Re: How are SEM probe scanning coils typically driven?

From: Phil (semtest_at_hotmail.co.uk)
Date: 02/22/05 

Date: 22 Feb 2005 04:42:59 -0800

Hi Jeff,

Hi Jeff,
My Hitachi S450 has 2 scan coils connected in series
for each axis i.e. 2X, 2Y.
Each axis has a scan power amplifier which drives the
two coils in series. The coils sit in the feedback loop
of the power amplifier to create a linear scan.
The power amplifiers are in fact audio PA modules (STK)
that were used in stereo music amplifiers in the 80's !

Is your intention to do a full digital scan including
replacing the ISI scan generators and amplifiers?

If all you want is digital images then a quick easy way
is to use an a/d and fifo plus maybe a PIC for timing control
to capture the slow (photo?) scan and pass to a PC.

The video signal will be available in the SEM somewhere
as will the pulses for vertical and horizontal scan
starts.

The data could be read in on the parallel port or maybe
USB if you searial;ised it.

Hope this helps
PhilH

jeff miller <cornheadorama@hotmail.com> wrote in message news:<T0xSd.5173$Pz7.3957@newssvr13.news.prodigy.com>...
> Hi,
>
> I'm converting my SEMs for digital image acquisistion. I'll be starting
> with an ISI Mini-SEM. I have the wiring diagram, but it falls short of
> complete schematic as it does not detail the internals of the many
> "modules".
>
> At first glance I noticed a pair of identical voltage dividers associted
> with the magnification rotaryt switch, and failed to notice that there
> are two complete sets of scanning coils, though in restrospect it
> certainly makes sense that if you deflect the beam off axis you'll have
> to deflect it back to get through the aperture.
>
> So it seems the situation is a tad bit more complicated than I thought.
>
> I have some theories. One is that the sets of coils are essentially
> identical and wired in series, with the second set wired backwards. But
> I question in that case whether the beam would ultimately be bent toward
> the aperture, or if instead it would merely be made parallel to the axis
> of the scope but shifted back and forth, missing the aperture.
>
> Another theory is that they are wired in series, but the second set of
> coils has twice as many turns as the first: or in some aother way
> (tighter pole pieces?) the net magnetc feild is twice as strong as the
> first coils, to impart twice as much gross deflection.
>
> Another is that they are driven semi-independently at a fixed ratio,
> perhaps -2:1.
>
> Anyone know how it's typically done? If I don't get any advice I'll try
> poking around with an o'scope, though it would be nice to have a current
> probe too.
>
> I think this is he last peice of the puzzle, the rest seems like a piece
> of cake.
>
> -Jeff

Relevant Pages

  • Re: How are SEM probe scanning coils typically driven?
    ... My Hitachi S450 has 2 scan coils connecfted in series ... Each axis has a scan power amplifier which drives the ... If all you want is digital images then a quick easy way is to ...
    (sci.techniques.microscopy)
  • Re: How are SEM probe scanning coils typically driven?
    ... The coils sit in the feedback loop ... > of the power amplifier to create a linear scan. ... I stumbled on a NI PCI-1422 high speed digital image aquisition ... do let me know about the mag switch eh? ...
    (sci.techniques.microscopy)
  • Re: How are SEM probe scanning coils typically driven?
    ... The coils sit in the feedback loop ... >> of the power amplifier to create a linear scan. ... One of the worst aspects of the diagram is that they collapse ... > was forced to consider that possibility because the mag switch seems ...
    (sci.techniques.microscopy)
  • How are SEM probe scanning coils typically driven?
    ... to deflect it back to get through the aperture. ... One is that the sets of coils are essentially ... with the second set wired backwards. ... coils has twice as many turns as the first: ...
    (sci.techniques.microscopy)