GA-72Cd Manual
Contents
1. 14 in 35 6cm Rugged all solid state Schonstedt Instrument Company 17 LIMITED WARRANTY The 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 5 years with the return of the Customer Registration Card after the shipment by Schonstedt to the original purchaser 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 proof in writing to our satisfaction of the defect If the fault has been caused by misuse or abnormal conditions of operation repairs will be billed at cost Prior to repair in this instance a cost estimate will be submitted Service or shipping information will be furnished upon notification of the difficulty encountered Model and serial numbers must be supplied by user Batteries are specif ically excluded under the warranty 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 SERVICE OR REPAIR Please ship locator in its case to Schons2. 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 nega tive when the locator is directly over a ferromagnetic object As shown the cover must be removed to change the setting of the Audio Output Switch Figure 4 Location of Audio Output Switch Schonstedt Instrument Company 3 Search Procedure Set the On Off Sensitivity control for L and grasp the locator as illustrated Because the upper sensor 15 near the locator s handle wrist watches may produce unwanted changes in the audio signal and in the meter indications and should be removed Keep the locator away from your shoes since they might contain magnetic material To obtain maximum area coverage sweep the locator 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 as shown in Figure 6 Figure 5 Searching With the Locator 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 be either a positive or negative level Figure 6 The Meter 5 Polarity Indication
3. 2 9 9 v 4 V sj4nq Awday POZL VD 16 Schonstedt Instrument Company SERVICE INFORMATION If your locator needs service please return it to the factory along with the following information Name Address Telephone Fax number Where Purchased Date and Description of Trouble s An estimate will be provided prior to service work being done See shipping information on page 19 SPECIFICATIONS Specifications subject to change without notice Input Power Supplied by two lithium 9 V batteries Battery 60 Hours intermittent usage Output Audio Output Signal increases or decreases in volume SWitCh at coo ee Lr RE DER with gradient field intensity Output Signal increases or decreases in frequency Switch at with gradient field intensity Visual fas Geass ies Digital readout expanding bar graphs Indicate polarity positive or negative and Relative strength of the magnetic field Battery BATT 4 segment LCD Weights 2s uA p Approximately 2 5 Ibs 1 14 kg Operating Temperature 13 to 140 F 25 to 60 C Overall 34 5 in 87 6cm Waterproof Length 21 in 53 3cm Nominal Sensor Spacing
4. 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 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 Hold the locator parallel with the direction of the wire Schonstedt Instrument Company 8 Searching Areas Along a Chain Link Fence Figure 17 Searching in the Vicinity of a Chain Link Fence Figure 16 Tracing Barbed Wire from Old Fence Lines 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 horizon tally with its long axis perpendicular to the fence as illustrated in Figure 17 This insures 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 This technique allows you to search an area several feet wide as you move forward Listen for an abrupt drop in the signal as shown by the null in Figure 18 that will occur
5. 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 temper atures 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 IN BUUL 100 to 25 25 to 20 20 to 10 10 to 1 Figure 3 Battery Voltage Status Indications Schonstedt Instrument Company 2 Audio Output Selection All GA 72Cds are shipped from the factory with the Audio Output Switch set to B This provides an audio signal that is always present If you prefer not to 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 As you move the locator across the object frequency of the signal does not change but unit increases in volume over the object then decreases in volume and turns off when the locator is moved out of range NOTE Ifyou 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
6. not respond to nonmetallic materials such as gold silver copper brass and aluminum Schonstedt Instrument Company 13 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 as illustrated in Figure 23 Gnd Tone DC Out 4 V FS Figure 23 Stereo Plug Connections for Analog Output Signal 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 15 for a few problems that you can correct in the field Replacement of Batteries The GA 72Cd is powered by two 9 volt lithium batteries which 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 as shown in Figure 24 CAUTION Always use lithium batteries Alkaline batteries produce magnetic fields that will affect performance of the locator particularly when set to the H or XH sensitivity range The locator is shipped with a spare set of lithium batteries conveniently stored in the carrying case It is recommended that when you use the spare batteries replace them as soon as possible so that you wil
7. to be accu rate and reliable But their accuracy reliability or completeness is not guaranteed Schonstedt s only obligation shall be to repair or replace any instrument proved to be defective within five years of purchase Schonstedt shall not be responsible for any injury to persons or property direct or consequential arising from the use of any instrument Schonstedt Instrument Company OPERATION Introduction The Model GA 72Cd Magnetic Locator detects the magnetic field of ferromagnetic objects It responds to the difference in the magnetic field between two sensors which are spaced about 14 inches apart The GA 72Cd is unique because it provides an audio signal and visual indications of both signal strength and polarity Although most objects can be located using either of the indications simultaneous use of both types will help you pinpoint a target and determine its orientation and identify magnetically detectable nonmetallic duct and cable Figure 1 illustrates an application of the locator in which it is used to detect an iron marker of the type used for property line identifi cation 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 neg
8. vary depending on the vertical or horizontal orientation of the drum and also how deep it is buried A fifty five gallon drum can be located at depths up to 8 feet SIGNAL PATTERN FOR DRUMS BURIED APPROXIMATELY 4 TO 8 FEET or SIGNAL PATTERN FOR DRUMS BURIED APPROXIMATELY 4 FEET OR LESS Figure 21 Signal patterns provided by steel drums Locating Magnetized Nonmetallic Duct and Cable Schonstedt s patented technology for incorporating magnetic materials into nonmetallic duct and cable makes it easy to locate these objects at various depths as listed in Table A This technology also provides magnetic signatures consisting of positive and negative polarities that alternate at specific intervals Different intervals see Table A provide each of the three categories of duct and cable with a unique magnetic signature used for posi tive identification Magnetic signatures also help to distinguish nonmetallic duct and cable from cast iron or steel pipe Table A Magnetic Signatures and Detection Depths for Magnetized Metallic Duct and Cable Applications MAGNETIC SIGNATURE APPLICATION Meter alternates between positive and negative DETECTION DEPTH CATV duct cable Every 4 feet Up to 4 feet Telephone Every 6 feet Up to 5 feet Electrical duct Every 7 feet Up to 5 feet Sensitivity set to XH Schonstedt Instrument Company 11 As shown in Figure 22 a magnetized nonmetallic fiber optic cable is easi
9. 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 Preface The Model GA 72Cde Magnetic Locator is a product of over forty six years experience in producing the world S finest flux gate magne tometers and magnetic detectors for aerospace military and civilian applications The GA 72Cde incorporates the knowledge obtained from manufacturing under the most rigid quality control standards The heart of the GA 72Cda is its patented Schonstedt HeliFluxa magnetic field sensors These sensors acknowledged to be the world s finest make possible the unequalled performance of the locator February 2009 Schonstedt Instrument Company Table of Contents Operation Introducti b Rr ol eL estet nd bete ttt pd be Mie e ee td bts 1 Turn on Sensitivity and Volume Settings 2 Battery Level Indication cack eee ERR C Gh at E et See ee 2 Audio Selection ve ue RE eee A 3 Search Procedures source sl D cgo eed alode o o etc e Lus ti io mak eue eR 4 Application Notes Basic Signal Patterns 35 nS eo va Na V RICE etg den RO UE 4 Strongly Magretized Markets eoe eu RU eee S Se Ur ed ess ye Ee aee 6 Correct Stake Orientation is Important 1 0 0 ehm e s 7 Locating Manholes Septic Tank
10. ative direction when the audio signal is at its highest frequency arn R z Figure 1 Detecting Magnetic Field of an Iron Marker When shipped the locator is set to provide an audio signal which is heard as long as the instrument is turned on If desired you can change this to an audio signal which is heard only when the instrument is within detection range of an object by using the internal Audio Output Switch as described on page 4 of this manual Schonstedt Instrument Company 1 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 You can increase the sensitivity 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 ON OFF Sensitivity Levels Headset Jack also output for Data Logger Volume Control Magnetic Field Signal Strength Polarity in differential milli gauss Selected Sensitivity Battery Charge Level Indicator Indicator Negative Polarity Positive Polarity Expanding Bar Graph Expanding Bar Graph Figure 2 Control and Meter Indications Battery Level Indication The meter s BATT indication displays the batteries voltage level As shown in Figure 3 when all four segments are black the voltage level
11. es 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 which gives the largest reading is the one that should be used This reading would be positive in the Northern Hemisphere and nega tive 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 which is fixed to the pin For maximum detection the stake should be driven into the ground such that the permanent magnetization is in the same direction as the induced magnetization Locating Manholes Septic Tanks and 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 Locating depth ranges up to 8 feet 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 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 AUDIO SIGNAL Figure 14
12. l never be without batteries in the field Schonstedt Instrument Company 14 BATTERIES CAPTIVE SCREWS Figure 24 Exploded View of the Electronic Unit Cover Troubleshooting Guide Symptom Possible Cause How to Check cee No response Dead batteries Batteries not making contact Battery leakage Loose connector s Intermittent Batteries not making good contact Loose connector s Uncontrollable Weak batteries screaming Replace Check for contact corrosion Do not remove batteries Visually inspect Check for corrosion Visually inspect Replace Clean contacts Return unit to factory Reconnect Clean contacts Reconnect Most battery manufactures warranties cover the cost of repair or replacement of any device damaged by their batteries Removing batteries that leak will void their warranty Schonstedt Instrument Company 15 Assy e qe2 1exyeeds Assy 2 Aeyeg untur A6 9525 jeuondo 2 maS ssy 19409 s sseyo Assy pg ule Assy Pg HALS 007 oseg jexseo Assy di v Assy pg punoy qouy ON LuVd WALI Lv 80c 6v 802 SVLZOE 9000 H 00S29NIANS 9v 80c 9 4806 cLEZOE GLEZOE ZEROS SVE80 S6L802 86802 90 80 20027 910027 8
13. ly identified by the GA 72Cd s visual indication which changes from positive to negative every six feet along with the audio signal which also peaks every six feet VISUAL SIGNAL 0 _ 6 feet 6feet AUDIO SIGNAL 0 Figure 22 Magnetically Detectable Nonmetallic Cable Provides a Unique Magnetic Signature Locating Ordinance and Weapons The versatile lightweight cost effective GA 72Cd is also designed to aid EOD technicians and law enforcement officers during area search operations Basic signal patterns from vertical and horizontal targets help to determine target orientation A 175mm projectile can be located up to 5 feet deep Schonstedt Instrument Company 12 An 81mm mortar can be located up to 12 inches deep MK81 Low drag bombs can be located up to 9 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 People drilling in an area where hazardous materials might be encountered should use the GA 72Cd to search the area prior to drilling Other Schonstedt gradiometers are available that can be lowered down the drill hole for periodic checks as drilling progresses Other Notes 1 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
14. nsitivity setting before you get a shovel Any signal that disappears when the locator is held higher is prob ably coming from a shallow target The signal from a rusty bolt or other small item see Figure 9 decreases much faster with distance than the signal from a larger target such as a 18 inch length of 3 4 rebar which can be located at depths up to 7 feet Figure 9 Raising the Locator Eliminates Unwanted Signals Strongly Magnetized Markers A strongly magnetized marker at or near the surface provides a weaker indication on both sides of the marker that could be mistaken for the 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 peaks directly over the marker and then decreases at point C From C to D the signals increase and decrease again So if you do not move the locator completely across the marker you might assume that the weaker indication on either side of the marker is its location Figure 10 Signal Pattern from a Strongly Magnetized Marker The two weaker indications 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 of digital indications are produced at these points When Placing Stak
15. s Help to Determine Target Orientation The audio signal bar graph and digital indications peak over each end of a horizontal pipe One end is positive the other is negative This will help you to distinguish between two vertical pipes or one horizontal pipe Usually two vertical pipes buried in close prox imity will produce digital indications with the same polarity Schonstedt Instrument Company 4 APPLICATION NOTES Basic Signal Patterns Audio signal peaks Audio signal peaks over each end directly over vertical of a horizontal target Visual indica target Visual indications tions peak positive over one end also peak as either and negative over the other end polarity 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 target and over the ends of a horizontal target The X pattern is ideal for pinpointing small objects A 1 1 4 inch PK nail buried up to 8 inches can be located so precisely with this technique that it can be uncovered using a 1 2 inch star drill Figure 8 X Pattern provides Precision Locating If you are looking for a corner marker and detect two or three signals in the same general vicinity raise the locator several inches above the ground or reduce the se
16. s and Well Casings 0 7 Locating Objects under Snow or Water and Traced Barbed Wire 0 0 00 cc cece cette 8 Searching Areas along a Chain Link rn 9 Locating Valve BOXES o os be asl ide dee Ang edhe lade dig ee e naa act ee bay lg ed 10 Locating Cast Iron Pipes nce Reto pee A ae ee ak Se PA Ie ER Re 10 Loca ng Steel Dr rms s Se oet ed RII deed i vA 11 Locating Nonmetallic Duct and Cable 11 Locating Ordnance and ehh 12 Additional Applications chee eels Oa TUER ee ete td EE RAN ee Ce ES 13 Other NOLES oc voe Ur edm ee oi oie pee Geb aia Duct eek Majed ee Nala ht ot aie Neti eh ped 13 Data Logger Output since GA D e ed kas ee beg So ek Herr ER ERR 14 Maintenance Replacementof Batteries qoo RS Re ee ee ee eS d 14 Troubleshooting vdd ee eh NU ee eed 15 GA 72Cd Repair Parts ue A A eh RR ay ee ee ee a a 16 Service hiformation BS ol ARS bec em t a e te ace ete ut e d eee gh e o tn 17 Specifications ERIT GRACE ee atv ee care Gate De PS ene ee eae Gee UE CERTE SCAN e 17 Warranty Shipping Information 0 0 0 0 eee ene Hh 9 he eh e hrs 18 Important Notice Schonstedt believes the statements contained herein
17. tedt Instrument Company 100 Edmond Road Kearneysville WV 25430 Attn Customer Service Dept PATENTS Manufactured under one or more of the following Patents United States 4 163 877 4 258 320 4 803 773 4 839 624 5 097 211 5 136 245 5 138 761 5 239 290 Other United States and foreign patents pending Schonstedt Instrument Company 18
18. 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 SIGNAL NULL WITH LOCATOR AS SHOWN Figure 18 Placement of Locator while Searching along a Chain Link Fence Schonstedt Instrument Company Locating Valve Boxes Both the valve and its casing when iron provide strong magnetic fields which 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 1 11 5 FEET Figure 20 Signal Patterns Provided by Cast Iron Pipes The initial search should be performed as follows Set the Sensitivity control for maximum XH indication Hold the locator vertically approximately 1 to 1 1 2 feet above the surface Walk along 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 Four inch pipes can be located at depths up to 8 feet oes D Schonstedt Instrument Company 10 Locating Steel Drums As shown in Figure 21 the GA 72Cd s signal pattern will
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