From: Borries Demeler <demeler@bioc09.v19.uthscsa.edu>
  To  : jphilo@mailway.com
  Date: Thu, 18 Nov 1999 12:54:37 -0600 (CST)

Re: unexpected monochromator movement during velocity runs

John,

I have seen this problem too, but not on our machine. I am running
3.01h on both our XLA and XLI, and that problem doesn't occur.
Another machine in someone else's lab had a similar problem, but
it was also running 3.01h. I'm tempted to think this may be 
hardware related for that reason. They ended up getting Beckman to
replace their machine because they couldn't fix the problem.
Hope yours is not victim of an unfixable problem.

Is the changed wavelength reported in the scanfile? In the machine
I mentioned this wasn't the case, i.e., the scanfiles reported the
same wavelength for all scans, although it clearly had shifted, 
but I don't think it ever happened in the middle of a scan.

If you can get a different monochromator, it may be worthwhile to 
swap it with yours and see if the problem goes away, in case it is
hardware related.

Good luck getting it solved.

-Borries
> 
> I am experiencing an instrument problem and I am wondering whether
> others are seeing the same thing.
> 
> During velocity runs I find that the wavelength occasionally changes
> during the middle of a run, even though all cells are set to the same
> wavelength. This causes the apparent concentration to suddenly go up
> or down (most noticeable in the plateau, of course). This produces
> major problems for all methods of analysis that I can think of, but is
> particularly bad for DCDT analysis.
> 
> This effect is especially large and noticeable when you are working on
> a steep part of the absorption curve rather than a peak. Examination
> of the file headers shows that indeed the recorded wavelength actually
> does sometimes change back and forth by a nanometer.
> 
> This problem was present some years back (? '92 or '93) because the
> instrument control software was asking for a wavelength 'seek'
> operation before every scan. The software was then altered to leave
> the wavelength alone during velocity scans when all cells were the
> same wavelength. I am suspicious that this same error has crept back
> in again.
> 
> If it's a software problem it may of course differ for different
> versions of the instrument software. I am running version 3.01h of the
> instrument control program (the "GUI").
> 
> I'd appreciate hearing from others whether you believe you have seen
> this problem, and also whether you are sure your system does NOT have
> this problem (and please include your GUI version).
> 
> Best regards to all,
> 
> John Philo, Alliance Protein Laboratories
> www.ap-lab.com
>