Instruction Manual

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7430‐0808‐01Rev.B
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GNAV540UserManual Page
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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GNAV540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GNAV540product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
Crossbowwebsite:
http://www.moog‐crossbow.com.
AdvancedSettings
TheGNAV540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,andcustomaxesconfiguration.
Theunit ds:
scanbeconfiguredviatwometho
• ation:
NAV‐VIEW2.2,aGUIapplic
• CLanguageProgramming:
Chapter7.ConfiguringGNAV540withNAVVIEW2.2
Chapter10.ProgrammingGuidelines.
IMUFunction
InertialMeasurementUnit(IMU)Functionprovidesinertialrateandaccelerationdataintheformsofchangesin
velocityandrotationangle(∆ѵand∆ф).TheIMUFunctionsignalprocessingchainconsistsofthe6‐DOFsensor
cluster,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IMUdata.The100HzIMUdataiscontinuouslybeingmaintainedinsidetheunit.Digital
IMUdataisoutputovertheRS‐422orEthernetlinkataselectablefixedrate(100,50,25,20,10,5or2Hz)oranon
requestbasisusingthe
GP(GetPacket)command.
ThedigitalIMUdataisavailableinoneofseveralmeasurementpacketformatsincludingScaledSensorData(S1
Packet)andDelta‐Theta,Delta‐V(S2Packet).IntheScaledSensorData(S1Packet)dataisoutputinscaled
engineeringunits.IntheDelta‐Theta,Delta‐Vformat(S2Packet)scaledsensordataisintegratedwithrespectto
thetimeofthelastoutputpacketandthedataisreportedinunitsofaccumulated(i.e.,delta)degreesand
meters/second.Forinformationaboutfullpackets,referto
Chapter9.CommunicatingwiththeGNA540Unitand
Chapter10.ProgrammingGuidelines.