Owner's manual

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7430‐0131‐01Rev.F
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NAV440UserManual Page23
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TheaxesformanorthogonalSAEright‐handedcoordinatesystem.Accelerationispositivewhenitisoriented
towardsthepositivesideofthecoordinateaxis.Forexample,witha440Seriesunitsittingonaleveltable,itwill
measurezerogalongthexandy‐axesand‐1galongthez‐axis.NormalForceaccelerationisdirectedupward,
whichwouldbedefinedasnegativeforthe440Seriesz‐axis.
Theangularratesensorsarealignedwiththesameaxes.Theratesensorsmeasureangularrotationratearounda
givenaxis.Theratemeasurementsarelabeledbytheappropriateaxis.Thedirectionofapositiverotationis
definedbytheright‐handrule.
Withthethumbofyourrighthandpointingalongtheaxisinapositivedirection,yourfingerscurlaroundinthe
positiverotationdirection.Forexample,ifthe440Seriesunitissittingonalevelsurfaceandyourotateitclockwise
onthatsurface,thiswillbeapositiverotationaroundthez‐axis.Thexandy‐axisratesensorswouldmeasurezero
angularrates,andthez‐axissensorwouldmeasureapositiveangularrate.
Themagneticsensorsarealignedwiththesameaxesdefinitionsandsignasthelinearaccelerometers.Forexample,
whenorientedtowardsmagneticNorth,youwillreadapproximately+0.25GaussalongX,0.0GaussalongY,and
+0.35GaussalongZdirection(NorthAmerica).Magneticvaluesatothergeographiclocationsareavailableat
http://www.ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml.
Pitchisdefinedpositiveforapositiverotationaroundthey‐axis(pitchup).Rollisdefinedaspositiveforapositive
rotationaroundthex‐axis(rollright).Yawisdefinedaspositiveforapositiverotationaroundthez‐axis(turn
right).TheanglesaredefinedasstandardEuleranglesusinga3‐2‐1system.Torotatefromthebodyframetoan
earth‐levelframe,rollfirst,thenpitch,andthenyaw.
ThepositionoutputfromGPSisrepresentedinLatitude,Longitude,andAltitude(LLA)conventionontheWGS84
Ellipsoid.Thisisthemostcommonlyusedsphericalcoordinatesystem.TheGPSvelocityisdefinedinNorth,East
andDownreferenceframe,whichcanbeconvertedtotheCartesiancoordinatesystem:Earth‐Centered,Earth‐Fixed
(ECEF).ECEFusesthree‐dimensionalXYZcoordinates(inmeters)todescribethelocationofaGPSuserorsatellite.
Severalonlineresourcesareavailabletohelpuserswiththistransformation.Applicationnotesareavailableonthe
MoogCrossbowwebsite:
http://www.moog‐crossbow.com.
AdvancedSettings
The440SeriesInertialSystemshaveanumberofadvancedsettingsthatcanbechanged.Thespecificsettings
availablevaryfromunittounit,andadetaileddescriptionofeachunitisfoundinthesubsequentsectionsofthis
manual.Allunitssupportbaudrate,power‐upoutputpackettype,outputrate,sensorlowpassfiltering,and
customa beconfiguredviatwomethods:
xesconfiguration.Theunitscan
• application,(
NAV‐VIEW2.2,aGUI
• Programcommands,
Chapter7.Configuringthe440SerieswithNAV‐VIEW2.2)
Chapter10.ProgrammingGuidelines)
IMU440Function
IMU440(InertialMeasurementUnit)providestheinertialmeasurementunitfunctionalitythattheunitprovidesby
outputtinginertialrateandaccelerationdatain6‐DOF(sixdegreesoffreedom).TheIMU440signalprocessingchain
consistsofthe6‐DOFsensorcluster,programmablelow‐passfilters,analogtodigitalconversion,andtheDSPsignal
processorforsensorerrorcompensation.Therateandaccelerationanalogsensorsignalsaresampledand
convertedtodigitaldataat1kHz.
Thesensordataisfilteredanddown‐sampledto100HzbytheDSPusingFIR(finiteimpulseresponse)filters.The
factorycalibrationdata,storedinEEPROM,isusedbytheDSPtoremovetemperaturebias,misalignment,scale
factorerrors,andnon‐linearitiesfromthesensordata.Additionallyanyadvancedusersettingssuchasaxes
rotationareappliedtotheIMU440data.The100HzIMU440dataiscontinuouslybeingmaintainedinsidetheunit.