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1、148containingtheswitch,oranyothertrackcircuit.Thechartwas16.5"wide,andmovedat3"perhour.A200-footrollofpaperwouldlastamonth.Apencouldbeprovidedforeachofupto40OSsections.Thedispatcherdrewshortlinesbetweenthedotstomakeacompleterecord.Thiswasonlyarecord,andwasnotveryusefultothedispatche
2、rinhandlingtrains.Thedispatchersignedthetrainsheetwhengoingoffduty.Thedispatcheralsohadatelephone,withaloudspeakeror,lessconveniently,earphones,andcouldsignalatraincreworsignalmaintainertocallhimatatelephoneboxbydisplayingalightinitsvicinity,usuallyontherelaybox.Thiswasveryimportant
3、,sincetherewerenolongeranyoperatorsalongthelinetohandlemessages.Now,ofcourse,thishasbeenreplacedbycontinuouscontactbymeansofradio.Toallowcontrolacompleteoperatingdivisionof100milesormore,withperhapstwentycontrolpoints,somewayhadtobefoundtoeconomizeonwires,sinceonecouldnotusedirectwi
4、recontrol.Thiswasfirstdonewiththeone-wiresystem,thatmanagedeachcontrolpointwithonlyonewire.Themachineinourexampleusesthelatertwo-wiresystem,amodemcodedsystem,whereeachcontrolpointhadauniquecode,andcommandscouldbesenttoanyofthecontrolpoints,whileanycontrolpointcouldreportconditionsto
5、thedispatcher.Thismachine,obviously,wasmuchmoreconvenienttousethantheold,andprovidedmuchmoreinformation.WhenswitchesandsignalswereinthevicinityoftheCTCboard(asinmanysmallinstallations)theywerecontrolledbydirectwire,notcodedsignals.CTCwasoneoftheearliestusesofpulsecodinginelectronics
6、,whichisnowwidespread.ExercisestotheMaterialChoosethebestansweraccordingtothematerial.(1)Whichofthefollowingisnottrueaboutthelatertwo-wiresystem?A.ItwasamoderncodedsystemB.Withthelatertwo-wiresystem,eachcontrolpointhadauniquecode,andcommandscouldbesenttoanyofthecontrolpoints,whilean
7、ycontrolpointcouldreportconditionstothedispatcherC.Itwasmuchmoreconvenienttousethantheone-wiresystem,andprovidedmuchmoreinformationD.Allswitchesandsignalswerecontrolledbydirectwire,notcodedsignals(2)Theword"economize"inlastparagraphisclosestinmeaningtoA.savingB.scantyC.economyD.retr
8、ench(3)Thedispatche
