Schonstedt Instrument GA-72Cd User manual

- 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:[e-mail]

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
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

- 2 -
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
SearchingAreasalongaChainLinkFence.............................................................................11
LocatingValveBoxes..............................................................................................................12
LocatingCast‐IronPipes.........................................................................................................12
LocatingSteelDrums.............................................................................................................13
LocatingOrdnanceandWeapons..........................................................................................13
AdditionalApplications..........................................................................................................15
OtherNotes...........................................................................................................................15

SECTIONIII:DataLoggerOutput..................................................................................................16

SECTIONIV:Maintenance
ReplacementofBatteries......................................................................................................17
TroubleshootingGuide..........................................................................................................18

SECTIONV:ServiceandShippingInformation.............................................................................18

SECTIONVI:Specifications...........................................................................................................19

SECTIONVII:WarrantyInformation.............................................................................................20

SECTIONVIII:RepairParts............................................................................................................21



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seven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.


- 3 -
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
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.

Figure1:DetectingMagneticFieldofanIronMarker

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(refertopage5ofthismanual
forinstructions).

- 4 -
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.


ON/OFFHeadsetJack
Sensitivity(alsooutputfor
LevelsDataLogger)


VolumeControl



MagneticFieldSignalStrength
Polarity(indifferentialmilligauss)

 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.Whenallfoursegmentsare
black,thevoltagelevelisbetween100%and25%(upto40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.

100 to 25% 25 to 20% 20 to 10% 10 to 1%

Figure3:BatteryVoltageStatusIndications

- 5 -
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.

AsshowninFigure4,thecovermustberemovedtochangethesettingoftheAudioOutput
Switch.
B
A

Figure4:LocationofAudioOutputSwitch

- 6 -
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.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.



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displayeitherapositiveora
negativelevel.
‐or+‐ +

AudioSignal

Figure6:TheMeter’sPolarityIndications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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.

- 7 -
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
technique,a1‐1/4inchPKnailburiedupto8inchescanbepreciselylocated.


Figure8:“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.

- 8 -
+ 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,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.




AudioSignal

BC
A00D
+or‐ +or‐ +or‐









IRONPIPE







Figure10:SignalPatternfromaStronglyMagnetizedMarker
IRONPIPE
+or‐

- 9 -
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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.


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.Thelocatingdepthformanholecovers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.


Figure12:LocatingManholeCoversFigure13:LocatingWaterWellCasings
Figure11: CheckingaStake’s
Orientation

- 10 -
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


- 11 -
Figure17: Searchinginthe
VicinityofaChainLinkFence
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
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(asshownbythenullinFigure18)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.

- 12 -
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.









+or‐ +or‐

1to1‐1/2Feet








Figure20:SignalPatternsProvidedbyCast‐IronPipes

- 13 -
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
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
+OR‐ +OR‐ +OR‐ +OR‐












Figure21:SignalPatternsProvidedbySteelDrums

LocatingOrdnanceandWeapons

Theversatile,lightweight,cost‐effectiveGA‐72Cdisalso
designedtoaidEODtechniciansandlawenforcement
officersduringareasearchoperations.



Figure22:BasicSignalPatternsfromVerticaland
HorizontalTargetsHelptoDetermineTargetOrientation

+or‐ + ‐

- 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.







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.



- 15 -
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.



- 16 -
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




- 17 -
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,replacethemassoonaspossiblesothatyouwillneverbewithoutbatteriesinthe
field.




Figure29:ExplodedViewoftheElectronicUnitCover


- 18 -
TroubleshootingGuide


SymptomsPossibleCauseHowtoCheckHowtoFix
DeadDeadBatteries

Batteriesnotmaking
contact

Batteryleakage
Replace

Checkforcontact
corrosion

Remove
‐‐‐‐‐‐‐‐

Cleancontacts


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,Address,TelephoneandFaxNumbers,EmailAddress,WherePurchased,Dateof
Purchase,andDescriptionofTrouble(s).Anestimatewillbeprovidedpriortoservicework
beingdone.Seeshippinginformationbelow:


FORSERVICEORREPAIR
Pleaseshiplocator(initscase)to:

SchonstedtInstrumentCompany
100EdmondRoad
Kearneysville,WV25430




- 19 -
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

BatteryCheck:...........................BATT4‐segmentLCD

Weight:......................................Approximately2.5lbs.(1.14kg)

OperatingTemperature:...........‐13°to140°F(‐25°to60°C)

OverallLength:..........................34.5in.(87.6cm)

WaterproofLength:...................21in.(53.3cm)

NominalSensorSpacing:...........14in.(35.6cm)

Construction:.............................Rugged,allsolidstate


**UnitspriortoSN:339698itisrecommendedtouseLithiumbatteries.UsingAlkalinebatteries
intheseunitswillproduceamagneticfieldthatwillimpactperformanceofthelocator
(especiallywhensettotheHorXHsensitivityrange).




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)


- 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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.