery Chassis Assembly
11208348Cover & Handle Assembly
12Screws (2 required)
13H30006Headset (optional)
14302145Case, Carrying
159V Lithium Battery (2 required)
16208349Interface Cable Assembly
17208347Speaker Cable Assembly
18L55002-1Latch
19L55002-2Latch Keeper
20207220End Cap

Parts & Accessories

Parts and accessories are available on shop.schonstedt.com. Use the links below to visit the listing in our store. If you need help, please contact Customer Care.

Related FAQs

How do magnetic locators work?

Magnetic locating diagram with iron marker and illustration of the two magnetic fields from the locator that are bent by the iron marker.
Visit How Magnetic Locators Work for an illustrated introduction!

How do I search along a chain link fence?

Searching in the vicinity of a chain link fence requires a reduced sensitivity setting and some control over the orientation of the locator. Position the locator horizontally with its long axis perpendicular to the fence. This ensures that the upper sensor is kept away from the fence.

Figure 13: Searching in the vicinity of a chain link fenceSearching in the vicinity of a chain link fence

Perform the search by slowly moving the locator forward along the fence while also moving it to the right and to the left. As you move forward, this technique will allow you to search an area several feet wide. Listen for an abrupt drop in the signal that will occur when the lower sensor, located 1-5/8 inches from the end of the locator, is directly over the stake. Any variation in the position of the locator will produce an abrupt rise in the frequency of the signal.

Figure 14: Placement of Locator While Searching Along a Chain Link FencePlacement of Locator While Searching Along a Chain Link Fence

What are the differences among the GA-52Cx, GA-92XT and GA-72Cd?

The GA-52Cx is an easy to use, reliable, magnetic locator. The GA-72Cd is basically the same as the GA-52Cx but has an LCD meter display reflecting the relative signal strength and polarity of the magnetic field detected. The GA-92XT is a portable, retractable version of the GA-72Cd, providing one-handed operation and easily removable battery.

What is the difference between metal detectors and magnetic locators?

Magnetic locators find objects with ferrous or iron content. They do not react to other metals such as copper, brass, or aluminum, as metal detectors do. Therefore they are less subject to interference from surface debris. Magnetic locators work deeper, measuring a magnetic field originating from the buried target, whereas a metal detector can only detect shallow objects, typically 9 to 12″ inches maximum.

Schonstedt’s magnetic locator, Maggie, searches for subsurface objects.

What type of batteries does my magnetic locator use?

The GA-52Cx and GA-72Cd each operate on two 9-V batteries.

The GA-92 and Maggie each operate on one 9-V battery.

 

What’s the difference between Magnetic and Pipe & Cable locators?

Many Schonstedt locators look the same, but there’s a BIG difference in how they work and what they find underground. Visit our Whats the Big Difference? Pipe & Cable vs Magnetic page to learn more.

Will your magnetic locators find old coins, brass, gold and such?

No, our magnetic locators will only locate ferromagnetic metals (i.e. iron, steel). Coins, gold and brass do not contain ferromagnetic materials.

Disclaimer

Important notice

Schonstedt believes the statements contained herein to be accurate and reliable; however, their accuracy, reliability, or completeness is not guaranteed. Schonstedt's only obligation shall be to repair or replace any instrument proven to be defective within one year of purchase. Schonstedt shall not be responsible for any injury to persons or property, direct or consequential, arising from the use of any instrument.