More on the Oscilloscope/Static pickup issue

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For those interested in my original blog on the oscilloscope probe/static
pickup phenomenon, you might be interested to read another blog commenting
on the issue:
http://www.edn.com/blog/1700000170/post/1120046912.html

All rather interesting discussion, so I quickly threw together another blog
(#20) showing the effect again using a regular coax cable, and also busting
the myth that it's the ground probe loop causing it.
See my blog link below.

Dave.
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Re: More on the Oscilloscope/Static pickup issue



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  Hi David,
 Just for kicks and another data point, put your 50 ohm termination directly
on the scope
without any coax and try your chair movement. Then directly short your scope
input
with a short wire and aluminum foil and repeat test.
                                   Thanks, Mike



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So, it's not a phenomenon of that scope, but an example of how long ground
clips can get you into trouble at high frequencies, regardless the tool at
the other end of the probe.

n.


Re: More on the Oscilloscope/Static pickup issue



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 Well, I guess that depends, do you believe the experts or your lying eyes!
:-)
                                                             Mike



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Nothing to do with the long clip lead on the end, as I demonstrated. Regular
issues with long ground clips at high frequency is another problem entirely.
You can have the best and shortest ground clip possible and you'll still get
this effect, picked up by the probe coax.
And the latest video shows you don't even need the cable connected at all to
get a response.

Enjoy.
Dave.
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Try with an older analog scope with a metal cabinet. I think you have
uncovered a shielding weakness with the newer digital scopes. The
resonant frequency is probably coincidental with the internal circuitry
or groundplane geometry of the scope

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"

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I was thinking that. The IEEE standard for characterising ESD pulse
generators requires the whole scope to be put in a Faraday cage.


--

John Devereux

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It is possible that even an older style CRT scope might be susceptible
given the opening for the CRT screen might be a sufficient aperture for
the ESD pulse.

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"

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Tek used to offer an option on their high-end 'scopes, having extra
bonding contacts around all the panels, and a mesh screen over the CRT
face. My 7104 is like that.

The old HP180 (lovely instrument, that was) came with a mesh CRT filter as
standard. Wish I'd still got mine.

--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
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I don't think so. These are so old they fall apart. I once bought a
HP183 (up to 300MHz) but it turned out to be a pile of junk.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
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And for those who still can't get enough.
Blog 21 has more static goodness, this time with anti-static lab coat and a
better oscilloscope.

Dave.

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Dang!  Thanks for the EDN link Dave.  I like your video blogs, but
let's face it we all make mistakes once in a while.  The above link
was exactly my take on the effect the first time I saw it.  I've made
lotsa RF pickup probes by hanging loops of wire on the end of X10
'scope probes.  A one turn probe just has less inductance.  And you
should see 'about' the same voltage electro-statically.... without the
probe shorted.   Part of the problem with static discharge
measurements is reproducing the discharge.  It's hard to get the same
amount of charge each time.  I've used the piezo sparkers from butane
lighters to try and deliver high voltage sparks.  (less than ideal
sources.)  I still like my idea of changing the loop area and seeing
if the voltage decreases.

George H.

(I haven't seen your latest V-blogs.)

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Nifty! You've done a good job of proving your point.

--
    W
  . | ,. w ,   "Some people are alive only because
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