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.
Table of Contents SECTION I: Operation Introduction ............................................................................................................................. 3 Turn‐on, Sensitivity and Volume Settings ................................................................................ 4 Battery Level Indication ........................................................................................................... 4 Audio Output Selection...................................................
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.
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 audio output level.
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.
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 in the other hand. Keep the locator away from your shoes; shoes may contain magnetic material. To obtain the maximum area of coverage, the locator should be swept from side to side.
APPLICATION NOTES Basic Signal Patterns Audio signal peaks directly over vertical targets. Visual indications also peak as either polarity. Audio signal peaks over each end of a horizontal target. Visual indications peak positive over one end and negative over the other end.
+ 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.
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 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.
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.
+ 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.
The initial search should be performed as follows: 1. 2. 3. 4. 5. Set the Sensitivity control for maximum (XH indication). Hold the locator vertically and approximately 1 to 1‐1/2 feet above the surface. Walk without turning or tilting the locator. Mark the locations where the maximum signal levels occur. 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.
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. Figure 26: A hunting knife under water can be located in up to 16 inches of silt. Figure 27: 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.
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.
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).
Troubleshooting Guide Symptoms Dead Possible Cause How to Check How to Fix Dead Batteries Replace ‐‐‐‐‐‐‐‐ Batteries not making contact Check for contact corrosion Clean contacts Battery leakage Remove Return unit to factory Intermittent Batteries not making good contact Check for corrosion Clean contacts Uncontrollable screaming Weak batteries Replace ‐‐‐‐‐‐‐‐ SERVICE INFORMATION If your locator needs service, please return it to the factory with the following information: Name, Addre
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 ...............................
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.
GA‐72Cd Repair Parts Item No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Part Number K20015 K20013 208306 208282 SS208195 208345 208323 IC8511000487* S35080* 208317 208348 SMVIN6C500W‐NP H30006 302145 B11013 208349 B15002* L55002‐1 L55002‐2 207220 J10014* Description Knob, Pointer Knob, Round Battery Board Assy with Cable Captive Screw (4 Req’d) Tip, Crutch Potentiometer Assembly Gasket, Base LCD / Meter Switch, On/Off/Sensitivity Battery Chassis Assembly Cover & Handle Assembly Screw, #6‐32 x
