11 Replies Latest reply on Oct 30, 2017 8:01 AM by eme091

    6890 GC flow issues FID/TCD


      I am currently having a flow issue with my 6890N GC(w/ G1888 HS).  I am doing yearly flow checks.  Hooked up a calibrated flow meter to DET exhaust and turned off all gases (pressure off, makeup He off, Air off everything). I then enabled them one at a time at varied levels.  FID= detector controlled gases worked fine and in spec.  When I set the column flow the reading was low out of spec tried the varying levels still no go.  Switched to the front which is a TCD.  Same result detector controlled gases worked fine, but as soon as I went to do the flow through the column low.  TCD was lower than the FID (TCD=1.36 on set of 2.5, FID was 1.8 on same setting).  Checked gas filters they were old but no problem.  2 different columns but check all parameters and re installed to ensure good connection.  Not really sure where else to go at this point.  Any help or suggestion would be greatly appreciated.





        • Re: 6890 GC flow issues FID/TCD

          Hi eme091,

          When trying to measure smaller flows with a flow meter there can be some difficulty. The volume of the meter tubing(should be small),adapter to the detector (tight and proper fit) etc can play a factor. Also I have had a meter that had trouble with low flows and it was only resolved by making sure the meter had the gas type set correctly and was attached to the detector output and left alone (not moved)  for 10 minutes to stabilize . There are also some meters out there that are not spec to read low flows. What meter are you using?




          I updated the tags on this post so it will have more visibility in the community and others can comment.

          • Re: 6890 GC flow issues FID/TCD

            So the EPC board did fix the back flow, I had improperly zeroed the new board.  So now the back flow is hitting right on the nose.  The front flow is still low.  if I increase the oven temp from 50 to 100 the flow reading moves from 1.4 to 1.78 on the meter (which I did verify on another instrument).  Currently inlet tot flow is 51.3, split mode.  So at least the back flow is back to normal.  Will continue to work on this, but the back line was the priority.  We only use the front TCD once in a while, but any other ideas would be great.  Thanks