Brunson 771 - Plate (Bulls Eye) Vial

37 Operation and Adjustment Manual
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Mountthetransitfirmlyonanystandhavinga3½”‐
8externalthread.Loosenthehorizontaltangent
screwlock.
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1.Viewtheplatevialfromaboveandbringitsbub‐
bletothecenterusingbothopposingpairsofinstru‐
mentlevelingscrews.Thisisidenticaltotherough
levelingprocessdescribedinChapter2.
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2.Now,rotatethestandards180°sothatthetele‐
scopeispointingintheoppositedirection.Checkto
seewhetherthebubbleisstillinthecenterofthe
platevial.Ifso,theplatevialisinadjustment.Ifthe
bubbledoesnotremaincenteredwhentheinstru‐
mentisrotatedtothissecondposition,removeone
halfofthebubbleerrorusingthelevelingscrews(moveittoward
theinscribedcircle,butonlybyhalfway).
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3.Securethehorizontaltangentclamplocktokeepthestandards
frommoving.Removetheotherhalfofthebubbleerrorusingthe
threesmallscrewslocatedaroundtheperimeterofthebaseofthe
platevial.Underthevialisathinspringwhichallowsthe
vialtotilt,sotighteninganygivenscrewwillmovethe
bubbleawayfromthatscrew,andlikewise,looseningany
givenscrewwillmovethebubbletowardthatscrew.
Whenyou’refinishedadjustingthebubblewiththesesmall
screws,itshouldbepreciselycenteredundertheinscribed
circle.
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4.Loosenthehorizontaltangentlockandturnthetele‐
scope180°backtothefirstposition.Thebubbleshould
stillbecentered
undertheinscribedcircle.Ifnot,repeat
theprocessaboveuntilthebubbleremainsinsidethecircle
inbothpositions.
CAUTION:Donʹt“bottomout”the
platevialadjustmentscrews.Ifyoudo
this,thespringunderthevialwillbe
flattenedandproperadjustmentwillbe
impossible.Ifthishappens,loosenallof
thescrewsbythesameamount(aturn
ortwo),andcontinuetheadjustment
process.
Plate(“bull’seye”)Vial
Description:Establishwhetherthe
platevialindicatesalinewhichis
paralleltotheverticalspindle.

Tolerance:Bubblestayswithinthe
inscribedblackcircle.
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Affectedparameters:None
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Requiredequipment:Instrument
stand,smallscrewdriver
Figure4.1