单点接地和 多点接地详解Single point grounding and multipoint grounding.docx

单点接地和 多点接地详解Single point grounding and multipoint grounding.docx

《单点接地和 多点接地详解Single point grounding and multipoint grounding.docx》由会员分享，可在线阅读，更多相关《单点接地和 多点接地详解Single point grounding and multipoint grounding.docx（8页珍藏版）》请在冰豆网上搜索。

单点接地和多点接地详解Singlepointgroundingandmultipointgrounding

单点接地和多点接地详解（Singlepointgroundingandmultipointgrounding）

Singlepointearthingmultipointearthing

Theproblemtobesolvedinasinglepointisthe"publicgroundimpedancecoupling"andthe"low-frequencyloop"",

Moreoftenthannot,itisaimedat"commonmodeinterference"causedbylongrunninglines

Inlowfrequencycircuits,theoperatingfrequencyofthesignalislessthan1MHz,anditswiringandinductancebetweenthedevicesarelessaffected,andthecirculationcausedbythegroundingcircuithasagreaterimpactoninterference,soitshouldadoptonepointgrounding.

Whenthesignaloperatingfrequencyisgreaterthan10MHz,thegroundimpedancebecomesverylarge.Atthispoint,thegroundimpedanceshouldbereducedasfaraspossible,andthegroundmultipointgroundingshouldbeadopted.

Whentheworkingfrequencyisbetween1and10MHz,ifonepointgroundingisadopted,thegroundwirelengthshallnotexceed1/20ofthewavelength,ormultipointgroundingmethodshallbeadopted.

Singlepointearthingbetweendigitalandanalogground,multipointconnectionwithindigitalground.

Groundwireinterferenceandgroundwiredesign

GrounddesignisaproblemthatpeoplepayattentiontoinEMCdesign,buttheydon'tknowhowtodoit.Afterunderstandingthemechanismoftheinterferencecausedbygroundwire,thereisadefiniteideainthedesignandimplementationofgroundwire.Thisissuebeginswiththeintroductionoftheprincipleofinterferencecausedbygroundwire,enablingreaderstounderstandthekeyandprinciplesofdesigninggroundwire.1whatistheearthwire?

Therearetwokindsofgroundwire:

safetyandsignal.Theformeristoensurepersonalsafetyandequipmentsafetyandsetthegroundwire,thelatteristoensurethatthecircuitworkscorrectlysetthegroundwire.Themainreasonforthecircuitinterferenceisthesignalground,sotheproblemofsignalgroundisonlydiscussedhere.

Thegeneraldefinitionofthesignalfieldisthepotentialreferencepointofthecircuit.

Moreappropriately,thisdefinitionisahypothesisinourdesignofcircuits.Fromthisdefinitionitisimpossibletoanalyzeandunderstandsomegroundinterferenceproblems.Fromnowon,wewillusethefollowingdefinitionwhenweanalyzeelectromagneticcompatibilityproblems.

Thegroundlineisthegroundimpedancepathofthesignalcurrentflowingbacktothesignalsource.

Sincethegroundwireisapathofthecurrent,thenthereisavoltageonthegroundlineaccordingtoOhm'slaw;sincetheearthisonavoltage,theearthlineisnotaequipotentialbody.Inthisway,whenwedesignthecircuit,thehypothesisaboutthepotentialofthegroundwireisnolongerestablished,sotherearevariouserrorsinthecircuit.Thisistheessenceofgroundinterference.

Howbigistheimpedanceofthe2wire?

Anincomprehensibleproblemisthatwhenwedesignthegroundwire,theresistanceofthegroundwireisverysmall,thenthepotentialdifferenceonthegroundwillbelargeenoughtocausethelevelofcircuiterrors.Tounderstandtheproblem,understandthecompositionofgroundimpedance.

ThegroundimpedanceofZbytheresistanceandinductancepartiscomposedoftwoparts,namely:

Z=RAC+LJ.

Resistancecomponent:

theresistanceoftheconductorisdividedintoDCresistanceRDCandACresistanceRAC.ForACcurrent,becauseoftheskineffect,thecurrentisconcentratedonthesurfaceoftheconductor,resultinginthedecreaseoftheactualcurrentcrosssection,theincreaseofresistance,andtherelationshipbetweentheDCresistanceandtheACresistance:

RAC=0.076rf1/2RDC

Type1:

theradiusofther=wire,theunitcm,thecurrentfrequencyofthef=flowingthroughthewire,theunitHz,thedirectresistanceoftheRDC=wire,theunitomega.

Inductance:

anyconductorhasaninternalinductance（whichisdistinguishedfromtheusualexternalinductance,

Theouterinductanceisafunctionoftheareaenclosedbytheconductor,andtheinductanceisindependentoftheareaenclosedbytheconductor.Forroundsections,conductorsareasfollows:

L=0.2S[ln（4.5/d）-1]（H）

TypeS=conductorlength（m）,d=conductordiameter（m）

Table1illustratesthegreatdifferencebetweentheDCandACimpedances.Theimpedanceofverylowfrequenciescanbeconsideredtobetheresistanceofaconductor,canbeseenfromthetable,withtheincreaseoffrequency,theimpedanceincreasesquicklywhenthefrequencyisabove100MHz,therearedozensofdiameter6.5mmohmimpedanceofthewirelengthisonly10cm.

Interferenceof3looproadandCountermeasures

Loopinterferenceisacommoninterferencethatoccursbetweendevicesthatarelongerapartbylongercables.Theintrinsicreasonisthegroundpotentialdifferencebetweentheequipment.Groundvoltageleadstotheearthl