deciding between usb and benchtop oscilloscope

Discussion in 'General Electronics Chat' started by huitlacoche, Nov 27, 2012.

  1. huitlacoche

    Thread Starter New Member

    Apr 29, 2009
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    Hi,

    As I'm getting more involved in electronics I think I need a scope. However since I don't know much about them I'm having a hard time deciding since the price difference is so large. I'd be fine with a benchtop model as long as it isn't a huge analog. Even then I can be convinced if it's crucial to have such a thing. Mostly I'm expecting to use to to check smoothness of voltage signals, capacitor charging/discharging and signals coming out of ICs. Nothing over 12 volts, typically. Can I do this sort of thing with a sub-$200 usb scope? Otherwise I'm willing to check out some sub-$400 DSO (Owon or Rigol).

    Thanks,
    -- Mark
     
  2. crutschow

    Expert

    Mar 14, 2008
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    A stand-alone oscilloscope is handier, as you might expect, but you pay for that.

    A USB oscilloscope will likely do what you want. You want a two-channel device with at least a 10MHz bandwidth on each channel. Some also have multi-channel logic analyzers which are handy for debugging digital circuits and digital bus signals, or even built-in function generators, but that all ups the price, of course.
     
  3. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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  4. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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  5. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    A good used TEK scope is a much better tool.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    If he wants an analog scope, but a used digital TEK scope may be pricey. I would recommend a digital scope for general purpose use.
     
  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Any good 100 MHz (or more) analog scope will give a true representation. A dig scope may or may not, depending on the speed of the signal. If you are looking for the typical switching spike noise on a supply rail from a switching converter, most dig scopes will just wave as it goes by. Unless a person needs to do a lot of storage of waveforms, IMHO a good analog scope is a better tool for general use.
     
  8. tshuck

    Well-Known Member

    Oct 18, 2012
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    Where an analog scope will offer true representation of the waveform, determining the waveforms characteristics on an analog scope will incur quite a bit of error.. "is that 3.5 divisions, or 3.6?"...

    There are certainly disadvantages to digital scopes, but I feel that the advantages make it a good overall choice for a wide range of requirements.

    Then again, I mostly work with digital systems, so I'm probably biased:p
     
  9. Veracohr

    Well-Known Member

    Jan 3, 2011
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    What kind of IC's? High speed digital?

    I got a cheap one that is slow, but good enough for audio-rate signals which is what I wanted it for.
     
  10. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Actually, the question proves my point. If you don't know exactly where dig scopes lie to you (and why) you shouldn't use them because you will never know if the data's valid.

    I still remember having this discussion once with my boss.... I used a TEK7904A scope (analog) for viewing real data and a TEK lunchbucket dig scope when I had to have a picture of a plot to print.

    I set up a demonstration for my boss of what each scope shows when reading a very sharp voltage turn off spike on a switching waveform. The analog scope shows the true waveform (and correct peak amplitude) and the dig scope showed a bunch of dots with the fast peak missing. And why care? Because voltage spikes kill switch transistors.

    Boss never gave me crap about my 7904A again.

    Sounds like pilot error.
     
  11. tshuck

    Well-Known Member

    Oct 18, 2012
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    Hmmm... you've stripped my quote out of context:p

    I meant in terms of timings, it is impossible to tell whether a signal is 3.5 divisions, or 3.6. Digital scopes are better for more accurate timing measurements as it doesn't require guesswork as to where the beam is crossing the X axis. A digital scope, on the other hand, has a resolution up to the sampling frequency.

    If you would have read my post instead of gleaning the tidbits that you wanted, you would have understood the part where I said I work with mostly digital systems. As such, I care primarily with the timing of signals.

    I find it interesting that you mention the analog scope's model, but not the digital. It's pretty hard to argue with someone pointing at one model and a hand-waving at the other....
    There is not a 1:1 correlation between bandwidth of an analog scope and a digital one. Where the analog scope's capabilities are defined by this number cut-and-dry, the digital scope is dependent of sampling frequency among a myriad of other variables. So, as far as I know, you tried to measure a 10ns pulse on a 500MHz analog scope with a 7A21N plug-in and a 100MHz digital scope... of course you will get a better resolution with the analog scope in such an event!
     
  12. MrChips

    Moderator

    Oct 2, 2009
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    If I may chime in, there is no one size fits all when it comes to choosing an oscilloscope.

    I can think of two questions to ask here:

    Are you (1) a hobbyist or (2) a professional?
    Are you interested in mainly (A) analog audio or (D) digital/microcontrollers?

    This results in four possible combinations.

    If you fall in the category of 1A on a limited budget I would opt for a used analog scope.

    If you are in 2D, a high quality digital scope is essential.

    If you are a hobbyist and working with digital (1D) on a budget I would set my sights on a digital scope for under $400.

    For 2A, as a professional, you would have both high bandwidth analog and digital scopes.

    There you go, a solution for every case.
     
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