FID won't stay lit

[Nikko]

I currently have a 6890 GC with two inlets. The front inlet will hold pressure and temperature before igniting the FID. Once the FID is turned on, the FID ignites (popping sound), the hydrogen quickly returns to 30 ml/min and the air flow (400mL/min) drops and starts to rise again. Once it reaches 400mL/min the system shuts down. I do not see any change in signal during this process. I have changed the FID control and igniter, the jet, the column, checked the flow through the FID and am still having these problems. The back lnlet works great. Any suggests on what might be my problem would be greatly appreciated. Thanks

[Consumer Products Guy]

Whenever I have any issues with an FID lighting or staying lit, first thing I clean the detector and clean/replace the jet.

On on EPC older models, I check the individual gas flows as well.

[mungss]

It's normal situation, drops and rise of air flow after ignited FID. In my opinion, system shut down cause of final air flow rate. There are no enough time to reach to 400 ml/min of air flow, so system was shut down.
At initial condition, i suggest to set 250 mg/min of air flow. After air flow reach to 250 ml/min and you can observe change of signal, increase air flow to 300 and 400 ml/min step by step.

[AICMM]

Two things I would look at. First, do you have enough line pressure to feed two FID's at 400 mL/min? At least 80 psi. Second, if that does not resolve the problem, try switching the EPC's. Put the fittings for the non-lighting FID on the EPC of the lighting EPC and see if the problem moves. Divide and conquer.

Best regards.

[Peter Apps]

Hi Nikko

You say that you have two inlets, does this mean that you have two detectors ?

What is the make up flow(s) ?, what carrier gas are you using and what is the volume (ml/min) flow rate(s) ?

Peter

[aldehyde]

What is your baseline? If your signal is very clean you may be falling below the 'lit offset' (the minimum signal before the instrument thinks it is no longer lit). This is usually set to 2.0 but sometimes must be changed to 1.0 or lower. To do this hit config then click the detector button and look for lit offset.