Cyclic UV detector noise - not a pump problem

[HW Mueller]

CPG, you had stop and go oscillations due to the lamp, yet there was enough light output during an oscillation phase to produce such large peaks as Conny sees them?

[Consumer Products Guy]

CPG, you had stop and go oscillations due to the lamp, yet there was enough light output during an oscillation phase to produce such large peaks as Conny sees them?

HB - in my case when I saw the oscillations in the baseline upon initial equilibration before starting the sequence, I didn't go further and inject any samples/standards. I fixed the problem.

I have also seen small oscillations which, when compared to the size of the sought-for peak, were negligible.

[HW Mueller]

What I would like to know is, whether anybody has seen oscillations due to a dying lamp (not due to electrical interference, etc.) which still had enough light output to create huge absorbances (peaks). Also what would cause a dying lamp to oscillate in repetition?
Conny, don´t you have a new lamp? (The trouble is, by the time the new lamp is put in the air problem could have resolved itself).

[bisnettrj2]

Yes, I have had a lamp go intermittently bad on me while still producing enough power to generate peaks of interest. While the only chromatogram we've seen is during a run, we can consider that the chromatographer has run a 'flow-off' situation with similar events. The easiest solution is flushing the flow cell and re-evaluating the error, although I consider a bubble in the flow cell a rather unlikely occurence. Based on what I've seen, a lamp power fluctuation is the cause, and it is very easy to swap a lamp and re-evaluate a problem. If the problem "goes away" after swapping the lamp, it is a throw away excuse that the "air bubble" went away following the lamp replacement.

[HW Mueller]

bisnettrj2, ok, I see that this has to be approached differently if I am not to go away from this discussion with another myth engrained in my head:
What was the S/N ratio of your "peaks of interest" during a bad phase of the lamp?
I still don´t know about the oscillations.