[RASMB] vacuum fluctuation

[Walter Stafford]

Hi Chin,

    This could be caused by the switch from the thermistor to IR temp. 
sensing mechanism. The switch occurs at 100 microns of pressure in the 
chamber. You can avoid this usually by turning on the diffusion pump 
while you are equlibrating the machine before the run. And to accomplish 
that you must enter a speed of 0 (zero) and press "Start". If your rough 
pump is not pulling the vacuum below 100 microns, the switch to the IR 
sensor will not occur before you start and the diff pump heats up. I 
have seen this on both my machines. It also sounds like your vacuum 
gauge calibration may be off. I am surprised that this lead to so much 
extra noise, tho.

Walter

QCZ wrote:
> Hi all,
> I have recently seen a vacuum jump from 9 microns to 45 microns during 
> the acceleration to 50K rpm. At the same time, the temperature goes up 
> to 20.4C from the set temp of 20.0C. It came back stepwise to 20C 
> after 2 minutes based on the temperature plot in sedfit.  My 
> experience is that this cooling took too long. The data fit was really 
> noisy with the rmsd of 0.015 (total OD280=0.9) or above and the 
> residual was bad for the first 45 scans. 
> Is this a vacuum issue or the temperature control problem? Any input 
> will be appreciated.  Thanks.
>  
>  
>  
> Chin
> ------------------------------------------------------------------------
>
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-- 
Walter F. Stafford, Ph.D.
Senior Scientist
Analytical Ultracentrifugation Research Laboratory
Boston Biomedical Research Institute
64 Grove Street
Watertown, MA 02472-2829
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