ThefollowinginformationistakefromQ&AbetweenIandmyChiefengineer
Q(1).Howtodefinetheenclosuretoclassifytheminthetwocategories,couldyougiveussomeadvice,weareveryappreciateifyoucangiveussomephotoassample.Andifweclassifytheenclosuretocategory1then,
Answer:Ifyoureadthestandardclosely,ThereareCategory1and2enclosuresforIP5X.Cat1isforequipmentwithelectricalcomponentsthatproduceheat.Theseneedtobetestedwithavacuum.Iftherearenoheatproducingcomponents,thenitcanbetestedorclassifiedasCat2andyoucantestwithoutavacuum.ForIP6X(readsection6),itsaysthattheenclosuremustbeconsideredaCat1(withorwithoutheatproducingcomponents).ThereforeyoumustperformthedusttestwithavacuumonallIP6Xenclosures.
Q(2).Howlongwillweconductthetest?(testcondition:extractionrate—lessthan40volumesperhour,maximumdepression-4kPaMaybewecan’tdothetestunderadepressionmorethan4kPa?)
Firstyoumustdeterminetheexchangeratefortheenclosure.Thisistheleakageratepertheenclosureunderacertainpressure.Standardsays2kPamaximumunderpressure(max.vacuum).Toputthedeviceundervacuum,youuseavacuumpumpattachedtotheenclosureandcreatea2kPavacuumontheenclosure.Onceyoureach2kPa,closeavalvesothatthevacuumismaintainedintheenclosurewiththepressuregaugeinthecircuit.Watchthepressuregaugetoseeifthepressurefallsfrom2kPa.Recordthetimeittakesforthepressuretogofrom2kPato0kPa.Thestandardrequirementis2hourstesttimefora40to60volumeperhourextractionrate(orleakagerate).1hr/40vol/hr=1.5minutes,1hr/60vol/hr=1.0min.Ifthepressurefallsfrom2kPato0kPain1.0to1.5minutes,thenyourleakagerateismorethan40volumesperhour.Ifitismorethan40volumes/hr,thenyoudothedusttestfor2hoursataconstantvacuumof2kPa.Youmustturnonthevacuumpumpandmaintainaconstant2kPavacuumduringthetestfor2hours.
Whencheckingyourinitialextractionrate(leakagerate)Ifyourpressuredropsfrom2kPato0kPainmorethan1.5minutes,thenyourextractionrateislessthan40volumes/hr(ie:enclosureapproachingnoleakageorair-tight).So,youmustconductthetestfor8hours,oruntil80volsofexchangehasoccurred.(ex.3minutestogofrom2kPato0kPa,thenyourunthetestfor60min/3=20exchangesperhour.Then80exchangestestrate/20exchangesperhour=4hours.Themaxtesttimeisnevermorethan8hours.
Ifyourpressuredropsfrom2kPato0kPainlessthan1.0minute,thenyourextractionrateismorethan60volumes/hr(ie:highleakage).So,youmusttryreducingthepressureuntilyougetaextractionrate(leakagetime)ofexactly1.0minuteandnotethepressure(vacuum)thatitoccursat.(ex.Youreducethepressureuntiltheexchangeratetakesexactly1minutetogofrom2kPato0kPa.(ex:Let’ssaythatpressureis1.5kPa.Youwouldthenconductyourtestat1.5kPafor2hours.)
