測繪工程專業(yè)英語：Section 4 Electronic Theodolites

Section4ElectronicTheodolitesAutomaticrecordingofcirclereadingsTheautomaticrecordingofcirclereadingshasreceivedmuchattentionovertheyears.OneoftheearliestdevelopmentswastheintroductionbyAskaniaoftheirPrecisionTheodoliteTpr,afterGigas,whosecirclereadingscouldbeobtaineddirectlyto0.2secondeithervisuallyorphotographically.Howeverinthelattercasethereadingswereobtainedfollowingasecondstepinwhichanaccessoryknownasafilmreaderwasused.Thus,althoughbookingerrorstendedtobeeliminated,thewholeoperationwasnotautomaticinsofarastheprovisionofthefielddatawasconcerned.Codetheodoliteswerethendevelopedbycertainmanufacturers,i.e.Fennel’sFLTinstrument,andtheseweresuchthatthefieldmeasurementscouldbeprocesseddirectlyviathecomputer.Thecirclereadingswereobtainedinacodedformonfilmwhich,afterprocessing,waspassedtoanelectronicconverterinwhichtherecordeddatawastransferredintoafive-channelpunched-tapecode.This,inturn,wasfedintoacomputerfortheevaluationoftherequiredinformation,includingcoordinates.Developmentsinelectronicshaveallowedthephotographystagetobeeliminated,andvarioussystemsof'electrical'readouthavebeenintroduced.Twoofthesearereviewedbrieflyintheremainderofthissection.FirstlythereistheSokkishasystemofembodyingmagneticallygraduatedcircleswithinthetheodolite.Eachofthetwomaincirclesisessentiallyadrum,madeofnon-magneticmaterial,uponwhichamagneticcoatinghasbeenapplied.Awavepatternismagnetizedontothiscoatingbyarecordingheadandwhenanangularmeasurementisbeingmadethewavepatternisscrutinizedbyanumberofmagneticheadsseparatedathalfthemagnetizedwavelength.Theseheadsestablishphasedifferencewithrespecttothemagnetizedgraduationsandthisisdulyconvertedintoangularmeasurement.Resetkeys,providedinthecontrolunit,areusedtozerothecirclesandtheangularmeasurementsarereferredtothesesettings,readingsbeingdisplayeddigitally,recordedonmagnetictapeorsenton-linetoacomputer.ThesecondsystemisbasedontheMoirephenomenon,andisusedforinstanceintheKernElectronicTheodoliteandintheWildTachymat.Essentiallytwogratingshavetobeformedsothattheycancreateinterferencefringes.Eachmaincircleisgraduated(butnotcodedornumbered)soastoformonegrating,thespacesbetweenthelinesbeingequaltothewidthsofthelines.IntheKerninstrumentasectionof200lines,enlarged1.01times,isprojectedontothediametricallyoppositesectiontherebyproducingthetwogratings,whilstintheWildinstrumenttwosensorsaremountedindiametricallyopposedpositions,eachincludingananalyzergrating.Asthetelescopepointingchangestheinterferencefringesmoveandthecirclereadingscanbeestablished,(i)coarselybycountingthenumberofMoireperiods,and(ii)finelybyaninterpolationprocedure,Fig.1showstheprinciplesoftheKernsysteminwhichfourlight-sensitivediodescoveradistanceequaltothree-quartersoftheMoireperiodwhichisassumedtohaveasine-waveform.Thepositionofthebrightfieldsorthedarkfieldsrelativetoareadoutwindowisameasurefortherelativepositioningofapairofdiametricallyopposedgraduationlineswhendecidingthefinereadings,whilstthecoarsereadingsarederivedbycountingthenumberofperiodspassingaspecificspotatthatwindow.AsintheSokkishainstrument,anglemeasuringsystemsareincrementalandvisualdisplaysarepresented,butrecordingunitscanbeattachedtoboththeKernandWildinstruments.Althoughemphasishasbeengiveninearliersectionsontheuseoffieldbooksfortherecordingofsurveydetails,othermethodsofdocumentationareavailable,i.e.theobservercouldbeinradiocontactwitharecorderorhecouldrecordthedetailsonsoundtape.Inadditiondatastacks(datarecorders)suchastheM50PortableMicroterminal,manufacturedbyUCSLMicrosystemsofBerkhamsted,canbeoperatedmanually.Amicroprocessorandinternalprogrammemoryareimportantfeaturesofsuchdevices,sincetheymakethedatastackprogrammabletosatisfyrequirements.HavingdefinedthetypeofinstrumentbeingusedtheobserverispromptedbymessagesonthedisplayscreenoftheM50toenterhisfieldmeasurementsinanappropriatesequence.Thedevicecanbecoupledtoacomputereitherdirectlyorbyatelephonelink.NewWordsandExpressionstheodolite：經(jīng)緯儀automaticrecording：自動記錄circle：圓，圓周，圓圈；度盤；軌道；循環(huán)，周期；范圍；旋轉(zhuǎn)；作圓周運動reading：讀，讀出，讀數(shù)circlereading：度盤讀數(shù)visually：在視覺上地，真實地，可視化地photographically：攝影地accessory：附件，零件filmreader：縮微膠片閱讀器bookingerror：記錄誤差Codetheodolite：編碼經(jīng)緯儀fieldmeasurement：實地測量，實測via：經(jīng)，通過，經(jīng)由codedform：編碼格式converter：變換器，轉(zhuǎn)換器，轉(zhuǎn)繪器，變頻器punched-tape：穿孔紙帶inturn：依次feedinto：輸入coordinate：坐標；坐標的；協(xié)調(diào)的electronics：電子學review：回顧，復習embody：包含，收錄，使具體化，具體表達graduatedcircle：度盤，刻度盤drum：鼓，圓鼓，滾筒；磁鼓；測微鼓coating：涂布，涂層，加膜wavepattern：波形，波圖magnetize：使磁化，吸引angularmeasurement：量角，測角scrutinize：細察wavelength：波長phasedifference：相位差duly：適時地convertinto：轉(zhuǎn)換成magnetictape：磁帶on-line：在線的，即時的forinstance：例如grating：格子，光柵，點陣；晶格interferencefringe：干涉條紋graduate：刻度，分度；分級，校準；量筒，量杯project：投影，投射；設計；計劃，方案；工程，項目；發(fā)射diametrically：作為直徑地，直接地interpolation：內(nèi)插