[3dem] Re: Slowly varying magnetic field

Thu Jun 4 12:57:48 PDT 2009

Dear John,

We have similar problems on our F30 here in New York, even though our  
room is shielded and has an active field compensation system. We  
haven't been able to find where the problem come from yet. If anybody  
has had that problem and has solved it, we are also interested in  
hearing about it.

Amedee

Amedee des Georges
Howard Hughes Medical Institute
Columbia University Medical Center
Black Building Room 2-221
630 West 168th Street
New York, NY 10032-3702
ad2720 at columbia.edu
Phone: 212-305-9524
Fax: 212-305-9500

On Jun 4, 2009, at 3:00 PM, 3dem-request at ncmir.ucsd.edu wrote:
> Today's Topics:
>
>   1. Slowly varying magnetic fields (John Rubinstein, U of T)
>   2. Re: Slowly varying magnetic fields (Henning Stahlberg)
>
> From: "John Rubinstein, U of T" <john.rubinstein at utoronto.ca>
> Date: June 3, 2009 3:23:23 PM EDT
> To: 3dem at ncmir.ucsd.edu
> Subject: [3dem] Slowly varying magnetic fields
>
>
> 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
>
>
>
>
>
>
> From: Henning Stahlberg <henning.stahlberg at unibas.ch>
> Date: June 3, 2009 3:33:36 PM EDT
> To: "John Rubinstein, U of T" <john.rubinstein at utoronto.ca>, 3dem at ncmir.ucsd.edu
> Subject: Re: [3dem] Slowly varying magnetic fields
>
>
> Hi John,
>
> Do you have NMR or MRI machines nearby?
>
> Henning.
>
>
> ___________________________________________________
>
> Henning Stahlberg
> Center for Cellular Imaging and Nanoanalytics (C-CINA)
> Structural Biology and Biophysics, Biozentrum,
> WRO-1058, Mattenstrasse 26
> University Basel, CH-4058 Basel, Switzerland
> Tel: +41 - 61 - 387 32 62 (office)
> Tel: +41 - 61 - 387 32 27 (administrative assistant)
> Fax: +41 - 61 - 387 39 86
> mailto:Henning.Stahlberg at unibas.ch
> Skype:henningstahlberg
> http://stahlberglab.org
> http://2dx.org
> ___________________________________________________
>
>
> On Jun 3, 2009, at 9:23 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
>>
>>
>> _______________________________________________
>> 3dem mailing list
>> 3dem at ncmir.ucsd.edu
>> https://mail.ncmir.ucsd.edu/mailman/listinfo/3dem
>
>
>
>
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