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<DIV><SPAN class=166484219-01062007><FONT face=Arial color=#0000ff
size=2>John,</FONT></SPAN></DIV>
<DIV><SPAN class=166484219-01062007><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=166484219-01062007><FONT face=Arial color=#0000ff size=2>First,
can you quantify what you mean by the noise is "quite bad". What is the r.m.s.
noise for a scan of an empty hole (<U>not</U> an empty cell) in the rotor
now, and what was it in the past?</FONT></SPAN></DIV>
<DIV><SPAN class=166484219-01062007><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=166484219-01062007><FONT face=Arial color=#0000ff size=2>These
intensity readings are never absolute---20,000 counts on one instrument might be
10,000 on one and 30,000 on another. The only thing that counts is what is
the ratio of the intensity when the lamp is clean versus now. Even a 2-fold
drop of intensity usually has a minimal impact on the noise level, so the real
source of the problem may be something else altogether (perhaps a dirty slit
assembly). </FONT></SPAN></DIV>
<DIV><SPAN class=166484219-01062007><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=166484219-01062007><FONT face=Arial color=#0000ff
size=2>John</FONT></SPAN></DIV>
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<DIV></DIV>
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left><FONT
face=Tahoma size=2>-----Original Message-----<BR><B>From:</B>
rasmb-bounces@rasmb.bbri.org [mailto:rasmb-bounces@rasmb.bbri.org] <B>On
Behalf Of </B>John E Harlan<BR><B>Sent:</B> Friday, June 01, 2007 11:49
AM<BR><B>To:</B> rasmb@server1.bbri.org<BR><B>Subject:</B> [RASMB] Lamp
Intensities on Analytical Ultracentrifuges<BR><BR></FONT></DIV><BR><FONT
face=Arial size=2>I am starting to have some problems with rapidly decreasing
lamp intensities on my analytical instruments. Within about 1 month of
moderate use after my service people were in (they cleaned the optics while
checking other things), I find the noise in my velocity absorbance scans is
quite bad. When I check the intensities I find maxima at 230nm to be
8300 for an XLA and 13000 for an XLI, well below the 20000 to 30000 I should
find for a well functioning instrument.</FONT> <BR><BR><FONT face=Arial
size=2>I have two questions:</FONT> <BR><BR><FONT face=Arial size=2>1)
What could cause such a rapid decay of performance. I suspect oil
leaks fouling the optics (I have observed droplets in the can on at least one
occasion). I understand alignment can also cause problems. Is
there something else to ask my service people to check?</FONT> <BR><BR><FONT
face=Arial size=2>2) I have heard that people that have upgraded to a
turbo-molecular vacuum pump have been quite pleased with performance.
Can this upgrade help keep my optics clean, if indeed that is the
problem?</FONT> <BR><BR><FONT face=Arial size=2>Thanks for your help in
advance.</FONT> <BR><BR><FONT face=Arial
size=2>John</FONT></BLOCKQUOTE></BODY></HTML>