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Preface
The GA‐72Cd Magnetic Locator is a product of over 60 years' experience in producing the world's
finest flux‐gate magnetometers and magnetic detectors for aerospace, military and civilian
applications. The GA‐72Cd incorporates the knowledge obtained from manufacturing under the
most rigid quality control standards. The heart of the GA‐72Cd is its patented Schonstedt
HeliFlux
magnetic field sensors. These sensors, acknowledged to be the world's finest, make
possible the unequalled performance of our locators.
June 2017
Instruction Manual
Model GA‐72Cd
Magnetic Locator
Manufactured By
Schonstedt Instrument Company
100 Edmond Road
Kearneysville, WV 25430
(304) 725‐1050
Fax (304) 725‐1095
Web: www.schonstedt.com
E‐mail: info@schonstedt.com
Made in USA
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Summary of Contents for Schonstedt Instrument GA-72Cd
- Page 1 Instruction Manual Model GA‐72Cd Magnetic Locator Manufactured By Schonstedt Instrument Company 100 Edmond Road Kearneysville, WV 25430 (304) 725‐1050 Fax (304) 725‐1095 Web: www.schonstedt.com E‐mail: info@schonstedt.com Made in USA Preface The GA‐72Cd Magnetic Locator is a product of over 60 years’ experience in producing the world’s finest flux‐gate magnetometers and magnetic detectors for aerospace, military and civilian applications. The GA‐72Cd incorporates the knowledge obtained from manufacturing under the ...
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Page 2: Table Of Contents
Table of Contents SECTION I: Operation Introduction .......................... 3 Turn‐on, Sensitivity and Volume Settings ................ 4 Battery Level Indication ...................... 4 Audio Output Selection ...................... 5 Search Procedure ........................ 6 SECTION II: Application Notes Basic Signal Patterns ........................ 7 Strongly Magnetized Markers .................... 8 Correct Stake Orientation is Important ................... 9 Locating Manholes, Septic Tanks and Well Casings .............. 9 Locating Objects under Snow or Water ................. 10 Locating and Tracing Barbed Wire .................. 11 ... -
Page 3: Section I: Operation
SECTION 1: OPERATION Introduction 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. Figure 1 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 ... -
Page 4: Turn-On, Sensitivity And Volume Settings
Turn‐On, Sensitivity and 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 ... -
Page 5: Audio Output Selection
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 ... -
Page 6: Search Procedure
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, wrist watches may produce unwanted changes in the audio signal and in the meter indications. Remove your wrist watch or hold the locator ... -
Page 7: Section Ii: Application Notes
APPLICATION NOTES Basic Signal Patterns Audio signal peaks Audio signal peaks over each end directly over vertical of a horizontal target. Visual indications targets. Visual indications peak positive over one end also peak as either and negative over the other end. polarity. + or ‐ + ‐ Figure 7: Signals from Vertical and Horizontal Targets 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, as shown in Figure 8, is ideal for pinpointing small objects. By using this ... -
Page 8: Strongly Magnetized Markers
+ or - + or - Figure 9: 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 Figure 10 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, ... -
Page 9: Locating Manholes, Septic Tanks And Well Casings
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 Figure 11. 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 ... -
Page 10: Locating Objects Under Snow Or Water
The GA‐72Cd can be used to precisely locate the metal handles or reinforcing bars on septic tank covers at depths up to 4 feet. + or - AUDIO SIGNAL + or - Figure 14: 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. Figure 15: Locating Objects under Snow or Water - 10 -... -
Page 11: Locating And Tracing Barbed Wire
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 bench marks and bits of embedded barbed wire. Then hold the locator parallel to the direction of the wire. Figure 16: Tracing Barbed Wire from Old Fence Lines 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 Figure 17, position the locator horizontally with its long axis perpendicular to the fence. This ensures that the upper sensor is ... -
Page 12: Locating Valve Boxes
SIGNAL NULL WITH LOCATOR AS SHOWN 1-5/8 Figure 18: 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. Figure 19: Locating Valve Boxes and Casings Locating Cast‐Iron Pipes As illustrated in Figure 20, cast‐iron pipes produce the strongest magnetic signals at their joints. ... -
Page 13: Locating Steel Drums
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. Locating Steel Drums As shown in Figure 21, 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 ... - Page 14 Figure 23: A 175mm Projectile can be located up to 4 feet deep. Figure 24: An 81mm Mortar can be located up to 12 inches deep. Figure 25: MK81 Low Drag Bombs can be located up to 7 feet deep. ...
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Page 15: Additional Applications
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. - 15 -... -
Page 16: Section Iii: Data Logger Output
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. Gnd Tone DC Out (+/‐ 4 V FS) Figure 28: Stereo Plug Connections for Analog Output Signal - 16 -... -
Page 17: Section Iv: Maintenance
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 on page 18. Replacement of Batteries The GA‐72Cd is powered by two 9‐Volt alkaline batteries. Access to the batteries is obtained by loosening the four captive screws and removing the electronics cover (as shown in Figure 29). It is recommended that you purchase spare batteries for this unit. When you use the spare batteries, ... -
Page 18: Troubleshooting Guide
Troubleshooting Guide Symptoms Possible Cause How to Check How to Fix Dead Dead Batteries Replace ‐‐‐‐‐‐‐‐ Batteries not making Check for contact Clean contacts contact corrosion Battery leakage Remove Return unit to factory Intermittent Batteries not making Check for corrosion Clean contacts good contact Uncontrollable Weak batteries Replace ‐‐‐‐‐‐‐‐ screaming ... -
Page 19: Section Vi: Specifications
SPECIFICATIONS (Specifications subject to change without notice) Input Power: ...... Supplied by two alkaline 9‐V batteries** Battery Life: ....... 40 Hours (intermittent usage) Output: Audio Output Option ... Signal increases or decreases in volume Switch at “A” with gradient‐field intensity Output Option ... Signal increases or decreases in frequency Switch at “B” with gradient‐field intensity Visual ....... Digital readout expanding bar graphs indicate polarity (positive or negative) and relative strength of the magnetic field ... - Page 20 LIMITED 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 ...
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Page 21: Section Viii: Repair Parts
GA‐72Cd Repair Parts Item No Part Number Description 1 K20015 Knob, Pointer 2 K20013 Knob, Round 3 208306 Battery Board Assy with Cable 4 208282 Captive Screw (4 Req’d) 5 SS208195 Tip, Crutch 6 208345 Potentiometer Assembly 7 208323 Gasket, Base 8 IC8511000487* LCD / Meter 9 S35080* Switch, On/Off/Sensitivity 10 208317 Battery Chassis Assembly 11 208348 Cover & Handle Assembly 12 SMVIN6C500W‐NP Screw, #6‐32 x ½” (2 Req’d) ...
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