Chromatography Forum

Hi, I have GC 6890 FID/FPD, on column injection. My problem is that FPD since some days doesn't want to ignite. It tries, and shuts down again. Temperature is OK (250degC), Gases are ok (FID flame stays on, but also higher temp 330degC), Mkup gas I changed into He, lit offset changed to 2, seems everything works fine, but still doesn't ignite. The only thing i noticed is that while ignition Air flow actual differ from the set point of 200, then drops down to 100, while actual shows 107...myabe it was always like that, but no clue what more i can do-any idea? cheers

Make the FID signal offset a higher number, like 2.

Make the FID signal offset a hogher number, like 2.

But FID is OK.


Is air inlet pressure sufficient ?

May you temporarily reduce makeup flow by a factor of 2 or 3 and see how detector behaves ?
Is there a jet which needs cleaning ?

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Edit

Try to temporarily set lit offset to 0,5.

You said you changed makeup gas to hel. Is there (I hope it is) a detector configuration setting where you declare what is your makeup gas ? (It may be important, because it influence makeup gas flow).

Thanks dblux_
FID indeed works fine on the same GC.
I m going to try your advice, and before i start to put the whole FPD into pieces i was thinking of some more tries out. I tried with lit before to 0,5 and didnt show any better. I do however change in the configuration the type of Mkup gas, so far we ran on N, then i swapped it week ago into He and it worked pretty well until last 2 days. Could be that i need to replace the ignitor? Thanks!

Thanks dblux_
... Could be that i need to replace the ignitor? ...

Dominika, I'm not familiar with FPD, but per analogiam to FID it may be blown ignitor filament.
Let us know when you find solution and good luck

It works after all. I removed the ignitor cable and then cleaned up the ignitor with IPA, there was some dust look like dirt inside. However, after switching GC ' on ' i left it for about 20 min to heat up, and then i pressed ignition 'on'. Flame came on. What's new for me, i did that while Mkup gas was still kept manually OFF during the whole process, once when flame came on, then i put Mkup gas on again. During automatic ignition Mkup gas comes off/on, but i noticed that this caused my problem back again. it's still a mystery to me, but i am happy with the end result

Two things I have observed. First, the FPD needs to be hot for a good long time before attempting ignition. I have even set it hotter to light it and then turned it down to operate. Second, I have found that pinching the exhaust tube helps quite a bit. You pinch it until you feel the pop, wait until it drops the air flow to it's proper operating point and then release the tubing.

Best regards,

AICMM

[quote="AICMM"]Two things I have observed. First, the FPD needs to be hot for a good long time before attempting ignition. I have even set it hotter to light it and then turned it down to operate. Second, I have found that pinching the exhaust tube helps quite a bit. You pinch it until you feel the pop, wait until it drops the air flow to it's proper operating point and then release the tubing.


Thank you AICMM, i will definitely try that one next time,
regards,

Hi, I have GC 6890 FID/FPD, on column injection. My problem is that FPD since some days doesn't want to ignite. It tries, and shuts down again. Temperature is OK (250degC), Gases are ok (FID flame stays on, but also higher temp 330degC), Mkup gas I changed into He, lit offset changed to 2, seems everything works fine, but still doesn't ignite. The only thing i noticed is that while ignition Air flow actual differ from the set point of 200, then drops down to 100, while actual shows 107...myabe it was always like that, but no clue what more i can do-any idea? cheers

You should to increase hydrogen pressure up to 100kPa, and air about 50/60 kPa. next, when the flame is ignited decrease the hydrogen @ 70kPa