Owner's manual


ual
7430‐0131‐01Rev.F
Page30
NAV440UserMan
Setting DefaultValue 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theaccelerometer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.
NAV440Function
TheNAVFunctionsupportsallthefeaturesoftheIMU440,VG440andAHRS440functions.Inaddition,theNAV
functionprovidesaninternalGPSreceiver,whichincludessoftwarerunning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IMU440data.
Atafixed100Hzrate,theunitcontinuouslymaintainsthedigitalIMU440data;thedynamicroll,pitch,andheading
data;aswellasthenavigationdata.Asshownin
Figure2onpage21,aftertheSensorCalibrationblock,theIMU440
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positiondata,and
outputasacompletenavigationsolution.