Toprolong the lifeofyourCCDdetector,use it instrict
accordancewithyourGCsystem’soperating instructions. For
instance,ifyouhaveanSRIMud-LoggerGC,youshouldconnect
yoursamplestreamsat10psi so thatnomore than5mL/minof
purehydrcarbonflowreaches theCCD. In theeventofasensor
burn-out,simplyremove thewhiteandblackwiresfrom the top
twonickel pins,
andmovethemto
thebottompairof
nickelpins toconnect them to thesecondsensor. Itdoes
notmatterwhichwiregoesonwhichpin. Toreplace the
CCDdetector,unscrew itsbrass fittingafter removing
thewires from thenickelpins. Pullout theoldoneand
removetheprotectivecapfromthereplacement. Sensor-
sidefirst, insertthereplacementintothe
fittingwithitshalf-moonshapedcut-out
on thebottom. Replace the fittingand
HANDTIGHTEN it. If the detector
fitting is screwed on too tightly, the
detectorwillnotreceivepropergasflow.
Next,sliptheblackandwhitewireplugs
over the pins, and your replacement
CCDdetector is ready touse.
Theory of Operation
TopViewofCCDDetector
TheCCDsensorelementsarethetiniestandmostimportant
partof thedetector. EachCCDdetectorcontains twosensor
elements,butusesonlyoneata time. Acatalyticcombustion
sensorconsistsofacoilofplatinumwirearoundanaluminacore
surroundedbynoblemetalcatalysts. Eachsensor issuspended
betweenapairofnickelpins. Thedetector isshippedwitha
protectivenyloncaptoppedwithsteelmesh,butisinstalledona
SRIGCwithoutit. Duringachromatogaphicrun,a150milliamp
currentheats thecatalyticceramicbead toaround500
o
C,hot
enough tocombust hydrocarbonmoleculesoncontact. The
CCD ismaintained inanoxidativeenvironmentbyusingairas
thecarrierormake-upgas. Thiscombustioncausestheincrease
in temperatureandchange inresistance that ismeasuredby the
sensor. ThischangeinresistancecausestheCCDdetectoroutput
to change, which produces a peak that is recorded by the
PeakSimpledatasystem.
SideViewofSensorElement
Sensors
DETECTORS
Catalytic Combustion Detector - CCD
