[RASMB] vacuum fluctuation

[Tom Laue]

Hi Chin-
This sounds like a "puff" of oil vapor being released during 
acceleration. The vapor is warmer than the rest of what the radiometer 
is viewing, so a rise in temperature is registered. The puff of oil 
vapor may indicate a problem in the seal between the drive and the 
chamber, but not necessarily so.
Noisy data would result if there is oil getting on the optics lowering 
the signal level.
I would suggest that you do a wavelength saving the data as intensities. 
Check that the 230 nm intensity peak is the highest. If not, the source 
and perhaps the detector need to be cleaned.
Best wishes,
Tom

Walter Stafford 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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>

-- 
Department of Biochemistry and Molecular Biology
University of New Hampshire
Durham, NH 03824-3544
Phone: 603-862-2459
FAX:   603-862-0031
E-mail: Tom.Laue at unh.edu
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