StandardTCDfilamentwithrubberO-ringgasket
8670-9120
High temperatureTCDfilamentwithcoppergasket
8690-9123
TCD Troubleshooting
WhentheTCDfailstoperformnormally,reviewoperatingconditionstoensure
that carrier gas flow to the detector is unimpeded, and that the column oven
temperature,carriergasflowrate,andcarriergasEPCpressureareallwithin the
desiredoperatingparameters. Ifallconditionsareproperlymetand thedetector
continues toperformpoorlyorfails toperformatall,check theTCDfilamentsfor
damage. Themaindiagnostictestistomeasuretheresistanceofeachfilamentusing
theohmeterfunctionofamultimeterorvolt-ohmeter(VOM). Atroomtemperature,
theresistanceofeachfilamentshouldbe32-34ohms. At100
o
C, thefilamentsare
around40ohmseach. Ifanyfilament issignificantlydifferentfrom theothers, the
TCDbridgewillbeunbalanced,noisyanddrifty. Alleightfilamentwiresmustbe
disconnectedand tested. Sinceall the leadsarebundled togetheras theyexit the
TCDdetectorassembly,youmayneed touse themultimeter orVOM todetermine
theactualpairs. It isnormal foreachfilament tohaveaslightlydifferent reading
within theappropriateoperatingrange,somatch thereadings todetermine the lead
pairs.
With thepower turnedoffand thepowercordunplugged from theelectrical
outlet, raise the red lid toaccess theTCDdetector. Exiting the right sideof the
TCDdetectoroven is thebundleof8 insulated,color-codedwires inpairs. Each
pairofwiresrepresentsonefilamentand isconnected to theappropriately labeled
terminal for itspairedcolors.Onefilamenthasred/green,onered/blue,oneblack/
green, and one black/blue. The red/green and black/blue are the sample side
filaments,and theoneswhich typicallydeterioratefirst. Remove the8wiresfrom
thebridgeterminalbylooseningtheretainingsetscrewswithasmallbladescrewdriver.
Measure theresistanceacross thefilament leadsusinganohmeter,makingsure the
correctpairofcoloredwiresistestedtogetherforeachfilament. Aninfinitereading
isan indication that thefilament isopen,orburnedout. Ifanyof thefilamentshasa
significantlydifferent resistance than theothers (whichshouldbe in the ranges
mentionedabove), itshouldbereplaced. Replacementfilaments,o-rings,andTCD
blockswithfournewfilamentsareavailablefromSRI. Inaddition to thestandard
filaments,optionalgold-platedfilamentsforimprovedcorrosionresistancearealso
available.
SRI TCDdetector replacement parts
DETECTORS
Thermal Conductivity Detector - TCD
Many multimeters are
available; these twoare
fromFlukeCorporation:
USA:1-800-44-FLUKE
EU: (3140)2678200
(filamentpart#sarealso listedon the topof theTCDoven inyourSRIGC)
