Advanced Motion Controls 12A8 - Wiring

MNALAZIN-02 19
Integration in the Servo System / Wiring
TheDCpowergroundandtheinputreferencecommandsignalgroundareoftentimesata
differentpotentialthanchassis/PEground.Thesignalgroundofthecontrollermustbe
connectedtothesignalgroundoftheAZdrivetoavoidpickingupnoiseduetothe"floating"
differentialservodriveinput.OnallAZdrives,theDCpowergroundandtheinputcommand
signalgroundarereferencedtoeachotherinternally.InsystemsusinganisolatedDCpower
supply,signalgroundand/orpowergroundcanbereferencedtochassisground.Firstdecideif
thisisbothappropriateandsafe.Ifthisisthecase,theycanbegroundedatthecentral
groundingpoint.
Wiring
Servosystemwiringtypicallyinvolveswiringacontroller(digitaloranalog),aservodrive,a
powersupply,andamotor.Wiringtheseservosystemcomponentsisfairlyeasywhenafew
simplerulesareobserved.
AswithanyhighefficiencyPWMservodrive,thepossibilityofnoiseandinterferencecoupling
throughthecablingandwirescanbeharmfultooverallsystemperformance.Noiseinthe
formofinterferingsignalscanbecoupled:
• Capacitively(electrostaticcoupling)ontosignalwiresinthecircuit(theeffectismore
seriousforhighimpedancepoints).
• Magneticallytoclosedloopsinthesignalcircuit(independentofimpedancelevels).
• Electromagneticallytosignalwiresactingassmallantennasforelectromagneticradiation.
• Fromonepartofthecircuittootherpartsthroughvoltagedropsongroundlines.
ExperienceshowsthatthemainsourceofnoiseisthehighDV/DT(typicallyabout
1V/nanosecond)ofthedrive’soutputpowerstage.ThisPWMoutputcancouplebacktothe
signallinesthroughtheoutputandinputwires.Thebestmethodstoreducethiseffectareto
movesignalandmotorleadsapart,addshielding,andusedifferentialinputsatthedrive.For
extremecases,useofaninductivefiltercardisrecommended.
Unfortunately,low‐frequencymagneticfieldsarenotsignificantlyreducedbymetalenclosures.
Typicalsourcesare50or60Hzpowertransformersandlowfrequencycurrentchangesinthe
motorleads.Avoidlargeloopareasinsignal,power‐supply,andmotorwires.Twistedpairsof
wiresarequiteeffectiveinreducingmagneticpick‐upbecausetheenclosedareaissmall,and
thesignalsinducedinsuccessivetwistcancel.
Wire Gauge
Asthewirediameterdecreases,theimpedanceincreases.Higherimpedancewirewill
broadcastmorenoisethanlowerimpedancewire.Therefore,whenselectingthewiregauge
forthemotorpowerwires,powersupplywires,andgroundwires,itisbettertoerrontheside
Grounding is important for safety. The grounding recommendations in
this manual may not be appropriate for all applications and system
machinery. It is the responsibility of the system designer to follow
applicable regulations and guidelines as they apply to the specific servo
system.
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