Instruction Manual

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GNAV540UserManual
7430‐0808‐01Rev.B
Page26
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NOTE:TheDelta‐Theta,Delta‐Vpacketisonlyrecommendedforuseincontinuousoutputmodeat5Hzorgreater.
Polledrequestsforthispacketwillproducevaluesaccumulatedsincethelastpollrequest;theyaresubjectto
overflow(datatypewraparound).
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IMUAdvancedSettings
TheIMUadvancedsettingsaredescribedinTable7below.AlloftheadvancedsettingsareaccessiblethruNAV‐
VIEW2.2undertheConfigurationMenu→UnitConfigurationsettings.ForinformationaboutusingNAV‐VIEW2.2,
referto
Chapter7.ConfiguringGNAV540withNAVVIEW2.2.
Table7IMUFunctionAdvancedSettings
Setting DefaultValue Comments
BaudRate 38,400 9600,19200,57600alsoavailable
PacketType S1 S2alsoavailable
PacketRate 100Hz
Thissetstherateatwhichtheselected
PacketTypepacketsareoutput.Ifpolled
modeisdesired,thenselectQuiet.IfQuietisselected,theunitwillonlysend
measurementpacketsinresponsetoGPcommands.
Orientation
See
Figure4on
page
24.
Toconfiguretheaxisorientation,selectthedesiredmeasurementforeachaxis:
NAV‐VIEW2.2willshowthecorrespondingimageoftheunit,soiteasyto
visualizethemodeofoperation.Referto
OrientationFieldonpage86forthe
twentyfourpossibleorientationsettings.Thedefaultsettingpointsthe
connectorAFT.
VerticalGyroscope(VG)Function
TheVerticalGyroscope(VG)FunctionprovidesdynamicrollandpitchmeasurementsinadditiontotheIMU
Functiondata.Thedynamicrollandpitchmeasurementsarestabilizedbyusingtheaccelerometersasalong‐term
gravityreference.TheVGFunctioncanalsooutputafreeintegratingyawanglemeasurementthatisnotstabilized
byamagnetometerorcompassheading.
Atafixed100Hzrate,theVGFunctioncontinuouslymaintainsboththedigitalIMUdataaswellasthedynamicroll
andpitchdata.Asshowninthesoftwareblockdiagram(
Figure2onpage23),aftertheSensorCalibrationblock,the
IMUdataispassedintoan
IntegrationtoOrientationblock.(IfusingexternalGPS,refertoFigure4onpage24.)The
IntegrationtoOrientationblockintegratesbodyframesensedangularratetoorientationatafixed100timesper
dsingul ealingwiththecosinerot
thmtop epropagation.
second.Forimprovedaccuracyandtoavoi aritieswhend ationmatrix,a
quaternionformulationisusedinthealgori rovideattitud
Alsoshowninthesoftwareblockdiagram(
Figure2,page23)theIntegrationtoOrientationblockreceivesdrift
correctionsfromthe
ExtendedKalmanFilterorDriftCorrectionModule.Ingeneral,ratesensorsandaccelerometers
sufferfrombiasdrift,misalignmenterrors,accelerationerrors(g‐sensitivity),nonlinearity(squareterms),andscale
factorerrors.
Thelargesterrorintheorientationpropagationisassociatedwiththeratesensorbiasterms.TheExtendedKalman
Filter(EKF)moduleprovidesanon‐the‐flycalibrationfordrifterrors,includingtheratesensorbias,byproviding
correctionstotheIntegrationtoOrientationblockandacharacterizationofthegyroscopebiasstate.IntheVG
Function,theinternallycomputedgravityreferencevectorprovidesareferencemeasurementfortheEKFwhenthe
unitisinquasi‐staticmotiontocorrectrollandpitchangledriftandtoestimatetheXandYgyroscoperatebias.
Becausethegravityvectorhasnohorizontalcomponent,theEKFhasnoabilitytoestimateeithertheyawangle
errorortheZgyroscoperatebias.