7/30/96
I have been having a bit of a problem with some stray EM (?) fields
on our SEM. The problem has been traced to the power feeding the wall
outlets. Anything plugged into these outlets and the microscope will affect
the images produced. Specifically the backscatter detector and the PC we use
to capture images digitally. The results are the same for images captured
photographically if either the backscatter or PC is plugged into the wall.
They are not the cause of the problem but simply feed the noise to the
microscope via any cables connected to it. If I unplug all from the outlets
or unplug cables leading to the microscope the problem is corrected. It
doesn't matter if they are on or not, it still feeds the noise.
We have so far simply run extension cords to other outlets in other
rooms and on other circuits in order to solve this problem but it has
worsened and I am running out of different outlets. I recently purchased an
APC line conditioner which is supposed to continuously condition the power
and give out a fresh signal but needless to say it hasn't worked or I
wouldn't be asking for your help.
If you would like to see an image with the problem go to the web
address at the bottom of this message and look in "What's New". You will
notice the vertical banding pattern produced.
Your help and expertise will be greatly appreciated. Vendors please
jump in with any advise you may have.
Sincerely
Scott D. Whittaker
Research Assistant
University Of Florida
ICBR EM Core Lab
218 Carr Hall
Gainesville, FL 32610
sdw@biotech.ufl.edu
ph 904-392-1295
fax 904-846-0251 http://www.biotech.ufl.edu/~emcl/
The home of " Tips & Tricks "
engineer for a SEM co.). The grounds for these outlets are not a common
point, until they get back to the power panel.
There are three ways to fix it. 1) Use the extension cords like you have
been 2) Get an electrician in and tell him or her that you need a dedicated
line with multiple outlets to feed all the equipment that will be hooked up
to the scope. 3) You could use a "cheater plug" for anything you plug into
the bad outlet . This is a three prong to a two prong adapter. This will
keep the ground currents from looping.
Good Luck
Rich2442@aol.com
power cord from shileded wire or twisted pairs and see if that helps. Also.
you may well find that there is a voltage difference between the
ground/neutral of the wall outlets and the microscope which can cause such
problems. Running everything toa common GOOD ground can often help. We had a
dedicated ground for the EM's a FSU tha twe tied everything into.
Bill Miller
Microbill@aol.com
We had a similar problem during installation of our SEM a few years ago. It seems the power
feeding the 110V outlets in the room adjacent to our SEM went under the floor beneath the SEM
in *plastic* conduit, rather than metal, and thus there were radial AC magnetic fields generated
anytime something was plugged into these outlets, and current was flowing.<p.
Try to trace the wiring from the outlets back to the power distribution box (circuit breakers), and
make sure it is shielded.
F. Scott Miller
Electron Microscope Lab
University of Missouri-Rolla
223 McNutt Hall
Rolla, MO 65401 USA
voice: 573 341 4727
fax: 573 341 6934
smiller@umr.edu
Oxford Instruments make an EM field cancelling system for just this type of
problem. Have you investigated this yet?? If you need I can put you in touch
with your nearest rep and can fax you a copy of the brochure.
Best regards, Les Brownlow
oisydney@ozemail.com.au
You might want to start by measuring with a voltmeter to see
if there is any difference in the ground potential between the troublesome
outlet and the microscope ground. Generally speaking all microscope
accessories should always run off he same oulet (or at least "circuit") as
the microscope. Otherwise ground loops can result. Sometimes this requires
getting the electricians to install a new outlet on the same circuit as the
microscope to effectively cure the problem. You might also want to elaboate
on when the problem first occurred. eg: Installation of a new accessory?
Paul Thomson
Technical Director
Thomson Scientific Instruments
Australia
Web: http://werple.net.au/~tsi/
Email: tsi@werple.mira.net.au
Your problem sounds like a ground fault. If the microscope and the
accessories (wall outlets) aren't referenced to the same ground, your will
get line noise. You should try to find a power source from the sem for
those accessories, or use an isolation xfmr for them and reference their
chassis ground to the sem. Any ground path with a potential difference
will cause current to flow through the grounding circuit and cause ripple.
Your service rep should be able to handle it, or just do it yourself.
Mike Warfield
mdwarfield@vcnet.com
it sounds like you have an earth loop. I have run into this problem before.
The simplest solution is to drive a copper spike into the ground outside
your lab and then make this the new earth for your microscope. Now change
earthing for both the wall sockets and the power supply for the microscope
to reference from this point. This should solve your problem.
If it does not then you may be looking at having phases slightly our of
sink. Check that the microscope power supply and the wall sockets are both
getting the same phases. In my case I have had all power taken from one
three phase supply line. The electrican has tried to balance the current
drawn on each phase to be equal. This minimises the production of stray
magnetic fields.
I would also suggest the book "Design of the Electron Microscope Laboratory
by Ronald H. Alderson, Practical Methods in Electron Microscopy"
Hope this is of some help.
Colin MacRae
C.Macrae@minerals.csiro.au
I suggest that you try to use a adaptor plug on the three prong plug for you
devices to remove the ground from the system. Make sure it puts three
prongs to two, a ground loop can be causing this problem that you describe.
Then you can connect the ground pin of the adaptor to the microscope on the
column or ground bar. I have seen this type of phenonmena before, this
usually fixes the "field" problem that you see.
Another way is to ask the electrician to ground the outlets to the
microscope for its accessories. This will again eliminate the ground loop
that may be causing your problem
Ray Spengler
ray@raven.cybercomm.net
Just to be on the safe side I send again my message directly to you. Please
keep me informed if any progress was made!
Here you are:
I am almost absolutely certain that your problem is associated with an
earthing (or grounding) loop. It is very important to have only one single
earth path. If you have separate earth path as supposedly exists with your
additional backscatter detector and/or PC (the microscope is connected to
the earth terminal, the PC is connected too, and both instruments are
connected to each other through their grounds), there are alternative,
physically separated earth paths, which will result in noise currents, and
almost certainly impair the performance of any electron microscope. Some
years ago we had similar problems with our computer and EDS system, but
there is a remedy. It would be too long and sketches are also needed to
explain. The best I can propose is to check a good textbook such as "Design
of the Electron Microscope Laboratory" by Ronald H. Anderson (North Holland,
1985, p61-66) or consult an expert electrician as a final solution. In case
you cannot obtain quickly the book I can fax you these pages.
Kristof KOVACS
Associate Professor
University of Veszprem, Central Laboratory
P.O.Box 158, Veszprem, HUNGARY
H-8201
Phone: +36-(88)-421-684
kris@almos.vein.hu
How is it you seem so convinced the problem is magnet? Try this: Get some
of the line cord adapters which eliminate the 3rd wire (the prong) and plug
them on line cords of all your extra instrumentation. If there is a ground
fault or eddie current problem this may eliminate it. Ideally, all your
instrumentation would all be grounded at one point. Also, there can be
problems with stray voltages on both the neutral and ground connections of
wall plugs.
Alex Greene
Scientific Instrumentation Services, Inc.
Austin, Texas.
ablue@mail.io.com
You are almost certainly setting up ground loops. ALL your equipment must
go back to a common, local ground. You need to go back to the mains power
source for your SEM and run extensions to all auxillary equipment from this
point. Be careful not to make these extensions too long, or you may suffer
pick-up from other sources. There should be some auxillary power outputs in
the back of your SEM and these are the prefered power source. However, if
you have a lot of auxillary equipment, you may risk overloading these.
Ideally, you should have a mains matching trasnformer between your SEM and
your local power supply - this helps to provide protection agianst power
surges, and some isolation from interference. You should tap in at this
point to provide additional power sources.
Larry Stoter
LPS@teknesis.demon.co.uk
If you are using a line conditioner and still have things plug into
the wall outlets, you may be still creating a ground loop between the
scope and the outlets giving you this problem.
You can isolate this by buying the 3-prong to 2-prong power cord
connector. This lifts the ground from the wall outlets. If this
still doesn't fix the problem then you may have to go to a separate
ground for the scope. i.e. dedicated to the scope only and not the
building.
Give this a try and if you need any more assistance please feel free
to contact me directly.
Larry Cessna
Hitachi
Cessna@hii.hitachi.com
One easy way to correct this is to modify a power strip.
If you have a strip with a metal shell, make sure that the outlets in the
strip are not electrically connected to the shell (use plastic screws if
necessary). Lift the ground wire from the power cable inside the strip and
connect it to the strip's metal shell for safety. Connect the outlets'
grounds together and attach a 14-guage insulated wire (preferably stranded
wire for flexibility) to that ground. You'll have to drill a hole in the
shell, of course, so this ground wire can fit through it. Connect the
14-guage ground wire to the ground connector on the SEM (or to the metal
body of the SEM if you can't find the connector).
I recently did this to four of my TEM's. Our problems were more subtle
than what you described.
Russell E. Cook
Electron Microscopy Center for Materials Research
Argonne National Laboratory
9700 South Cass Avenue
MSD-212
Argonne, IL 60439
(708)252-7194
FAX: (708)252-4798
this is to get a adaptor plug with no ground and plug your sem accessories, i.e.
bsd, printer into that.
Regards
Mike Webber
102413.2660@CompuServe.COM
Linear Reasearch Associates (it's a small company) is Curt Dunnam
(crd4@cornell.edu). He's the chief engineer, and will likley be happy to
talk.
Ben Simkin (simkin@egr.msu.edu)
simkin@egr.msu.edu
In my experience, the "high mag jaggies" are most often caused by a
mechanical vibration. Often the roughing pump is the problem. Sometimes
a couple of tennis balls under the roughing pump will decrease the effect
substantially. It's not always this simple though. Also check for cables
touching the vacuum line from the RP. They can transmit these vibes.
John Best
jbest@vicon.net
jagginess problem that John Best deicribes. JEOL has been here and we have
looked for electrical fields. Not a problem. A shield was installed in the
consol to eliminate fields emmanating from the CRT's. No effect The company
service people are stumped, and we are left unable to use the SEM a high mags.
This outlet problem intrigues me, however. Please keep this thread going for a
while.
Bob Schmitz
rschmitz@uwspmail.uwsp.edu
or
rschmitz@macsrv1.uwsp.edu
(note its macsrv"one" not "el")
Robert (Bob) J. Schmitz
Department of Biology,
University of Wisc. Stevens Point.
Stevens Point, Wisconsin 54481
ph 715-346-2420
We also had an interesting stray fields problem which showed up in high
noise counts in X-ray spectra - the amount depending on the scan rate in
the SEM! This was traced to a high frequency earth loop (no DC connection)
with capacitive coupling associated with the thin plastic shin isolating
the X-ray detector from the column. This was solved by passing a few loops
of the whole cable going to the X-ray detector through a large toroid to
increase the high frequency impedance of this part of the loop.
Alan Wilson alan.wilson@dsto.defence.gov.au
Senior Research Scientist
Ship Structures and Materials Division
Aeronautical and Maritime Research Laboratory
Defence Science and Technology Organization
506 Lorimer St
Fishermens Bend 3207
Victoria Australia
ph 61 3 9626 7508, fax 61 3 9626 7816 or 61 3 9626 7087
there was another thread a while back posted to the server which I have
archived. Go to the web page listed at the end of this message. Click on the
"Tips & Tricks" button. You will find a link for "SEM Techniques &
Instrumentation" which wil point to another link called "Dealing with Drift,
SEM". It may prove useful. If you do not have web access, let me know and I
will be happy to get the info to you some other way.
Scott D. Whittaker
Research Assistant
University Of Florida
ICBR EM Core Lab
218 Carr Hall
Gainesville, FL 32610
ph 904-392-1295
fax 904-846-0251
sdw@biotech.ufl.edu http://www.biotech.ufl.edu/~emcl/
The home of " Tips & Tricks "
6300. Viewed at TV rate at >50,000x the interference seemed to have a
fairly high frequency and underwent rapid variations in amplitude. Some
days it was there and other days it wasn't. It was indeed caused by a
mechanical vibration -- but in our case it was coming from the stage
motors, in particular the Z-axis motor. The effects of this vibration only
started to become visible above about 15-20,000x, and it could only just be
felt on some days by very lightly touching the motor once you already "knew
it had a vibration". Our Jeol engineer was the one who finally figured this
out and then he measured a ~2 volt sawtooth ripple on top of the DC holding
current to the stage motors. The problem was eliminated by changing some
resistors in the (non-Jeol) motor driver hardware, on the recommendation of
its vendors, to reduce the DC holding current and hence presumably the
absolute magnitude of the ripple that came with it. We have not had any
trouble since.
Arthur Day, Electron Microscope Unit
Ansto Materials Division
PMB 1, Menai (Sydney), NSW, 2234
Australia
http: //www.ansto.gov.au/
Phone: 61-2-717-3457
Fax: 61-2-543-7179
Email: ard@atom.ansto.gov.au
We are in the process of tracking down similar problems. One avenue that we
are examining is mechanic vibration in the column due to the location of the
EDS dewar. The dewar is essentially a large undamped liquid mass hung out
to the side of the object that must remain vibration-free. Well the
location of the dewar is approximately equidistant to the two adjoining
sides of the room. By placing a small mirror over the top of the dewar, we
can watch the LN2 shimmer. By moving sound-absorbing foam sheets around the
area between the dewar and the walls, we can see a difference in the
vibration. We have more work to do on this, but it seems like the dewar is
in the "sweet spot" in the room if you were going to set up a stereo system.
We are also going to move the 3-phase transformer that sits on the other
side of the wall (less than 3 feet from column and console) in the surface
analysis lab to get rid of the known electrical vibration.
Harold J. Crossman
OSRAM SYLVANIA INC.
Lighting Research Center
71 Cherry Hill Dr.
Beverly, MA 01915
Phone: (508) 750-1717
E-mail: crossman@rd.sylvania.com
Our web sites: www.sylvania.com
www.osram.de
www.siemens.com
loose gears/bearings in the stage. Enviro vibes, which normally
did not create a problem, caused "jaggies" as low as 5000x.
Etec FYI: My system has been modified by removing the diff pump and
installing a turbo. Beware of ball bearing units. The Etec is far
too susceptible to their vibrations. I have been using a Leybold
maglev pump since they became available and can see no pump induced
vibes below about 30Kx.
Woody White
Babcock & Wilcox Research Ctr.
woody.n.white@mcdermott.com
woody.white@worldnet.att.net
your area. When I was at George Washington Univ. Med School my lab was
on the 5th. floor. Never had problems with vibration until one day I was
looking at cilia at 200,000 times and saw it. Zeiss came in to look at
the scope and the surrounding area and couldn't find what was causing the
problem. They saw vibration only when they put the meter on the desk of
the scope. Put it on the floor, no vibration detectable. We looked at
another TEM on the floor below us and they had no problem even at 300,000x.
After much hunting we found a air handling unit 2 floors below us and
about 100ft. away from the scope with a bad rubber foot pad. We had the
physical plant dept. replace it and our vibration problem disappeared.
Apparently this was causing low level vibration that my scope was picking
up and the other scope (floor below) wasn't. Vibration, especially low
level can be anywhere, construction several blocks away, bad feet on a
centrifuge, new equipment, just about anything. So if you're having a
problem with vibration check everything you can, don't rule anything out
unless you've checked it out, this includes anything touching your
mechanical pumps such as cables, hoses or even boxes you might have set on
the backing hoses.
rutledge phil
prutle1@gl.umbc.edu
I'd recommend just living with not using the outlet. AC fields can be activly
supressed if they are from an external source (we have purchased a system
from Linear Research Associates; they run ads in Microscopy Today (I don't
have the address with me right now)), but this sounds much more like a ground
loop, and the solutions to that (so I've been told) include either sinking
your own dedicated common ground (anywhere from easy to nearly impossible), or
disconnecting the ground connection between your asscessories and your SEM,
and running a "floating ground". I've discussed this as one solution with
our SEM service technician, and he says it sometimes works (assuming the
noise it adds to your instrument signal from the differance in "ground"
potentials is acceptably low).
Ben Simkin (simkin@egr.msu.edu)
Dept. Mat. Sci. and Mech.
Michigan State University