flow H2 and air goes down en up

[HP]

Hi,
I am using a 6890 Agilent GC. Currently the flow of H2 is 40ml/min and air flow 450ml/min.
The instrument is ready if this is OK. Normaly it is ready and after 2min is again not ready. The flow goes down en up after 2min (ready and not ready).What could be happening. My guess was JET replace. I made it and after this it is again the same.

Please help me. Thanks

[Peter Apps]

Check that the pressure of air and hydrogen in the supply to the GC is not fluctuating.

Is it only the hydrogen that fluctuates, or the air and the hydrogen ? If both I suspect an electronics or hardware problem.

Check on the software, presumably Chemstation that you are not accidentally programming the flows, or turning the detecotr on and off.

Peter

[Radish]

Could it be that your flame is going out? When this happens, the software will decrease the gas flows and then increase them as it tries to re-light.

[HP]

Hi,
thenk jou everybody!!! I found the problem it was a lit offset. I put 1 and everything is ok now