Inside the Trimble X9: Deep Dive into Trimble X9 Auto-Calibration 9
Automatic Distance Calibration
TheElectronicDistanceMeasurement(EDM)isakeycomponenttotheperformanceofa3Dlaser
scanner.Ahigh-quality3DpointcloudisdependentontheEDMperformingconsistentlyand
reliablyoverextremeworkingconditions.IntheX9,Trimblehasintegratedproprietarytechnology
toguaranteeasurvey-grademeasurementperformanceforitscustomers.Oneofthechallengesto
addressistoguaranteearangeaccuracyoverthelifetimeoftheinstrument,atalltemperatures
andforalltargetreflectivity.Toachievethis,TrimblehasintegratedintoitsEDManinnovative
calibrationroutinethatiscarriedoutbeforeeveryscan.
TheX9EDMisbasedontheprincipleofpulsedtime-of-flight.Infigure5,weshowaschematic
representationoftheEDM.
Figure 5: Schematic of EDM
Thelaseristriggeredtosendahighpowerlaserpulse.Atthesametimea"Start"signalissentto
theTime-to-DigitalConverter(TDC)tostartthe"stopwatch."Thelaserpulsetravelstotheobjectto
bemeasuredatthespeedoflight.Asmallamountofthelaserpulseisreflectedofftheobjectand
travelsbackintothetelescopeandisdetectedbyaphotodetector.Thephotodetectormeasures
thesignallevelandsendsastopsignaltotheTDC,whichstopsthe"stopwatch,"andthe
time-of-flightofthelaserpulseismeasured.Thisisthenconvertedtoameasurementofdistance.
TheX9operatesbetweenalargetemperaturerangeof-20°Cto+50°C(-4°Fto+122°F).In
addition,ithasaverylargedynamicrange,meaningthatitcandetectbothveryweakandvery
strongopticalsignallevels.FortheX9tomeasureaccuratelytheabsolutedistance,itusesan
innovativeauto-calibrationtechnique.
