Unit7ElectronicInstrumentIntroductionTextKeywordsTechnicaltermsExpressionsNotestothetextText

TherearemanykindsofElectronicinstruments;theleadingpurposeistomeasurevariousphysicalquantitiessuchascurrent,voltage,resistance,temperature,soundlevel,pressure,etc.

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

Herewe’llgivethefundamentalintroductionsofsomeelectronicinstrumentsincommonuse.

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.Keywords

quantity n.量，數(shù)量

pressure n.壓，壓力，電壓

delicate adj.精密的

sensitive adj.靈敏的

instruction n.指示，說明(書)，指令

manual n.手冊，指南

purchase vt./n.買，購買

specification n.詳述，規(guī)格，說明書，規(guī)范

limitation n.限制，局限性

accurate adj.正確的，精確的

phase n.相位

voltmeter n.伏特計(jì)

calibrate v.校準(zhǔn)

sine n.正弦

significant adj.有意義的，重大的，重要的

harmonic n.諧波

oscilloscope n.[物]示波器

resolution n.分辨率

vertical

adj.垂直的

division

n.分開，分割

centimeter

n.厘米

scale

n.刻度，進(jìn)制

interpolate

v.插入

maintenance

n.維護(hù)，保持

decibel

n.分貝

jack

n.插孔，插座

polarity

n.極性

facilitate

vt.使容易，使便利

compensate

v.償還，補(bǔ)償

battery n.電池

parallel adj.并聯(lián)的

series n.串聯(lián)

generator

n.發(fā)電機(jī)，發(fā)生器

versatile

adj.通用的，萬能的

triangle n.?[數(shù)]三角形

attenuation n.衰減

scanner n.掃描器，掃描儀Technicalterms

VOM 電子伏特表

peak-to-peakvalue 峰-峰值

RMS(root-mean-square) 均方根值(有效值)

troubleshootingmanuals 故障手冊

general-purposemeter 通用儀表

functionsignalgenerator 函數(shù)信號(hào)發(fā)生器Expressions

befamiliarwith… 對…熟悉

inrelationto… 與…有關(guān)；涉及

multiply…by… 用…乘…

beconvertedto… 把…轉(zhuǎn)換成

becapableof 能夠

inparallelwith… 與…并聯(lián)

take…asanexample 以…為例

rangesfrom…to…