[3dem] Re: Slowly varying magnetic field

Thu Jun 4 13:13:00 PDT 2009

I recall from years ago that those plug-in transformers that deliver  
low voltage for small electronics were a problem...

Ron

On Jun 4, 2009, at 12:57 PM, Amedee des Georges wrote:

>
> 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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