More on the Oscilloscope/Static pickup issue

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

On Sun, 26 Jul 2009 05:22:31 -0700, David L. Jones wrote (in article ):

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.

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

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.

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.

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

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

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.

og

ng

rnatezone.com/eevblog/

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.)

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

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.

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.