DETECTORS
HID - Helium Ionization Detector
Groundelectrode
Arcelectrode
1-2mmgap
Use the arcwindow
to check arc and
groundelectrode
positioning.
4mm
Screw
clamp
stop
Cleaning the HID
1. Unclip theamplifier leadandslide itoff thecollectorelectrode.
Unclipand remove the leads from thepointedand flatelectrodes
(note that the green wire is
connected to the pointed
electrode, and the redwire is
connected to the flat
electrode).
2. Remove the the arc and
groundelectrodesbyloosening
the1/8” fittings thathold the
electrodes in thearccross.
3. Removethecollectorelectrodebylooseningthe1/4”fittingthatsecures
it in thedetectorbody.
4. Useapieceof100-400grain sandpaper toclean the surfaceof the
collectorelectrodeand thepointof thegroundelectrode. Sand the tipof
thearcelectrodeso that it isflushagainst theceramic insulation,and to
removeanyresidue. Whilehandlingtheelectrodes, trytominimizehand
contactbyholding themwithacleanpaper towel.
5. Removeanysandingresiduefrom theelectrodesusingapaper towel
optionallymoistenedwithmethanoloranotherquick-evaporatingsolvent.
6. Replace the electrodes and check for
proper alignment. The collector electrode
should extend about 4mm into thedetector
body. Anexisting screwclamp stopon the
collectorelectrodeshouldallowreplacement
withoutreadjustment. Should
adjustmentberequired,loosen
thescrewclamptopositionthe
electrode,thentightenittohold
theposition. Topositionthearc
andgroundelectrodes, remove thearccross from thedetectorbodyby
loosening the1/4” fittingconnecting the twopartsof thedetector (this
fittingalsosecures thesupportbrace). Thegroundandarcelectrodesshouldhaveagapof
about1-2mm (0.040-0.080”)between them,with thegapcentered in thearccross. Hold
thearccrossup to the lightandverify theelectrodes’positionsby looking through thearc
window. Once theelectrodesarepositioned, tighten themsecurelywithawrench.
IfyourHIDbaselineseemsnoisy, trycleaning theelectrodesfollowing thestepsbelow. Over time, theHID
electrodescandevelopacoatingofsoot,whichcancause thearc
toflickerorchangeposition,resulting insuddenbaseline jumps.
Greenwire
Redwire
