[RASMB] intensity issues

[Borries Demeler]

> Hi Borries,
> 
> Your plot gives the intensity as a function of scan number; it would
> be interesting to see whether the period of the fluctuation is a
> constant time (implying some slow cycling process in the machine, maybe
> cooling or vacuum?); or related to speed or interval between scans
> (perhaps implying some kind of curious timing problem).
> 
> Do you know if the period changes at different speeds?

Hi Andrew,

I agree with you, this period is very peculiar. I was thinking about asking
them to run it again at a different speed, but right now I don't have any
data from different speeds. I guess they don't want to run it again until
it is fixed. At any rate, the period is on the scale of minutes, which is
probably not speed related, but I am just speculating. Tom's earlier comment
seems plausible - some underlying oscillation in the electronics of the 
machine are visible because the intensity is so low the oscillation's amplitude
becomes apparent. Beckman service is supposed to show up today and fix it.
I was just hoping to provide them some addtl. info so they could troubleshoot
this quicker. I'll post to the list when they find the problem.

-Borries

> 
> Borries Demeler wrote:
> > Dear Colleagues,
> > 
> > I have an issue with an XLI at FSU - it has a strange problem with
> > intensity. First, it is very low, and second, it has a regularly spaced 
> > intensity oscillation. Please see the attached image. It was generated
> > by scanning a channel containing just water in intensity mode and 
> > averaging the intensity in the flat region over all points. The plot
> > shows the average intensity of the scans over a number of scans. The
> > entire run shows this consistent intensity fluctuation, and it is 
> > apparent in all cells. The run was done at 50,000 rpm. Does anyone
> > have a good suggestion as to what flaw in the XLI could potentially
> > cause such a pattern? Is this a lamp firing issue, or a voltage issue
> > with the PM tube or flash lamp? The machine was just newly installed
> > and configured by Beckman service, and this is the pattern it produces.
> > 
> > Thanks, -borries
> > 
> > 
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> -- 
> Dr Andrew Leech                   *  Laboratory Manager
> Technology Facility               *  Molecular Interactions Laboratory
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