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2. Evaluate the level of leakage current in the
FID. This is the amount of current flowing in
the FID electrometer with the flame extin-
guished. The FID should be at operating tem-
perature (300°C minimum). To perform the
test, turn the FID off from the GC front panel
or Control Module. Allow the FID background
to stabilize: it should immediately drop to
2 to 3 pA and then slowly be moving
towards 0 pA. The output on the display
should also be very stable at this point, not
jumping more than ±0.1 pA at a time.
Released: April 2004
6850 Series Gas Chromatograph Service Procedures
If the background stays above 5 pA or is
very unstable, the following components are
suspect:
a. The interconnect or spring could be
contaminated, loose or deformed. Never
touch the interconnect or spring with
bare hands as this will contaminate them
and cause leakage current.
b. The Teflon insulators that electrically
isolate the collector or the collector
itself could be contaminated. They can
be cleaned in solvent or replaced.
c. One of the two detector electronic
assemblies (the electrometer or the FID
electronics board) could be noisy
If the leakage current test passes, proceed
with the next test.
298
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