[RASMB] vacuum fluctuation

[QCZ]

Thanks Walter. The difussion pump was on.  I did try longer equilibration
time (>3.5hours).  It helped stabilize the vacuum. But I still suspect that
the pump is having the problem.  The temperature shift may be OK.

Chin


On 10/20/08, Walter Stafford <stafford at bbri.org> wrote:
>
> 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
> -------------------------
> mailto:stafford at bbri.org
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> receptionist:  617-658-7700
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>
>
>
>
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