[RASMB] Radial-dependent noise in Beckmann XL-I

[John Philo]

Anna, I have a somewhat different view from the others about the cause of
this problem. Noise that shows up only at certain radii and independent of
wavelength is characteristic of a mechanical motion issue with the slit
assembly. I'm not at all clear why the slit assembly motion problem occurs
only at low temperatures, but the characteristics of the noise itself are
exactly what one expects for this sort of problem. Usually these problems
are caused by a burr or some dirt getting between the slit assembly and the
gold-plated ring that caps the PMT. Occasionally the thin foil piece in
which the slit is formed comes partially un-glued from the body of the slit
assembly and catches on the PMT ring cap at certain radial positions.

John


  _____  

From: rasmb-bounces at rasmb.bbri.org [mailto:rasmb-bounces at rasmb.bbri.org] On
Behalf Of anna vitlin
Sent: Thursday, January 26, 2012 4:33 AM
To: Subject: [RASMB] Radial-dependent noise in Beckmann XL-I



Hello,
 
We have a Beckmann XL-I running a An-60 Ti rotor. 
When running sedimentation velocity experiments at 4 deg. we have noticed
protein-independent, time-independent, radial-dependent noise, consistently
between 6.2 and 6.4 Radius. 
This phenomenon occurs using different cell assemblies, different
wavelengths and different velocities but does not occur at 20 deg. 
Has anyone detected behavior like this and how do we troubleshoot it?
Should we call for service?
 
Thank you
Anna Vitlin 
Tel-Aviv university
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