Flame Ignition Problems - Agilent Technologies 6890 Series Service Manual

Flame ignition problems

Note The flame is easier to light at higher detector temperatures.
If the flame doesn't light at all, be sure the glow plug circuit is working. Try
to ignite the flame while watching the visual display. If the display does not
momentarily go to greater than 65500 counts, the glow plug is either damaged
or not receiving power. Check the pin connections at the printed circuit board,
the lead connection on the glow plug and the appropriate 5A fuse on the GC
main circuit board. If the glow plug has failed, replace it.
If the FPD flame won't light or stay lit, check/do the following:
1. Be sure there is a problem. The flame normally does not make any sound
when it ignites and the increase in signal offset on the visual display is
often only a few counts. To verify flame ignition, remove the vent line
from the top of the detector and hold a mirror or shiny surface near the
aluminum exhaust tube. If the flame is lit, condensation will form on the
mirror.
Check the displayed air flow rate. The display should go to 200 mL/min
while trying to ignite to flame. If not, there is insufficient supply pressure.
Check the Lit offset value. If it is zero, autoignition is turned off. If
2.
it is too large, the software will not recognize that the flame is lit and will
shut the detector down.
3. Increase the air supply pressure to the pneumatics module. This makes
the flame easier to light but does not affect the air flow rate setpoint.
4. Under some operating conditions, the flame may be more easily lit with
the rubber drip tube removed. After lighting the flame, reinstall the drip
tube.
5. If the flame still won't light, there may be a large leak in the system. This
results in measured flow rates very different from actual flow rates.
Thoroughly leak check the whole system.
Jun 2001
Detectors
Agilent 6890 Gas Chromatograph Service Manual
Flame Photometric Detector (FPD)
Diagnostics
350
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