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  • EEVblog #14 – An unusual Oscilloscope phenomenon!

    Posted on June 21st, 2009 EEVblog 16 comments

    A rather unusual Oscilloscope phenomenon!

    Here is an old paper on the ESD chair issue: http://www.emcesd.com/pdf/eos93.pdf

    Here is

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    • Eric

      very neat!

      Keep emm commin!!!

      E

      • http://www.alternatezone.com/eevblog admin

        Wow, didn’t know about that, thanks!
        I just quickly filmed another blog to clear up the myth it’s the ground loop! – stay tuned.

    • Anthony

      Very nice demonstration Dave. My father’s previous life as an ESD researcher gave away the answer but thought you explained it very well. Please keep up the great work!

    • George Herold

      Hi Dave, Only one ‘nit-picky’ point. You pointed to the cable inductance as the route through which the signal got into the scope. I think the route is through the one turn loop you made by connecting the probe to ground. This is easy to test. Make the loop area smaller (wind the ground around the probe.) and see if the pickup is smaller.

      Otherwise lotsa fun!

      • http://www.alternatezone.com/eevblog admin

        Nope, you can remove the loop (i.e. don’t short out the probe) and it still works. But I figured people would be more surprised if they saw the probe was shorted and the signal still gets in.

    • Andy

      With all of your presentations on various bench-type digital scopes vs PC scopes, I wonder if the Cleverscope (www.cleverscope.com) price/performance mix would tempt you into a PC-based scope? I recognise the Rigol (and other similar well made scopes) is a nice unit, but for those of us that do a fair amount of travel with our jobs, the ability to effectively put (what appears to me to be) a well-spec’d scope in the same bag as your laptop represents a pretty good deal. At the price. With the performance quoted. And made with a reasonable effort at quality.

      Just wondered.

      • http://www.alternatezone.com/eevblog admin

        It’s not a matter of being “tempted” to switch to a PC based scope, it’s about “horses for courses” as they say.
        PC based scopes have their place, and can be better than a bench scope for many applications (like portable use as you mention). My blog was about whether or not a PC based scope for general use is a good value replacement for a bench scope, and the clear answer is a big no on a price/performance evaluation.
        The CleverScope is quite nice, and I’ve met the designer personally. It was one of the first PC based scopes to realise the value of a HUGE memory depth. But it’s still only got 100MS/s, that’s 10MHz effective single shot bandwidth. 1/5th that of the Rigol, and it costs more than double the Rigol! It trades off sample speed for vertical resolution, and if that suits your needs then it’s a good choice.
        Also, I’m not a fan of the CleverScopes rather quirky user interface (written in LabView), but it has got some rather powerful and innovative features.
        Dave.

    • Andy

      Yes, you’re right. ‘Tempted’ is the wrong word. And you answered the intended question.

      However (why is there always a ‘however’ just down the road?) I see increasing use for the ability to grab measurements from the bench for post-analysis in a PC. Such interfacing is obviously an advantage of PC Scopes. Won’t work without it!

      What’s your experience with the Rigol (or similar scopes) when importing info into the PC in some useful format (i.e not JPG etc)?

      • http://www.alternatezone.com/eevblog admin

        Yes, getting the scope data into a PC is an important requirement. However(!), I’ve found I only rarely need to post-analyse captured scope data in say Excel or some other program, my main requirement 99% of the time is to simply screen capture the waveform image for inserting into Word documents etc. And when I do need to post-analyse data, it’s usually not just scope data but long capture data logger type info, which of course a PC based data logger/scope or NI DAQ card is better suited for.

        You can capture the data in usable (comma delimited format) on most modern scopes, including the Rigol. In fact that’s how they started, you could only get the data in raw format in older scopes, and not the BMP/JPG screen dump you usually wanted!

        And of course USB memory stick is best, as you can capture data in the field and then bring it back to the desk for post-analysis.
        Got to admit the Rigol is not the easiest to dump the screen to a stick with, it’s a bit convoluted. A simple “Print” button would have helped a lot.

        Dave.

    • ewertz

      Wow, you really stirred-up the RF brainiacs at EDN…

      http://www.edn.com/blog/1700000170/post/1120046912.html

    • Marius Rowell

      Love to know how you do it. I have a 1GHz sampling scope (10GS/s) and 500MHz probes (10MOHM//8pF) and nothing I do makes that happen, with or without the ground clip.
      I have a feeling what you’re seeing is either an artifact of your scope, or maybe just poor shielding in your probe leads. Typical screening from coax shields is only ~ 30dB at 100MHz+, so a static discharge can easily go through the shield and get into the high impedance inner conductor. It could also be capacitive coupling from your body to the nearest ground (the probe shield) and from there to the inner conductor. Since I play with scope leads which cost more than most people scopes cost I am at a disadvantage to offer anything I can’t reproduce or see for myself.

      • http://www.alternatezone.com/eevblog admin

        You are simply not generating enough broadband static energy.
        If you use the ground loop probe clip, that is an excellent RF detector probe, so it’s not because you are using a top dollar probe.
        In my later blogs I still show the effect using no lead at all, and using other scopes, so the coax lead is a read herring.

    • Alessandro

      Sorry but I’m not english…
      I didn’t understand what generate the static electricity?

      Thank

      • http://www.alternatezone.com/eevblog admin

        The action of standing up from the chair generates the static electricity. Because my butt has a large surface area(relatively speaking!), and I stand up quickly, a large static voltage is generated. I can also generate it by wiping my jumper on the chair seat, but it’s not as high amplitude.

    • Geoff Graham

      Nope, did not work with me (100MHz Rigol DS1102E).

    • sonicj

      i wonder if shaving your legs has any affect on this phenomenon…? =)

      obviously your choice of clothing has an affect on static generation. something less obvious could be the type of plastic the chair is composed of. black plastics are often conductive!

      “static guard” is a great product i’ve used for years to curb static generation from clothing. occasionally treating your chair and work area might not be a bad idea for those with static troubles.
      -sj