ultrasonic ranging in air.pdf

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1、ULTRASONICRANGINGINAIRG.E.RudashevskiiandA.A.GorbatovUDC534,321.9:531.71.083.7Oneofthemostimportantproblemsininstrumentationtechnologyistheremote,contactlessmeasurementofdistancesintheorderof0.2to10minair.Suchaproblemoccurs,forinstance,whenmeasuringtherelativethree-dimensionalpositionof

2、separatemachinemembersorstructuralunits.Interestingpossibilitiesforitssolutionareop-enedupbyutilizingultrasonicvibrationsasaninformationcarrier.Thephysicalpropertiesofair,inwhichthemea-surementsaremade,permitvibrationstobeemployedatfrequenciesupto500kHzfordistancesupto0.5mbe-tweenamembe

3、randthetransducer,orupto60kHzwhenrangingonobstacleslocatedatdistancesupto10m.Theproblemofmeasuringdistancesinairissomewhatdifferentfromotherproblemsintheapplicationoful-trasound.Althoughthepossibilityofusingacousticrangingforthispurposehasbeenknownforalongtime,andatfirstglanceappearsver

4、ysimple,neverthelessatthepresenttimethereareonlyarenal1numberofdevelopmentsusingthismethodthataresuitableforpracticalpurposes.Themaindifficultyhereisinprovidingareliableacous-ticthree-dimensionalcontactwiththetestobjectduringseverechangesintheair'scharacteristic.Practicallyallacousticar

5、rangementspresentlyknownforcheckingdistancesuseamethodofmeasuringthepropagationtimeforcertaininformationsamplesfromtheradiatortothereflectingmemberandback.Theunmodulatedacoustic(ultrasonic)vibrationsradiatedbyatransducerarenotinthemselvesasourceofin-formation.Inordertotransmitsomeinform

6、ationalcommunicationthatcanthenbeselectedatthereceivingendafterreflectionfromthetestmember,theradiatedvibrationsmustbemodulated.Inthiscasetheultrasonicvibra-tionsarethecarrieroftheinformationwhichliesinthemodulationsignal,i.e.,theyarethemeansforestablishingthespatialcontactbetweenthemea

7、suringinstrumentandtheobjectbeingmeasured.Thisconclusion,however,doesnotmeanthattheanalysisandselectionofparametersforthecarriervibrationsisofminorimportance.Onthecontrary,thefrequencyofthecarriervibrationsislinkedinaveryclosemannerwiththecodingmethodfortheinformationalcommunic