[3dem] Current measurement with viewing screen
Bob Grassucci
rg2502 at columbia.edu
Tue Nov 9 09:16:47 PST 2010
Hi Fred,
We have been using a BS factor of 0.85at 200 kV and 0.75 for 300 kV. It
can be set so that it is used in low dose if you are comfortable
editing the registry.by the following settings.
regedt32
Hkeylocalmachine
software
FEI
Lowdose
BS factor 200 0.85
300 0.75
After you do this the low dose options tab should have the correct dose
readings, I am told that this is routinely done with the newer scopes
but was not early on. Of course a faraday cup is the most accurate way
to go but not everyone has access to one. I hope this helps.
Bob
On 11/9/2010 12:01 PM, Fred Sigworth wrote:
> To calibrate our CCD camera we have been using the viewing screen to measure the beam current in our Tecnai F20. Of course this measurement is in error due to backscattering, secondary electrons, etc. and the right way is to use a Faraday cup. But, has anyone compared the value from a Faraday cup with the screen current? If the conversion factor is known, even approximately, that would help us a lot.
>
> Fred Sigworth
>
> Fred J. Sigworth
> Department of Cellular and Molecular Physiology
> Department of Biomedical Engineering
> Yale University
> New Haven, CT 06520
> tel. 203 785 5773
> fax 203 785 4951
> fred.sigworth at yale.edu
>
>
>
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> 3dem at ncmir.ucsd.edu
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>
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