ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
";iH•J'? .....// Lessons Learned fromtheDesign andImplementation ofaPotentiometer Assembly foranAntenna Pointing Mechanism Application Bradley Arkwright*, PietroDiLeonardo*, ColinFrancis'* andRichard Gahart** Abstract Potentiometers areoftenusedasposition sensing devices forpositioning mechanisms. Theyhave proven tobealow-cost, reliable telemetry devicewhenusedinthecorrect environment andfabricated usingcontrolled processes. Several lessons learned wererealized fromadevelopment effortinwhich rotarypotentiometers wereusedinanantenna positioning mechanism. Inthisapplication, eachactuator makes useoftworotarytypepotentiometers: oneforfinetelemetry andoneforcoarse telemetry. The unitsarerequired tooperate between -45°Cand+105°C, witharequired life(forthefinepotentiometer) inexcessof1,800,000 revolutions. Lesson learned andissuesthatwillbediscussed include: •Dealing withpotentiometer noiseatlowtemperature •Workmanship, cleanliness, andhandling issuesassociated withfabrication ofpotentiometers •Material selection forthepotentiometer wiperassembly •Resistive trackdeadband geometry andsize •Testequipment andflightelectronics design precautions andrecommendations thatshould be employed whentestingoroperating potentiometers Thefollowing performance parameters andtrenddataresulting fromqualification andlifetestingwillalso bediscussed inthepaper: •Potentiometer element resistance valuesasafunction oflifeandtemperature •Potentiometer accuracy asafunction oflifeandtemperature •Wiperpreload Introduction Figure1illustrates anexploded viewofarotaryactuator assembly thatutilizes acoarse potentiometer andfinepotentiometer intandem toindicate theprecise position oftheactuator output.Thedesignissues discussed hereinhaveallbeenresolved andtheunitshavecompleted fullqualification, lifetestingand production, andarecurrently accumulating onorbitlifeaboard several commercial communication satellites. Inthestandard actuator design, aredundant potentiometer assembly isintegrated directly ontheback endofthemotorthatserves asthefinetelemetry output. Thefinepotentiometer isatwopieceunit mounted directly onthebackendofthemotorshaft.Inthefinaldesign, theprimary andredundant resistive trackseachhaveanapproximate 15-degree deadband withtheprimary andsecondary deadbands oriented 180°apart.Thisconfiguration ensures continuous electrical readout over360 degrees whenbothtracksaremonitored. Whenusedinconjunction withthecoarse potentiometer (of similarconstruction) ontheoutputshaftoftheactuator, thefinepotentiometer provides precise positional output.Thecoarse potentiometer andfinepotentiometer onthemotoraredifferent indiameter butvery similar inconstruction andmaterials. Thecoarse potentiometer isnon-redundant butitonlyprovides roughpositioning datainordertospecifywhichrevolution thefinepotentiometer ison. iHoneywell Aerospace Electronic Systems, Glendale, AZ SpaceSystems /Loral,PaloAlto,CA Proceedings ofthe3_hAerospace Mechanisms Symposium, AmesResearch Center,May9-11,2001 163
Duetothemoreseverelifeandenvironment requirements, thisdiscussion willfocusonthefine potentiometer (showninFigure2andFigure3)whichisintegraltothesteppermotorassembly. However, allofthelessonslearneddiscussed hereinarealsoapplicable tothecoarsepotentiometer design. Therotarypotentiometer beingdiscussed hereinisoftheconductive plastictype.Precious metalwiper fingerscontactaco-molded conductive plasticresistance element tocomplete acircuitandindicate a rotarylocation ofashaftasshowninFigures2and3.Theoutputofthepotentiometer isavoltagetrace thatislinearlyproportional totherotarypositionontheresistive track.Thefinepotentiometer schematic ispresented inFigure4.Theoutputofthepositionsensorisasawtoothtypewaveform. Thesecondary signalisofthesameformbutoffsetbyapproximately 180degrees. Amorecomplete description of potentiometer operation isincluded inReference 1. Although therotarypotentiometer issimpleinconcept, therearemanydesignandmanufacturing issues tobeconsidered whenincorporating thistypeoftelemetry intoanactuator. Thefollowing sections describe somedesign,handling, andmanufacturing issuesthatwereencountered duringtheprojectand werefoundtobeverycriticaltoproperunitoperation. STOP RING OUTPUT COARSE POTENTIOMETEROUTPUT FLANGE BEARINGS MOUNTING FLANGEHARMONIC DRIVE ASSEMBLY MOTOR /FINEPOTENTIOMETER ASSEMBLY S858-104-4p s.tif Figure1.RotaryActuator Exploded View 164
Figure2.FinePotentiometer Assembly (PartofStepper MotorAssembly) {Thefinepotentiometer assembly ismounted directly tothebackendofthestepper motorassembly. Itiseasilyaccessible forinspection viatheremoval ofabackcover.} .......................................... ik_,i¸........ Figure3.FinePotentiometer Assembly- WiperDetail 165
Potentiometer NoiseatColdTemperature inVacuum Duringlifetesting, afterapproximately 45,000 motorrevolutions, thefinepotentiometer beganexhibiting noisetracesasshowninFigure5duringcoldthermal vacuum testing. Witheachsuccessive cycle,theminimum temperature atwhichthenoisebeganslowlyincreased (i.e., thenoiseappeared atawarmer temperature). Athorough causeandeffectinvestigation wasinitiated to determine therootcauseoftheanomaly. Theinvestigation focused onseveral possible causes: Dynamic Instability: Thenoisecouldhavebeencaused bydynamic instability ofthemotorasit stepsthrough itsdetentpositions. Mechanical Interference: Thenoisecouldhavebeencaused byinterference between themotor backcoverandtherotating wiperassembly onthefinepotentiometer. Surface Contamination: Thenoisecouldhavebeencaused bytheintroduction ofcontaminants between thecontacting surfaces. Theinvestigation proceeded todemonstrate thatthenoisewasactually caused bythedynamic formation ofanelectrical insulator attheinterface ofthewiperandtheresistive element ofthepotentiometer. This phenomena leadtoathorough examination andcharacterization oftheelectrical interfaces andtheir surrounding materials. Thebaseline wipermaterial wasPALINEY_7 (Ref.2),aprecious metalalloycomprised ofpalladium, silver,copper, goldandplatinum. Thepotentiometer substrate material isDiallylPhthalate (DAP)witha resistive trackco-molded intothesubstrate material. Theliterature inRef.2(seeTable1)citesPalladium andPlatinum asthetwomosthighlycatalytic metalsintheformation offrictional polymers. Thissupports thetheoryforpolymer formation sincePALINEY'_7 contains largeamounts ofPalladium andPlatinum. Duringoperation, thisveryreactive surface ridesonshortchainpolymers fromtheDAPresistive glaze formulation alongwithlithiumsterates usedasmoldreleases bythepotentiometer manufacturer. This creates anidealenvironment fortheformation ofapolymeric film.Theunitsensitivity tothisfilmis increased atcoldtemperature whenthefilmsolidifies andcreates aninsulating barrierbetween the wipers andresistive track.Undertheseconditions itisnotunexpected toobserve noisyornonlinear voltage outputfromthepotentiometer duetothislackofintimate wipercontact withtheelement surface. Adesignchange wastheninstituted whichchanged thewipermaterial fromPALINEY®7 toNEYORO _' G,whichisagoldalloy.Theliterature inRef.2citesGoldasseveral times(-20X) lesscatalytic than Palladium orPlatinum (seeTable1). Basedonsurface analyses resultswhichshowed evidence ofgeneral debrisandcontamination onthe elements, itwasalsodeemed necessary toimplement strictercleanliness precautions whilehandling or viewing potentiometers. Allpersonnel withintheimmediate areaofanexposed potentiometer arenow required towearcleanroomhatsandmasks. Thehatandmaskareinaddition tothegeneral requirement ofsmocks andlintfreegloves. Thepotentiometers arehandled withinaClass100,000 rated areaandaClass100flowhood.Onlywhenthepotentiometers areclosedupinsideaunitisthehatand maskrequirement relieved. 166
PR,.ARYRES,S ,VE II _(,_, )] ,aA2(GRAY) _hl_k _ // "B2(WHITENIOLET) /XX//TOTELEMETRYSECONDARY RESISTIVE _ // BOARD TRACK __J °tt°A1(BROWN) A3(VIOLET) 5.0VRETURN 5.0VFROM DRIVE ELECTRONICS SECONDARY TRACK 5.0V / ov ® @ ®®® ®0 ®VOLTAGE (TELEMETRY) Figure4.FinePotentiometer Schematic ::._.i!...!.E........;......... :::_:.M:,,._ ":'_i';"':"_" !h:":_"_:..,:::.:=....,.'_':_'..,"--_':..,::,,.:."i..:_'t_._'_,"m._.._o_ ,..'_."_.'_.' --:":£O. ..... "_'._........ ...,--,--_............._.............................. /__._.......-:......... : ............... ,... 'OL_.................. _ ......... _L'4_Z :.................... +__, ....... ::=:::=_:.... "'" _'[.|__ff_: :.-,.. .:i_:.:i hi!i'!" .:::.:::::.":.,::::::::::::::::::::=_:=::::u:'"'" "i!!!!':!EITi__iilh.:_..:: i!!!_!:!£L':iiJ::!: ................. _.... ,........... :..,..... .,.,L., =It:Ix::=:;_:::: :::: :_:: Figure5.NoiseEventTraces Detected During LifeTesting (After45,000motorrevolutions) - PALINEY ®7Wipers {Example ofafinepotentiometer "noise" eventwhiletheunitisoperating atcoldtemperature (-45_C). Wipermaterial isPALINEY _=7.Noisetraceswereattributed topolymer formation atthecontacting surface. Theseeventswereeliminated bychanging thewipermaterial toNEYORO _G(SeeTable1).} 167
Table1.Relative Polymer Formation ofSelected Metals andAlloys(Ref.2) {Thistablewasveryusefulinhelping makeadecision tochange thewipermaterial fromPALINEY :+7to NEYORO '_`G} Platinum (in..PALINEY® 7) Palladium (inPALINEY® 7) 'Ruthenium 69Au,25Acj,6Pt 75Au,25PdPlatinum Palladium Ruthenium Palladium 75Au,25Pd Quartz Palladium 70Au,30Ag Gold 69Au,25A9,6Pt Gold(inNEYORO® G) Silver Copper ZincPalladium Palladium 69Au,25A9,6Pt Gold Silver100 I.. 95 55 50 37 3O 20 16 12 5 0 Copper 0 Zinc 0 Ultimately thechange toNEYORO® Gwipersprovedtobesuccessful. Figure6illustrates partofastrip chartrecording takenduringfinalcoldfunctional testing (-45°C),undervacuum conditions, atthe conclusion oftherequired lifetestduration of1,825,000 potentiometer revolutions. I Ifi _i;i_]..:!:+!_:L._±_'_ Ji:'+12':'i_!i:i[:25:1:r::,: 5/:: Figure6.EndofLifeFinePotentiometer Traces -NEYORO ®GWipers {Stripchartexample ofthefinepotentiometer outputwhiletheunitisoperating atcoldtemperature (-45°C). Wipermaterial isNEYORO _G,Thisreading wastakenduringfinalfunctional testattheendof life(after1,825,000 potentiometer revolutions). Nominal output signals fromthepotentiometer observed. Note:Thechartspeedisdifferent thantheoneshowninFigure5.} FinePotentiometer Failures Caused byDeadband Shorting Theactuator finepotentiometers experienced another catastrophic typefailureduringlifetesting. The failuremanifested itselfearlywithsudden andcomplete outputsignallossfromtwofinepotentiometers. Furthermore, thesignals werenotlostsimultaneously. Upondisassembly, inspection andfailureanalysis ofthepotentiometer itwasdetermined thatthedead bandareahadshorted. Figures 7and8illustrate veryclearlytheextentofthedamage inthedeadband 168
areas. Further observation oftheotherfinepotentiometer tracksontheunitrevealed a"smearing" phenomena (asshowninFigure9),whichwasdeemed asoneofthecauses ofthefailure.Thetendency overtimeisfortheconductive material andDAPtosmearacrossthedeadbandarea.Thisphenomena is actually expected tooccurovermanyrevolutions, butothercontributors alsomadethesituation worse. Figure7.Shorting inDeadBandArea-Example 1 {Catastrophic failureofonepotentiometer trackcaused byshorting acrossdeadband.Thefailurewas triggered bywiperwearand"smearing" ofconductive material overthegaparea.} Figure8.Shorting inDeadBandArea-Example 2 {Amoresevereexample ofshorting acrossthedeadband.Failureoftheconductive trackcouldhave beenavoided byusingacurrent limitedpowersupply.} 169
Figure9."Smearing" EffectofConductive TrackAcross DeadBandArea {Overmanyrevolutions (1,825,000) thisisanexpected effect.Butwithasmalldeadbandgapand expected wiperwear,thisphenomenon provedtobecatastrophic. (SeeFigures 7and8)} Normal wiperwearovermanyrevolutions causes aflatpatchformation onthecontact areaofthewipers asshowninFigure10.Asthewipertraverses acrossthedeadbandareaoverlifeandthewearpatch getslarger,thewipersactually canbridgeacross thedeadbandasthewearpatchexceeds thegap width.Thedeadbandgaptherefore needstobelargeenough toaccommodate thenormal, expected wearpatchonthewiperassembly. Workmanship issueswerealsoidentified withthedeadbandmanufacturing process asshowninFigure 11.Thesmalldeadbandrequirement caused themanufacturing process tobeverydifficult andnot repeatable. Theprocess involved amechanical removal oftheconductive material, whichcaused the qualityoftherequired deadbandgaptobelessthanacceptable andcertainly veryuncontrollable in termsofsizeandgeometry. Thisprocess alsocaused theexposure ofsilverepoxyusedtocreatethe wiretabconnections forthepotentiometer. Exposed silverepoxyisvisiblealongoneedgeofthegap. Although itwasneverdetermined thattheexposed silverepoxyinthedeadbandareaactually wasa partialcauseofthefailure,itcertainly wasundesirable. Furthermore, theinvestigation revealed thatthe5Vpower supply beingusedtopowerupthe potentiometers wasnotcurrent limited lowenough toprotect thepotentiometers. During nominal operation thiswouldnotbeanissue.However, thisaddedtothecatastrophic typefailuresincethetest equipment didnotoffersufficient protection against mis-wiring oragainst inadvertent current drawsbythe unit.Acurrent limitedsupplywasthenimplemented toprotectthehardware fromexcessive currentgoing through theunit. Figure12showsasample ofastripchartoutputthatcaptures theshorting phenomena acrossthedead band.Bymonitoring thecurrent limitedsupplylineonthestripchartchannels itwaspossible tocapture theshorting eventsononepotentiometer track.Thehashmarksindicate additional current drawfromthe supply. Thisonlybecame visiblewhenacurrent limitedsupplywasusedsincetheaddedcurrent drawis relatively small. 170
Figure10.Typical WiperWearPatch {Asthelifetestingprogressed, thewidthofthewiperwearpatch(0.35mmor0.014"typ)approached and exceeded thewidthofthedeadband(0.25mmor0.010"typ)ontheconductive tracks.} Figure12showsindications ofshorting across thedeadbandoftheprimary finepotentiometer. Thisis proofthatthewiperisactually bridging acrossthedeadbandasittravelsovertheresistive trackmaterial. Twostripchartchannels wereusedtomonitor thepowersupplyvoltage toeachpotentiometer. The vertical hashmarksindicate additional current drawforthatparticular powersupply. Figure13showstheresults ofrunning the"smallgap"finepotentiometer withacurrent-limited power supplyoverapproximately 300,000 revolutions. Whiletheunitexhibited bridging acrossthedeadband, thepotentiometer element wasprotected bythecurrent limitedsupply. Thepowersupplywasnotas effective inprotecting thewipers. AsshowninFigure13,boththeprimary, andsecondary wiperswere damaged. Therepeated arcingatthedeadband location created localheating onthewiperfingers such thattheywereessentially melted overtime.NoticethatinFigure13,thetwowiperbundles ontheleft havebeenshorted duetotherepeated wipermelting. Incontrast, thewiperbundleontheright,whichis associated withtheslipring,didnotexperience thelocalarcingphenomena andisinnominal condition at endoflife.Thistestproved that,although theoutputsignals ofthepotentiometer werenominal, thedead bandbridging wasstilldetrimental physically tothecomponent. Aperformance compromise was necessary toalleviate theproblem. Thesolution wasobtained bybeingabletoopenthespecification requirement forthedeadbandgapwidth. 171
Figure11.Workmanship IssuesCaused bySmallDeadBandRequirement ;iiI:!:.:t i!l:,j :l_.-:rl-::::1!:!'l:_::_:.._:,.._d. ":,'1:__l:/q'i''k =-:'" ':':::._::: I:'5""'1""""'-'".................... __'....:}-:::. .-5}:÷:7!!:<!.;5:__i_::'"'"'"i:i_;ii_"7iiii!ii __iii_!i;_!!!!t!!i!!!!_,'!ii!!!!_i!i_!!i!fZ !!q i!_:!:::!f_iI 7 i_::7....I.I.,L:;.-,I;I......I. "77{{:::',: :::--i__f!!!_t:.--r-!....[{4-:_-:i: :?:z:_7-:2;Z::I: iX'-'::i::: :- '.:1..J.....=,, ,-t-t-+--,i---.- ....i.i. I.... .i.i.•,+l.,t.... ....i...°_.... !r-_ib::.!t Figure 12.DeadBand"Shorting" Phenomena asSeenonaStripChartPrintout 172
V Figure 13.WiperWearAfterRunning aLifeTestWithaCurrent Limited Supply Thenewconfiguration showninFigure14opened thegapwidthfrom0.25mmto1.5mm(0.010" to 0.060"). Thiswidthhadsubstantial margin overthepredicted wiperwearpatch(shown inFigure10). Thiswidegapconfiguration proved tobeeasytomanufacture andcontrol. Thevendorwasnowableto useaveryrepeatable andprovenmasking technique togenerate thelargergap. Afinallifetestwasconducted tovalidate thefinalgapconfiguration. Figure15showsthesamedead bandcrossing atthecompletion ofover1,825,000 cycles. Figure 14.Corrected DeadBandConfiguration -PreLifeTest 173
Figure 15.FinalDeadBandandFinalWiperCondition -PostLifeTest Potentiometer Performance Trends Duetothemultiple lifetestsperformed onthisproject, therewasconsiderable potentiometer performance trenddataavailable. ThefinallifetestusingNEYORO® Gwipersandthelargedeadbandgapdesign wasperformed forfinalassurance thatthecorrective actions takenwereindeedvalid.Oncethedesign, workmanship, andhandling issues wereresolved, thepotentiometers werefoundtobehave very accurately andconsistently. Potentiometer Element Resistance Table2summarizes thepotentiometer's trackresistance asmeasured atdifferent phases ofthelifetest. Theresultsdemonstrate thattheresistance remains relatively constant overlife,evenundervacuum and thermal conditions. AsshowninTable3,themaximum deviation fromtheinitialresistance valuewasonly 3.5%overthetestedtemperature rangeinthermal vacuum conditions duringa2-month lifetest. Table2.Potentiometer Element Resistance TrendDuring LifeTesting TestPoint : ____!,_:_!i_!_i___ PreLifeTestFunctional Testat Ambient InitialHot(105°C) Thermal Vacuum (TN)Functional InitialCold(-45°C) TNFunctional Post912,500 Revolutions - Cold(-45°C) T/VFunctional Post912,500 Revolutions - Hot(105°C) T/VFunctional Post1,825,000 Revolutions - Hot(105°C) TNFunctional Post1,825,000 RevolutionsCold(-45°C) TNFunctional Post1,825,000 Revolutions - Functional TestatAmbient8926Secon_w FinePot. Element Resistance "(ohms) 9444 8914 9386 9073 9587 9169 9671 9035 9584 9110 9695 9239 9783 9121 9684 174
Table3.Potentiometer Resistance Maximum Deviation Case ....Maximum Negative' Deviation fromInitial Maximum Positive Deviation fromInitialPrimary Potentiometer Percent .....,Resistance Change -0.5% +3.5%Secondary Potentiometer Percent Resistance Change , -0.6% +3.5% Potentiometer Accuracy Potentiometer linearity oraccuracy overlifewasalsoaparameter ofprimary concern. Theoutputvalueof thepotentiometer atoneprescribed motordetentposition wasmeasured atvarious pointsduringthelife test.ThedatainTable4showsthevariation ofthepotentiometer read-out atdifferent phases ofthelife test.Thereference position isamechanical scribemarklocated onthemotoroutputshaftandmotor mounting housing. Theprimary andsecondary finepotentiometer readings wereveryrepeatable overlife. Ascanbeseenfromthevoltage readings, theaccuracy driftoverlifedidnotvarybymorethan0.01volt, whichisequivalent to0.46degree atthemotor.Goingthrough thegearratio,thisconverts toonly0.003 degreeattheoutputofthisparticular actuator design. Table4.Potentiometer Accuracy DriftOverLife {Ascribemarkwasusedasareference position. Thedataindicates thevariation ofthefine potentiometer readings forthesamebaseline scribeposition, overlife.} i,,i,lu,i Baseline ScribeReading' +105°C Pre-life testFunctional Scribe PositionPrimary Fine pote,ntiometer Voltage;(v ) 3.832Secondary Fine potent!ometer Voltage (v) 1.245 3.834 1.245 -45°CPre-life testFunctional Scribe 3.833 1.243 Position 1,200,000 Revolutions +105°C 3.836 1.244 Functional ScribePosition 1,200,000 Revolutions -45°CFunctional 3.831 1.241 ScribePosition 1,200,000 Revolutions Ambient Scribe3.839 1.240 Reading 1,825,000 Revolutions Final+105°C3.842 1.239 Functional Scribe Position 1,825,000 Revolutions Final-45°C 3.838 1.237 Functional ScribePosition 1,825,000 Revolutions Ambient Scribe3.840 1.239 Reading Note: Average Potentiometer Performance: 69degrees/volt or0.0145volt/degree Linearity ofthepotentiometer wasalsofoundtobewellwithinspecification overlife.Table5tabulates the linearity errorthatwasmeasured overthecourseofoneofthelifetests.Itshowsthatthepotentiometer wasveryaccurate overalltemperature ranges, duringthelifetestandattheendoflife.Table5shows thattheendoflifelinearity errorisonly0.0274voltor1.89degrees atthemotorshaft.Notethatthiserror alsoincludes amaximum errorof0.2degree attributed tomotorsteperror.Goingthrough thegearratio, thisconverts toonly0.012degree attheoutputofthisparticular actuator design. 175
Table5.Potentiometer Linearity Errorduring LifeTesting Case'Temperature (°C)*_imary Fine Potentiometer Linearity Error(o) PreLifeTestFunctional Test Ambient 0.911 InitialT/VFunctional 105 4.347 4.416 InitialT/VFunctional -45 0.214 0.193 Post912,500 Revolutions TN -45 0.145 0.386 Functional Post912,500 Revolutions TN 105 0.200 0.276 Functional Post1,825,000 Revolutions 105 3.105 3.036 TNFunctional Post1,825,000 Revolutions -45 3.064 3.098 TNFunctional PostLifeTestFunctional Test Ambient 1.891 1.435 atAmbient *Notethatthisisthelinearity erroratthemotorshaftasreadbythepotentiometer*Secondary Fine Potentiometer Linearity,Error (o) 0.897 WiperPreload Wiperfingerpreload ontheelement caneffectbothnominal performance andwearlife.Ifwiperpreload is toolow,thenitispossible thatthewiperfingerscanlosecontact withtheelement atcertaintemperature extremes andtheoutputsignalwouldbelost.Ifwiperpreload istoohigh,thenwiperwearcanbe accelerated andtotaloperational lifewillbecompromised. However, duringthisprojectaratherbroad rangeofpreloads wasfoundtoperform successfully. Figure13presented earlier, showshowthewiper tipsweremelted duetothelocalarcingatthedeadband. Clearly thewiperpreload wasdrastically effected duetothiswiperdamage andyetthepotentiometer outputsignalshowed nominal performance atendoflife. Conclusions Oneofthefirstconsiderations tobetakenwhenselecting acomponent tobeincorporated intoa mechanism oranydesign, shouldbeheritage ofthatcomponent. Specifically, itisimportant thatthe proposed application beverysimilartopastheritage andshould besupported byqualification andlife testing. Itisnecessary toscrutinize anyperformance requirements thatarenotsupported byheritage experience orapplications. Onesuchexample inthisproject wastheinitialsmalldeadband size. Although itwasaheritage sizeforadeadband forthepotentiometer vendor onsomepastdesigns, those applications didnotactually havethewiperstravelling overthedeadband duringactualoperation. Itis veryimportant tomakesurethatavendor clearlyunderstands theapplication oftheircomponent inthe endproduct evenifitappears tobewelldefined intheprocurement specification. Typically, whatever component isscrutinized theleastinadesignusuallyhasthemostriskrelatedtoit. Therewereanumber oftechnical andproducibility typelessons learned onthisproject. Because ofthe relative simplicity oftherotarypotentiometer, itisveryeasytooverlook allthedetailsofthedesignthat canhaveaveryrealeffectontheperformance oftheunit. Electrical outputnoisefromarotarypotentiometer hasbeenanissuethatmanyhaveexperienced. Wiper material choiceandelement cleanliness hasadefinite effectonthetendency forelectrical outputnoiseto occur.Theformation ofanyinsulating polymer layersontheelement surface seems tobemuchless prevalent whenagoldalloytypewiperlikeNEYORO _'Gisutilized instead ofapalladium orplatinum type alloylikePALINEY_7. However, thesepotentiometers seemed onlytobesensitive tothispolymerization formation atrelatively coldtemperature. Itisrecommended thatthesetypesofpotentiometers notbe utilized attemperatures lessthanapproximately -20°Cunlessthedesign isproven bysignificant life testing. 176