[3dem] Vibration issues

[Thorsten Mielke]

Hi Alok,

sounds a bit like the problems we observed during the installation of 
our Polara in 2004: Although our site was surveyed by FEI prior to the 
installation, we observed mechanical vibrations in the ground in the 2-8 
Hz region, which disturbed the resolution below ~3 A. Since the 
vibrations varied in time and intensity, they could not have been 
detected with the instrument (or integrating measurement?) FEI used at 
the time for the site survey. The vibrations could be measured within a 
radius of some kilometers around the institute (including the living 
room of a former colleague ...). They were never constant over time and 
occurred more or less randomly during day or night. We could never 
identify the source. Since the vibrations matched exactly the resonance 
frequency of the dampers, FEI first tried to tune the damper system of 
the Polara and finally installed a compensation system from Integrated 
Dynamics Engineering (IDE). However, we could never really test this 
system while measuring the vibration level at the same time, but our 
overall data looks OK. Due to building of new EM sites at our institute 
and a neighboring institute in about 1 km distance, the vibration level 
in the ground was measured again recently: the low frequencies are still 
present, but seem to be less strong. The experts still speculate about 
the source. To compensate the vibrations, the architect went for a 
massive concrete foundation. Hope this information helps. Maybe you 
should contact FEI regarding a compensation system or some other advice 
to mechanically uncouple the TEM base from the foundation (a platform on 
steel springs, ...)


Best,

Thorsten





On 06.06.2012 02:12, Alok Mitra wrote:
>
> Dear colleagues:
>
> At the proposed installation site for our TF20 (with GIF and STEM 
> functionality)  there is what appears to be unacceptable level of 
> vibrations in the 2-4Hz range. We can not pinpoint the source, based 
> on measurements at various times of day (including weekends and at 
> night) it appears to be endemic, irrespective of the volume of traffic 
> on the street in the vicinity of the location.
>
> I would be very thankful to get feedbacks from those who have 
> experienced such pre installation issues and have undertaken remedial 
> measure as to what that was.
>
> Thanks in anticipation
>
> Alok K. Mitra
>
> School of Biological Sciences
>
> University of Auckland
>
> Auckland
>
> New Zealand
>
>
>
> _______________________________________________
> 3dem mailing list
> 3dem at ncmir.ucsd.edu
> https://mail.ncmir.ucsd.edu/mailman/listinfo/3dem


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Dr. Thorsten Mielke
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Max Planck Institute for Molecular Genetics		
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D-14195 Berlin 					
							
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Fax: +49-(0)30 8413-1385
E-mail: mielke at molgen.mpg.de

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