Instruction Manual




7430‐0808‐01Rev.B
GNAV540UserManual Page39

Chapter4. MagnetometerCalibrationandAlignmentGuidelines
Thischa ingandaligningamagnetometerwiththeGNAV540unit.pterprovidesgeneralguidelinesforcalibrat
•
CompensationforMagneticFields,page39
•
MagnetometerAlignmentUsingNAV‐VIEW2.2
• Code
,page39
MagnetometerAlignmentUsing ,page40
• InstallationGuidelines,page40
Thissectionprovidesguidelinestocalibrateandalignthemagnetometer.Thisinformationapplieswhen
implem
entingAHRSFunctionorNAVFunction(
AHRSFunctiononpage29,NAVFunctiononpage31).
NOTE:Foreffectivecalibrationresults,theGNAV540unitmustbeinstalledinthesystemduringthealignment
process.Thisalsoappliestoanexternalmagnetometer.Ifcalibratedoutsideofthesystem,themagnetismof
thesystemwillnotbemeasured.Withoutthosevalues,theGNAV540willnotbeabletocompensatemagnetic
readings:eitherheadingreadingswillbeincorrectorerrormessageswillbedisplayed.
CompensationforMagneticFields
Magneticsensorsmeasuremagneticfieldswhicharethenusedtocomputeheading.Acorrectheadingangleisbased
onlyontheearth’smagneticfield.However,themagneticfieldsoftheGNAV540unitandthesurroundings(suchas
thesystem/vehicleinwhichtheunitisinstalled)arealsomeasured,whichaffectthemagneticreading.To
compensateforthesemagneticfieldsandensureaccurateheadingreadings,theGNAV540unitmustbecalibrated.
TheGNAV540unitcompensatesfortheextramagneticfield(s)bytakingaseriesofmeasurementsandthen
applyingthosemeasurementstoatwo‐dimensionalalgorithm.Thealgorithmisusedtocalculatethehardironand
softironeffects,thevaluesofwhicharethenstoredasconstantsintheEEPROMoftheunit.Thoseconstantsare
usedforcorrectingthemagneticreadings,ensuringaccurateheadingoutput.Hardironeffectsareshiftsinthe
magneticfieldfromferrousobjectsorothermagneticmaterialintheproximityofthemagneticsensor.Softiron
effectsarethechangeofdirectionofamagneticfield;thischangeiscausedbyhardironontheinputdirection.Hard
nmagneticfieldsaretemporary:softironcanbemagnetized
ngoperation.
ironmagneticfieldsarepermanentwhereassoftiro
andthendemagnetized,orhavevaryingeffectsduri
Follo in
w gisanoverviewofthecalibrationprocess:
1. InstalltheGNAV540inthesysteminwhichitwillbeused
2. Ifanexternalmagnetometerisused,installthatdeviceinthesystem
neticinterference
3. Selectanappropriatetestlocation,freeofmag

4. Runthecalibrationandalignmentprocedure
5. SetthecalibrationreadingsintheGNAV540

NOTE:Ensurethetestlocationisappropriateformagneticcalibration.Thecalibrationprocessprovidescorrections
formagneticfieldsfromfixedlocationsthatarerelativetothepositionoftheunit.Thecalibrationdoesnot
compensatefortimevaryingfields,orfieldscreatedbymagneticmaterialthatmovesrelativetothe
GNAV540unit.
MagnetometerAlignmentUsingNAV‐VIEW2.2
Duringthecalibrationprocedure,theunitmakesaseriesofmeasurementswhiletheusersystemisbeingturned
throughacomplete360degreecircle.A360degreerotationgivestheunitvisibilitytohardandsoftirondistortion