SWITCHES & KEYBOARDS 23
Relays
move the
world
When we look around us today in our high-
tech world, particularly with regard to the
trend towards extreme miniaturization offering
the same or even increased functionality and
usability, the question arises as to how electro-
mechanical relays (EMR), seen by many as
“antiquated”, fit into this picture.Tim Haas,
Product Marketing Manager E-Mech at
AvnetTime EMG, knows the answer.
Thephysicalsizeofelectro-mechanicalrelaysandthemechanical andlatching.Non-latchingmeans,thatforswitchinganEMRrequires
functionalitythathasbeenaroundfordecadescannotbeoverlooked. acoilvoltagethatisconstantlyapplied.Inotherwords,oncetheEMR
Needlesstosay,theEMRhavealsobeenadaptedinlinewiththis hasswitchedandeitheractivatedordeactivatedtheotherelectric
trendandhaveshrunkconsiderablyinsizewithoutlosingtheir circuit,thevoltagemuststillbeappliedatthecoil,asotherwise,when
desiredproperties.Thankstonewmaterials,someofthesehaveeven switchingoffthecoilvoltagethearmaturewillalsobereleasedagain
becomemoreefficientthantheirpredecessors.Butintermsofthe fromthecoil,therebybreakingthecontacts.Accordingly,thiseffectis
functionalityinsidetheEMR,virtuallynothinghaschanged. notparticularlypracticalwithinthescopeofenergyefficiency
Arelayactsasaswitch,whichhoweveriselectricallyactuated. measures.Inthisregard,alatchingEMRfunctionsentirelyinlinewith
Relaysareoftenusedforswitchingextremelyhighcurrentsor suchmeasures.Oncetheswitchingoperationhasbeenperformed,
frequencies,whicheithercouldnotbeachievedusingother thecoilvoltagecanbeswitchedoff,whilstthecontactsremaininthe
componentsoronlywithavastamountofadditionaloutlayfor desiredstate.Naturally,thisentailsamorecomplexdesignthanthat
protectivecircuits. ofanon-latchingrelay.Theserequirementstranslateashighercosts,
Themaincomponentsarethecoil,throughwhichtheelectric whichhoweverhavetobeseenofcourseinrelationtothesaved
currentflows,thearmature,whichiseitherattractedorrepelledin energycostsandwhichoftenworkoutcheaperoverall.
accordancewiththevoltageapplied,andthecontact(s)thatis/are ThethingthatmakesEMRanexcellentchoicewithregardto
mechanicallyconnectedwiththearmature.EMRcanhavevarious componentselectionistheirabsoluterobustness,whichalsoforgives
releasestates.Thecontactsareeitheropen(normallyopen(NO), minor“flaws”ofothercomponentparts,nottomentionthetechnical
FormA,makecontact),closed(normallyclosed(NC),FormB,break sophisticationduetotheongoingresearchanddevelopment
contact),oritispossibletoswitchbetweentwocircuits(changeover spanningdecadesthatgointoproducingeveryEMR.Newversionsare
(CO),FormC,change-overcontact).Dependingonthenumberof constantlybeinglaunchedontothemarket,whichareevenbetter
contacts,anEMR(NO/NC)alwaysisolatesatleasttwoelectriccircuits suitedforcorrespondingapplicationsandwhich,asaresult,
fromeachother.Withachange-overcontact(CO),youhavethreeor contributetotheoverallbenefit.Semiconductortechnologyhasinthe
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moreelectriccircuits,oneofwhichisalwaysactivatedanddeactivates meantimealsofounditswayintothefieldofelectricswitching
theother(s)atthesametime.Asalreadymentioned,theswitching operationsand,withtechnicalattributesandspecialfeatures,is
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operationiseffectedbythecoil,thearmatureandthecontacts.The securingeverlargersharesofthismarketforitself.Onesuchspecial
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principleisbasedonthefactthataconductorthroughwhichelectric featureiscontactlessswitchingusingPhotodiodesinPhotomos
currentflowsacquiresmagneticproperties.Sincethearmatureis technology.Thistechnologyiscurrentlystilllimited,however,owing
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madefrommagnetisablemetal,theinteractionbetweenattraction tothelowcurrentsthatcanbeswitched.Ontheotherhand,however,
andrepulsionsoonbecomesapparent.Theswitchingoperationis thesecomponentpartscanbecombinedwithlogicalmodules,which
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effectedbymeansofanactuatingleverwherethecontactsandthe isneitherpossiblenorpracticalwithEMRandtheyhaveaverylong
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armatureareconnected. lifetimeduetonon-mechanicalswitching.
ThefieldsofapplicationforEMRandsemiconductorrelaysare
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DC or AC voltages? extremelydiverse.Theyrangefromprotectivecircuitsinmachine
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InadditiontothetypicalDCvoltages,relaysarealsoavailableforAC construction,communicationsengineeringandconsumergoodsas
voltages.Theseareusedlessfrequently,sincetheyaremorecomplex wellasdialysisandx-rayequipment.Strictlyspeakingnothinginthe
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toproduceandcomparedwithDCvoltagerelays,arealsomore worldwouldmoveorworkanymorewithoutrelays,andelectronic
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expensive.WithEMR,itisnecessarytodistinguishbetweentwo communicationwouldnotevenbepossible.
fundamentalmodesofoperation.Theseareknownasnon-latching > www.avnettime.com E
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