《电子信息类专业英语》课件-第7章

Unit7ElectronicInstrumentIntroduction科技英语中各种数、符号的表达(二)

Therearemanykindsofelectronicinstruments,theleadingpurposeistomeasurevariousphysicalquantitiessuchascurrent,voltage,resistance,temperature,soundlevel,pressure,etc.

Mostinstrumentsaredelicate,sensitivedevicesandshouldbetreatedwithcare.Beforeusinganinstrumentoneshouldbethoroughlyfamiliarwithitsoperation.Thebestsourceofinformationaboutaninstrumentistheoperatingandinstructionsmanual,whichisprovidedwithanynewinstrumentpurchased.Ifyouarenotthoroughlyfamiliarwithaninstrument’soperation,specifications,functions,andlimitations,readthemanualbeforeusingtheinstrument.

1. Oscilloscope

Anoscilloscopecanpresentanaccurateelectronicpictureofthechangingvoltageswithinacircuit.Ithasbothadvantageanddisadvantagewhenusedtomeasurevoltage(orcurrent).Themostobviousadvantageisthattheoscilloscopeshowswaveform,frequencyandphasesimultaneouslywiththeamplitudeofthevoltage(orcurrent)beingmeasured.TheVOMorelectronicvoltmetershowsonlyamplitude.Likewise,mostmetersarecalibratedinrelationtosinewaves.Whenthesignalsbeingmeasuredcontainsignificantharmonics,thecalibrationsareinaccurate.Withtheoscilloscope,thevoltageismeasuredfromthedisplayedwave,whichincludesanyharmoniccontent.

Theonlymajordisadvantageofusinganoscilloscopeforvoltage(orcurrent)measurementistheproblemofresolution.ThescalesofsimpleinexpensiveVOMsorelectronicvoltmetersareeasiertoreadthananoscilloscope.Inmostcases,theoscilloscope’sverticalscalesareusedforvoltage(orcurrent)measurements,witheachscaledivisionrepresentingagivenvalueofvoltage(orcurrent).Whenvoltagesarelarge,itisdifficulttointerpolatebetweendivisions.

Theamplitudeofavoltagewaveformonanoscilloscopescreencanbedeterminedbycountingthenumberofcentimeters(cm),vertically,fromonepeaktotheotherpeakofthewaveformandmultiplyingitbythesettingofthevolts/cmcontrol.Asanexample,iftheamplitudewas4cmandthecontrolwasseton1V/cm,thepeak-to-peakvoltagewouldbe4V.Usuallythepeak-to-peakvalueisrequiredtobeconvertedtoRMS,becausemostvoltagesspecifiedinelectronicmaintenanceandtroubleshootingmanualsareRMS.

Tosumup,iftheonlyvalueofinterestisvoltageamplitude,usethemeterbecauseofitssimplicityinreadout.Usetheoscilloscopewhenwaveshapecharacteristicsareofequalimportancetoamplitude.

2. Multimeter

Amultimeterisageneral-purposemetercapableofmeasuringDCandACvoltage,current,resistance,andinsomecases,decibels.Therearetwotypesofmeters:analog,usingastandardmetermovementwithaneedle,anddigital,withanelectronicnumericaldisplay.Bothtypesofmetershaveapositive(+)jackandacommonjack(-)forthetestleads,afunctionswitchtoselectDCvoltage,ACvoltage,DCcurrent,ACcurrent,orohmsandarangeswitchforaccuratereadings.Themetersmayalsohaveotherjackstomeasureextendedrangesofvoltage(1-5kv)andcurrent(upto10A).Therearesomevariationstothefunctionsusedforspecificmeters.

Theanalogmeterusuallyincludesthefunctionandrangeswitchesinasingleswitch.Itmayalsohaveapolarityswitchtofacilitatereversingthetestleads.Theneedlewillhaveascrewformechanicaladjusttosetittozeroandalsoazeroadjustcontroltocompensateforweakeningbatterieswhenmeasuringresistance.Ananalogmetercanreadpositiveandnegativevoltagebysimplyreversingthetestleadsormovingthepolarityswitch.Adigitalmeterusuallyhasanautomaticindicatorforpolarityonitsdisplay.

Metersmustbeproperlyconnectedtoacircuittoensureacorrectreading.Avoltmeterisalwaysplacedacross(inparallel)thecircuitorcomponenttobemeasured.Whenmeasuringcurrent,thecircuitmustbeopenedandthemeterinsertedinserieswiththecircuitorcomponenttobemeasured.Whenmeasuringtheresistanceofacomponentinacircuit,thevoltagetothecircuitmustberemovedandthemeterplacedinparallelwiththecomponent.

3. FunctionSignalGenerator

TaketheEE1641BModelfunctionsignalgeneratorasanexample.Thesignalgeneratorisaversatilesignalsourcethatcanbeusedinavarietyofengineering,industrial,educationalandhobbyistapplications.Thisgeneratorprovidesthefollowingtypesofwaveformforoutput:(1)Sine;(2)Square;(3)Triangle.

Pressthebuttonbelowthewaveformsketchmapstochoosethegeneratedsignalofyourinterests.Thewidefrequencyofthesignalgeneratorrangesfrom0.2Hzto2MHz,andthemaximumoutputpeak-to-peakvalueofthesignalis10volts.So,youshouldchoosetheproper“frequencyrange”buttonandadjustthe“amplitude”knobtoobtainthesignalyouwantfromthe“50Ω”outputterminal.Theattenuationbuttons“20dB”and“40dB”areneededforthesignalwhichamplitudeissmallthan1volt.

Besidesthefunctionofgeneratethethreekindsofwaveformsgivenabove,thissignalgeneratorisalsoacounterorascanner.Itmaybeusedinexternalsweepingandcounting,herenomoreunnecessarydetailswillbegiven.

科技英语中各种数、符号的表达(二)

1.年份的表达年份用基数词,日期用序数词。例如：1988年5月1日可以写做May1(st)，1988，读做Maythefirst,nineteeneighty-eight；或读作thefirstofMay，nineteeneighty-eight。

英语年份的读法：一般先读前两位数，再读后两位数。例如：

1983→nineteeneighty-three