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<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=536303516-28062011>Peter,</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=536303516-28062011></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=536303516-28062011>Yes, perhaps a slit sticking problem could explain
what you are seeing, but it looks like the instrument thinks the slit is moving
along during the 'stuck' periods, which suggests the potentiometer is actually
rotating, which in principle it cannot do without the slit moving too. Thus
it might be a mechanical problem with the drive gear or other parts of
the motor-potentiometer assembly. The set screws on the shafts in the
motor-pot assembly can sometimes work loose, allowing slippage, and if memory
serves that effect is similar to what you are seeing. But clearly mechanical
slippage would be aggravated if the slit assembly cannot move freely, so you
could have two problems needing correction.</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=536303516-28062011></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=536303516-28062011>You could check yourself for dirt or a burr on the slit
assembly (remember to power off before you remove it so room light doesn't blow
out the PMT pre-amplifier). But if the problem is in the motor-pot assembly
you'll need your service tech.</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=536303516-28062011></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=536303516-28062011>John</SPAN></FONT></DIV><BR>
<DIV dir=ltr lang=en-us class=OutlookMessageHeader align=left>
<HR tabIndex=-1>
<FONT size=2 face=Tahoma><B>From:</B> rasmb-bounces@rasmb.bbri.org
[mailto:rasmb-bounces@rasmb.bbri.org] <B>On Behalf Of </B>Peter Edward Prevelige
Jr<BR><B>Sent:</B> Tuesday, June 28, 2011 8:25 AM<BR><B>To:</B>
rasmb@rasmb.bbri.org<BR><B>Subject:</B> [RASMB] Plateaus in
Absorbance?<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV class=WordSection1>
<P class=MsoNormal>Hi All –<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>We are observing what appear to be plateaus in the absorbance
profile in both equilibrium and velocity runs. The plateaus are seen with
different samples and different rotor speeds. Our current hypothesis is that the
slit in front of the detector is sticking and releasing. It appears that
these are lost steps as after the slit releases the exponential is shifted along
the radial distance axis. Some representative data is attached showing different
speeds and cells. The superimposed scans (cell 1 35K, & cell 1 44K) are
scans recorded about 10 hours apart in time.<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>Is it reasonable to think that the slit is sticking? How can
we diagnose and fix this problem?<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>Peter<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal><SPAN style="FONT-FAMILY: Consolas; FONT-SIZE: 10.5pt">Peter
E. Prevelige Jr.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: Consolas; FONT-SIZE: 10.5pt">Professor<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="FONT-FAMILY: Consolas; FONT-SIZE: 10.5pt">Dept.
of Microbiology, BBRB 416/6<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="FONT-FAMILY: Consolas; FONT-SIZE: 10.5pt">Univ.
of Alabama @ Birmingham<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="FONT-FAMILY: Consolas; FONT-SIZE: 10.5pt">845
19th St. South<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: Consolas; FONT-SIZE: 10.5pt">Birmingham AL.
35294-2170<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="FONT-FAMILY: Consolas; FONT-SIZE: 10.5pt">Phone
205 975-5327<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="FONT-FAMILY: Consolas; FONT-SIZE: 10.5pt">FAX
205 975-5479<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="FONT-FAMILY: Consolas; FONT-SIZE: 10.5pt"><A
href="mailto:prevelig@uab.edu">prevelig@uab.edu</A><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="FONT-FAMILY: Consolas; FONT-SIZE: 10.5pt"><A
href="http://www.microbio.uab.edu/faculty/prevelige/prevelige-p.htm">http://www.microbio.uab.edu/faculty/prevelige/prevelige-p.htm</A><o:p></o:p></SPAN></P>
<P class=MsoNormal><o:p> </o:p></P></DIV></BODY></HTML>