实用电力英语PPT课件.ppt

实用电力英语 任惠华北电力大学电力工程系 保定 1 2 考试 分组5人一组自由分组 4月10日上课前提交分组结果开卷试题 翻译词汇 文章或若干段落 英译汉 评分 所有小组成员分数相同考试时间 4月10日发题 4月17日交卷 每小组交一份答案 要求提供答案的打印件和电子文档 文档中注明小组成员姓名班级 其他可以要求单独承担翻译 最多10名 电力系统通信基础 3 4 DigitalandAnalogCommunicationSystem Communicationsystemm t electricalsignalrepresentingmessagesm t electricalsignalsenttotheuser mprimet maybenotthesameasm t duetonoiseorsystemunlinearity 5 message words pictures voices valueofvoltage current Electricsignal representingmessage Signal sparameterschangeaccordingtomessage SineWave 正弦波 amplitude 幅值 frequency phaseoffset 相移 Pulsewave 脉冲波 amplitude period markspaceratio 占空比 marktime spacetimedutycycle hightime period 100 continuousmessage voices discretemessage words statusofcircuitbreakers Analogsignaldigitalsignal amplitude 6 Transmitter dealingwiththesourcem t formoreefficienttransmission Forexample signalprocessing analoglowpassfilter 低通滤波器 inanalogcommunicationsystemtorestrictthebandwidth 带宽 ofm t analog to digitalconverter 模数转换器 usedtotransmitananaloginformationthroughadigitalcommunicationsystem sourcecoding 信源编码 errorcorrectcoding 差错控制编码 tothedigitalwordtoachieveerrordetectionandcorrectioncausedbynoise channelcoding 信道编码 carrier 载波 circuits convertsthebasebandsignal 基带信号 intoafrequencybandsignal 频带信号 thatisappropriateforthetransmissionmedium 传输媒质 modulation 调制 anddemodulation 解调 7 Transmissionmedium channel twisted pairtelephonelines 双绞线coaxialcables 同轴电缆fiberopticcables 光纤wireless无线Noise naturalelectricaldisturbances e g lightning man madenoise e g electromagneticinterference 8 Definition aDigitalCommunicationSystemtransfersinformationfromadigitalsourcetothesink user anAnalogCommunicationSystemtransfersinformationfromananalogsourcetothesink Notes anelectronicdigitalcommunicationsystemcanalsotransmitanalogsourcetothesink 9 Generaldigitalcommunicationsystem Encoder includingsourcecodingandchannelcoding 10 ComparisonbetweenDigitalandAnalogCommunicationsystem AdvantagesofdigitalCommunication Inlong distancesystems noisedoesnotaccumulatefromrepeater 中继器 torepeater 11 Channel noise repeater 12 Errorscanbedetectedandcorrectedbytheuseofcoding 编码 Datafromvoice video anddatasourcesmaybemergedandtransmittedoveracommondigitaltransmissionsystem Privacyispreservedbyusingdataencryption 加密 Relativelyinexpensivedigitalcircuitsmaybeused Disadvantages Generally morebandwidth 带宽 isrequiredthanthatforanalogsystems Synchronization 同步 isrequired 13 CommunicationModes Simplex 单工 datacanbetransmittedinonedirectiononlyHalfduplex 半双工 twointerconnecteddevicescanexchangedatainbothdirectionalternately e g awalkie talkie 步话机 Duplex 全双工 fullduplex dataareexchangedbetweenthetwoconnecteddevicesinbothdirectionssimultaneously 14 15 InformationMeasure Whatisinformationexactly message information InformationisthevaluablepartamessagecontainsReadthefollowingsentences Tomorrow thesunwillrisefromtheEast Thephonewillringinthenextonehour ItwillsnowinHainanthiswinter 16 Howmanyinformationdoesamessagehave Definition TheSelf Informationofthemessagejisgivenbywhere Pjistheprobabilityoftransmittingthejthmessage IjiscalledSelf Informationofeventj 17 Theunitof I ifthebaseofthelogarithmis2 theunitsare bits 比特ifthebaseise theunitsare nats ifthebaseis10 theunitsare hartley 18 Communicationsystem sperformance RealiabilityEquipmentreliabilityDatatransmissionreliabilityAccuracyReal time 20 Equipmentreliability theprobabilitythatasystemwillperformitsintendedfunctionunderspecifiedconditionsduringaspecifiedperiodoftime Availability 可用率 thereferenceperiodoftimeincludesoperationtimeandcorrectiveandpreventivemaintenance 维修 time Ap MTBF MTBF MTTR where ApispredictedavailabilityMTBF mean time between failure 平均故障间隔时间 MTTR mean time to repair 修复的平均时间 includingadministrative transport andrepairtime 21 Datatransmissionreliability BitErrorRate 比特差错率 tovaluethequalityofcommunication Itisgivenby Accuracyoverallaccuracy 总准确度 istheoffsetbetweenthedatasourceanddatasinkthroughtransformandprocessing transformer analog to digitalconverter digital to analogconverter isgivenby offset 偏差 fullscale 满量程 22 Real time tobevaluedbyoveralltransmissiontime 总传输时间 Forexample fortele meteringortele indication itreferstotheperiodoftimefromaeventhappenedoravaluechangedatsubstationorpowerplanttothisinformationdisplayedonthescreenofoperator scomputer forimportantanaloginputs 3sforlessimportantanaloginputs 10sorlongerforstatus lessthan3s forcontroloradjustingcommand lessthan3s forothers suchasdispatchingplans logs minutesorlonger 23 Signalandspectra LineCodes Bipolarcode 双极性码 usingpositivepulseandnegativepulsetorepresentlogical1and0 Non Return to Zero NRZ 不归零码 signaldoesn tdroptozerobetweeneachpulse Return to Zero RZ 归零码 signaldropstozerobetweeneachpulse NRZBipolarcode RZBipolarcode 24 Unipolarcode 单极性码 usingpositivepulseandgroundedpulsetorepresentdigit1and0 Advantage easytocreate Disadvantage UnipolarcodewillcreateasignificantDC value whichisnotpossibletotransportaDC componentthroughlongwires Solution RZunipolarcodecouldbeusedtoreducetheDC component Orusingmodulationanddemodulationtechniques Thiscodeisusedintelecontrolsystem 25 AlternateMarkInversion 交替极性码 usingpositive negativeandgroundedpulsestorepresentlogicalvalues Logical0isrepresentedwithagroundedpulse andalogical1bypulsesofalternatingpolarity 26 Manchestercode 裂相码 27 SignalandSpectrum frequencyanalysis whitelightcanbebreakupbyaprismintothecolorsoftherainbow Spectrumisfirstusedtodescribethecontinuousbandsofcolorsproducedbyaprism Theanalysisoflightintocolorsisactuallyaformoffrequencyanalysis FourieranalysistoolsFourierseries Fouriertransform 28 spectrum isusedwhenreferringtothefrequencycontentofasignal Frequencyorspectrumanalysis theprocessofobtainingthespectrumofagivensignalusingthebasicmathematicaltools 29 30 Features Envelopehasashapeofsinx x Thespectrumofperiodsignaliscomposedofdiscretespectralcomponents Ckdecaystozerowhenf iszeroatmultiplesof1 31 Bandwidth Generally inengineeringdefinitions thebandwidthwouldbef2 f1 forbasebandwaveform f1isusuallytakentobezero andf2isthefirstnullintheenvelopeofthemagnitudespectrumalongthepositivefrequencyaxis So forthisperiodicrectangularwaveform BandwidthB 1 32 Channelsandnoise Whatisachannel Thepropagatingmediumorelectromagneticpathconnectingthetransmitterandreceiveriscalledthechannel Openwire seldomusednowadaystwistedPairCable 双绞线 Twoinsulatedwiresaretwistedaroundeachother andcombinedwithothersintoacable Twoforms UTP unshieldedTwistedPair STP shieldedtwistedpair 33 coaxialcables 同轴电缆 hasasinglecore withanouterconductoractingasashield 屏蔽 Thesignalistransmittedontheinnercore Theinnercoreandtheoutershieldareseparatedbyaninsulator normallyplastic Ithasalargerbandwidththantwistedcable usedintelevision radio andEthernetLANs 34 Theatmospheremicro wavesystem 微波 aradiosystemwhichusesveryhighfrequenciestosendandreceivedata Becauseofthehighfrequenciesinvolved stationsarelocatedabout30kilometersapartandinlineofsight 目视距离 microwavesystemsareusedinanumberofareas suchaslinkinglocalareanetworkstogetherbetweencampusbuildings sendingradiosignalsfromaradiostationtoitstransmittersite andthesendingofvideooraudiosignalsfromanoutsidesportseventbacktoaTVbroadcastingstudio 35 fiberopticcables 光纤 madefromfinestrandsofsilica glass coatedwithaplasticsheath 36 CommunicationsystemsEngineering OrganizationofthebookBeforeweembarkontheanalysisanddesignofcommunicationsystems weprovideabriefreviewofbasicfrequency domaincharacteristicsofsignalsandlinearsystemsinChapter2 EmphasisisplacedontheFourierseriesandtheFouriertransformrepresentationofsignalsandtheuseoftransformsinlinearsystemsanalysis