furtherreduceparticulatecontamination, theentirevacuumchamberwasorientedonitsside,sothatany errantparticleswouldbepulledbygravitytothesideofthechamberinsteadoflandingontheadjacent cartridge.Barrierfilmwasusedtopreventlubricantlossesduetocreeping. Toheatandcoolthebearingsevenly,athermalshroudwasplacedbetweenthebearingtestfixtureand theinsideofthebelljar.Thethermalshroudwassimplyalargesheetofcopperwithcoppertubing solderedontotheexteriorsurfaceinan"S"pattern.Toincreasetheemissivityoftheinteriorsurfaceof theshroud, aBallAerospace-developed blackpolyimide paintwasapplied. Thisassembly wasthenrolled intoacylinder. Theendsofthetubingwererunthrough liquidfeed-throughs intheaccess ring.Hotorcold liquidcouldthenbepumped through theshroud, whichcouldthenradiatively heatorcoolthebearings. In ordertooffsettheheatsinking caused bythevacuum chamber flangeandhousing, thehousing was wrapped withthermal tape.Bybalancing theshroud andhousing temperatures, afairlyuniform end-toendtemperature wasachieved. Theprocess ofcollecting dataforalong-term testpresented someinteresting challenges tothedesignof thedatalogging system. Although themeasurement ofthedataneeded tobeaccurate, theprocess only needed tooccuraboutonceeveryhour.Atypicalprintout isshowninFigure5.Reliability andflexibility became moreimportant thanbandwidth. An"elegant" solution wasfoundbyusingadataloggersystem manufactured byValidyne Engineering Corp.Thissystem consisted ofaninterface boardontowhichthe signatwireswereconnected andaprocessing card,wflichplugsintoasparestotinapersonat computer. Forthistest,asurplus 386-50wasusedwithDOS5.0astheoperating system. Date Time 1 2 3 4 T1 T2 05/27/98 14:49:15 0.000 0.1706 0.1679 0.1293 29.36 29.54 05/27/98 14:59:15 0.000 0.1835 0.1478 0.1203 29.12 29.18 05/27/98 15:09:15 0.000 0.1801 0.1573 0.1116 28.88 29.03 05/27/98 15:19:15 0.000 0.1974 0.1329 0.1231 29.13 29.30 Key:1=emptybay;2=FreonTFprocessed bearingpairretention force(pounds); 3=VertrelXFprocessed bearingpair;4=HFE-7100 processed bearingpair;T1=BaseTemperature (C);T2=TopTemperature (C) Figure5.Typical printout Theoutputs fromthestraingagesaswellasthermocouple leadswerepassed through electrical feedthroughs intheaccess collarofthevacuum chamber. Thesewireswerethenattached totheinterface board,whichalsoconverted thesignalfromanalogtodigital.Theinterface boardcanbeconfigured many wayssothateachoftheeightchannels canbehooked uptomonitor voltage, current ortemperature. This boardisconnected tothecomputer bya50-wire ribboncable. Thedisplay ismeant tobetoggled between twomodes. Theset-upmodeallowsdataacquisition properties suchasreportfrequency andaveraging tobeset.Alsointhismode,channel titlesandnumber ofdecimal placesareselected. Inthelogging mode,dataisbeinggathered anddisplayed onthescreen. Upto32different channels canbemonitored andviewed atthesametime. TheValidyne processor canprocess information muchfasterthanwhatwasneeded forthistest,butit alsoallowslongperiods oftimebetween cycles. Forthistest,thetimeperiodbetween readings was initially setat3600seconds, butincreased tosixtimesperhourafter2.85e106 revolutions. Atthe appropriate time,thedataloggerwouldreadthestraingagevaluesaswellasthetemperature values. Thereported valueswereactually anaverage of50instantaneous values. Thedate,timeandeightdata valueswerethenprintedinasinglerowontheprinter, andalsoappended tofilesonaboththeharddisk, anda3.5-inch floppy. Forhardcopybackup, awide-carriage, tractor-feed, dot-matrix printerallowed printing ofallrelevant dataonasingleline.Aboxoffan-fold paperwouldlastmanymonths without interruption. 29