Bruker BPHG 90 - Purge Function; Start Function

Operation
48 Z33081_00_001
7.3 PurgeFunction
BeforetheBPHG90canbecooleddownforthefirsttime,theinstrumentmustensurethat
no gases other than H
2
 will be present in any internal tubing and in the conversion
chamber.ThisistoavoidablockagecausedbythefreezingofothergasessuchasCO
2
,
N
2,
etc.ForthispurposetheworkingvolumeisfirstevacuatedandthenfilledwithH
2
gas.
The process is executed twice and takes a few minutes. The user can select this purge
procedurebytappingthePurgebuttonontheStandbyscreen(seefigureStand‐by Screen
with Warm‐up Conversion Chamber [}44]).
During the process, the instrument reports progress through the Purge in progress
screens,indicatingthepassnumberinthetitlebar.Thepurgeprocesscanbeabortedby
tapping the Abort Purge button (see the figure System check with low coolant level
warninginthesectionSystem Check Window [}43]).
Wheneveramaintenanceoperationisperformed(e.g.achangeofhydrogensupplybottle,
purifiercartridgereplacement)andthereisthepossibilitythatforeigngasseshaveentered
thegenerator,thenapurgeoperationmustbecarriedout.
Apurgeoperationcannotbecarriedoutwhenthesystemiscold.InthiscasethePurge
buttonintheStandbyscreen isgreyedoutandthe system needstobewarmed up first
(seesectionGenerator Shut‐down [}53]).
Figure7.13:PurgeinProgressScreen
7.4 StartFunction
OncetheworkingvolumeoftheBPHG90hasbeenpurged,theStandbyscreen(seethe
figureStandbyScreenwithWarmupConversionChamberinthesectionStand‐by Mode [
}43])reappearsandtheinstrumentisreadytobecooleddown.Thecooldownprocedure
isinitiatedbytappingtheStartbutton.
The conversion chamber in the BPHG 90 is contained within the vacuum space of the
cryostat,toprovide aneffectivethermal isolation fromtheenvironment. Itisessential for
theefficientlowtemperatureoperationoftheinstrumentthattheresidualpressureinthe
vacuumchamberisbelowapresetlimit(5mbar)beforetheconversionchamberiscooled
down.Thesystemstartsthecooldownprocedurebytestingand,ifnecessary,improving
the vacuum. Prepumping of the cryostat vacuum, by the internal diaphragm pump, will
takeafewminutes.