Repeating signal during method run

[novelcs]

Our HP5890 with FID shows a stable/flat baseline, and then when acetone is injected a proper peak is detected and displayed on the computer screen.

But when we load and run a method, which we believe are the same as the methods on our other 2 HP5890s, the spectrum on the screen gives a repeating pattern of a big peak (response 24000) followed by a little peak (response 2500) that repeats itself every 1.5 minutes. The acetone shot on the column does not show up during the run. As soon as the run is over and the GC begins to cool from 300 C, then the repeating pattern ends and the stable base line is resumed.

Suggestions?

[AICMM]

novelcs,

You are probably looking at Test Plot. You don't mention a third peak (which would confirm test plot) but I suspect it is there if you look closely enough.

If using Chemstation, go into the Signal section of the method and make sure it is looking at Det A or Det B (as appropriate.)

If using some other data system, look at Sig1 or Sig2 on the front keypad of the GC to see what is assigned.

Best regards.