Instruction Manual




GNAV540UserManual
7430‐0808‐01Rev.B
Page31

Setting DefaultValue Comments
RestartOn
OverRange
OFF
Thissettingforcesanalgorithmresetwhenasensoroverrangeoccurs,i.e.,a
rotationalrateonanyofthethreeaxesexceedsthemaximumrange.Thedefault
settingisOFF.Algorithmresetreturnstheunittoahighgainstate,wherethe
ack
unitrapidlyestimatesthegyroscopebiasandusestheaccelerometerfeedb
heavily.
Thissettingisrecommendedwhenthesourceofover‐rangeislikelytobe
sustainedandpotentiallymuchgreaterthantheratesensoroperatinglimit.
Largeandsustainedangularrateover‐rangesresultinunrecoverableerrorsin
rollandpitchoutputs.AnunrecoverableerrorisonewheretheEKFcannot
stabilizetheresultingrollandpitchreading.
Iftheover‐rangesareexpectedtobeofshortduration(<1sec)andamodest
percentageoverthemaximumoperatingrange,itisrecommendedthatthe
restartonoverrangesettingbeturnedoff.Handlingofaninertialratesensor
over‐rangeiscontrolledusingtherestartOnOverRangeswitch.Ifthisswitchis
off,thesystemwillflagtheoverRangestatusflagandcontinuetooperatethrough
it.Ifthisswitchison,thesystemwillflagamasterFailerrorduringanover‐range

conditionandcontinuetooperatewiththisflaguntilaquasi‐staticconditionis
mettoallowforanalgorithmrestart.
Thequasi‐staticconditionrequiredisthattheabsolutevalueofeachlow‐pass
ratesensorfallsbelow3deg/sectobegininitialization.Thesystemwillthen
attemptanormalalgorithmstart.
Dynamic
Motion
ON
ThedefaultsettingisON.Turningoffthedynamicmotionsettingresultsina
highergainstatethatusestheaccelerometerfeedbackheavily.Duringperiodsof
doff
timewhenthereisknownlowdynamicacceleration,thisswitchcanbeturne
toallowtheattitudeestimatetoquicklystabilize.
TurnSwitch
threshold
0.5deg/sec
Withrespecttocentripetalorfalsegravityforcesfromturningdynamics(or
coordinatedturn),theunitmonitorstheyaw‐rate.Iftheyawrateexceedsagiven
TurnSwitchthreshold,thefeedbackgainsfromtheaccelerometersignalsfor
attitudecorrectionarereducedbecausetheyarelikelycorrupted.

NAVFunction
TheNAVFunctionsupportsallthefeaturesoftheIMU,VGandAHRSfunctions.Inaddition,theNAVfunction
integratesthesensorinformationfromaninternalorexternalGPSreceiver,andrunsinternalsoftwareontheDSP
processorforcomputingnavigationandorientationinformation.Inthisfunction,theunitoutputsGPSinformation
(Latitude,Longitude,andAltitude),inertial‐aided3‐axisvelocityinformation,aswellasheading,roll,andpitch
measurementsinadditiontodigitalIMUdata.
Atafixed100Hzrate,theunitcontinuouslymaintainsthefollowing:digitalIMUdatathedynamicroll,pitch,and
headingdata,aswellasthenavigationdata.Asshownin
Figure2onpage23,aftertheSensorCalibrationblock,the
IMUdataispassedintoanIntegrationtoOrientationblock.TheIntegrationtoOrientationblockintegratesbody
framesensedangularratetoorientationatafixed100timespersecond.Forimprovedaccuracyandtoavoid
singularitieswhendealingwiththecosinerotationmatrix,aquaternionformulationisusedinthealgorithmto
provideattitudepropagation.Followingtheintegrationtoorientationblock,thebodyframeaccelerometersignals
arerotatedintotheNEDlevelframeandareintegratedtovelocity.Atthispoint,thedataisblendedwithGPS
,andou
positiondata tputasacompletenavigationsolution.
Asshownin
Figure2onpage23,theIntegrationtoOrientationandtheIntegrationtoVelocitysignalprocessing
blocksreceivedriftcorrectionsfromtheExtendedKalmanFilter(EKF)driftcorrectionmodule.Thedriftcorrection