[3dem] Slowly varying magnetic fields

[Fred Sigworth]

What about elevators?  That seemed to be the source of fields we  
recently discovered in our facility.

-Fred Sigworth

Fred J. Sigworth
Professor
Department of Cellular and Molecular Physiology
Yale School of Medicine
New Haven, CT  06520
fred.sigworth at yale.edu
203 785 5773


On Jun 3, 2009, at 3:23 PM, John Rubinstein, U of T wrote:

> Dear Colleagues,
>
> We recently identified a slow varying magnetic field (e.g. changes  
> on the time scale of ~1 second) in our microscope room.  Looking at  
> our FEI engineer's EMF meter, the minimal 60 Hz AC fields in the  
> room appear to be carried on a (much larger) background that  
> resembles the rising and falling of an ocean surface (but less  
> regular).  This pattern would be quite pretty to look at if the  
> fields did not cause random displacement of our electron beam of up  
> to  ~5 mm on the phosphor screen at 600 kx magnification (Tecnai F20  
> operating at 200 kV).  These fields were not present 2 years ago  
> when we installed the microscope.  We are not near any elevators and  
> our room is on the 3rd floor so we know we are far from any subway  
> tracks.  These "DC" fields are strongest as you go up in our room,  
> but are stronger in our room than in the room above ours.  The only  
> ductwork and wires in our ceiling are those we put in for our air  
> conditioner and dehumidifier and the fields persist with this  
> equipment turned off.  Naturally, I am concerned that something has  
> changed far away in the building causing these effects and that the  
> fields are being transmitted to our room via metal beams or rebar.
>
> Has anybody come across this sort of problem before, identified the  
> source of the fields, and/or solved the problem in some way?  Any  
> insight from experience would be greatly appreciated.
>
> Best regards,
> John
>
> -- 
> John Rubinstein
> Molecular Structure and Function Program
> The Hospital for Sick Children
> 555 University Avenue, Rm. 3330
> Toronto, ON
> Canada
> M5G 1X8
> Tel: (+001) 416-813-7255
> Fax: (+001) 416-813-5022
> www.sickkids.ca/research/rubinstein
>
>
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